Biological control of cotton aphid (Aphis gossypii Glover) in cotton (inter)cropping systems in China : a simulation study

J. Xia

Research output: Thesisinternal PhD, WUAcademic

Abstract

<p>Cotton aphid ( <em>Aphis gossypii</em> Glover) is the key insect pest of seedling cotton ( <em>Gossypium hirsutum L.</em> ) in China, particularly in the North China cotton region. The resulting annual losses amount to 10-15% of the attainable yield. Sole reliance on insecticides against the cotton aphid in the past four decades has brought about a rapid development of insecticide resistance, serious outbreaks of key pests, resurgence of secondary pests, and risk for man and environment. Biological control of the cotton aphid by naturally-occurring seven-spot beetle ( <em>Coccinella septempunctata L</em> .) is the first priority for integrated pest management in cotton to avoid early season application of insecticides and lay a foundation for biological control of aphids and other pests during the season. Augmentation of the seven-spot beetle by intercropping cotton with wheat is the most commonly used approach for cotton aphid biological control. Disadvantages of intercropping are decreased fiber and seed quality, increased outbreaks of cotton bollworm ( <em>Helicoverpa armigera</em> Hubner) and verticillium wilt ( <em>Verticillium dahliae</em> Kleb.), and difficulties with mechanization. There is, therefore, a demand for developing more sociologically, economically and ecologically sound cotton-wheat intercropping systems. Systems research provides an appropriate framework to analyse biological control systems and prototype promising biological control strategies. The objective of this study is (1) to better understand and quantify the major processes in <em>C. septempunctata-A. gossypii</em> system in cotton monoculture and cotton-wheat intercrop; (2) to develop simulation models of the dynamics of the coccinellid- aphid system in both cotton cropping systems by integrating process-level knowledge; and (3) to use the models to obtain insight in the dynamic behavior of the system and explore intercropping strategies that are not only favorable for biological control but also advantageous with respect to labor requirement, fiber and seed quality, and suppression of the cotton bollworm and verticillium wilt by cultural practices.<p>A major factor affecting <em>A. gossypii</em> population growth is temperature. Life table parameters of the cotton aphid were determined at 10, 15, 20, 25, 30 and 35 ± 0.5°C in the laboratory (Chapter 2). The relationship of temperature with the developmental rate of each life stage (the reciprocal of the stage duration) was described using Logan curves. The relationship of temperature with the relative mortality rate of each prereproductive stage and each adult age class was described using parabolas. The relationship of temperature with the mean reproductive rate of each adult age class was described using the Weibull model. Development of <em>A. gossypii</em> was fastest at 30°C, with a pre-reproductive period of 4.6 d. The greatest survival from birth to adult (81 %) was obtained at 25°C. Fecundity was maximum at 25°C , with a total fecundity of 28.3 nymphs per female and a mean reproductive rate of 3.1 nymphs per female per day. Threshold temperatures for development of the first to fourth instar and the adult were 8.2, 8.0, 7.2, 6.2 and 7.9°C, respectively; and the thermal constants were 24.2, 23.7, 23.0, 25.5 and 168.8 degree-days (D°), respectively. <em>A. gossypii</em> obtained its greatest intrinsic rate of increase (0.386 d <sup>-1</SUP>) at 25°C. High relative rate of population increase at 25°C resulted in a daily population increase of 47% and a doubling time of 1.8 d, illustrating the tremendous growth capacity of <em>A. gossypii</em> under favorable conditions. Comparison to similar records from other crops indicates a relatively high heat tolerance of <em>A. gossypii</em> on cotton in North China. The data gathered are used to construct a simulation model of <em>A. gossypii</em> population dynamics in cotton.<p>Temperature and food quantity are two major factors affecting C. <em>septempunctata</em> population growth. Life history parameters of the seven-spot beetle feeding on <em>A. gossypii</em> were determined in two experiments in the laboratory (Chapter 3). The first experiment addressed the effect of five temperatures (15, 20, 25, 30 and 35 ± 0.5°C) on the beetle bionomics, while the second one addressed the effect of food quantity on the beetle bionomics at a temperature of 25°C. The relationship between temperature and the developmental rate of each life stage was described with Logan curves. The relationship of temperature with the relative mortality rate of each pre-oviposition stage and each adult age class was described with parabolas. The relationship between temperature and the mean oviposition rate of each adult age class was described with the Weibull model. <em>C.</em><em>septempunctata</em> developed most rapidly at 35°C, with a preimaginal period of 10.8 d. The highest survival from egg to adult (47%) was obtained at 25°C. Oviposition was greatest at 25°C, with a total oviposition of 287.4 eggs per female and a mean oviposition rate of 22.4 eggs per female per day. Threshold temperatures for development of eggs, larvae, pupae and adults ranged from 10.9 to 13.9°C, with 12.6°C for the entire life span; and thermal constants were 42.0, 103.7, 63.6 and 302.9 D°, respectively. Over the range of prey densities tested, a 3.54-fold increase in prey density resulted in a 2-fold reduction in larval development time and a 3-fold increase in larval survival. A 2-fold increase in prey density led to a 2-fold increase in total oviposition and the mean oviposition rate. The data gathered are used to construct a simulation model of <em>C.</em><em>septempunctata</em> population dynamics in cotton.<p>Functional responses of five foraging stages of <em>C. septempunctata</em> on three sizegroups of <em>A. gossypii</em> (mixed first and second nymphs, mixed third and fourth nymphs, and adults) at five temperatures (15, 20, 25, 30 and 35 ± 0.5°C) were determined in the laboratory (Chapter 4). All functional responses were of type 11 and were adequately described by Rogers' random predator equation. The search rate increased linearly from 15 to 35°C with a factor of 3-8. The handling rate showed a curvilinear relation to temperature and was lowest at 15°C. There was a considerable variation in the latter response curves in different predator-prey stage combinations. In some predator-size- groupsprey interactions, handling rate increased consistently with temperature, while in other combinations, the relationship had a maximum at an intermediate temperature. Search rate increased with 50-100% from one larval predator instar to the next but decreased from the fourth instar to the adult predator. There was only moderate difference in search rate between prey size-groups for the same predator stage (&lt; 50% between extremes). Handling rate increased with 50-100% from one predator stage to the next, but it was somewhat similar in the fourth instar and adult predators. Handling rate towards early instar, late instar and adult prey varied with a ratio of about 3:2:1. The functional responses are incorporated in the simulation model of <em>C.</em><em>septempunctata-A. gossypii</em> population interaction and dynamics in cotton.<p>In Chapter 5, a simulation model of the temporal dynamics of the coccinellid-aphid system in cotton monoculture was developed by integrating process-level knowledge. Six submodels were distinguished: cotton aphid, seven-spot beetle, predator-prey interaction, parasitism, cotton plant, and abiotic factors. The model was tested and evaluated at three levels of the system complexity: laboratory, field cage and open field. At each level of complexity, processes were added to the model, based on discrepancies between "original model" behaviors and observations, and additional experimentation. Processes included in the model at the laboratory level were temperature-dependent development, survival and reproduction of both insects; and prey density, prey size-group and temperature- dependent predation. Adaptations for the field cage level were density dependence of wing induction and reproduction of <em>A</em> . <em>gossypii,</em> extrapolation of the functional response from single stage interaction in experimental arenas in the laboratory to multiple stage interactions on plants, and a higher mortality for <em>C</em> . <em>septempunctata</em> than observed in the laboratory. Adaptations for the open field level were immigration rates of both insects; time- dependent parasitization of alate immigrants by <em>Allothrombium,</em> apterous aphids by hymenopterous parasitoids and seven-spot beetle pupae by <em>Tetrastichus coccinellae</em> Kurjumov; prey density-dependent departure rate of seven-spot beetle adults; prey density and prey size-group dependent predation by <em>Propylaea japonica</em> (Thungberg); and accumulated (D°)-driven cotton canopy growth. The simulated and observed data were in reasonable agreement at all levels, though discrepancies increased with the level of scale. Simulations at the open field level show that <em>C. septempunctata</em> plays a key role in controlling <em>A.</em> gossypii in cotton monoculture, but its numbers increase too late to guarantee a sufficient biological control. Predation by <em>P</em> . <em>japonica</em> and parasitism by <em>Allothrombium</em> and hymenopterous parasitoids play only a minor role. Variations in temperature or immigration of alate <em>A.</em> gossypii alone can not explain between-season differences in aphid population dynamics. Immigrating numbers of seven- spot beetle adults is the key factor.<p>Based on the model of Chapter 5, a simulation model of the spatio-temporal dynamics of the coccinellid-aphid system in cotton-wheat intercropping was developed in Chapter 6. Six submodels were distinguished: temporal dynamics of <em>A. gossypii</em> populations, temporal dynamics of <em>C.</em><em>septempunctata</em> populations on wheat, seven-spot beetle dispersal from wheat into cotton, predator-prey interaction on cotton, cotton plant, and abiotic factors. In addition to the processes common in cotton monoculture and cotton-wheat intercrop, processes related to the cotton-wheat intercrop were experimentally characterized and included: (a) immigration of alate aphids into intercropped cotton and seven-spot beetle adults into intercropped wheat; (b) prey density-dependent emigration of seven-spot beetle adults from ripening wheat by flight; (c) prey density-dependent dispersal of foraging predators from wheat into cotton by walking; (d) time-dependent parasitization in apterous aphids and seven-spot beetle pupae; and (e) accumulated (D°)-driven cotton canopy growth. Dispersal of foraging seven-spot beetles from wheat into cotton was modelled as a diffusion process. There was satisfactory correspondence between the simulated and observed data. Simulations show that the low abundance of the cotton aphid in the current cotton-wheat intercropping system is due to a combined effect of increased predation and parasitism, and decreased aphid immigration, of which predation by the seven-spot beetle is the most important. Current cotton-wheat intercropping has an "overcapacity" for biological control. Simulations indicate that effective biological control can still be achieved when the immigration rate of alate aphids is increased by a factor 4, and the proportion of the seven-spot beetle foraging on cotton and the parasitization of apterous aphid are decreased by 40%. These results suggest that it is possible to increase distance from wheat to cotton strips in the current intercropping system and maintain effective biological control of the cotton aphid.<p>Based on models developed and insights gained in this study, a promising strategy of cotton-wheat strip cropping was proposed, which would be not only favorable for <em>A. gossypii</em> biological control but also advantageous with respect to labor requirement, fiber and seed quality, and suppression of the cotton bollworm and verticillium wilt by cultural practices. For its validation, field work is required. More research is needed to determine the effect of distance from wheat to cotton strips on immigration of alate aphids into cotton and dispersal of major predators from wheat into cotton. With these parameters included in the model of Chapter 6, the promising strategy of cotton-wheat strip cropping can be identified and tested on a large scale. Observations should be also made for effectiveness and profitability of the proposed strategy for further improvement and development of cotton cropping systems in North China.
Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
Supervisors/Advisors
  • Rabbinge, R., Promotor, External person
  • van der Werf, Wopke, Co-promotor
Award date2 Jun 1997
Place of PublicationS.l.
Publisher
Print ISBNs9789054857136
Publication statusPublished - 1997

Fingerprint

Aphis gossypii
cropping systems
biological control
cotton
China
wheat
Coleoptera
Aphidoidea
intercropping
temperature
immigration
predators
Coccinella septempunctata
oviposition
simulation models
parasitism
instars
Helicoverpa armigera
Verticillium wilt
nymphs

Keywords

  • biological control
  • insects
  • beneficial insects
  • cotton
  • Aphididae
  • Coccinellidae
  • mixed cropping
  • intercropping
  • multiple cropping
  • interplanting
  • computer simulation
  • simulation
  • simulation models
  • China
  • Aphis gossypii
  • Coccinella septempunctata

Cite this

@phdthesis{ce91c5ba65764b0d91d4fe9ba4d91bfc,
title = "Biological control of cotton aphid (Aphis gossypii Glover) in cotton (inter)cropping systems in China : a simulation study",
abstract = "Cotton aphid ( Aphis gossypii Glover) is the key insect pest of seedling cotton ( Gossypium hirsutum L. ) in China, particularly in the North China cotton region. The resulting annual losses amount to 10-15{\%} of the attainable yield. Sole reliance on insecticides against the cotton aphid in the past four decades has brought about a rapid development of insecticide resistance, serious outbreaks of key pests, resurgence of secondary pests, and risk for man and environment. Biological control of the cotton aphid by naturally-occurring seven-spot beetle ( Coccinella septempunctata L .) is the first priority for integrated pest management in cotton to avoid early season application of insecticides and lay a foundation for biological control of aphids and other pests during the season. Augmentation of the seven-spot beetle by intercropping cotton with wheat is the most commonly used approach for cotton aphid biological control. Disadvantages of intercropping are decreased fiber and seed quality, increased outbreaks of cotton bollworm ( Helicoverpa armigera Hubner) and verticillium wilt ( Verticillium dahliae Kleb.), and difficulties with mechanization. There is, therefore, a demand for developing more sociologically, economically and ecologically sound cotton-wheat intercropping systems. Systems research provides an appropriate framework to analyse biological control systems and prototype promising biological control strategies. The objective of this study is (1) to better understand and quantify the major processes in C. septempunctata-A. gossypii system in cotton monoculture and cotton-wheat intercrop; (2) to develop simulation models of the dynamics of the coccinellid- aphid system in both cotton cropping systems by integrating process-level knowledge; and (3) to use the models to obtain insight in the dynamic behavior of the system and explore intercropping strategies that are not only favorable for biological control but also advantageous with respect to labor requirement, fiber and seed quality, and suppression of the cotton bollworm and verticillium wilt by cultural practices.A major factor affecting A. gossypii population growth is temperature. Life table parameters of the cotton aphid were determined at 10, 15, 20, 25, 30 and 35 ± 0.5°C in the laboratory (Chapter 2). The relationship of temperature with the developmental rate of each life stage (the reciprocal of the stage duration) was described using Logan curves. The relationship of temperature with the relative mortality rate of each prereproductive stage and each adult age class was described using parabolas. The relationship of temperature with the mean reproductive rate of each adult age class was described using the Weibull model. Development of A. gossypii was fastest at 30°C, with a pre-reproductive period of 4.6 d. The greatest survival from birth to adult (81 {\%}) was obtained at 25°C. Fecundity was maximum at 25°C , with a total fecundity of 28.3 nymphs per female and a mean reproductive rate of 3.1 nymphs per female per day. Threshold temperatures for development of the first to fourth instar and the adult were 8.2, 8.0, 7.2, 6.2 and 7.9°C, respectively; and the thermal constants were 24.2, 23.7, 23.0, 25.5 and 168.8 degree-days (D°), respectively. A. gossypii obtained its greatest intrinsic rate of increase (0.386 d -1) at 25°C. High relative rate of population increase at 25°C resulted in a daily population increase of 47{\%} and a doubling time of 1.8 d, illustrating the tremendous growth capacity of A. gossypii under favorable conditions. Comparison to similar records from other crops indicates a relatively high heat tolerance of A. gossypii on cotton in North China. The data gathered are used to construct a simulation model of A. gossypii population dynamics in cotton.Temperature and food quantity are two major factors affecting C. septempunctata population growth. Life history parameters of the seven-spot beetle feeding on A. gossypii were determined in two experiments in the laboratory (Chapter 3). The first experiment addressed the effect of five temperatures (15, 20, 25, 30 and 35 ± 0.5°C) on the beetle bionomics, while the second one addressed the effect of food quantity on the beetle bionomics at a temperature of 25°C. The relationship between temperature and the developmental rate of each life stage was described with Logan curves. The relationship of temperature with the relative mortality rate of each pre-oviposition stage and each adult age class was described with parabolas. The relationship between temperature and the mean oviposition rate of each adult age class was described with the Weibull model. C.septempunctata developed most rapidly at 35°C, with a preimaginal period of 10.8 d. The highest survival from egg to adult (47{\%}) was obtained at 25°C. Oviposition was greatest at 25°C, with a total oviposition of 287.4 eggs per female and a mean oviposition rate of 22.4 eggs per female per day. Threshold temperatures for development of eggs, larvae, pupae and adults ranged from 10.9 to 13.9°C, with 12.6°C for the entire life span; and thermal constants were 42.0, 103.7, 63.6 and 302.9 D°, respectively. Over the range of prey densities tested, a 3.54-fold increase in prey density resulted in a 2-fold reduction in larval development time and a 3-fold increase in larval survival. A 2-fold increase in prey density led to a 2-fold increase in total oviposition and the mean oviposition rate. The data gathered are used to construct a simulation model of C.septempunctata population dynamics in cotton.Functional responses of five foraging stages of C. septempunctata on three sizegroups of A. gossypii (mixed first and second nymphs, mixed third and fourth nymphs, and adults) at five temperatures (15, 20, 25, 30 and 35 ± 0.5°C) were determined in the laboratory (Chapter 4). All functional responses were of type 11 and were adequately described by Rogers' random predator equation. The search rate increased linearly from 15 to 35°C with a factor of 3-8. The handling rate showed a curvilinear relation to temperature and was lowest at 15°C. There was a considerable variation in the latter response curves in different predator-prey stage combinations. In some predator-size- groupsprey interactions, handling rate increased consistently with temperature, while in other combinations, the relationship had a maximum at an intermediate temperature. Search rate increased with 50-100{\%} from one larval predator instar to the next but decreased from the fourth instar to the adult predator. There was only moderate difference in search rate between prey size-groups for the same predator stage (< 50{\%} between extremes). Handling rate increased with 50-100{\%} from one predator stage to the next, but it was somewhat similar in the fourth instar and adult predators. Handling rate towards early instar, late instar and adult prey varied with a ratio of about 3:2:1. The functional responses are incorporated in the simulation model of C.septempunctata-A. gossypii population interaction and dynamics in cotton.In Chapter 5, a simulation model of the temporal dynamics of the coccinellid-aphid system in cotton monoculture was developed by integrating process-level knowledge. Six submodels were distinguished: cotton aphid, seven-spot beetle, predator-prey interaction, parasitism, cotton plant, and abiotic factors. The model was tested and evaluated at three levels of the system complexity: laboratory, field cage and open field. At each level of complexity, processes were added to the model, based on discrepancies between {"}original model{"} behaviors and observations, and additional experimentation. Processes included in the model at the laboratory level were temperature-dependent development, survival and reproduction of both insects; and prey density, prey size-group and temperature- dependent predation. Adaptations for the field cage level were density dependence of wing induction and reproduction of A . gossypii, extrapolation of the functional response from single stage interaction in experimental arenas in the laboratory to multiple stage interactions on plants, and a higher mortality for C . septempunctata than observed in the laboratory. Adaptations for the open field level were immigration rates of both insects; time- dependent parasitization of alate immigrants by Allothrombium, apterous aphids by hymenopterous parasitoids and seven-spot beetle pupae by Tetrastichus coccinellae Kurjumov; prey density-dependent departure rate of seven-spot beetle adults; prey density and prey size-group dependent predation by Propylaea japonica (Thungberg); and accumulated (D°)-driven cotton canopy growth. The simulated and observed data were in reasonable agreement at all levels, though discrepancies increased with the level of scale. Simulations at the open field level show that C. septempunctata plays a key role in controlling A. gossypii in cotton monoculture, but its numbers increase too late to guarantee a sufficient biological control. Predation by P . japonica and parasitism by Allothrombium and hymenopterous parasitoids play only a minor role. Variations in temperature or immigration of alate A. gossypii alone can not explain between-season differences in aphid population dynamics. Immigrating numbers of seven- spot beetle adults is the key factor.Based on the model of Chapter 5, a simulation model of the spatio-temporal dynamics of the coccinellid-aphid system in cotton-wheat intercropping was developed in Chapter 6. Six submodels were distinguished: temporal dynamics of A. gossypii populations, temporal dynamics of C.septempunctata populations on wheat, seven-spot beetle dispersal from wheat into cotton, predator-prey interaction on cotton, cotton plant, and abiotic factors. In addition to the processes common in cotton monoculture and cotton-wheat intercrop, processes related to the cotton-wheat intercrop were experimentally characterized and included: (a) immigration of alate aphids into intercropped cotton and seven-spot beetle adults into intercropped wheat; (b) prey density-dependent emigration of seven-spot beetle adults from ripening wheat by flight; (c) prey density-dependent dispersal of foraging predators from wheat into cotton by walking; (d) time-dependent parasitization in apterous aphids and seven-spot beetle pupae; and (e) accumulated (D°)-driven cotton canopy growth. Dispersal of foraging seven-spot beetles from wheat into cotton was modelled as a diffusion process. There was satisfactory correspondence between the simulated and observed data. Simulations show that the low abundance of the cotton aphid in the current cotton-wheat intercropping system is due to a combined effect of increased predation and parasitism, and decreased aphid immigration, of which predation by the seven-spot beetle is the most important. Current cotton-wheat intercropping has an {"}overcapacity{"} for biological control. Simulations indicate that effective biological control can still be achieved when the immigration rate of alate aphids is increased by a factor 4, and the proportion of the seven-spot beetle foraging on cotton and the parasitization of apterous aphid are decreased by 40{\%}. These results suggest that it is possible to increase distance from wheat to cotton strips in the current intercropping system and maintain effective biological control of the cotton aphid.Based on models developed and insights gained in this study, a promising strategy of cotton-wheat strip cropping was proposed, which would be not only favorable for A. gossypii biological control but also advantageous with respect to labor requirement, fiber and seed quality, and suppression of the cotton bollworm and verticillium wilt by cultural practices. For its validation, field work is required. More research is needed to determine the effect of distance from wheat to cotton strips on immigration of alate aphids into cotton and dispersal of major predators from wheat into cotton. With these parameters included in the model of Chapter 6, the promising strategy of cotton-wheat strip cropping can be identified and tested on a large scale. Observations should be also made for effectiveness and profitability of the proposed strategy for further improvement and development of cotton cropping systems in North China.",
keywords = "biologische bestrijding, insecten, nuttige insecten, katoen, Aphididae, Coccinellidae, gemengde teelt, tussenteelt, meervoudige teelt, tussenplanting, computersimulatie, simulatie, simulatiemodellen, China, Aphis gossypii, Coccinella septempunctata, biological control, insects, beneficial insects, cotton, Aphididae, Coccinellidae, mixed cropping, intercropping, multiple cropping, interplanting, computer simulation, simulation, simulation models, China, Aphis gossypii, Coccinella septempunctata",
author = "J. Xia",
note = "WU thesis 2271 Proefschrift Wageningen",
year = "1997",
language = "English",
isbn = "9789054857136",
publisher = "Xia",

}

Biological control of cotton aphid (Aphis gossypii Glover) in cotton (inter)cropping systems in China : a simulation study. / Xia, J.

S.l. : Xia, 1997. 173 p.

Research output: Thesisinternal PhD, WUAcademic

TY - THES

T1 - Biological control of cotton aphid (Aphis gossypii Glover) in cotton (inter)cropping systems in China : a simulation study

AU - Xia, J.

N1 - WU thesis 2271 Proefschrift Wageningen

PY - 1997

Y1 - 1997

N2 - Cotton aphid ( Aphis gossypii Glover) is the key insect pest of seedling cotton ( Gossypium hirsutum L. ) in China, particularly in the North China cotton region. The resulting annual losses amount to 10-15% of the attainable yield. Sole reliance on insecticides against the cotton aphid in the past four decades has brought about a rapid development of insecticide resistance, serious outbreaks of key pests, resurgence of secondary pests, and risk for man and environment. Biological control of the cotton aphid by naturally-occurring seven-spot beetle ( Coccinella septempunctata L .) is the first priority for integrated pest management in cotton to avoid early season application of insecticides and lay a foundation for biological control of aphids and other pests during the season. Augmentation of the seven-spot beetle by intercropping cotton with wheat is the most commonly used approach for cotton aphid biological control. Disadvantages of intercropping are decreased fiber and seed quality, increased outbreaks of cotton bollworm ( Helicoverpa armigera Hubner) and verticillium wilt ( Verticillium dahliae Kleb.), and difficulties with mechanization. There is, therefore, a demand for developing more sociologically, economically and ecologically sound cotton-wheat intercropping systems. Systems research provides an appropriate framework to analyse biological control systems and prototype promising biological control strategies. The objective of this study is (1) to better understand and quantify the major processes in C. septempunctata-A. gossypii system in cotton monoculture and cotton-wheat intercrop; (2) to develop simulation models of the dynamics of the coccinellid- aphid system in both cotton cropping systems by integrating process-level knowledge; and (3) to use the models to obtain insight in the dynamic behavior of the system and explore intercropping strategies that are not only favorable for biological control but also advantageous with respect to labor requirement, fiber and seed quality, and suppression of the cotton bollworm and verticillium wilt by cultural practices.A major factor affecting A. gossypii population growth is temperature. Life table parameters of the cotton aphid were determined at 10, 15, 20, 25, 30 and 35 ± 0.5°C in the laboratory (Chapter 2). The relationship of temperature with the developmental rate of each life stage (the reciprocal of the stage duration) was described using Logan curves. The relationship of temperature with the relative mortality rate of each prereproductive stage and each adult age class was described using parabolas. The relationship of temperature with the mean reproductive rate of each adult age class was described using the Weibull model. Development of A. gossypii was fastest at 30°C, with a pre-reproductive period of 4.6 d. The greatest survival from birth to adult (81 %) was obtained at 25°C. Fecundity was maximum at 25°C , with a total fecundity of 28.3 nymphs per female and a mean reproductive rate of 3.1 nymphs per female per day. Threshold temperatures for development of the first to fourth instar and the adult were 8.2, 8.0, 7.2, 6.2 and 7.9°C, respectively; and the thermal constants were 24.2, 23.7, 23.0, 25.5 and 168.8 degree-days (D°), respectively. A. gossypii obtained its greatest intrinsic rate of increase (0.386 d -1) at 25°C. High relative rate of population increase at 25°C resulted in a daily population increase of 47% and a doubling time of 1.8 d, illustrating the tremendous growth capacity of A. gossypii under favorable conditions. Comparison to similar records from other crops indicates a relatively high heat tolerance of A. gossypii on cotton in North China. The data gathered are used to construct a simulation model of A. gossypii population dynamics in cotton.Temperature and food quantity are two major factors affecting C. septempunctata population growth. Life history parameters of the seven-spot beetle feeding on A. gossypii were determined in two experiments in the laboratory (Chapter 3). The first experiment addressed the effect of five temperatures (15, 20, 25, 30 and 35 ± 0.5°C) on the beetle bionomics, while the second one addressed the effect of food quantity on the beetle bionomics at a temperature of 25°C. The relationship between temperature and the developmental rate of each life stage was described with Logan curves. The relationship of temperature with the relative mortality rate of each pre-oviposition stage and each adult age class was described with parabolas. The relationship between temperature and the mean oviposition rate of each adult age class was described with the Weibull model. C.septempunctata developed most rapidly at 35°C, with a preimaginal period of 10.8 d. The highest survival from egg to adult (47%) was obtained at 25°C. Oviposition was greatest at 25°C, with a total oviposition of 287.4 eggs per female and a mean oviposition rate of 22.4 eggs per female per day. Threshold temperatures for development of eggs, larvae, pupae and adults ranged from 10.9 to 13.9°C, with 12.6°C for the entire life span; and thermal constants were 42.0, 103.7, 63.6 and 302.9 D°, respectively. Over the range of prey densities tested, a 3.54-fold increase in prey density resulted in a 2-fold reduction in larval development time and a 3-fold increase in larval survival. A 2-fold increase in prey density led to a 2-fold increase in total oviposition and the mean oviposition rate. The data gathered are used to construct a simulation model of C.septempunctata population dynamics in cotton.Functional responses of five foraging stages of C. septempunctata on three sizegroups of A. gossypii (mixed first and second nymphs, mixed third and fourth nymphs, and adults) at five temperatures (15, 20, 25, 30 and 35 ± 0.5°C) were determined in the laboratory (Chapter 4). All functional responses were of type 11 and were adequately described by Rogers' random predator equation. The search rate increased linearly from 15 to 35°C with a factor of 3-8. The handling rate showed a curvilinear relation to temperature and was lowest at 15°C. There was a considerable variation in the latter response curves in different predator-prey stage combinations. In some predator-size- groupsprey interactions, handling rate increased consistently with temperature, while in other combinations, the relationship had a maximum at an intermediate temperature. Search rate increased with 50-100% from one larval predator instar to the next but decreased from the fourth instar to the adult predator. There was only moderate difference in search rate between prey size-groups for the same predator stage (< 50% between extremes). Handling rate increased with 50-100% from one predator stage to the next, but it was somewhat similar in the fourth instar and adult predators. Handling rate towards early instar, late instar and adult prey varied with a ratio of about 3:2:1. The functional responses are incorporated in the simulation model of C.septempunctata-A. gossypii population interaction and dynamics in cotton.In Chapter 5, a simulation model of the temporal dynamics of the coccinellid-aphid system in cotton monoculture was developed by integrating process-level knowledge. Six submodels were distinguished: cotton aphid, seven-spot beetle, predator-prey interaction, parasitism, cotton plant, and abiotic factors. The model was tested and evaluated at three levels of the system complexity: laboratory, field cage and open field. At each level of complexity, processes were added to the model, based on discrepancies between "original model" behaviors and observations, and additional experimentation. Processes included in the model at the laboratory level were temperature-dependent development, survival and reproduction of both insects; and prey density, prey size-group and temperature- dependent predation. Adaptations for the field cage level were density dependence of wing induction and reproduction of A . gossypii, extrapolation of the functional response from single stage interaction in experimental arenas in the laboratory to multiple stage interactions on plants, and a higher mortality for C . septempunctata than observed in the laboratory. Adaptations for the open field level were immigration rates of both insects; time- dependent parasitization of alate immigrants by Allothrombium, apterous aphids by hymenopterous parasitoids and seven-spot beetle pupae by Tetrastichus coccinellae Kurjumov; prey density-dependent departure rate of seven-spot beetle adults; prey density and prey size-group dependent predation by Propylaea japonica (Thungberg); and accumulated (D°)-driven cotton canopy growth. The simulated and observed data were in reasonable agreement at all levels, though discrepancies increased with the level of scale. Simulations at the open field level show that C. septempunctata plays a key role in controlling A. gossypii in cotton monoculture, but its numbers increase too late to guarantee a sufficient biological control. Predation by P . japonica and parasitism by Allothrombium and hymenopterous parasitoids play only a minor role. Variations in temperature or immigration of alate A. gossypii alone can not explain between-season differences in aphid population dynamics. Immigrating numbers of seven- spot beetle adults is the key factor.Based on the model of Chapter 5, a simulation model of the spatio-temporal dynamics of the coccinellid-aphid system in cotton-wheat intercropping was developed in Chapter 6. Six submodels were distinguished: temporal dynamics of A. gossypii populations, temporal dynamics of C.septempunctata populations on wheat, seven-spot beetle dispersal from wheat into cotton, predator-prey interaction on cotton, cotton plant, and abiotic factors. In addition to the processes common in cotton monoculture and cotton-wheat intercrop, processes related to the cotton-wheat intercrop were experimentally characterized and included: (a) immigration of alate aphids into intercropped cotton and seven-spot beetle adults into intercropped wheat; (b) prey density-dependent emigration of seven-spot beetle adults from ripening wheat by flight; (c) prey density-dependent dispersal of foraging predators from wheat into cotton by walking; (d) time-dependent parasitization in apterous aphids and seven-spot beetle pupae; and (e) accumulated (D°)-driven cotton canopy growth. Dispersal of foraging seven-spot beetles from wheat into cotton was modelled as a diffusion process. There was satisfactory correspondence between the simulated and observed data. Simulations show that the low abundance of the cotton aphid in the current cotton-wheat intercropping system is due to a combined effect of increased predation and parasitism, and decreased aphid immigration, of which predation by the seven-spot beetle is the most important. Current cotton-wheat intercropping has an "overcapacity" for biological control. Simulations indicate that effective biological control can still be achieved when the immigration rate of alate aphids is increased by a factor 4, and the proportion of the seven-spot beetle foraging on cotton and the parasitization of apterous aphid are decreased by 40%. These results suggest that it is possible to increase distance from wheat to cotton strips in the current intercropping system and maintain effective biological control of the cotton aphid.Based on models developed and insights gained in this study, a promising strategy of cotton-wheat strip cropping was proposed, which would be not only favorable for A. gossypii biological control but also advantageous with respect to labor requirement, fiber and seed quality, and suppression of the cotton bollworm and verticillium wilt by cultural practices. For its validation, field work is required. More research is needed to determine the effect of distance from wheat to cotton strips on immigration of alate aphids into cotton and dispersal of major predators from wheat into cotton. With these parameters included in the model of Chapter 6, the promising strategy of cotton-wheat strip cropping can be identified and tested on a large scale. Observations should be also made for effectiveness and profitability of the proposed strategy for further improvement and development of cotton cropping systems in North China.

AB - Cotton aphid ( Aphis gossypii Glover) is the key insect pest of seedling cotton ( Gossypium hirsutum L. ) in China, particularly in the North China cotton region. The resulting annual losses amount to 10-15% of the attainable yield. Sole reliance on insecticides against the cotton aphid in the past four decades has brought about a rapid development of insecticide resistance, serious outbreaks of key pests, resurgence of secondary pests, and risk for man and environment. Biological control of the cotton aphid by naturally-occurring seven-spot beetle ( Coccinella septempunctata L .) is the first priority for integrated pest management in cotton to avoid early season application of insecticides and lay a foundation for biological control of aphids and other pests during the season. Augmentation of the seven-spot beetle by intercropping cotton with wheat is the most commonly used approach for cotton aphid biological control. Disadvantages of intercropping are decreased fiber and seed quality, increased outbreaks of cotton bollworm ( Helicoverpa armigera Hubner) and verticillium wilt ( Verticillium dahliae Kleb.), and difficulties with mechanization. There is, therefore, a demand for developing more sociologically, economically and ecologically sound cotton-wheat intercropping systems. Systems research provides an appropriate framework to analyse biological control systems and prototype promising biological control strategies. The objective of this study is (1) to better understand and quantify the major processes in C. septempunctata-A. gossypii system in cotton monoculture and cotton-wheat intercrop; (2) to develop simulation models of the dynamics of the coccinellid- aphid system in both cotton cropping systems by integrating process-level knowledge; and (3) to use the models to obtain insight in the dynamic behavior of the system and explore intercropping strategies that are not only favorable for biological control but also advantageous with respect to labor requirement, fiber and seed quality, and suppression of the cotton bollworm and verticillium wilt by cultural practices.A major factor affecting A. gossypii population growth is temperature. Life table parameters of the cotton aphid were determined at 10, 15, 20, 25, 30 and 35 ± 0.5°C in the laboratory (Chapter 2). The relationship of temperature with the developmental rate of each life stage (the reciprocal of the stage duration) was described using Logan curves. The relationship of temperature with the relative mortality rate of each prereproductive stage and each adult age class was described using parabolas. The relationship of temperature with the mean reproductive rate of each adult age class was described using the Weibull model. Development of A. gossypii was fastest at 30°C, with a pre-reproductive period of 4.6 d. The greatest survival from birth to adult (81 %) was obtained at 25°C. Fecundity was maximum at 25°C , with a total fecundity of 28.3 nymphs per female and a mean reproductive rate of 3.1 nymphs per female per day. Threshold temperatures for development of the first to fourth instar and the adult were 8.2, 8.0, 7.2, 6.2 and 7.9°C, respectively; and the thermal constants were 24.2, 23.7, 23.0, 25.5 and 168.8 degree-days (D°), respectively. A. gossypii obtained its greatest intrinsic rate of increase (0.386 d -1) at 25°C. High relative rate of population increase at 25°C resulted in a daily population increase of 47% and a doubling time of 1.8 d, illustrating the tremendous growth capacity of A. gossypii under favorable conditions. Comparison to similar records from other crops indicates a relatively high heat tolerance of A. gossypii on cotton in North China. The data gathered are used to construct a simulation model of A. gossypii population dynamics in cotton.Temperature and food quantity are two major factors affecting C. septempunctata population growth. Life history parameters of the seven-spot beetle feeding on A. gossypii were determined in two experiments in the laboratory (Chapter 3). The first experiment addressed the effect of five temperatures (15, 20, 25, 30 and 35 ± 0.5°C) on the beetle bionomics, while the second one addressed the effect of food quantity on the beetle bionomics at a temperature of 25°C. The relationship between temperature and the developmental rate of each life stage was described with Logan curves. The relationship of temperature with the relative mortality rate of each pre-oviposition stage and each adult age class was described with parabolas. The relationship between temperature and the mean oviposition rate of each adult age class was described with the Weibull model. C.septempunctata developed most rapidly at 35°C, with a preimaginal period of 10.8 d. The highest survival from egg to adult (47%) was obtained at 25°C. Oviposition was greatest at 25°C, with a total oviposition of 287.4 eggs per female and a mean oviposition rate of 22.4 eggs per female per day. Threshold temperatures for development of eggs, larvae, pupae and adults ranged from 10.9 to 13.9°C, with 12.6°C for the entire life span; and thermal constants were 42.0, 103.7, 63.6 and 302.9 D°, respectively. Over the range of prey densities tested, a 3.54-fold increase in prey density resulted in a 2-fold reduction in larval development time and a 3-fold increase in larval survival. A 2-fold increase in prey density led to a 2-fold increase in total oviposition and the mean oviposition rate. The data gathered are used to construct a simulation model of C.septempunctata population dynamics in cotton.Functional responses of five foraging stages of C. septempunctata on three sizegroups of A. gossypii (mixed first and second nymphs, mixed third and fourth nymphs, and adults) at five temperatures (15, 20, 25, 30 and 35 ± 0.5°C) were determined in the laboratory (Chapter 4). All functional responses were of type 11 and were adequately described by Rogers' random predator equation. The search rate increased linearly from 15 to 35°C with a factor of 3-8. The handling rate showed a curvilinear relation to temperature and was lowest at 15°C. There was a considerable variation in the latter response curves in different predator-prey stage combinations. In some predator-size- groupsprey interactions, handling rate increased consistently with temperature, while in other combinations, the relationship had a maximum at an intermediate temperature. Search rate increased with 50-100% from one larval predator instar to the next but decreased from the fourth instar to the adult predator. There was only moderate difference in search rate between prey size-groups for the same predator stage (< 50% between extremes). Handling rate increased with 50-100% from one predator stage to the next, but it was somewhat similar in the fourth instar and adult predators. Handling rate towards early instar, late instar and adult prey varied with a ratio of about 3:2:1. The functional responses are incorporated in the simulation model of C.septempunctata-A. gossypii population interaction and dynamics in cotton.In Chapter 5, a simulation model of the temporal dynamics of the coccinellid-aphid system in cotton monoculture was developed by integrating process-level knowledge. Six submodels were distinguished: cotton aphid, seven-spot beetle, predator-prey interaction, parasitism, cotton plant, and abiotic factors. The model was tested and evaluated at three levels of the system complexity: laboratory, field cage and open field. At each level of complexity, processes were added to the model, based on discrepancies between "original model" behaviors and observations, and additional experimentation. Processes included in the model at the laboratory level were temperature-dependent development, survival and reproduction of both insects; and prey density, prey size-group and temperature- dependent predation. Adaptations for the field cage level were density dependence of wing induction and reproduction of A . gossypii, extrapolation of the functional response from single stage interaction in experimental arenas in the laboratory to multiple stage interactions on plants, and a higher mortality for C . septempunctata than observed in the laboratory. Adaptations for the open field level were immigration rates of both insects; time- dependent parasitization of alate immigrants by Allothrombium, apterous aphids by hymenopterous parasitoids and seven-spot beetle pupae by Tetrastichus coccinellae Kurjumov; prey density-dependent departure rate of seven-spot beetle adults; prey density and prey size-group dependent predation by Propylaea japonica (Thungberg); and accumulated (D°)-driven cotton canopy growth. The simulated and observed data were in reasonable agreement at all levels, though discrepancies increased with the level of scale. Simulations at the open field level show that C. septempunctata plays a key role in controlling A. gossypii in cotton monoculture, but its numbers increase too late to guarantee a sufficient biological control. Predation by P . japonica and parasitism by Allothrombium and hymenopterous parasitoids play only a minor role. Variations in temperature or immigration of alate A. gossypii alone can not explain between-season differences in aphid population dynamics. Immigrating numbers of seven- spot beetle adults is the key factor.Based on the model of Chapter 5, a simulation model of the spatio-temporal dynamics of the coccinellid-aphid system in cotton-wheat intercropping was developed in Chapter 6. Six submodels were distinguished: temporal dynamics of A. gossypii populations, temporal dynamics of C.septempunctata populations on wheat, seven-spot beetle dispersal from wheat into cotton, predator-prey interaction on cotton, cotton plant, and abiotic factors. In addition to the processes common in cotton monoculture and cotton-wheat intercrop, processes related to the cotton-wheat intercrop were experimentally characterized and included: (a) immigration of alate aphids into intercropped cotton and seven-spot beetle adults into intercropped wheat; (b) prey density-dependent emigration of seven-spot beetle adults from ripening wheat by flight; (c) prey density-dependent dispersal of foraging predators from wheat into cotton by walking; (d) time-dependent parasitization in apterous aphids and seven-spot beetle pupae; and (e) accumulated (D°)-driven cotton canopy growth. Dispersal of foraging seven-spot beetles from wheat into cotton was modelled as a diffusion process. There was satisfactory correspondence between the simulated and observed data. Simulations show that the low abundance of the cotton aphid in the current cotton-wheat intercropping system is due to a combined effect of increased predation and parasitism, and decreased aphid immigration, of which predation by the seven-spot beetle is the most important. Current cotton-wheat intercropping has an "overcapacity" for biological control. Simulations indicate that effective biological control can still be achieved when the immigration rate of alate aphids is increased by a factor 4, and the proportion of the seven-spot beetle foraging on cotton and the parasitization of apterous aphid are decreased by 40%. These results suggest that it is possible to increase distance from wheat to cotton strips in the current intercropping system and maintain effective biological control of the cotton aphid.Based on models developed and insights gained in this study, a promising strategy of cotton-wheat strip cropping was proposed, which would be not only favorable for A. gossypii biological control but also advantageous with respect to labor requirement, fiber and seed quality, and suppression of the cotton bollworm and verticillium wilt by cultural practices. For its validation, field work is required. More research is needed to determine the effect of distance from wheat to cotton strips on immigration of alate aphids into cotton and dispersal of major predators from wheat into cotton. With these parameters included in the model of Chapter 6, the promising strategy of cotton-wheat strip cropping can be identified and tested on a large scale. Observations should be also made for effectiveness and profitability of the proposed strategy for further improvement and development of cotton cropping systems in North China.

KW - biologische bestrijding

KW - insecten

KW - nuttige insecten

KW - katoen

KW - Aphididae

KW - Coccinellidae

KW - gemengde teelt

KW - tussenteelt

KW - meervoudige teelt

KW - tussenplanting

KW - computersimulatie

KW - simulatie

KW - simulatiemodellen

KW - China

KW - Aphis gossypii

KW - Coccinella septempunctata

KW - biological control

KW - insects

KW - beneficial insects

KW - cotton

KW - Aphididae

KW - Coccinellidae

KW - mixed cropping

KW - intercropping

KW - multiple cropping

KW - interplanting

KW - computer simulation

KW - simulation

KW - simulation models

KW - China

KW - Aphis gossypii

KW - Coccinella septempunctata

M3 - internal PhD, WU

SN - 9789054857136

PB - Xia

CY - S.l.

ER -