Abondance de Hypothenemus hampei Ferr., scolyte des graines de cafe, en fonction de sa plante-hote et de son parasite Cephalonomia stephanoderis Betrem, en Cote d'Ivoire

V.J.M. Koch

Research output: Thesisinternal PhD, WU

Abstract

<br/> <br/>INTRODUCTION<p/>The discovery of <em>Cephalonomia stephanoderis</em> BETREM, a new parasite of the coffee berry borer <em>Hypothenemus hampei</em> FERR. (syn. <em>Stephanoderes hampei</em> Ferr.), seemed to open new prospects for biological control of the pest.<p/>However the phenomenon that <em>C.</em><em>stephanoderis</em> uses <em>H. hampei</em> both as Prey and host for oviposition made us suppose that the parasite had particular relations with its host, in order to enable both insects to survive. The main reason of this study was to examine this relationship.<p/>To estimate the effect of the parasite on the population of <em>H. hampei</em> and therefore on the attack of coffee, a study of component factors in this attack was necessary and therefore of the relationship between hostplant and harmful insect.<p/>TICHELER (1961) had shown that the attack on coffee berries depended on the population density of <em>H. hampei</em> in the field, but the susceptibility of different coffee varieties to attack by this insect was hardly known.<p/>In our field trials at Institut Français de Café et Cacao (IFCC) in the Ivory Coast, the progress of the attack on the berries was studied in three varieties (Robusta INEAC, Robusta Ebobo and Kouilou) during two subsequent coffee seasons (chapter 4.).<p/>Particular attention was paid to the influence of regular harvesting of the ripe berries (every 2 or 4 weeks) on the progress of the attack. The same was studied in a part of the plots where no berries were harvested.<p/>FACTORS IN THE RELATIONSHIP: HOSTPLANT TO PEST INSECT. (CHAPTER 5.)<p/>Of the three varieties, Kouilou was known to be most susceptible to attack by <em>H. hampei</em> (LEEFMANS, 1923a; PORTERES, 1959). However, in our trials Kouilou turned out to be definitely less susceptible than the two other varieties.<p/>To assess the differences in susceptibility of the varieties, use was made of 'monocyclic' and 'polycyclic' tests (ZADOKS, 1972). 'Cyclic' stands for the sequence of processes from the entrance of the insect into the coffee berry through egg laying to the emergence of its offspring from the berry. To compare the results of the different tests, the most susceptable variety was used as control. The results of the tests measuring the components of susceptibility were used to compose an index of susceptibility.<p/>In the polycyclic tests, the susceptibility of the variety was assessed in the field where the host (fruits of a tree or of a plantation) were infested by several generations of beetles.<p/>Certain components contribute less to the progress of attack in the field in Kouilou than in the two other varieties. This proved that partial resistance of Kouilou to attack by <em>H. hampei</em> is due to certain properties of the seeds in the berries.<p/>The seeds of the variety Kouilou are less suitable for the scolytid, than seeds of the varieties R. INEAC and R. Ebobo.<p/>FACTORS IN THE RELATIONSHIP OF THE PEST INSECT TO ITS PARASITE (CHAPTER 6.)<p/>In the study of the bionomy of <em>Cephalonomia stephanoderis,</em> the conditions were investigated for predation and oviposition. These two activities influenced one another only when prey was scarce. The parasitic and predatory activities of <em>C. stephanoderis</em> were confined to the population of <em>H. hampei</em> on only one berry.<p/>The rate of development and longevity of the adult parasite accord well with those of the host.<p/>Field trials showed that the parasite was most abundant when the host population was at its peak. There is only a short period when <em>C. stephanoderis is</em> abundant, since the population of the host <em>H. hampei</em> decreases because of food scarcity and lack of appropriate conditions for egg laying (chapter 7).<p/>EFFECT OF THE PARASITE ON THE PEST<p/>The effect of presence of the parasite on the population of living pest hosts was studied in parts of the plots that were not disturbed by picking the coffee berries. This effect was estimated in two different ways:<br/>- By using the proportion of infested berries containing living parasites (%Pa).<br/>- By estimating the mortality of beetles in the berries.<p/>Both estimates show that the population of <em>H. hampei</em> decreases by 20-30 %, because of the presence of <em>C.</em><em>stephanoderis</em> at the end of the coffee season, but this effect falls to 5 % in the period between seasons.<p/>In conclusion, the presence of the parasite in a coffee plantation could exert a favourable influence on the persistance of a population of <em>H. hampei</em> between seasons.
Original languageFrench
QualificationDoctor of Philosophy
Awarding Institution
Supervisors/Advisors
  • de Wilde, J., Promotor, External person
Award date19 Dec 1973
Place of PublicationWageningen
Publisher
Publication statusPublished - 1973

Keywords

  • insects
  • plant pests
  • coffea
  • coffee
  • biological control
  • beneficial insects
  • scolytidae
  • cote d'ivoire

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