Biocontrol in store: spatial and behavioural aspects of foraging by Uscana lariophaga, egg parasitoid of Callosobruchus maculatus, in stored cowpea

C. Stolk

Research output: Thesisinternal PhD, WU

Abstract

<p> </p><p>Cowpea ( <em>Vigna unguiculata</em> Walpers), an important crop for West African subsistence farmers, is often infested in storage by the bruchid beetle <em>Callosobruchus maculatus</em> Fabricius. The indigenous egg parasitoid <em>Uscana lariophaga</em> Steffan (Hym.: Trichogrammatidae) is responsible for substantial mortality of <em>C. maculatus</em> eggs and might therefore be used in a conservation strategy of biological control. This thesis focuses on foraging behaviour of <em>U. lariophaga</em> females in a spatial context. In stored cowpea, the bruchid oviposits in clusters. <em>Uscana lariophaga</em> is well adapted to such clusters, since it shows a strong arrestment response after an encounter with an unparasitized host. Previous investigations had already shown attraction of the parasitoid to host-related odours; it is now shown that directed search probably occurs at a short distance (4-6 beans) from the host patch. The probability that a host patch in stored cowpea is found decreases rapidly with increasing distance between the host patch and the site of release of the parasitoid. The 'critical distance' within which the host patch is quickly found by the parasitoid increases if more searching time is allowed. If an experienced parasitoid arrives in a host patch and encounters parasitized hosts, it is likely to superparasitize, but it will stop superparasitizing as soon as an unparasitized host has been encountered in the same patch. Superparasitism by experienced females is not due to failure in host discrimination, as appears from the fact that females adapt the sex ratio of their offspring during superparasitism. If no or few hosts are available, the parasitoid lives shorter than when many hosts are available. This reduced longevity at low host densities may be due to an increased walking activity at low host densities. Finally, the potential of a simulation model of <em>U. lariophaga</em> behaviour is shown, and consequences of behaviour for the prospects of biological control are discussed.
Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
  • Wageningen University
Supervisors/Advisors
  • van Lenteren, Joop, Promotor
  • van Huis, Arnold, Promotor
  • van der Werf, Wopke, Promotor
Award date6 Dec 2002
Place of PublicationS.l.
Print ISBNs9789058087416
Publication statusPublished - 2002

Keywords

  • cowpeas
  • vigna unguiculata
  • callosobruchus maculatus
  • stored products pests
  • trichogrammatidae
  • parasitoids
  • feeding behaviour
  • host-seeking behaviour
  • biological control

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