Abstract
The aim of this study was to investigate the influence of volatile compounds from four secondary host plants on the ability of Dinarmus basalis Rond. (Hymenoptera: Pteromalidae) to locate, recognize, and parasitize its host, 4 th instar larvae or pupae of Callosobruchus maculatus F. (Coleoptera: Chrysomelidae). To examine this, strains of D. basalis were transferred from cow-pea seeds ( Vigna unguiculata (L.) Walp. (Fabales: Fabaceae)) to pigeon pea ( Cajanus cajan (L.) Millsp.) and two varieties of Bambara groundnut ( Vigna subterranea (L.) Verdc.) seeds. The ability of D. basalis females to recognize the volatile compounds emanating from their complex host plant was tested by using a Y-tube olfactometer and a three-dimensional device. The results suggest that when females have a choice between pure air and the air emanating from their com-plex host of origin, they are attracted to the air tainted by the volatile compounds they have become accustomed to. They spent significantly more time ( p < 0.0001) in the branch of the tube leading to the odorous air than in the tube leading to the pure air. When females from pigeon pea seed hosts were offered a choice between cowpea and pigeon pea seeds, all containing 4 th instar larvae, the familiar odor of pigeon pea seeds were most attractive. When females from Bambara groundnut (white and striped) seed hosts were offered a choice between cowpea and pigeon pea seeds, all containing 4 th instar larvae, they were significantly attracted to the odour of cowpea seeds. In the three-dimensional system, the females from the four strains did not appear to have any preference for a given type of seed containing 4 th instar larvae or pupae. The parasitism rate remained high on all four types of seeds used. These results show that the use of D. basalis as a biological control agent is possible in host changing situations where C. maculatus starts to attack other legumes. The results of this study also provide information supporting the behavioral plas-ticity of D. basalis . Understanding the mechanisms involved in the adaptive phenomena of biological control agents is discussed in the context of the development of adequate methods of pest control.
Highlights
Dinarmus basalis Rond. (Hymenoptera: Pteromalidae) is a solitary ectoparasitoid of larvae and pupae in the family Bruchidae
When D. basalis females from all four strains had a choice between pure air and air contain
When D. basalis females had the choice between the odor of cowpea seeds and the odor of seeds of the other plants, their responses varied relative to their strain of origin
Summary
Dinarmus basalis Rond. (Hymenoptera: Pteromalidae) is a solitary ectoparasitoid of larvae and pupae in the family Bruchidae. (Hymenoptera: Pteromalidae) is a solitary ectoparasitoid of larvae and pupae in the family Bruchidae. These hosts, which can be found within seeds of the bean family Fabaceae, provide both a laying site and a food stock for the developing offspring. D. basalis females lay their eggs on the host tegument within the seed. The D. basalis larvae will attach to their Bruchid host and develop (Sanon et al 1998; Sanon et al 2005). Studies using D. basalis as a biological control against legume-eating Bruchids were carried out in South Asia (Islam and Kabir 1995), Latin America (Schmale et al 2002; Schmale et al 2006), and West Africa (Mondedji et al 2002; Sanon et al 2005; Amevoin et al 2007). Studies focusing on the ability of this parasitoid to locate its host within unusual host plant seeds are scarce
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