Changes in the insecticide susceptibility and physiological trade-offs associated with a host change in the bean weevil Acanthoscelides obtectus

For most of the seed weevils (Coleoptera: Chrysomelidae: Bruchinae), the ability to survive environmental stresses like insecticide exposure and reproduction is variable and depends on the host. Here, we evaluated the physiological costs and benefits of a host shift from kidney beans of the landrace "Vermelho" to cranberry beans of the landrace "Manteigo" in the bean weevil Acanthoscelides obtectus. We assessed the susceptibility of A. obtectus to the commercial pyrethroid deltamethrin and clove and cinnamon essential oils as potential alternative insecticides and measured its reproductive performance (e.g., oviposition and emergence rates) on both hosts. The females of A. obtectus reared on kidney beans were less susceptible to both deltamethrin and clove essential oil and showed more sources of energy in the trophocytes although the attraction of adult females to both hosts was similar. However, the females reared on cranberry beans had higher reproductive performances and respiration rates, indicating that more energy was expended on reproduction than on the mitigation of the insecticide actions. Thus, with a change in hosts, a trade-off between reproductive fitness and the susceptibility to insecticides was demonstrated for A. obtectus. These results should not only affect the management of A. obtectus in storage units but also the understanding of these insects' host adaptativeness.