Deltamethrin‐induced feeding plasticity in pyrethroid‐susceptible and ‐resistant strains of the maize weevil, Sitophilus zeamais

Abstract

Phenotypic plasticity contributes to the adaptative evolution of populations exposed to new or altered environments. Feeding plasticity is a component of phenotypic plasticity not usually considered in insect strains adapted to insecticide‐altered environments, but which may either accentuate or mitigate insecticide resistance. This is a concern in the pyrethroid‐resistant strains of the maize weevil Sitophilus zeamais Motsch. (Col., Curculionidae), and the reason for this study. A pyrethroid‐susceptible and two pyrethroid‐resistant strains of maize weevil were subjected to free‐choice and no‐choice tests with maize grains sprayed with increasing doses of the pyrethroid, deltamethrin. The insects from the pyrethroid‐resistant strains exhibited higher feeding avoidance with increased deltamethrin doses than insects from the susceptible strain when subjected to free‐choice tests. The strains of maize weevil physiologically resistant to pyrethroids were also behaviourally resistant to deltamethrin – an additional management concern. The resistant strains avoid deltamethrin‐sprayed grains and are less nutritionally affected by this compound, with divergent responses from the susceptible strain with increased doses of deltamethrin. Furthermore, the higher relative growth rate and consequently higher efficiency of food conversion observed in the insecticide‐resistant strains were significant even without insecticide exposure, indicating that these traits are stimulus‐independent and may persist even without further insecticide selection, potentially limiting the options available for their management.

Weevil x Insecticide: Does ‘Personality’ Matter?

“…Only the maize kernels, rather than the vials, received deltamethrin application, allowing the insects to crawl on the vial’s unsprayed inner walls. In addition, deltamethrin is known to frequently induce some behavioral avoidance in populations of the maize weevil [46], [68], [69], which also stimulates their escape to untreated areas, lowering insecticide exposure and explaining the observed association between an increase in the distance walked and an increase in survival to deltamethrin exposure. Furthermore, more active individuals able to cover greater distances are likely of better quality, healthier and thus potentially able to withstand the insecticide effects for longer.…”

Novel Approaches to Application and Performance Assessment of Insecticide Applications to Crop Leaves

“…However, most of the recently developed insecticides do not necessarily cause immediate mortality or knockdown of target insects; instead they may interfere with arthropod feeding (Harrewijn and Kayser 1997, Castlea et al 2009, Hannig et al 2009, Reding and Persad 2009, behavior (Charleston et al 2005, Foster et al 2007, van Herk et al 2008, Oxborough et al 2008, Guedes et al 2009, Thieme et al 2009), or fertility (Shaalan et al 2005, Wang et al 2005, Deng et al 2006, George et al 2007, Bielza et al 2008. Performance assessment of these novel insecticides requires observations and experimental designs that encompass more than just simple assessment of knockdown effect.…”

Hermetic storage for control of common bean weevil, Acanthoscelides obtectus (Say)

“…There is a growing social concern regarding residual pesticide levels in foods and the risks that they pose to consumers' health. Moreover, there is also the risk that insect pests will develop resistance to these insecticides (Guedes et al, 2006(Guedes et al, , 2009. Thus, there arises the need for studies on alternative protection and conservation techniques of stored products.…”