Abstract
The wheat aphids, Rhopalosiphum padi (Linnaeus) and Sitobion avenae (Fabricius), are key pests on wheat crops worldwide. Management practices rely primarily on insecticides. The pirimicarb (carbamate) is used extensively as an effective insecticide to control these two aphids. In addition to the mortality caused by pirimicarb, various sublethal effects may occur in aphids when exposed to low lethal or sublethal doses. Understanding the general effect of pirimicarb on aphids could help increasing rational use of this insecticide. Under laboratory conditions, we assessed the sublethal effects of a low lethal concentration of pirimicarb (LC25) on biological traits and acetylcholinesterase (AChE) activity of R. padi and S. avenae. Both direct and transgenerational effects, i.e. on parent and the F1 generations were assessed, respectively. We found that R. padi and S. avenae responded differentially to the LC25 of pirimicarb. The parent generation of R. padi showed a 39% decrease in fecundity and multiple transgenerational effects were observed in the F1 generation; overall juvenile development, reproductive period, adult longevity and lifespan were longer than those of the control group. By contrast, LC25 of pirimicarb showed almost no effects on S. avenae biological traits in both the parent and F1 generations; only the pre-reproductive duration was reduced in F1 generations. Demographic parameter estimates (e.g. rm) showed similar trend, i.e. significant negative effect on R. padi population growth and no effect on S. avenae. However, AChE activity decreased in both R. padi and S. avenae treated by the LC25 of pirimicarb. We demonstrated sublethal and transgenerational effects of pirimicarb in the two wheat aphid species; it hinted at the importance of considering sublethal effects (including hormesis) of pirimicarb for optimizing Integrated Pest Management (IPM) of wheat aphids.
Highlights
The bird cherry-oat aphid, Rhopalosiphum padi (Linnaeus) and grain aphid, Sitobion avenae (Fabricius) are destructive pests of wheat, sorghum and other small grain crops worldwide [1,2,3]
Sublethal effects of pesticides on arthropods may be negative or positive [11], e.g. positive effects may occur through hormesis [42]
Due to the variable distribution and continuous degradation of active ingredients on plants after initial pesticide applications [36], arthropod populations may be exposed to sublethal concentrations of pesticides
Summary
The bird cherry-oat aphid, Rhopalosiphum padi (Linnaeus) and grain aphid, Sitobion avenae (Fabricius) are destructive pests of wheat, sorghum and other small grain crops worldwide [1,2,3]. Pirimicarb is a selective carbamate aphicide and mainly used for management of wheat aphid [8, 9]; it has been used for the control of wheat aphids since the 1990s in China [10] In addition to their lethal effects, insecticides may impair various key biological traits of aphids in the exposed insects through sublethal effects [11]. Understanding the general effect of pirimicarb on the aphids would help increase rational use of this insecticide in wheat and increase its sustainable use In this context, we investigated the direct effect of pirimicarb on wheat aphids under a low lethal concentration (LC25) on exposed individuals i.e. the parent generation, as well as the transgenerational effect on the subsequent generation (F1) [33]. The LC25 was used because such low concentration may occur in fields when insecticides degrade following initial application ([e.g. see [36])
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