Abstract
Environmental stress in newly-emerged adult insects can have dramatic consequences on their life traits (e.g., dispersion, survival and reproduction) as adults. For instance, insects sublethally exposed to environmental stressors (e.g., insecticides) can gain fitness benefits as a result of hormesis (i.e., benefits of low doses of compounds that would be toxic at higher doses). Here, we experimentally tested whether sublethal exposure to the insecticide imidacloprid would hormetically affect the sexual fitness of newly-emerged adults of the Neotropical brown stink bug Euschistus heros (Hemiptera: Heteroptera: Pentatomidae), which is the most abundant and prevalent insect pest in Neotropical soybean fields. We evaluated the sexual fitness of four couple combinations: unexposed couples, exposed females, exposed males, and exposed couples. Sublethal exposure to dry residues (i.e., contact) of imidacloprid (at 1% of recommended field rate) did not affect insect survival, but led to higher mating frequencies when at least one member of the couple was exposed. However, the average mating duration was shortened when only females were exposed to imidacloprid. Moreover, exposed males showed higher locomotory (walking) activity, lower respiration rates and induced higher fecundity rates when mated to unexposed females. Although the reproductive tracts of exposed males did not differ morphometrically from unexposed males, their accessory glands exhibited positive reactions for acidic and basic contents. Our findings suggest that males of the Neotropical brown stink bug hormetically increase their sexual fitness when cued by impending insecticidal stress in early adulthood.
Highlights
Events occurring in the early adulthood of insects can have substantial effects on their life traits as adults
Once these insecticide molecules are poured on such ecosystems, they are likely to act on other non-targeted organisms or their interactions with the target pests may occur at lower doses, which may not lead to direct mortality but instead may result in sublethal consequences that potentially interfere with their survival and/or reproduction [3,4,9,10,11,12,13,14]
When these sublethal exposures to insecticides lead to stimulatory responses in exposed insects, it is referred as insecticide-induced hormesis, which has been identified in a number of arthropod species by influencing their reproductive output [9,15,16,17,18,19]
Summary
Events occurring in the early adulthood of insects can have substantial effects on their life traits (e.g., dispersion, survival and reproduction) as adults. Such inevitable exposure derives from the fact that one of the fundamental tenets of pest management is the deliberate use of insecticides aimed at reducing pest populations as much as possible, thereby minimizing losses in yield [3,8] Once these insecticide molecules are poured on such ecosystems, they are likely to act on other non-targeted organisms or their interactions with the target pests may occur at lower doses, which may not lead to direct mortality but instead may result in sublethal consequences that potentially interfere with their survival and/or reproduction [3,4,9,10,11,12,13,14]. When these sublethal exposures to insecticides lead to stimulatory responses in exposed insects, it is referred as insecticide-induced hormesis, which has been identified in a number of arthropod species by influencing their reproductive output [9,15,16,17,18,19]
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