Sexual Success after Stress? Imidacloprid-Induced Hormesis in Males of the Neotropical Stink Bug <i>Euschistus heros</i>

<div><p>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 <i>Euschistus heros</i> (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.</p></div

Histological sections of <i>E</i>. <i>heros</i> accessory glands stained with hematoxylin and eosin.

<p>Sections of the accessory glands of 10 day old males of <i>E</i>. <i>heros</i>, stained with hematoxylin and showing basic (<b><i>bs</i></b>) and acidic (<b><i>as</i></b>) secretions Black arrows indicate the cell nucleus.</p

Behavioral and physiological responses of E. heros after being sublethaly exposed to imidacloprid.

<p>Walking activities (A) and respiration rates (B) of recently emerged (< 24 h) <i>E</i>. <i>heros</i> males and females sublethally exposed to imidacloprid. (C) Body masses of recently emerged <i>E</i>. <i>heros</i> males and females. Each histogram represents the mean (± SE) of 20 replicates. Vertical lines (A and B) and horizontal lines (C) indicate no differences according to a Tukey´ s HSD test (<i>P</i> < 0.05). Asterisks indicate significant differences between responses of imidacloprid-treated and untreated insects.</p