Nutrient declines in overwintering Halyomorpha halys populations.
Brown marmorated stink bug, Halyomorpha halys (Stål) (Hemiptera: Pentatomidae), has become a major pest for agricultural growers since it arrived in the USA and Europe. To better understand the energetic requirements of overwintering, dispersal, and reproduction of this invasive pest, we monitored the weight, egg load, lipid, glycogen, and sugar levels of adult H. halys populations in western Oregon, USA, over 2 years. In the first study, overwintering H. halys collected monthly from inside shelters exhibited a consistent decline in weight, glycogen, and sugar levels from October to June. In the second study, post-overwintering adults that exited shelters in late spring had lower lipid, glycogen, and sugar levels than those that exited in early spring. Also, adults that just exited shelters had lower weight, glycogen, sugar, and sometimes lipids than adults that remained in diapause. Sugar levels declined the most during winter, followed by lipid and glycogen. These findings suggest that nutritional depletion may cause H. halys to emerge from diapause. In the third study, overwintered and first-generation adults (G1) were simultaneously collected from holly in July and August. Overwintered adults often had lower nutrient levels than G1 adults, which may reflect overwintered adults having expended energy for dispersal and reproduction. In the fourth study, we evaluated whether the Nutrient Index [weight (mg)/prothorax width (mm)3], a convenient index of physiological status, correlated with nutrient reserves. The Nutrient Index correlated with the adults' lipid, glycogen, or sugar levels in 57% of cases, ranging from weakly negative to moderately positive correlations.