Geographic variation in diapause in Nezara viridula (Hemiptera: Pentatomidae)

Diapause is a state of developmental arrest that enables an organism to survive predictable periods of unfavorable conditions. Often, diapause “triggers” consist of reduced photoperiods, temperatures, and host availability, which are indicative of deteriorating environmental conditions. Diapause can often be characterized by reduced metabolic rates, reduced activity levels, decreased feeding, reduced reproductive effort (production of eggs), increased levels of fat bodies, desiccation resistance, and the production of anti-freezing proteins. Several researchers have demonstrated that photoperiod was the primary environmental cue in initiating diapause in the southern green stink bug (Nezara viridula (L.)). In addition, diapause has previously been shown to be essential to N. viridula overwintering survival in Japan. It is often the case in many insects that variation in diapause incidence and susceptibility is due to the geographic and environmental variability among populations at differing latitudes.

Geographic variation in diapause in the southern green stink bug between three separate populations along the southeastern United States was studied by experimental manipulation of photoperiod.  Response to decreased photoperiod varied geographically. Northern populations responded to intermediate photoperiods with a significantly increased incidence of diapause, whereas southernmost populations responded significantly only to short photoperiod conditions. A similar geographic pattern of response was found in body size. Diapausing individuals in northern populations were significantly smaller (length & width) than non-diapausing individuals.  Understanding sensitivity of economically important crop pests to environmental conditions can provide integrated pest management programs with the tools necessary to understand both current and future pest geographic distribution.