Predation and Parasitism of Halyomorpha halys (Hemiptera: Pentatomidae) Eggs in Minnesota.

The brown marmorated stink bug, Halyomorpha halys (Stål) (Hemiptera: Pentatomidae), has spread across North America and is causing serious economic damages. Current management of this pest is based primarily on use of insecticides, which can disrupt integrated pest management programs. Alternatively, biological control is a more benign management tactic. This study provides the first examination of potential impact of parasitoids and predators of pentatomid eggs in Minnesota. Over 2 yr, 10,074 fresh and 9,870 frozen H. halys eggs were deployed in two forest and two soybean habitats in St. Paul, Minnesota from June to August. Our results demonstrate that rates of parasitism and predation were low, accounting for only 0.4 and 3.7%, respectively, across years, habitats, and egg states. In general, the parasitoid Telenomus podisi Ashmead (Hymenoptera: Scelionidae), had higher impacts on H. halys eggs in soybean, and generalist predators were more prevalent in forest habitats. Overall, predation was higher on fresh versus frozen eggs, and parasitism was not consistent across egg states. Although the rates of H. halys mortality due to natural enemies were low, results of our study may be conservative estimates of their true impact. Also, sentinel egg mass surveys should account for undeveloped parasitoids to better quantify H. halys egg mortality by native parasitoids. Alternative management tactics, such as the introduction of Trissolcus japonicus (Ashmead) (Hymenoptera: Scelionidae), could be considered to improve biological control of H. halys. Our findings serve as the foundation for future work on biological control of this pest and other pentatomids.

Host-mediated shift in the cold tolerance of an invasive insect.

While many insects cannot survive the formation of ice within their bodies, a few species can. On the evolutionary continuum from freeze-intolerant (i.e., freeze-avoidant) to freeze-tolerant insects, intermediates likely exist that can withstand some ice formation, but not enough to be considered fully freeze tolerant. Theory suggests that freeze tolerance should be favored over freeze avoidance among individuals that have low relative fitness before exposure to cold. For phytophagous insects, numerous studies have shown that host (or nutrition) can affect fitness and cold-tolerance strategy, respectively, but no research has investigated whether changes in fitness caused by different hosts of polyphagous species could lead to systematic changes in cold-tolerance strategy. We tested this relationship with the invasive, polyphagous moth, Epiphyas postvittana (Walker). Host affected components of fitness, such as larval survivorship rates, pupal mass, and immature developmental times. Host species also caused a dramatic change in survival of late-instar larvae after the onset of freezing-from less than 8% to nearly 80%. The degree of survival after the onset of freezing was inversely correlated with components of fitness in the absence of cold exposure. Our research is the first empirical evidence of an evolutionary mechanism that may drive changes in cold-tolerance strategies. Additionally, characterizing the effects of host plants on insect cold tolerance will enhance forecasts of invasive species dynamics, especially under climate change.