The effects of warm and cold periods on resource depletion and emergence synchrony in diapausing Hypena opulenta: Implications for biological control of invasive swallow-worts in North America

Temperature plays an important role in winter diapause of temperate insects. Its effects can cause problems for biological control programs, both for the establishment of insects in novel climates and for the mass rearing of insects in the laboratory. Hypena opulenta (Christoph) (Lepidoptera: Erebidae), a biological control agent for invasive swallow-wort species in North America, has been observed to enter diapause in mid-summer in its introduced range. Additionally, H. opulenta has proved complicated to mass-rear, in part because individuals sometimes enter diapause unexpectedly, meaning that diapausing pupae may need to be stored over winter for varying lengths of time. We conducted pupal storage experiments to determine the effects of high pre-winter temperatures, like those experienced by early diapausing individuals in the field, on lipid store depletion. We conducted a second experiment to compare the effects of cold treatments of different lengths (1, 3, and 6 months), during diapause, on pupal mortality, development times, and the synchrony of adult emergence. Exposure to warm periods ranging from 25 to 75 days during early diapause did not affect pupal weight, adult emergence rates, or lipid store depletion in H. opulenta. Conversely, the length of cold exposure (between 1 and 6 months) during diapause clearly affected moth mortality, and the timing and consistency of adult emergence. Longer cold periods (3 and 6 months) resulted in earlier, more synchronous adult emergence, and lower diapause mortality, than shorter cold periods (1 month). Our results indicate that in terms of energy depletion, early diapause will not affect the fitness of emerging adults, which is important for the viability of univoltine populations in the southernmost part of the introduced range. Additionally, our results will assist with the H. opulenta mass rearing program, indicating the timing required to synchronize adult emergence.