Heat tolerance of the swallow-wort biological control agent, Hypena opulenta

Sydney Chratian


Hypena opulenta is a moth species, native to Ukraine, that is an USDA-approved biological control agent for invasive swallow-worts. Swallow-worts compete with native plants in pastures and can harm Monarch butterfly populations due to their competition with milkweeds as oviposition sites for Monarchs. The larvae of H. opulenta feed exclusively on the leaves of swallow-worts and show promise in the potential for management of swallow-wort populations.  

The purpose of this research was to gain information on the effect of short-term heat exposures on the survival and fecundity of H. opulenta to determine optimal timing for field releases. To accomplish this, we exposed groups of adult H. opulenta in growth chambers to either 25°C, 33°C or 40°C for four hours. Following an initial 24-hour recovery period, survival and oviposition was monitored every other day after exposures. Results were compared among the three exposure groups using one-way ANOVA tests. Adult survival within 24 hours after the temperature exposure differed significantly among the three temperature groups, with the lowest percentage of survival from the 40°C group. Longevity also differed significantly, with adults from the 40°C group surviving for significantly less days than the 25°C or 33°C groups. Total oviposition within the 14-day period after exposure did not differ significantly, but the number of eggs laid among the 40°C group was lower than the 25°C and 33°C groups. As a result of these findings, we suggest that adult releases should be conducted in May or June when temperatures are closer to 20°C in order to positively influence fecundity and survival of H. opulenta.  Future research should include heat tolerance experiments with a temperature value set greater than 40°C to establish an upper lethal temperature for H. opulenta adults and include follow-up experiments to determine the impacts of heat exposure on the viability of eggs.