The Effects of Photoperiod on Diapause Induction in Hypena opulenta (Lepidoptera: Erebidae), a Biological Control Agent Against Invasive Swallow-Worts in North America
Citation
Jones, I.M., Seehausen, M.L., Bourchier, R.S., Smith, S.M. (2020). The Effects of Photoperiod on Diapause Induction in Hypena opulenta (Lepidoptera: Erebidae), a Biological Control Agent Against Invasive Swallow-Worts in North America, 49(3), 580-585. http://dx.doi.org/10.1093/ee/nvaa030
Plain language summary
Diapause is a resting state for insects to enhance survival in unfavorable environments which are usually defined in terms of climate or food availability. The moth Hypena opulenta is a potential biocontrol agent for control of dog strangling vine which has recently been established at 2 locations in Ontario. This study assessed the role of daylength in initiating diapause for this species. In experiments moth pupae were found to enter diapause at day-lengths of less than 15 h 35 min, which occurs in Ottawa around the summer solstice. The significance of this result is that the moth will likely only have one generation through much of its new range, if it establishes in the United States, whereas locations in Canada may have 2 generations. More generations mean more impact on the host plant. The results can be used to control the initiation of diapause during mass-rearing of the biocontrol agent, which will assist in storing Hypena pupae for releases. It will also be used an input for a combined daylength and temperature dependent development model that is being built to better predict the eventual range and impact of the moth in Canada.
Abstract
© The Author(s) 2020. Published by Oxford University Press on behalf of Entomological Society of America. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com. Many insects exhibit a short-day diapause response, whereby diapause is induced when daylength falls below a critical threshold. This response is an adaptation to ensure synchrony between periods of insect activity, and the availability of resources, but it can cause problems when organisms are moved to new locations, where early or late-induced diapause can prove a barrier to establishment. We explored the role of photoperiod in diapause induction in Hypena opulenta, a recently introduced classical biological control agent for invasive swallow-worts in North America. We conducted four experimental cage releases as well as a growth chamber experiment to determine the threshold photoperiod for diapause induction in H. opulenta. We determined that the critical photoperiod for inducing diapause in 50% of H. opulenta is 15 h 35 min, which the moth only experiences in the Ottawa release site around summer solstice. This may lead to univoltinism, premature diapause, and poor establishment at some North American release sites. Our results can inform practical aspects of the biological control program for H. opulenta, such as fine-tuning methodologies for stockpiling diapausing pupae in the laboratory and narrowing down the optimal time window for releases at a given location. Additionally, our results will be important for the development of a temperature-based phenology model to more accurately predict voltinism in H. opulenta across the invasive range of swallow-worts in North America.