Establishing a Western Bean Cutworm Colony in the Laboratory
In the Agroecosystems Entomology Laboratory at the West Central Research and Extension Center in North Platte, we conduct experiments that address the ecology and management of agricultural pests in field crops. The western bean cutworm (WBC) is an important pest of corn and dry beans that can negatively impact both crop quantity (yield) and quality. As such, WBC is a major focus of our research program. We have spent the past several summers conducting experiments to assess WBC growth and development, plant-to-plant and within-plant movement of WBC, the efficacy of insecticides and Bt traits at controlling WBC at various infestation rates, and potential biological control for WBC.
WBC can be a challenging insect to study, in part, because it has only one generation per year. WBC spends the winter as prepupae, a quiescent or resting stage, and then pupates and completes development during the following spring and early summer. Adult moths start to emerge in early July in Nebraska and females lay eggs on corn or dry beans during July and August. In corn, larvae prefer to feed on fresh tassel tissue right after hatching and will later move to protected areas of the plant to feed on whorl tissue, pollen, and/or silks before moving into and feeding on developing ears. Once WBC larvae have eaten enough and reached their final instar, they will drop off the plant in late summer or early fall and burrow into the soil where they will spend the winter as prepupae, starting the cycle over again. Because WBC are active for only two to three months each year, we have limited time during the summer months to conduct research.
One way to overcome this hurdle and to extend our research season is to establish a WBC colony in the laboratory. Our WBC colony is one of only three colonies in the world, making this a unique resource to be able to conduct research on this critical pest for Nebraska. In general, lab colonies such as ours can also play a vital role in field research. Because WBC populations vary from year to year at a site and egg-laying may vary with planting date, having a reliable WBC population available in the laboratory increases the likelihood that field experiments will be successful. For example, when WBC infestation rates in some experimental plots were not high enough this past summer, we used female and male moths from our colony to infest corn plants in those plots by confining them in large sunflower pollination bags placed over the whorl until females laid eggs.
The successful rearing of an insect species in the laboratory involves providing the insects with suitable substitutes for environmental resources that they need to complete their life cycle, such as food, shelter, and egg-laying sites. Débora Montezano, a PhD student in our lab, has worked over the past three years to adapt and optimize WBC rearing methods that were originally developed by researchers at Iowa State University. Along with Montezano, Priscila Colombo da Luz, a visiting scientist from Brazil, has been organizing and maintaining the WBC colony in our laboratory this year. Priscila received her master's degree in zoology at the University of Brasília and brings with her several years of experience related to rearing insects in the laboratory, moth species in particular. She is one of several Brazilian scientists who have visited our lab in the past few years to conduct research.
The photos show the major steps involved in raising WBC moths in the laboratory, including collecting adult moths in the field (Figure 1), providing adults with proper nutrition and egg-laying substrates in the laboratory (Figure 2), collecting egg masses (Figure 3), providing larvae with an artificial diet (Figure 4), and caring for larvae as they eat and grow (Figure 5), prepare to pupate (Figure 6), and “overwinter” as prepupae (Figure 7) under controlled environmental conditions (Figure 8) in the laboratory. Currently, we estimate we have almost 5,000 WBC individuals in our colony and are looking forward to using the next generation of WBC in laboratory experiments this fall.