Western bean cutworm (Striacosta albicosta) (WBC) was first detected in Ontario in 2008 (Figure 1). Over the past decade, WBC populations have expanded their range eastward from the Central High Plains and into the Great Lakes Region. This range expansion has raised questions in Ontario about the biology of this insect, and the potential for damage on vegetable crops.
WBC has one generation per year; they overwinter in soil chambers as full-grown larvae and pupate in the spring. It is believed that moths prefer to lay eggs on pre-tassel corn. Larvae feed on corn ears, rendering sweet corn unmarketable. In beans, larvae can cause ‘window paning’ feeding damage on leaves (Figure 2); however the biggest concern is feeding on the pods (Figures 2 & 3). Detailed information on identification and monitoring methods for western bean cutworm can be found at the following website: http://www.cornpest.ca/default/index.cfm/wbc-trap-network/.
There has been only one study published examining the host range of WBC, and that was conducted in Idaho 30 years ago. Based on larval feeding and survival, it was determined that corn and garden beans were likely the original hosts of WBC, but some feeding and survival was observed on other legumes and solanaceous plants. As WBC has spread north and east across the Midwest US and into Ontario, damage has been reported primarily from corn and dry bean crops. However, Ontario has a varied agricultural landscape, with vegetable and field crops grown in relatively close proximity. WBC may thus represent a threat to Ontario’s vegetable crop production, particularly sweet corn, snap beans and tomatoes.
To determine if WBC is present in Ontario sweet corn and snap bean fields, a small survey was conducted at 17 locations in Essex, Kent, Middlesex and Norfolk counties in 2010. Moths were observed at all trap locations. The highest trap counts were recorded in snap beans in Middlesex County, where the average total moth count per trap for the season was 101.5. No economic damage was reported from any of the commercial fields included in the survey, and compared to field corn and dry bean fields in the same regions, trap counts were relatively low.
To evaluate survival and development of WBC larvae on potential host plants in Ontario other than corn, laboratory and field bioassays were conducted at the University of Guelph, Ridgetown Campus in 2010 in collaboration with Dr. Christina DiFonzo and her graduate student, Megan Chudlinski at Michigan State University.
In the lab, newly hatched larvae were fed leaf tissue from 8 different dry bean types, soybeans, green beans and peas, 9 other vegetable and 6 weed species for 31 days. Percent survival and larval development were measured at the end of the experiment (Figure 4).
In the field, each of these host crops was infested with a WBC egg mass and caged to prevent larvae from escaping. After 28 days, the surviving larvae were counted, measured and weighed to assess their development. High survival (65-100%) occurred on most dry bean cultivars tested, as well as on garden peas, cucumber, squash, lamb’s quarters, eastern black nightshade, red root pigweed and hot peppers (Figure 4). Medium survival (40-60%) was measured on soybeans, green beans, gourds and gladiolas. Poor survival (0-35%) was measured on tomato, potato, bell pepper, hairy crabgrass, green foxtail and velvetleaf. Generally, larval development was delayed or reduced on the hosts with medium to poor survival. On these hosts, larvae were typically smaller in size and did not develop to the same instar stage during the length of the experiment as did larvae feeding on the host plants where survival was high.
Studies to date have only examined feeding by larvae placed directly on plants, rather than looking at where female moths prefer to lay their eggs. In order to determine the host range of the WBC populations that have moved into Ontario, researchers at the University of Guelph are conducting field and lab studies to look at what vegetables, field crop and weed species WBC females will lay eggs on, which are preferred hosts for egg-laying and larval feeding, and how larval growth and survival differs among potential host plant species. Studies are also being conducted on the overwintering habits and success of WBC in Ontario with different soil types. This information, in combination with monitoring of vegetable crops for the presence of WBC, will be used to assess the level of risk that WBC poses to vegetable crops in Ontario.