Month: August 2023

Contributing Author: Dr. Francis Reay-Jones

More than 80% of field corn grown in the U.S. has been genetically engineered to express one or more insecticidal toxins from Bacillus thuringiensis, called Bt toxins. Bt corn was first commercialized in the U.S. in 1996, expressing a single Bt toxin targeting the European corn borer. Newer Bt corn hybrids express two or more Bt toxins, which has increased the number of target pests to include the corn earworm and the fall armyworm. Benefits of planting Bt corn can include protecting yield from insect damage, reducing the need to use insecticide, and improved grain quality. However, such benefits can be impacted by the development of resistance in target insects.

Dr. Francis Reay-Jones is continuing this year to evaluate the efficacy of Bt traits and the impact Bt toxins have on the life cycle of the corn earworm, with implications on resistance evolution. “We have been conducting field efficacy trials with a range of Bt traits since 2009. Since then, we have seen some traits become less effective over time because corn earworm has developed resistance. We saw in particular a shift in 2015 when resistance to some of the Cry toxins expressed in Bt corn became more widespread not just in South Carolina, but across the southeastern U.S.” Although the corn earworm is generally not a significant economic pest of field corn, the same species is a serious pest in cotton, where it is known as bollworm. Because Bt cotton expresses the same or similar toxins as Bt corn, selection for resistance in Bt corn is likely driving resistance issues to Bt cotton. “Planting a non-Bt refuge is the only tool we have to manage resistance. Preventing resistance development in Bt corn is crucial so that the insect does not cause more damage to Bt cotton later in the season, where the corn earworm (or bollworm) is a major economic pest.”

While resistance in corn earworm is widespread to most Cry toxins used in Bt corn and Bt cotton, one toxin, called Vip3A, remains highly effective. Trials in South Carolina continued this year to evaluate Bt corn hybrids expressing Vip3A. Examination of hundreds of corn ears in 2023 showed that these hybrids remain highly effective, with no ear injury found due to corn earworm feeding. In corn, this toxin is expressed in Trecepta, Optimum Leptra, and Agrisure Viptera products. While Vip3A remains effective, reports of unexpected injury in recent years in the mid-south underline the need for continued resistance monitoring. Vip3A toxins are also expressed in new Bt cotton varieties, and planting of non-Bt refuge in corn is crucial, since only a single Bt toxin is currently available with very good activity for this key pest.

Dr. Tom Bilbo, Clemson’s vegetable and strawberry entomologist stationed at the Coastal Research and Education Center in Charleston, began his research and extension program late in 2021. Since starting here at Clemson, Dr. Bilbo has rapidly expanded his program and has started addressing a number of different economically important pest concerns for vegetable and strawberry growers. “The primary goal of my research program is to enhance sustainable food production through protection of yields from crop pests and enhancement of yields through conservation of beneficial insects” Dr. Biblo says. The primary areas of focus for his research are 1) developing new biological control strategies for key pests, 2) reducing pest potential through modification of farming practices and systems, and 3) improving insecticide use and managing insecticide resistance. When it comes to Extension and stakeholder interaction, focus areas include 1) identifying key entomological issues in vegetables and strawberries, 2) encouraging adoption of improved practices through demonstration of efficacy and profitability, and 3) improving stakeholder knowledge of advances in IPM and IRM.

“Overall, my research uses our understanding of insect ecology to reduce pest problems and enhance the role of beneficial species, especially predators and parasitoids” Dr. Bilbo says, “much of my research is conducted on commercial farms in coordination with local growers.” The reason for much of the research being conducted with collaborating growers in twofold. 1) Insect ecology entails insects moving around, and insects don’t care about the arbitrary plot borders researchers construct. So small plot experiment station trials make it difficult to tease apart treatment effects as well as not being a realistic representation of how insects behave on vegetable and fruit farms. 2) On-farm trials allow Dr. Bilbo to build relationships with growers to understand the pest problems better and create management strategies that are feasible, economical, and effective.

Some of Dr. Bilbo’s on-going projects include pest management in brassicas, strawberry, tomato, watermelon, and cucurbits. In brassicas, the primary focus is effective integrated management of the diamondback moth, the major economic pest of most brassica crops worldwide. His work on diamondback moth includes determining how predator and parasitoid activity varies with the use of intercropped flowers (to optimize flower plantings), evaluating mating disruption as a potential management strategy, and determining which plants are best at attracting natural enemies of diamondback moths and other pests in both spring and fall crops. Much of this diamondback moth research is conducted in collaboration with specialists at NC State, Virginia Tech, and Tennessee State University. These types of regional efforts allow for a greater understanding of pest status and management options on a larger spatial scale.

In strawberry, his primary research focus is on enhancing the role of beneficial predatory mites to manage spider mites. A survey of commercial farms for the presence of these beneficial mites will provide a baseline level of knowledge on their natural occurrence and role in suppressing pest mites. Other projects include evaluation of tomato and watermelon cultivars for spider mite preference, evaluating pheromone traps for pickleworm moth in cucurbit crops, continued Bt resistance monitoring in corn earworm, and conducting insecticide trials to evaluate new and existing products for important pests. All of this research and subsequent extension work to disseminate the results of these studies will directly benefit vegetable growers in South Carolina by maximizing their pest management and providing a full range of tools to effectively address those pests.