1995 Annual Report for AS95-020
Natural Enemies, Viral Insecticides and Improved Information Delivery for Management of Lepidopterous Pests in Transgenic B.t. Cotton
Summary
Insect management on conventionally produced cotton in the Southeast still depends on repeated applications of synthetic chemical insecticides even though the "Boll Weevil Eradication Program" (BWEP) has resulted in reductions of these applications. Research in South Carolina has demonstrated that early-season applications for control of tobacco budworm (Heliothis virescens) to protect initial fruiting structures are not generally needed because of plant compensation. Also, research has quantified that natural enemies of insects increase substantially in early season in the absence of these applications. With the advent of transgenic B.t. cotton and its integration into grower production systems, we will be afforded even greater opportunities for substantial reductions in "hard" pesticides for insect control.
B.t. cotton is essentially a genetically different crop, particularly in relation to insect management. Current information indicates that it will virtually eliminate H. virescens as an economic pest; control of the cotton bollworm (Helicoverpa zea) is good except under very high pressure; and some suppression of soybean looper (Pseudoplusia includens) occurs. However, fall armyworm (Spodoptera frugiperda) and beet armyworm (S. exigua) are not controlled and can cause extensive damage in B.t. cotton in the southeast. Because viruses have demonstrated effectiveness against these pests on conventional cotton in the past, and since populations of natural enemies have been severely reduced by synthetic chemical insecticides, a strong effort is needed to determine and utilize their combined effectiveness in B.t. cotton production systems.
Objectives
1.) To quantify and assess impact of insect pests and their natural enemies in transgenic B.t. cotton compared with conventionally managed cotton.
2.) To determine efficacy of and develop viral microbial insecticides against lepidopterous pests developing in transgenic B.t. cotton.
3.) To develop delivery methods for the integration of B.t. cotton and viral insecticides into grower-driven crop production systems.
Approach
We used large on-farm plantings in several locations as well as on experimental stations to conduct the research. Large areas treated early in the season with synthetic chemical insecticides to destroy beneficials were compared with untreated areas to determine the role of beneficials in two cotton types; the genetically engineered B.t. cotton and conventional or standard cotton. Then small plot tests were conducted to compare microbial (or viral) insecticides with currently used synthetic chemicals to determine caterpillar control and their impact on beneficials.
Beneficial parasites and predators were sampled before and after use of "harsh" insecticides in early season in large plantings. Also, counts of all insects, pests and beneficials were made before and after applications of the "soft" viral and "harsh" synthetics to control caterpillars later in the growing season.
Results
Our results demonstrated that farmers should not apply "harsh" synthetic chemical insecticides in June to either the genetically engineered B.t. cotton or conventional cotton because of high mortality to beneficials. Where beneficials were destroyed in B.t. cotton, populations of important caterpillars such as bollworm and fall armyworm increased to economic levels later in the season, requiring additional controls. We also found that, to control these caterpillars, "soft" insecticides were not as effective as expected. Synthetic chemicals applied judiciously in mid- to late-season controlled these caterpillars better than microbials, producing higher yields. Destruction of beneficials at this time of the season did not cause pests to resurge to damaging levels later in the season. Also, there was no long-term damage to beneficials, and they increased during the fall and spring to reach high levels by the next year (1995-1996).
Impact of Results
Some 19 percent of South Carolina’s 350,000 acres were planted to B.t. cotton in 1996. Growers have indicated an increase in their B.t. acreage in 1997. Our results have helped growers adapt this "environmentally friendly" technology to their farming systems. We will continue to examine "soft" controls and conservation of beneficials in B.t. cotton; and our results should play a vital role in sustaining B.t. cotton systems.
December 1996.