New moth may curb pests, delay Bt crop resistance

Diamondback moths are notorious pests of crucifer crops, including canola and such vegetables as cabbages, broccoli and mustards, costing farmers worldwide some $5 billion each year.

They also have developed resistance to many insecticides, including Bt (Bacillus thuringiensis), a soil bacteria that can be sprayed on plants and also has been genetically engineered into corn and cotton to prevent insect attack.

A new study published in the 16 July issue of BMC Biology describes greenhouse trials of a genetically engineered (GE) diamondback moth that not only suppresses populations of pest diamondback moths (Plutella xylostella), but also reduces their resistance to Bt. Traditional insecticides and Bt crops kill pest insects, but steady exposure may lead to insects developing resistance to them.

The researchers used the diamondback moth and Bt broccoli as a model system to study a new approach to integrated pest management. Though Bt broccoli is not commercially available, and there are no Bt crops on the market that diamondback moth larvae feed on, the study's findings could apply to commercial Bt corn and Bt cotton to delay or prevent the evolution of resistance in pests that feed on those crops.

''We are at a crossroads right now with how we control pests, reduce pesticides and provide food for a growing world population in a changing climate,'' said Anthony Shelton, professor of entomology at Cornell's New York State Agricultural Experiment Station (NYSAES) in Geneva, New York, and co-author of the paper. ''We need to put our heads together to solve these problems with new solutions.''

One possible solution is a genetically engineered moth developed by the United Kingdom's Oxitec Ltd. The male moth carries a gene that prevents females from effectively reproducing.

The paper describes greenhouse trials where high numbers of GE male moths were released into cages containing pest diamondback moths. Shelton and colleagues found that in just a few generations, the engineered moths mating with the pest females led to a rapid decline of the pests.

In additional experiments, the researchers released low levels of the GE male moths in cages with Bt broccoli and pest moths. They discovered that the GE males kept pest populations in check and also delayed the buildup of resistance to the Bt broccoli.

''Adding the two biotechnologies together – engineered insects and Bt plants – demonstrates that you could both suppress the pest population and also decrease the number of Bt-resistant individuals in the population. The way forward in farming is responsible integrated pest management to improve available methods and to introduce new methods for safe and sustainable insect pest control,'' Shelton said.

The research team is planning follow-up caged field trials this summer to see how the moths fare, Shelton said.

The paper's first author is Tim Harvey-Samuel at the University of Oxford and Oxitec; co-authors include Neil Morrison of Oxitec and Luke Alphey at the Pirbright Institute in the UK.

The study was supported by the Biotechnology and Biological Sciences Research Council in the UK.