Diamondback Moth Larva
Diamondback Moth
Three life stages of the
diamondback moth:
A: Larva B: Cocoon C: Adults
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Diamondback Moth
Thinking about using Bt to solve an insect problem? Read this!
The following is excerpted from Circular 899/May, 2006 from the University of Georgia Cooperative Extension, authored by David G. Riley, Associate Professor of Entomology Coastal Plain Experiment Station and Alton “Stormy” Sparks Jr., Associate Professor of Entomology, Cooperative Extension Service.
Emphasis by B&J Garden Solutions
The Diamondback Moth (DBM): The diamondback moth, Plutella xylostella L. (Lepidoptera: Plutellidae), is a common pest of Brassica crops including cabbage, collards, turnip greens, mustard greens, broccoli, cauliflower and other leafy greens. The eggs are laid on the leaves of these crops; then larvae hatch out and develop through four instars while feeding on the leaf. The larvae will then pupate in a cocoon on the leaf or the stem, usually after extensive leaf damage has occurred.
The life cycle of DBM changes with temperature from over two months in cool periods of the year to as little as two weeks during the summer in Tifton, Georgia. This means that the population can build rapidly during the months in late spring, summer and early fall but slows down in winter.
History of DBM Resistance to Insecticides: For our discussion here, resistance is defined by Sawicki (1987) as “a genetic change in response to selection by toxicants (i.e., insecticides) that may impair control (of DBM) in the field.” The first report of DBM resistance to an insecticide was to DDT in 1953 in Indonesia. By 1981 DBM had become resistant to more than 36 insecticides across multiple chemical classes including chlorinated hydrocarbons, carbamates, organophosphates and pyrethroids (Miyata et al. 1986). By 1990 resistance to abamectin, benzophenyl ureas, and various strains of Bacillus thuringiensis [Bt] had been reported in many parts of the world (Sun 1990). It is interesting that even the overuse of Bacillus thuringiensis kurstaki resulted in resistance in the field in Hawaii (Tabashnik et al. 1990) despite this pesticide having multiple modes of action and preserving beneficial arthropods. Thus even overuse of biorational insecticides can lead to resistance. Most recently, resistance to newer insecticide chemistries, including spinosad, indoxacarb and emamectin benzoate, has also been reported (Zhao et al. 2006).
The mechanisms of resistance within the DBM are also diverse (Sun 1990), including acetylcholines-terase insensitivity, reduced penetration, nerve insensitivity and detoxification of insecticides. The presence of these multiple mechanisms of resistance suggests that DBM is likely to become resistant to any class of insecticide given enough time, consistent selection pressure, and a large enough DBM population for selection to occur. Thus any new insecticide chemistries being developed face similar resistance selection problems beginning with their first use. Without proper insecticide resistance management, DBM will continue to overcome insecticides when used as a solitary control tactic.
This article also recommends that commercial growers “Use B.t.s when populations are low or some damage can be tolerated (i.e., early season; they can also be rotated with synthetic insecticides within a DBM generation).”
Read more about Bt resistance and disadvantages.
Why tolerate any pests at all?
Use the Moth-Blocker™ for 100% complete organic control!
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