Chemical and biological insecticides: Resistance mechanisms and management in diamondback moth

摘要

The diamondback moth ( DBM), Plutella xylostella L. , is a highly injurious, cosmopolitan pest of cruciferous crops. A well-known reason for this pest status is its remarkable ability to rapidly evolve insecticide resistance. When a new compound becomes available, growers may adopt it because of inability of existing insecticides to provide adequate control; but over-use and the absence of management strategies usually result in the appearance and spread of new resistance from focal points to wider geographic areas. DBM was the first species to develop resistance to Bt toxins in open field populations. Overuse of Bt sprays was responsible; and future attempts to control DBM using Bt-expressing transgenic plants must be mindful of this precedent. Resistance management strategies may attempt to delay the onset of resistance, such as the high-dose/refuge strategy employed for pests of transgenic Bt-cotton, or to manage existing levels of resistance to economically sustainable amounts when it has already appeared. The latter approach, such as when rotations are employed, is successful only when resistance carries with it a substantial fitness cost in the absence of insecticide, and the magnitude and types of such costs are in general poorly known. Combinations of chemical insecticides or "pyramiding" of insecticidal genes in plants can delay the onset of resistance, but if DBM has already developed some resistance to one of the components, the effectiveness of this strategy is compromised. One approach that deserves more attention is the exploitation of the key adaptation by which DBM detoxifies glucosinolates in its cruciferous hostplants. A highly active sulfatase expressed in the midgut has been shown to cleave off the sulfate group, preventing activation of the glucosinolate to more toxic compounds by the myrosinase enzyme of the plant. This sulfatase has not been detected in any other insect, and may be unique to DBM; thus targetting this enzyme may provide a highly specific method of control.