Effects of metabolic inhibitors on activity of Cry1Ab toxin to inhibit growth of Ephestia kuehniella larvae.
BACKGROUND
Although the toxins of Bacillus thuringiensis Berliner (Bt) are frequently used to control lepidopteran pests, the tolerance or resistance of some lepidopteran moth strains may limit Bt applications. In this study, insecticidal cocktails consisting of sublethal doses of Cry1Ab toxin and additive compounds were tested for their suppressive effect on larval relative growth rate (RGR) in Ephestia kuehniella Zeller under laboratory conditions.


RESULTS
In the first step, the suppressive effect of diflubenzuron, soybean trypsin inhibitor (STI) and chitinase on RGR was confirmed. In the second step, these compounds were incorporated into a mixture of crushed kernels of Bt maize hybrid MON 810-YieldGard and its isoline with concentrations of Cry1Ab toxin ranging from 0.011 to 0.091 microg g(-1) diet. An additive effect on the suppression of larval RGR in E. kuehniella was found in a combination of diflubenzuron, STI and STI + chitinase as secondary compounds in insecticidal cocktails. Chitinase showed no additive effect on RGR.


CONCLUSIONS
The highest suppression level was found in cocktails with STI + chitinase as a secondary compound. It is hypothesized that the protease inhibitor (STI) protects both chitinase and Cry1Ab proteins from endogenous proteases in the larval midgut and prolongs their insecticidal activities. The possible application of insecticidal cocktails in the control of E. kuehniella is discussed.
Hubert
Jan
J
Crop Research Institute, Drnovska 507, Praha 6, Czech Republic. hubert@vurv.cz
Nesvorná
Marta
M
Zemek
Rostislav
R
Stará
Jitka
J
Stejskal
Václav
V
D000818:Animals; D000963:Antimetabolites / Q000494:pharmacology*; D001413:Bacillus thuringiensis / Q000378:metabolism; D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins / Q000494:pharmacology*; D002688:Chitinases / Q000494:pharmacology; D004132:Diflubenzuron / Q000494:pharmacology; D004357:Drug Synergism; D004731:Endotoxins / Q000494:pharmacology*; D006460:Hemolysin Proteins / Q000494:pharmacology*; D007306:Insecticides / Q000494:pharmacology*; D007814:Larva / Q000187:drug effects / Q000254:growth & development*; D009036:Moths / Q000187:drug effects / Q000254:growth & development*; D010572:Pest Control, Biological; D014361:Trypsin Inhibitors / Q000494:pharmacology
D000963:Antimetabolites; D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins; D004731:Endotoxins; D006460:Hemolysin Proteins; D007306:Insecticides; D014361:Trypsin Inhibitors; C030956:insecticidal crystal protein, Bacillus Thuringiensis; D002688:Chitinases; D004132:Diflubenzuron