Susceptibility of Ostrinia furnacalis to Bacillus thuringiensis and Bt Corn Under Long-Term Laboratory Selection

The susceptibility of the Asian corn borer, Ostrinia furnacalis to Bacillus thuringiensis (Bt) formulation and Bt corn was evaluated using insect bioassays for 6 years. Four strains of O. furnacalis were developed by laboratory selection from the laboratory strain reared on a non-agar semi-artificial diet. The RR-1 strain was exposed to a commercial formulation of B. thuringiensis subsp. kurstaki (Btk) incorporated into the artificial diet,the RR-2 strain was exposed to Bt corn (MON810) tissue incorporated into the diet, and the SS-1 and SS-2 strains were reared on the standard diet with or without non-Bt corn tissues material. Decreasing susceptibility of O. furnacalis to Bt and to Bt corn were found in each selected strain although the ED50 and larval weight fluctuated from generation to generation. The resistance of Bt-exposed strain (RR-1) to Btk increased 48-fold by generation 39; the Bt corn-exposed strain (RR-2) increased its resistance 37-fold to Btk by generation 24. No larvae of SS-1 survived when they were exposed to the leaves of Bt corn, Bt11 and MON810. However, 2-54% of the RR-1 (generation 46) and RR-2 (generation 20) larvae survived a 3 day-exposure to the leaves of Bt11 and MON810. The survival of both selected strains on Bt corn silk increased by 10-69%, and the larval weights after many generations selection were increased by 15-22% compared with the unselected susceptible strain. The young larvae were much more susceptible to Bt than older larvae. The highest mortality occurred when the larvae were exposed to Bt at the neonate stage. All of the results suggested that ACB could not only develop resistance to Bt preparation but also to Bt corn. Bt had significant effects on the growth and development of Asian corn borer than on the larval mortality. In order to maintain the long-term effectiveness of Bt pesticide and Bt corn, the resistance management should pay much attention to the larvae that may have opportunities to grow and developed on non-Bt corn or alternate hosts before they attack the Bt corn plants and the survival of larvae after Bt application.

Quantification of CrylAb Toxin in Bt Maize for Ostrinia nubilalis （Lep.： Crambidae） Bioassay

Two variants of diet composition were prepared to evaluate the susceptibility of ECBs to CrylAb toxin as follows： 1） 38-0600 Stonefly Heliothis Diet mixed with purified CrylAb protein and 2） 38-0600 Stonefly Heliothis Diet mixed with lyophylized leaves of Bt maize MON 810-YieldGard. A method of sample preparation and extraction of Bt toxin for reproducible ELISA quantification were optimized. The qualitative DAS-ELISA kit from Agdia was optimized for use in quantitative analysis of Cry lAb toxin. The mortality of ECB larvae from the laboratory strain on the diet with CrylAb toxin did not differ significantly from the mortality on the diet with Bt maize leaves with the same rate of Cry lAb toxin. Similarly, the mortality of the ECB larvae from the field population on the diet with Bt maize leaves did not differ significantly from the mortality of ECB larvae from the laboratory strain on the same type of diet. Therefore, the incorporation of Bt maize leaves into the diet did not influence the efficacy of CrylAb toxin against ECBs. Using this method, a susceptibility of one field population of ECBs from the Czech Republic to CrylAb toxin was determined （LC50 of 2.16 μg of Cry 1Ab g^-1 of diet）.

减施化学杀虫剂对亚洲玉米螟的防控效果

为构建玉米螟绿色防控技术体系,在肇东和宾县开展化学杀虫剂减量施用及新型Bt制剂防治玉米螟的田间试验。结果表明:两个添加助剂的杀虫剂处理在施药量减少30%后对玉米螟的防治效果均达到84%以上,减药加入助剂后的高效氯氟氰菊酯处理的防效要比常规的高效氯氟氰菊酯处理防效略高,挽回损失率在4.6%~6.5%,增产8.2%~8.7%。氯虫苯甲酰胺常规用量处理对玉米螟的防效最高,两试验地防效分别为92.5%和92.9%,在肇东和宾县两地的挽回损失率分别是6.8%和4.8%,增产10%以上。Bt制剂比化学杀虫剂的防效要低,两地防效均在81%以上,挽回损失率4.4%以上,增产率5.2%以上。因此,减量施用化学杀虫剂添加助剂的防控技术和新型Bt制剂均可有效防控玉米螟,可以作为玉米螟绿色防治技术手段应用于生产实践。