Abstract
Anticarsia gemmatalis (velvetbean caterpillar) and Chrysodeixis includens (soybean looper) are two important defoliation pests of soybeans. In the present study, we have investigated the susceptibility and brush border membrane-binding properties of both species to Bacillus thuringiensis Cry1Ea toxin. Bioassays performed in first-instar larvae demonstrated potent activity against both soybean pests in terms of mortality or practical mortality. Competition-binding studies carried out with 125Iodine-labelled Cry1Ea, demonstrated the presence of specific binding sites on the midgut brush border membrane vesicles (BBMV) of both insect species. Heterologous competition-binding experiments indicated that Cry1Ea does not share binding sites with Cry1Ac or Cry1Fa in either soybean pest. This study contributes to the knowledge of Cry1Ea toxicity and midgut binding sites in A. gemmatalis and C. includens and sheds light on the cross-resistance potential of Cry1Ea with other Bt proteins aimed at controlling lepidopteran pests in soybeans.
Highlights
Soybean (Glycine max (L.)), is an important crop that has been increasingly planted worldwide, and reached an annual production of about 363 million tons in 2018–191
C. includens was more susceptible to this toxin in terms of mortality as the LC50 was calculated as 46 ng/cm[2], whereas the LC50 versus A. gemmatalis was calculated as 1311 ng/cm[2]
The LC50 value for practical mortality, which accounts for moribund insects, suggests that C. includens (LC50 = 14 ng/cm2) and A. gemmatalis (LC50 = 22 ng/cm2) survivability to Cry1Ea is nearly identical
Summary
Soybean (Glycine max (L.)), is an important crop that has been increasingly planted worldwide, and reached an annual production of about 363 million tons in 2018–191. The use of alternative insecticides such as biopesticides based on Bacillus thuringiensis (Bt) has assumed a prominent position to control insect pests because they have a high degree of specificity, are environmentally friendly, reduce grower costs and reduce the exposure of farmers to hazardous chemicals[6,7,8]. Bt proteins kill lepidopteran pests following their specific interaction with receptors found in the insect midgut, leading to pore formation in the apical membrane of the cells, provoking osmotic imbalance and disrupting the gut barrier. Its insecticidal activity has been reported for several lepidopterans[24,25,26] including soya pests[27], and studies with Cry1Ac resistant strains suggested no common receptors with Cry1Ac, since a low or no cross-resistance to Cry1E was observed[26,28]. The identity of the Cry1E receptors in the insect midgut remains unknown
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