Toxicity of Seven <I>Bacillus thuringiensis</I> Cry Proteins Against <I>Cylas puncticollis</I> and <I>Cylas brunneus</I> (Coleoptera: Brentidae) Using a Novel Artificial Diet

Abstract

"Sweetpotato weevils" Cylas puncticollis (Boheman) and Cylas brunneus F. (Coleoptera: Brentidae) are the most important biological threat to sweetpotato, Ipomoea batatas L. (Lam), productivity in sub-Saharan Africa. Sweetpotato weevil control is difficult due to their cryptic feeding behavior. Expression of Cylas-active Bacillus thuringiensis (Bt) Cry proteins in sweetpotato could provide an effective control strategy. Unfortunately, Bt Cry proteins with relatively high toxicity against Cylas spp. have not been identified, partly because no published methodology for screening Bt Cry proteins against Cylas spp. in artificial diet exists. Therefore, the initial aim of this study was to develop an artificial diet for conducting bioassays with Cylas spp. and then to determine Bt Cry protein efficacy against C. puncticollis and C. brunneus by using this artificial diet. Five diets varying in their composition were evaluated. The highest survival rates for sweetpotato weevil larvae were observed for diet E that contained the highest amount of sweetpotato powder and supported weevil development from first instar to adulthood, similar to sweetpotato storage roots. Seven coleopteran-active Bt Cry proteins were incorporated into diet E and toxicity data were generated against neonate C. puncticollis and second-instar C. brunneus. All Bt Cry proteins tested had toxicity greater than the untreated control. Cry7Aa1, ET33/34, and Cry3Ca1 had LC50 values below 1 microg/g diet against both species. This study demonstrates the feasibility of using an artificial diet bioassay for screening Bt Cry proteins against sweetpotato weevil larvae and identifies candidate Bt Cry proteins for use in transforming sweetpotato varieties potentially conferring field resistance against these pests.

Agrobacterium-Mediated Transformation of Cry8db Gene in Vietnam Sweet Potato Cultivar

“…The sweet potato weevil is the major sweet potato insect pest worldwide, however, only three reports on transformed plants with insecticidal genes cowpea trypsin inhibitor, snowdrop lectin genes and cryIII gene have been published thus far [17,18,31]. Also, it is known that Bt is widely used in pest control agents, especially highly activate against lepidopteran pests.…”

Potential of bacterial derived biopesticides in pest management

“…Craveiro et al (2010) reported the efficient biological control of sugarcane giant borer caused by the Lepidopteran larvae Telchin licus licus (Castniidae) by variants of Cry1Ia toxins. Other studies reported the high toxicity of B. thuringiensis Cry protein towards Anthonomus grandis Boheman (Coleoptera: Curculionidae) (de Souza Aguiar et al, 2012) and towards Cylas puncticollis and Cylas brunneus (Coleoptera: Brentidae) (Ekobu et al, 2010).…”

Structural classification of insecticidal proteins – Towards an in silico characterisation of novel toxins

“…A number of the Etx/Mtx2 family of Cry toxins are also reported to require a binary partner for full activity. Cry23Aa (also known as ET33) acts with Cry37 (ET34) and has activity against various coleopteran insects Ekobu et al, 2010). Cry15Aa and Cry33Aa form binary partnerships with two other proteins (40kDa and NT32KD respectively) that, due to their lack of individual activity, have not been assigned Cry names, and share no obvious sequence similarity with any other characterized protein (Kim et al, 2003;Naimov et al, 2011).…”