Evaluation of ten botanical insecticides against the sweet potato Weevil, Cylas formicarius (Fabricius, 1798) (Coleoptera: Brentidae)

Abstract

The sweet potato weevil, Cylas formicarius (Fabricius) (Coleoptera: Brentidae), is a destructive insect pest that damages sweet potatoes both in the field and during storage. To identify new environmentally friendly insecticides to control this insect pest, three assays (olfactory test, anti-feeding assay, and toxicity assay) were conducted to evaluate the efficacy and mode of action of 10 botanical insecticides against C. formicarius adults in 2015 and 2016. Of these 10 botanical insecticides, tea saponin, pyrethrins, and veratrine showed significant repellency in olfactory tests. Eight botanical insecticides showed anti-feeding effects in the feeding choice test. Five botanical insecticides had high toxicity. Among them, the lethal concentrations of rotenone were lowest followed by pyrethrins. The lethal time values of rotenone were shortest followed by nicotine. In conclusion, rotenone, pyrethrins, nicotine, and toosendanin have the potential to control C. formicarius adults. Of these, pyrethrins and toosendanin are more environmentally friendly than rotenone and nicotine and were identified as better insecticides to control C. formicarius.

Laboratory and Greenhouse Evaluation of Melia volkensii Extracts for Potency against African Sweet Potato Weevil, Cylas puncticollis, and Fall Armyworm, Spodoptera frugiperda

“…Dichloromethane extracts of Duguetia lanceolata stem have exhibited a LC 50 of 946.5 µg/mL against the first instar of S. frugiperda [40]. Previous laboratory bioassays of pure botanical insecticides pyrethrins, toosendanin, veratrine, matrine, stemonine, rotenone and nicotine showed AFI indices of 97.9%, 97.9%, 59.4%, 33.9%, 69.3%, 35.4% and 39.9% respectively, against SPW at a 0.2% concentration [28]. Results from this study show that crude nut and pulp extracts both exhibit an AFI of 51%.…”

“…The antifeedant index against S. exigua was calculated using the formula described by Akhtar and Isman [27], while the antifeedant index against C. puncticollis was calculated using the formula described by Liyun et al [28], with a slight modification, whereby determination of the number of feeding holes in the tubers was replaced by determination of the weights of treated and untreated tubers after 24 h.…”

Bioactivity-guided isolation of toosendanin and salanninolide from Melia volkensii and their antifeedant activity against economically important insect pests

“…The rearing of African sweet potato weevils, C. puncticollis, S. frugiperda and T. castaneum was done as described by Liyun et al (2020), Jaoko et al (2021), andJbilou et al (2006), respectively.…”

“…Five 3 rd instar-larvae that had previously been starved for 3 hours were placed in the Petri dish. The leaf area of both control and treated diet was measured after 8 hours by placing the leaf on a 1 mm graph paper and counting the feeding holes on the leaf (Liyun et al 2020). An antifeedant index against S. frugiperda was calculated using the formula described by Akhtar and Isman (2004).…”