Efficacy of bioactive compounds and their association with different cowpea cultivars against their major stored pest

Background: Stored grain insects are controlled with fumigant insecticides which can select resistant insect populations and cause environmental and applicator contamination. Thus, resistant cultivars and chemical constituents of essential oils are an alternative to the almost exclusive use of these insecticides. The effects of the combination of cowpea cultivars Vigna unguiculata (L.) Walp. with chemical constituents of essential oils against Callosobruchus maculatus were determined. Four cowpea cultivars: BRS Tracuateua, BR 17 Gurgueia, Epace 10 and Sempre Verde (insect rearing) untreated were used in the experiments and combined with chemical constituents of essential oil: eugenol, geraniol and trans-anethole. The biological parameters observed were: total egg number and eggs per grain, egg viability (%), insects emerged and insects per grain, immature stage viability (%), instantaneous rate of growth (ri), insect dry weight (mg), grain weight loss (%) and egg-adult period.

Results: When comparing all biological parameters, the cultivars BRS Tracuateua and BR 17 Gurgueia were harmful to C. maculatus. In the toxicity tests, the results showed that LC₃₀ and LC₅₀ of the chemical constituents ranged from 54.77 to 103.48 ppm and 60.99 to 125.18 ppm, respectively. In most of the biological parameters, LC₅₀ had adverse effects significantly higher than LC₃₀ and BR 17 Gurgueia treated were harmful to C. maculatus.

Conclusions: Overall, the findings showed that BR 17 Gurgueia combined with eugenol and geraniol more significantly affected the biological parameters of C. maculatus than when associated with trans-anethole, reducing egg number, insects emerged and egg viability.

Keywords: Vigna unguiculata; botanical insecticides; cowpea weevil; plant resistance.