Toxicity of gaseous ozone to the different life stages of cowpea beetle, Callosobruchus maculatus (Coleoptera: Bruchidae), under laboratory conditions

Abstract

SummaryThe cowpea beetle, Callosobruchus maculatus (Fabricius), is recognized as a common insect pest of cowpea worldwide. The present study aimed to evaluate the insecticidal activity of ozone gas against all life stages (egg, larva, pupa and adult) of C. maculatus at a concentration of 600 ppm (1.2 g/ m3) after 6 exposure times of 0.5, 1, 2, 3, 4 and 5 h under laboratory conditions. The mortality percentages of all life stages were significantly increased with increasing exposure time. Similarly, longer exposure time to ozone caused higher reduction of adult emergence from eggs, larvae and pupae. Treatment with ozone for 5 h caused egg mortality of 72.3%. Total mortality of adults was observed 5 days after treatment with ozone for 0.5 h. Moreover, treatment with ozone for 5 h resulted in 75, 100 and 94.1% reductions in adult emergence from eggs, larvae and pupae, respectively. The results also indicated that the larvae and adults were more susceptible to ozone gas than the eggs and pupae. Based on the findings, ozone showed promising insecticidal activity against all stages of C. maculatus and could be used as potential fumigant for management of this insect.

Ozonation of Cowpea Grains: Alternative for the Control of Callosobruchus maculatus and Maintenance of Grain Quality

“…Similar results were found in maize, in which ozone did not influence germination [15]. Cowpea seeds were protected from attacks and weight loss caused by C. maculatus and C. chinensis by ozone treatment at a concentration of 2.0 g/m 3 , which did not significantly reduce seed germination compared to the control [18]. In a study using P. lunatus lima beans, increasing doses of ozone gas at a concentration of 1.61 mg resulted in an increase in the percentage of germination from 67.25% to 93.75% [22].…”

“…Consequently, our results of the exposure period, as well as the dose, were different, since these parameters affect the effectiveness of ozone, and consequently, the mortality of adult insects. It is worth mentioning that our study also evaluated the quality of the grains after the use of ozone gas, which was not observed in the study with different stages of life [18].…”

“…In the present study, the ozone concentration, while initially fixed, increased insect mortality with increased exposure to the gas. Our study, unlike the one carried out with different life stages of the insect [18],…”

“…Studies conducted to test the toxicity of ozone gas at different life stages of C. maculatus under laboratory conditions showed that adult insect mortality was observed in cases of treatments with 4 and 5 h of direct exposure at a concentration of 1.2 mg L −1 [18]. The insecticidal effect of ozone on C. maculatus infestation was optimized by increasing the concentration and dosage (exposure time) [20].…”

“…Furthermore, its degradation results in the production of oxygen [14,16]. These traits have led to studies demonstrating the effectiveness of ozone gas in controlling insect pests in stored grains, including C. maculatus, Zabrotes subfasciatus, Rhyzopertha dominica, Ephestia cautella, Plodia interpunctella, Trogoderma granarium, and Tribolium castaneum [17][18][19][20][21][22].…”