Use of methanolic plant extracts against maize weevil (Sitophilus zeamais) (Curculionidae: Coleoptera)

The maize weevil poses significant global concerns as it causes huge economic losses to stored grains. The chemical control methods are popular among farmers but raise serious concerns regarding human and environmental safety, highlighting the urgent need for novel and safe strategies. Plant extracts are seen as safe substitutes to toxic chemicals. Therefore, this study investigated the efficacy of methanolic plant extracts prepared from Azadirachta indica (seeds), Caralluma tuberculata (succulent fruits), Allium sativum (rhizomes), Curcuma longa (rhizomes), Citrullus colocynthis (succulent fruits) and Calotropis procera (leaves) against maize weevil under constant conditions of 27 ± 2 ⁰C, 65% R.H). The experiments were carried out using a CRD design having five replications in the laboratory of the Entomology department, Gomal University, Dera Ismail Khan, Pakistan. The methanolic plant extracts were tested at 0.5, 1.0, 1.5, 2.0, 2.5 and 3.0% (v /w), concentrations, respectively. The parameters investigated, included, the number of days to F₁ generation, emergence of F₁ progenies, percent infestation and weight loss of grains, adult life span and sex ratio (male/female). Each methanolic plant extract was mixed with 20 g maize grains. Among the treatments, the A. indica and C. longa extracts showed greater effectiveness at the maximum concentration (3.0%), significantly delaying the emergence of F₁ adults to 40.20 and 38.80 days, respectively, compared to the control group which emerged in 26.20 days. Least number of F₁ adult emergence (11.60) was observed in A. indica extracts followed by C. longa having (18.00) while the highest number (45.80) was observed in C. procera treated grains at the maximum concentration of 3.0% compared to 81.20 in the untreated grains. The A. indica extracts showed the least infestation rate (2.14%) followed by C. longa (3.15%). Conversely, higher infestation rates were noted in C. tuberculata (8.38%) and C. procera (9.20%) treated grains at the maximum concentration of 3% compared to 35.20% in the control group. The minimum (1.10%) weight loss was observed in A. indica extracts treated grains whereas; maximum weight loss was observed in C. procera (5.11%) treated grains at the maximum concentration compared with control (27.50%). The minimum adult life span of 32.40 days was observed in maize grains treated with A. indica extracts followed by C. longa (34.20 days) and maximum adult life span was documented in C. procera (37.60 days) and C. tuberculata (37.00 days) treated grains at the maximum concentration compared with control (46.00 days). All the tested methanolic plant extracts had no significant effect on the sex ratio of the weevil adults. It is concluded from the results that the methanolic extracts of A. indica and C. longa could be used as allele-chemicals to control maize weevil under storage conditions.