Vol. 15 No. 106- 115 (2024): Effect of Malathion Insecticide Application on Immature Duration of Development of Beans Weevil (Callosobrochus maculatus) raised on Insecticide-treated Seeds in Storage

Study was conducted to determine the time of commencement of life stages and duration of
time spend in each immature life stages of beans weevil (Callosobrochus maculatus) raised
on insecticide-treated grains in storage. White cowpea (Vigna unguiculata) was obtained
from Minna Central market, sowed during 2016 raining season without applying any
insecticide/pesticide in order to clear the beans seed from potential chemical processing
during storage. The experimental design was completely randomized, involving 7 test, 2 as
control (positive and negative controls) and the remaining 5 were treated with varying
concentration of malathion insecticide prior to commencement of the study. Results were

recorded for two phases of immature life stages with larval and pupal stages having sub-
stages of development. The results further revealed that the time of commencement of next

life stage from previous once were significantly (P = 0.05) faster in days with decrease in
insecticide concentrations in storage. In another development, there was significant increase
in the duration (days) egg spend before hatching, from the maximum time allowed for
oviposition uniformly (5.00±0.00 and 4.00±0.00 days for highest and lowest insecticide
application) respectively, as the concentration of insecticide increases. More so, total larval
duration (TLD) and total immature duration (TID) also varied significantly as the former
(15.00±0.00 and 18.00±0.00 days for TLD and 21.00±0.00 and 24.00±0.00 days for TID)
respectively, although there was no significant difference in total pupal duration (TPD)
(6.00±0.00 days) among weevils raised in all treatments. This result is an indication that,
insecticide in storage could affect egg hatching and larval developmental duration within the
beans seed. This information if articulated, can serve as early warning signals/biomarker of
grains treated with abused insecticide concentration for consumers and stakeholders of
cowpea and the knowledge can be applied to other stored product having similar immature
development process.