The insecticidal effect of Cassava (Manihot esculenta) leaf extract on maize weevils (Sitophilus zeamais) in laboratory conditions.

This study was aimed to investigate the insecticidal effect of Cassava leaf extract (Manihot esculenta) on the maize weevils (Sitophilus zeamais) under laboratory conditions. A completely randomized design was used in the present study. One kilogram of leaf was dried and two liters of chloroform was used for the extraction. The maize weevils brought from the unwanted corn thrown by the farmers which was filled with weevils. There was plain untreated, distilled water used in the control group. Ten percent and 20% leaf extract of cassava (Manihot esculenta) were used in the experimental group to prove the mortality of the weevils. There were cylindrical barrels created with the base of cotton socking in which they were sprayed with the 10% and 20% leaf extract with each 5 puffs to present the weevils from drowning in the concentration. There were 10 set-ups for each control and experimental group in total 40 cylindrical treatment barrels. Each cylindrical barrels had 10 number of weevils tested in this set-up in a particular time intervals 10, 20 and 30 minutes respectively.

Among the 10, 20 and 30 minutes time interval, more number of weevils died in a longer time interval which is 30 minutes. There was a gradual increase in the mortality of the weevils when it is exposed more to the time interval when sprayed with the leaf extract. Twenty percent leaf extract had higher percentage of mortality when compared to 10% leaf extract by 6%. Mann-Whitney U test indicated that there was a significant median percentage mortality difference between 10% and 20% leaf extract after 30 minutes, z= -3.841, p< 0.05. Twenty percent leaf extract had higher percentage mortality compared to 10% leaf extract by 8.5%.

The researchers therefore concluded that 20% cassava leaf extract (Manihot esculenta) showed a higher percent of mortality of weevils when compared to 10% cassava leaf extract. In the interest of future studies, the student researchers would like to recommend the following: to know the chemical components present in the leaf extract which used to cause the death of the weevils; usage of other insects in the same leaf extract with higher levels of concentrations.