Laboratory assessment of insecticidal properties of Tagetes minuta crude extracts against Brevicoryne brassicae on cabbage

The cabbage aphid, Brevicoryne brassicae is one of the most serious insect pests of cabbage in Lesotho. Chemical insecticides for efficient control of this pest are often unaffordable for resource-poor farmers. As a first step in a search for effective pest management techniques that can be affordable and easily available to these farmers, the aphicidal activities of Tagetes minuta crude extracts were evaluated against the cabbage aphid. A comparison was made on lethal and sub-lethal effects of T. minuta crude extracts from acetone, methanol, water and a mixture of acetone/methanol/water (7:7:1, v:v). The solvent system that produced the most toxic extract was the mixture, followed by methanol and water, whereas acetone produced the least toxic extract. The sub-lethal effect on cabbage aphid fecundity was well described by linear regression equations that showed significant reduction in fecundity as the concentration of crude extracts increased. The extract from the mixture solvent system had the strongest effect on fecundity. Key words: Brevicoryne brassicae, cabbage aphid, Tagetes minuta, crude extracts, lethal concentration, sub-lethal, fecundity.