Exploring varietal resistance and Ocimum gratissimum essential oil for groundnut protection against khapra beetle, Trogoderma granarium

Abstract: This study explored the potential of combining differential susceptibility of
groundnut cultivars to khapra beetle (Trogoderma granarium) with insecticidal Ocimum
gratissimum essential oil for the management of the pest. Five groundnut cultivars (Samnut 10, Samnut 21, Samnut 22, Samnut 23, and Samnut 24) were evaluated for their comparative
susceptibility to T. granarium in a completely randomized design experiment. At seven (7)
weeks after infestation, data were collected. Ocimum gratissimum essential oil was evaluated
for toxicity in two groundnut cultivars (Samnut 24 and Samnut 21) at 0.5-2.0 ml/kg of seeds.
The bioassays were laid out in a randomized completely block design (RCBD). Data were
analyzed using analysis of variance and means were separated using Newman Keuls test at
5 % level of significance. Samnut 24 was significantly (p < 0.05) less damaged
(7.01 undamaged seeds) than Samnut 10 (4.03). Samnut 24 had higher number of undamaged seeds (7.80) than other cultivars (6.08-6.83) and significantly lower F1 progeny (0.71) than Samnut 23 (1.46) in the larval bioassay. For both Samnut 10 and Samnut 24, toxicity of the essential oil applied at 2.0 ml/kg against larvae or adults competed favourably with Chlorpyrifos.