Effectiveness of Cordyceps sp. and Beauveria bassiana against large cabbage-heart caterpillar, Crocidolomia pavonana Fabricius (Lepidoptera: Crambidae)

Abstract

Crocidolomia pavonana Fabr. (Lepidoptera: Crambidae) is a major pest on various cabbage crops in Indonesia. Various insecticides have been used to control this insect pest including several entomopathogenic fungi, and this cabbage caterpillar has become resistant to various insecticides. In order to develop insecticides from entomopathogenic fungi, species or varieties from natural area such as forest are needed. A bioassays of Cordyceps sp. and Beauveria bassiana has been carried out in the laboratory. Inoculum of Cordyceps sp. obtained from the Dipterocarpaceae forest in South Kalimantan, Indonesia recovered from dead ants by the mycelium of Cordyceps sp. Four concentration of Cordyceps sp. and Beauveria bassiana inoculum and tween80 as a control were tested against 3rd instar larvae of C. pavonana with five replications. Field efficacy trial was carried out in a screen house (8 x 12 M2) using Chinese cabbage plants (Brassica juncea) aged 28 days after sowing, with a spacing of 0.4 M between rows. Three formulation of Cordyceps sp. and tween80 as a control were used with 6 replications. The result of the bioassays in the laboratory showed that Cordyceps sp. with concentration of 1 x 107 conidia mL-1 was able to give 100% mortality od C. pavonana larvae, while B. bassiana with the same concentration caused morality of C. pavonana larvae of 98.33%, although statistically not significantly different. The results of probit analysis also showed that LC90 Cordyceps sp. against cabbage caterpillar larvae was 1.57 x 106 conidia mL-1, while B. bassiana required a concentration of 2.6 x 106 conidia mL-1 to reach the LC90 value. The results of filed trial showed that the formulation of Cordyceps sp. 1 x 107 conidia mL-1 using palm oil cooking oil was able to give an average mortality of 86.7%, and significantly higher (P<0.05) than the other treatment. The results of this study indicate that the inoculum of Cordyceps sp. from Dipterocarpaceae forest is very promising to be developed as an insecticide to control C. pavonana in cabbage.