Biological Control of Helopeltis sp., the Major Pest of Acacia crassicarpa Tree Plantation with Entomopathogenic Fungi Beauveria bassiana and Lecanicillium lecanii

Abstract

Helopeltis sp. have been known as one of major pests on tea, cacao and cashew plantation. Recently, Helopeltis sp. have been also reported attack Acacia crassicarpa plantation in Sumatra and Kalimantan. For such extensive plantation, low cost biocontrol agents such as entomopathogenic fungi are choosen because of the simplicity for mass production. The information about biology of Helopeltis sp. in agricultural commodities especially tea plantation is quite common. However, it is very few reported in forest plantation. The research will contribute the data on biology of Helopeltis sp. in acacia plantation. The objective of this study was also to measure the effectiveness of Beauveria bassiana and Lecanicillium lecanii as biocontrol agent against Helopeltis sp. Both fungi that were used in this study were obtained from IPB Insect Pathology Laboratory. The tested insect, Helopeltis sp. was collected from Gunung Mas tea plantation and kakao plantation, University Farm IPB Sukamantri. The insects were reared in laboratory. Fifteen pairs of adult Helopeltis sp. were placed in fifteen plastic cages (Ф 20 cm, h 35 cm) with young acacia plant. Praoviposition, oviposition, and each stadia period were observed every day until the insect died. Three hosts of Helopeltis sp.; tea shoot, acacia shoot, and cacao pod,were placed in plastic container (Ф 35 cm, h 25 cm). Preference host test was observed during 5 hours after introduction of the nymph into container. Insect preference for egg laying was observed during 3 days after one pair of adult Helopeltis sp. have been entered. Four levels of conidial density, 109, 108, 107, 106 conidia/ mL were applied to adult Helopeltis sp. (B. bassiana) and 3rd instar nymph (L. lecanii). Daily mortality was observed until seven days post treatment. The result showed that female Helopeltis sp. produced 13-23 eggs after mating, egg stadia was 9 days, 1st – 5th instar nymph were 2, 3, 4, 3, 3 days.The adult stadia was approximately 15 days. Helopeltis sp. prefered to attend tea shoot (20%) greater than cacao pod (14%) and acacia shoot (10.33%). Helopeltis sp. prefered to lay eggs in cacao pod (133 eggs), rather than tea shoot (91 eggs) and acacia shoot (30 eggs). B. bassiana at 106 conidia/ mL density caused 81.25% mortality of adult Helopeltis sp., while 100% mortality at five days observation could be attained by using 108 conidia/ mL. The LC50 of B. bassiana was 3.2 x 104 conidia/ mL, at four days observation and LT50 was 4.214 days at 106 conidia/ mL. On the other hand, L. lecanii at 106 conidia/ mL caused 96.25% mortality of 3rd instar nymph of Helopeltis sp. at six days observation with the LC50 value at two days observation was 1.03 x 106 conidia/ mL, LT50 was 1.198 days and LT95 was 5.25 days. The results of these study showed that two fungi were effective against Helopeltis sp. in this bio assay.