Evaluation of Isolated Fungal Entomopathogens and Seed Extracts of Piper Guineense Against Larvae of Helicoverpa armigera (Lepidoptera: Noctuidae) in the Laboratory

ABSTRACT

A major constraint to increased and sustainable production of tomatoes is its infestation by insect pests particularly the tomato fruit worm Helicoverpa armigera (Hubner) (Lepidoptera: Noctuidae). The control of this insect relies heavily on the use of synthetic insecticides which have negative environmental effects. Some insects have developed resistance to certain insecticides. Efforts are therefore being made to look for alternative control strategies that are environmentally-safe and sustainable. This study determined the insecticidal effects of West African black pepper, Piper guineense (Schum and Thonn) seed extracts in combination with some indigenously isolated fungal entomopathogens on the larvae of tomato fruit worm, H. armigera and monitored the population trend of the pest on tomato fields during the major and minor tomato growing seasons. The entomopathogenic fungi were isolated from soil samples collected from around the University of Ghana, Legon, Accra and its neighbouring areas, using larvae of Tribolium spp. as baits. The results obtained in this study showed that there were more tomato fruit worms on tomato fields in the first cropping season than the second season. Only one of the entomopathogenic fungi was re-isolated from dead H. armigera and this was identified as Aspergillus sp. The pure isolate of fungus (Aspergillus sp.) and methanolic seed extract of P. guineense were bioassayed on H. armigera using topical application. Aspergillus sp. and the seed extract induced significant levels of mortality to the H. armigera larvae. Aspergillus sp. and seed extract induced 20% and 50% mortality, respectively. After six days of treatment but the seed extract inhibited the growth of Aspergillus sp. The study showed that fungi isolates and P. guineense seed extract could be potential control agents in the management of the tomato fruit worm.