Interactions among vegetable-infesting aphids, the fungal pathogen Metarhizium anisopliae (Ascomycota: Hypocreales) and the predatory coccinellid Cheilomenes lunata (Coleoptera: Coccinellidae)

Abstract

Entomopathogenic fungi are among biocontrol agents being considered for the control of aphids on a variety of crops. Predatory coccinellids, although generalist, are also among important natural enemies that must be conserved for aphid management. Laboratory studies were carried out to investigate the interaction between three vegetable-infesting aphids, Metarhizium anisopliae isolate ICIPE 62 and the coccinellid predator Cheilomenes lunata. At a concentration of 1 × 10⁸ conidial ml^–1, the fungus was found to cause mortality of 7.5% to C. lunata, compared to 2.5% mortality in the control at 10 days post-treatment. Female adult C. lunata to which fungus-infected aphids were offered as prey never accepted them as food source in non-choice bioassays. However, live and dead non-infected aphids were fed upon. In choice bioassay, a total of 1–3 out of 24 infected non-sporulating aphids per species (average of 0.1–0.4 aphids per arena) were consumed by 48 h-starved C. lunata within a period of 60 min, but avoided sporulating cadavers. Foraging adult C. lunata enhanced the spread of conidia of M. anisopliae from infected cadavers to fourth instars Aphis gossypii feeding on okra (0.8–15.0% mortality), Brevicoryne brassicae (3.3–15.0% mortality) and Lipaphis pseudobrassicae (0.8–14.2% mortality) on kale plants. Results of this study demonstrate compatibility between M. anisopliae and C. lunata, and could provide a sustainable strategy for effective management of aphids on crucifers and okra cropping systems.

Keywords:

• entomopathogenic fungus
• coccinellid
• aphids
• starvation
• spread

Acknowledgements

This study was jointly supported by funds from the German Ministry of Economic Cooperation and Development (BMZ) through a joint International Institute of Tropical Agriculture (IITA)/icipe/World Vegetable Centre/Friedrich-Schiller-University of Jena, German Academic Exchange Service/Deutcher Akademischer Austausch Dienst (DAAD) through the African Regional Postgraduate Programme in Insect Science (ARPPIS) of the International Centre of Insect Physiology and Ecology (icipe). The authors are grateful to Dr Daisy Salifu and Mr. Benedict Orindi for assisting in statistical analysis, and Mr. Gordon Otieno and Oreng Pascal for technical assistance.

Disclosure statement

No potential conflict of interest was reported by the authors.