An atoxigenic L-strain of Aspergillus flavus (Eurotiales: Trichocomaceae) is pathogenic to the coffee twig borer, Xylosandrus compactus (Coleoptera: Curculionidea: Scolytinae)

Abstract

This study isolated and evaluated virulence of fungal entomopathogens of Xylosandrus compactus – an important pest of Robusta coffee in Sub-Saharan Africa. A survey was conducted in five farming systems in Uganda to isolate entomopathogens associated with X. compactus. Four fungal isolates were screened for virulence against X. compactus in the laboratory at 1 × 107 conidia ml−1 where an atoxigenic L-strain of A. flavus killed 70%–100% of all stages of X. compactus compared with other unidentified isolates which caused 20%–70% mortalities. The time taken by A. flavus to kill 50% of X. compactus eggs, larvae, pupae and adults in the laboratory was 2–3 days; whereas the other unidentified fungal isolates took 4–7 days. The concentrations of A. flavus that killed 50% of different stages of X. compactus were 5 × 105, 12 × 105, 17 × 105 and 30 × 105 conidia ml−1 for larvae, eggs, pupae and adults respectively. A formulation of A. flavus in oil caused higher mortalities of X. compactus larvae, pupae and adults in the field (71%–79%) than its formulation in water (33%–47%). The atoxigenic strain of A. flavus could therefore be developed into a safe biopesticide against X. compactus.