Biological activity of metarhizium anisopliae¹ strains and essential oils alone and in combination against diaphorina citri²

Biological activity of five strains of Metarhizium anisopliae Metschnikoff (Hypocreales: Clavicipitaceae) and six essential oils was tested in bioassays against the Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Psyllidae). Each agent, either conidia from fungal strains or essential oil was sprayed onto adults fed on orange branches in laboratory tests. Combinations of the most pathogenic strain or least pathogenic strain with most-toxic essential oil were tested on natural psyllid populations on Mexican lime trees in field experiments. Results in the laboratory showed Ma57 was the most pathogenic strain killing 77%, while Ma62 was the least pathogenic strain killing 6.1%. Cypress oil was the most toxic oil killing 56% while eucalyptus killed 15%. Results in the field showed the combination of Ma57 and cypress oil killed 56.73% of Asian citrus psyllids on Mexican lime trees. The combination showed additive interaction compared to activity of individual agents. Combination of Ma62 and cypress oil killed 39.4%. The combination showed synergistic interaction compared to activity of individual agents. Combination of a fungal strain and an essential oil might be a good alternative to control the pest, but more studies are needed to increase biological activity of the pathogenic and toxic agents.