Insecticidal activity of entomopathogenic fungi (Hypocreales) for potato psyllid, Bactericera cockerelli: development of bioassay techniques, effect of fungal species and stage of the psyllid

The potato psyllid, Bactericera cockerelli (Šulc), is a pest of potato, tomato, and some other solanaceous vegetables and has also been incriminated in the transmission of a bacterial pathogen, Candidatus Liberibacter solanacearum, resulting in a serious disease known as “zebra chip”. Although there are several reports of fungal pathogens in psyllids, there are none from B. cockerelli, nor have any fungi been evaluated against it. Five isolates of fungi, one Beauveria bassiana, two Metarhizium anisopliae and two Isaria fumosorosea, were bioassayed against B. cockerelli on potato leaves under ideal conditions for the fungi. All applications were made with a Potter spray tower. With the exception of concentration-effect studies, all other applications were made using 107conidia/ml in a 2 ml aqueous suspension. All isolates except B. bassiana, produced 95-99% mortality, corrected for control mortality, in adults 2-3 days after application of conidia and 91-99% in nymphs 4 days after application. The corrected mortalities for adults and nymphs treated with B. bassiana were 53 and 78%, respectively 4 days after application. I. fumosorosea Pfr 97 produced 95% corrected mortality in both 1st and late 3rd instar nymphs. M. anisopliae (F 52) produced 96% corrected mortality in 1st and 3rd instar nymphs. Pfr 97 and F 52 were evaluated for insecticidal activity against 3rd instar B. cockerelli using 105, 106, and 107 conidia per ml. Mortality produced by I. fumosorosea Pfr 97 ranged from 83 to 97% and that of M. anisopliae F 52 was 88 to 95% at these concentrations.