Influence of host plant on susceptibility of the aphid Acyrthosiphon pisum (Hemiptera: Aphididae) to the fungal pathogen Pandora neoaphidis (Zygomycetes: Entomophthorales)

The performance of the aphid-specific fungal pathogen Pandora neoaphidis was studied in relation to changes in herbivore resources for the pea aphid, Acyrthosiphon pisum, on different host plant species. Dose-response bioassays were conducted with A. pisum which had been reared on dwarf bean then inoculated with P. neoaphidis and returned to dwarf bean or inoculated and transferred to field bean, pea or lucerne. The smallest estimated median lethal concentration (LC50) was 7.7 conidia mm(-2) (95% confidence interval 5.4-11.2) for aphids returned to dwarf bean, with LC50S of 13.0 (9.2-19.1) and 14.6 (10.2-21.5) conidia mm-2 for aphids transferred to field bean or pea, respectively. The LC50 when aphids were transferred to lucerne [2941.0 conidia mm(-2) (237.3-2.1 x 10(9))] was greater than for the other three plants. In a subsequent experiment, A. pisum were reared on pea as well as dwarf bean for four generations before bioassays. The LC50 was 7.3 conidia mm(-2) (4.4-12.4) for aphids reared and incubated on dwarf bean, compared to 13.3 (8.0-23.9) and 15.3 (8.8-29.9) conidia mm(-2) when aphids were transferred between dwarf bean and pea, and vice versa, respectively. The LC50 for aphids reared then incubated on pea plants was 27.9 (15.8-57.3) conidia mm(-2). Hence, the virulence of P. neoaphidis, measured by LC50, was greatest when A. pisum was reared and maintained on dwarf bean, the plant used for long-term routine culturing of the aphid in our facilities. In conclusion, virulence of P. neoaphidis was greater on plant species to which A. pisum had become adapted during long-term laboratory rearing. Plant resources may affect infection by P. neoaphidis and the fungal entomopathogen will have a greater impact on aphid herbivores which are not suffering physiological stress related to a change in host plant.