Effect of dual inoculation with nematodes and fungal pathogens on the survival of Phyllophaga polyphylla larvae (Coleoptera: Scarabaeidae)

摘要

Phyllophaga polyphylla (Coleoptera: Scarabaeidae) is an important pest of maize and other crops in Mexico. Previous reports showed that this pest was highly resistant to fungal and nematode infection when each pathogen was inoculated separately; in this study, we evaluated whether dual inoculation of fungi and nematodes, in all possible pair-wise combinations and orders of inoculation and including an evaluation of a time separation of 73 hours between each pathogen's inoculation, would increase mortality in P. polyphylla larvae. The pathogens were two isolates of Heterorhabditis bacteriophora applied at a concentration of 50 infective juveniles (IJ) mL(-1), an isolate of Beauveria pseudobassiana and of Metarhizium pingshaense both applied at a concentration of 1 x 10(8) conidia mL(-1). In the first experiment, the combined mortality when pathogens were dualinoculated (13%), although significantly higher than single-inoculated treatments (8%), demonstrated that antagonistic interactions were ongoing between the pathogens, as confirmed by the chi(2)-test. In a separate experiment, using only the B. pseudobassiana isolate (1 x 10(8) conidia mL(-1)) and one isolate of H. bacteriophora (100 IJ mL-1), we studied the effect of different order of inoculations but included a two-week separation between inoculation of each pathogen. Mortalities obtained were similar to the previous experiment; all interactions resulted in antagonistic effects, except when the fungal pathogen was inoculated first, which resulted in an additive interaction. Understanding the mechanisms for the interaction requires further study but, for practical biological control, we suggest that more virulent fungal and nematode isolates are necessary to achieve control of P. polyphylla.