SELECTIVE BREEDING OF STEINERNEMA-FELTIAE (FILIPJEV) (NEMATODA, STEINERNEMATIDAE) FOR IMPROVED EFFICACY IN CONTROL OF A MUSHROOM FLY, LYCORIELLA-SOLANI WINNERTZ (DIPTERA, SCIARIDAE)

A method of selecting a Steinernema feltiae strain that is effective against a mushroom fly, Lycoriella solani, is described in detail. The pest control efficacy of the selected nematode strain was evaluated and compared with the efficacy of two unselected strains. The selection procedure was designed to give preference to nematode individuals with the greatest ability (1) to search effectively for the target insect larvae in their natural habitat, (2) to infect them shortly after application and (3) to reproduce in their haemocoel. Thirty-four rounds of selection achieved a 4-fold improvement in nematode ability to find and parasitize third- and fourth-instar larvae of the pest in the mushroom substrate. In 24-h laboratory experiments, mortality of the insect caused by nematode juveniles rose from 22.5%, recorded for the original unselected isolate, to 92.5% for the selected strain. In a 51-day experiment conducted on a mixed age mushroom house population of L. solani, the enhanced pest control ability of the selected strain was detected shortly after nematode application and remained high throughout the experimental period. During the first 4 weeks of the trial the selected nematode strain was significantly better than both unselected strains and caused 91.1-92.7% reduction of the fly emergence from the mushroom substrate. No difference was observed between the efficacy of the selected nematodes applied at 1 x 10(6) and 3 x 10(6) infective juveniles per m2, while the unselected strains performed significantly better at the higher concentration. All the nematodes examined showed good persistence in the mushroom casing apparently due to recycling in the insect host.