ENTOMOPATHOGENIC NEMATODES FOR BIOLOGICAL-CONTROL OF THE LEAFMINER, LIRIOMYZA-TRIFOLII (DIPT, AGROMYZIDAE)

In the laboratory, mortality rates of the agromyzid leafminer larvae, Liriomyza trifolii (Burgess), ranged from 48 to 98 % by 20 strains and/or species of steinernematid and heterorhabditid nematodes. In the greenhouse, abamectin provided superior control of larval leafminers, killing 100 % of them as compared with Steinernema carpocapsae (Weiser) All strain (24 to 43 % leafminer mortality) or S. carpocapsae Liriomyza-selected strain (8 to 44 % leafminer mortality); the maximum relative humidity (r.h.) ranged between 81 and 91 % and the minimum r.h. between 50 and 70 %. In the foghouse under high r.h., the commercially available All strain and the Hawaiian isolate of S. feltiae (Filipjev) MG-14 strain caused 69 and 67 % mean mortality, respectively. There was a significant correlation (P < 0.01) between nematode mortality of leafminers and r.h., including the mean, standard deviation, and minimum r.h. during the 48 h after treatment. Average r.h. > 92 % with a standard deviation of < 9 % r.h. and a minimum of 72 % r.h. provided S. carpocapsae All strain mortality rates of leafminers > 65 %. The major constraint against the use of nematodes against leafminers in the foliar environment is low r.h. The use of nematodes against L. trifolii can be successful if the r.h. remains high and if nematodes enter leafmines before desiccation, and the nematodes should be integrated with chemical insecticides such as abamectin to manage pesticide resistance in L. trifolii.