DIFFERENTIAL SUSCEPTIBILITY OF DYSMICOCCUS-VACCINII (HOMOPTERA, PSEUDOCOCCIDAE) TO ENTOMOPATHOGENIC NEMATODES (RHABDITIDA, HETERORHABDITIDAE AND STEINERNEMATIDAE)

The susceptibility of the mealy bug, Dysmicoccus vaccinii Miller & Pol avarapu, to infection by various species and strains of entomopathogen ic nematodes was investigated in laboratory sand-dish and sand-column assays. Steinernema carpocapsae (Weiser) (All strain), S. feltiae (Fil ipjev) (AB [Australia] strain!, and S. glaseri (Steiner) (NC strain) w ere ineffective small against individual mealybugs in sand-dish assays conducted in small petri dishes (I cm high by 3.5 cm diameter) at 25 degrees C with doses of infective juvenile nematodes ranging up to 500 or 1,000 infective juveniles and exposure periods up to 5 d. However, Heterorhabditis bacteriophora Poinar (HP88 strain and 2 New Jersey is olates), H. hawaiiensis Gardner, Stock & Kaya (MG-13 strain), and H. i ndicus Poinar, Karunakar & David (EMS-13 strain) induced significant m ortality (65.0-90.0%) at doses as low as 100 infective juveniles and a n exposure of 5 d. H. bacteriophora (HBNJ strain) was effective at dos es of 500 and 1,000 infective juveniles but, together with H. zealandi ca Poinar (V16 strain) and 4 other H. bacteriophora isolates from New Jersey, was ineffective at doses of 100 infective juveniles. Removal o f the waxy coating from the mealybugs did not influence susceptibility to H. bacteriophora (HP88 strain). In the sand-column assay (5.5 cm h igh by 5 cm diameter, 5-d exposure, 25 degrees C), which more closely resembles host-finding in the field, H. bacteriophora (HP88 strain) in duced no significant mortality against individual mealybugs at doses o f 100 infective juveniles but produced 93.8% mortality at 500 infectiv e juveniles, whereas H. indicus (EMS-13 strain) induced 56.3 and 100% mortality at 100 and 500 infective juveniles, respectively. H. bacteri ophora (HP88 strain and some New Jersey isolates), H. hawaiiensis (MG- 13 strain), and H. indicus (EMS-LS strain) successfully reproduced in and emerged from mealybug cadavers. This study demonstrates strong var iability in the susceptibility of D. vaccinii to different species and strains of entomopathogenic nematodes, and implicates certain heteror habditids as promising candidates for the biological control of this i nsect.