INFECTIVITY OF THE ENTOMOPATHOGENIC NEMATODE STEINERNEMA-SCAPTERISCI (NEMATODA, STEINERNEMATIDAE)

Infectivity of the entomopathogenic nematode Steinernema scapterisci to a range of insect species was evaluated using the standard petri dish/filter paper assay. The nematodes infected and reproduced in insects in the orders Coleoptera, Diptera, Lepidoptera, and Orthoptera, but some insects were resistant. Resistent insects were the coleopteran larva Leptinotarsa texana, the dermapteran adult earwig Forficula auricularia, the orthopteran adult Periplaneta americana, and the lepidopteran pupae Spodoptera exigua. S. scapterisci from two geographical areas (Argentina and Uruguay) infected and reproduced equally in the last-instar wax moth Galleria mellonella . The nematodes were more pathogenic to G. mellonella larvae than to the adult house cricket Acheta domesticus with the LC50 (median lethal concentration) for A. domesticus being 38 times higher than that for G. mellonella. The host finding tactic of S. scapterisci appears to be similar to that of Steinernema carpocapsae wherein a large proportion of infective juveniles ambush hosts. In a sand-based assay, temperature affected the infectivity (penetration ability and insect mortality) of both S. scapterisci and S. carpocapsae, S. scapterisci being more infective at higher temperatures than S. carpocapsae. The optimum temperature for nematode penetration and establishment in G. mellonella larvae was 24°C for S. carpocapsae and 32°C for S. scapterisci. Temperature also affected the rate of G. mellonella mortality by the nematodes; compared with S. carpocapsae, S. scapterisci killed hosts slowly. In water, S. scapterisci survived and retained infectivity during the 16-week test period; however, percentage survival was greater at 10 and 25°C than at 4°C. The greater infectivity, development, reproduction, and storage stability of S. scapterisci at relatively higher temperatures indicate their probable adaptation to warm climates. It is concluded that the wide experimental host range, characteristic of entomopathogenic nematodes, also holds true for S. scapterisci. © 1993 Academic Press. All rights reserved.