Suitability of Lymantria dispar (Lepidoptera: Lymantriidae) as a Host for the Entomogeneous Nematode, Steinernema feltiae (Rhabditida: Steinernematidae)

Abstract

Larvae, pupae, and adults of the gypsy moth, Lymantria dispar (L.), were susceptible to the entomogeneous nematode, Steinernema feltiae Filipjev (=Neoaplectana carpocapsae Weiser). The original inoculum, obtained from the wax moth, Galleria mellonella (L.), was infective at a dosage as low as 10 infective-stage nematodes per ml (LC50 = 38 nematodes per ml). After two passages through gypsy moth larvae, the pathogenicity increased (LC50 = 15 nematodes per ml), and remained stable thereafter. Nematodes reproduced within gypsy moth cadavers and progeny emerged 5 to 7 days after initial challenge. Nematode progeny increased from 35 per host (neonate larvae); 1,475 per second-instar larvae; 3,910 per third-instar larvae; to 11,106 per fourth-instar larva. Nematode progeny production in fifth-instar male larvae remained unchanged at 10,700; decreased in pupae to 8,900; and increased in adults to 13,500. Nematode production reached its peak among fifth-instar female larvae (43,000 per host), but decreased dramatically among sixth-instar female larvae (3,200 per host), and continued to decline in pupae (200 per host) and adult females (50 per host). Tissue extracts (10%) obtained from neonates, fourth- and fifth-instar larvae had little effect or inhibited nematode progeny production, while extracts from second- and third-instar larvae appeared to be stimulatory. The addition of sixth-instar (female) larval, prepupal, pupal, and adult female extracts increased nematode production slightly but was still below that of the standard (H2O). On the other hand, the addition of male prepupal, pupal, and especially adult male extracts resulted in greater numbers of nematodes than the standard.