Effects ofBlepharipa pratensis [Dip.: Tachinidae] on the pathogenicity of nucleopolyhedrosis virus in stage V ofLymantria dispar [Lep.: Lymantriidae]

Abstract

The effects of myiasis caused by Blepharipa pratensis (Meigen) on the pathogenicity of 3 dosages (1.00 • 104 PIB, 3.75 • 104 PIB and 7.50 x 104 PIB) of nucleopolyhedrosis virus (NPV) in stage V of Lymantria dispar (L.) were tested. When fed only NPV, 44 % of the larvae fed the low dosage died, 67 % of the larvae fed the mid-level dosage died, and 73 % of those fed the high-level dosage died. At the low dosage, mortality was significantly lower than at the other dosages. The presence of the parasite significantly increased mortality due to NPV ; 65 % of the larvae fed the low dosage died, 77 % of the larvae fed the mid-level dosage died, and 80 % of the larvae fed the highlevel dosage died. For biological control, the combination of NPV and parasite would increase mortality, but at the expense of the parasite.Although nucleopolyhedrosis is considered to be the prime cause of collapse of dense populations of Lymantria dispar (L.) (Campbell & Podgwaite, 1971), the processes that initiate epizooties and the mechanisms whereby nucleopolyhedrosis virus (NPV) spreads through the host community are not well understood. Because entomophagous parasites have an intimate association with juvenile L. dispar, and move about freely in the host community, they may be important in the epizootiology of nucleopolyhedrosis. Reardon & Podgwaite (1976) found positive correlations between the incidence of NPV and the incidence ofParasetigena silvestris (Robineau-Desvoidy) andApanteles melanoscelus (Ratzeburg) in natural populations ofL. dispar. Under laboratory conditions A. melanoscelus has been found capable of transmitting NPV (Raimo et aL, 1977). We have shown that the.presence ofBlepharipa pratensis (Meigen) in stage IV larvae enhanced deaths to NPV by about 38.7 % (Godwin & Shields, 1982).B. pratensis is thought to be the most successful insect parasite of L. dispar (PsehornWaleher, 1974 ; Angalet, 1974 (1)). It lays a microtype egg on leaves, and the egg must be swallowed for myiasis to be initiated. The number of the eggs on leaves increases as the season progresses ; late instars eat proportionately more eggs than do young larvae ; and the parasite (1) G

Parasitoids and pathogens in a collapsingLymantria dispar(Lepidoptera: Erebidae) population in Lower Austria

“…Compared to previous studies, NPV-induced mortality was high in young larvae, but low in older larvae (Hoch et al, 2001(Hoch et al, , 2019Maier, 1990;Turcáni et al, 2001). Due to the longer exposure time (Godwin & Shields, 1984;Reardon & Podgwaite, 1976) and increased environmental contamination with occlusion bodies, NPV prevalence typically increases with larval maturation (Murray et al, 1989) and causes a second wave of high mortality (Woods & Elkinton, 1987). April 2020 was warm (Figure 1), very dry (Figure 3), and had the most sunshine hours ever recorded in Lower Austria (ZAMG, 2020).…”