Parasitoids in low-level populations ofLymantria dispar [Lep.: Lymantriidae] in different forest physiographic zones

Abstract

A 2-year study was conducted on the distribution of parasitoids of gypsy moth, Lymtmtria dispar (L.) (Lep. : Lymantriidae), in mesic and adjacent higher elevation transition and xeric forest habitats in Vermont (U.S.A.). In both years, overall parasitism ranged from 12-18 % in each habitat. When analyzed according to the life stage at which the host was collected, parasitism rates of greater than 40 % were obtained among the late instars. Parasetigena silvestris (Robineau-Desvoidy) and Phobocampe disparis (Viereck) were recovered most commonly from the mesic habitat, and Cotesia melanoscehts (Ratzeburg) and Blepharipa pratensis (= Sturmia scutellata) (Meigen) were most common in collections from the xeric area. Parasitism by Compsiho'a concinnata (Meigen) occurred at similar levels in all three habitats, and this species was responsible for the highest parasitism rates on the site, reaching 40 % among the late instars in 1985. Percent parasitism by C.concinnata increased three-four-fold from 1984 to 1985, while parasitism by other species declined.

Gypsy moth parasitoids in the declining outbreak in Lithuania

“…The parasitism was summed over 3 years and for all stages comprised 34.4 ± 0.8%, ranging from 25.0 ± 2.0% in the earlier phase of outbreak collapse to 36.3 ± 1.2% and 35.2 ± 1.4% afterwards (table 2), and in the first year significantly lower parasitism was recorded than in subsequent years (χ 2 =10.2 for second, χ 2 =7.83 for third year after outbreak maximum, P<0.01). Some authors indicate that a lot of gypsy moth die from unascribed parasitism (S KINNER et al., 1993), but this was not true in our study. Only a small number of first and second instar larvae (total 1.3 ± 0.5%, 0.6 ± 0.2% and 5.6 ± 0.7% in subsequent years after peak defoliation, table 2) died from reasons, which could not be attributed either to pathogen or parasitoid impact, but rather to disability to feed on artificial diet or dessication; and this number was significantly greater in the third year after the outbreak (χ 2 =12.38 and 64.06, respectively, for first ands second year), showing a decrease of general larval vitality in the declining outbreak.…”

“…The differences in percentage parasitism of all other instars was not significant between years. The potential of this species appears to be more important than cited in Germany (M AIER , 1990) or USA (S KINNER et al., 1993).…”

“…was not screened in Lithuania. This species was assumed to be effective against late instar larval and pupae parasitoids (M AIER , 1990), appearing at high rates (> 20%) in the first post‐culmination year (S ISOJEVIC , 1975; F UESTER , 1988), but more prevalent in mesic than xeric forest habitats (S KINNER et al., 1993) and therefore outcompeted by the dominant P. silvestris in Lithuania.…”

The natural enemy complex of the gypsy moth, Lymantria dispar (Lep., Lymantriidae) in different phases of its population dynamics in eastern Austria and Slovakia – a comparative study

“…These species seem to be inferior to the guild of more specialized, oligophagous parasitoids that attacked L. dispar at our locations. It is of interest to compare these data with the finding of S KINNER et al. (1993) who ascertained a significant increase of parasitism by C. concinnata in Vermont in a year when parasitism by the specialists P. silvestris and C. melanoscela had decreased.…”

“…Generalists, such as polyphagous tachinids like C. concinnata , which frequently causes high parasitism in North America (e.g. B ARBOSA et al., 1975; T ICEHURST et al., 1978; G OULD et al., 1990; S KINNER et al., 1993), or like Exorista lavarum or Drino incospicua that together with C. concinnata accounted for the highest percentage parasitism in latent gypsy moth populations in former Yugoslavia (S ISOJEVIC , 1979) were recovered only in very low numbers. These species seem to be inferior to the guild of more specialized, oligophagous parasitoids that attacked L. dispar at our locations.…”