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Des tests et des denombrements directs ont permis d'estimer l'abondance des spores de reserve du champignon Entomophaga maimaiga Humber, Shimazu et Soper, un pathogene de la Spongieuse Lymantria dispar (L.), dans des sols forestiers. Les spores de reserve recoltees en octobre, janvier et mars et refrigerees ont germe aussi facilement que les spores recoltees en avril, mais la germination etait plus rapide chez ces derniers. Des tests biologiques sur les spores de reserve de plusieurs sites du Connecticut etaient fortement relies aux resultats de denombrements directs des sols et en correlation faible avec un test anterieur a l'echelle de la foret. Le nombre de spores de reserve a un site etait inversement proportionnel au nombre d'annees ecoule depuis la derniere defoliation par la Spongieuse, ce qui semble devoir etablir implicitement a approximativement 10 ans la viabilite maximale des spores de reserve. Cette estimation de la longevite maximale correspond a la valeur obtenue par mesure directe de la viabilite a long terme des spores de reserve. Les resultats indiquent que la quantite de spores de reserve contenue dans le sol peut etre un facteur determinant important de l'efficacite du pathogene dans la lutte contre la Spongieuse.

From 1985 through 1995, burlap flaps were stapled to 100 trees in a 10 by 10 grid in a 4-ha forest plot. Each year, the number of fourth- to six-instar larvae of gypsy moth, Lymantria dispar L., under each burlap flap was recorded at least weekly in June and into July. From 1987 through 1990,100 000–120 000 hatching gypsy moth larvae were released near the center of this plot in early May at the time of natural hatch. In the 4 years that releases occurred, there was a distinct, single cluster of large larvae under the burlap flaps near the center of the plot. This pattern did not occur in other years. Results are interpreted to mean that total dispersal of larvae from first to ultimate instar is limited, even though first instars are readily dispersed by wind.

Forest ants in Connecticut, especially Formica neogagates Emery and F. subsericea Say (Hymenoptera: Formicidae), feed on first- to third-instar larvae of gypsy moths, Lymantria dispar L. (Lepidoptera: Lymantriidae), but mainly forage on the ground while most young caterpillars are in trees. It would be helpful to obtain information about the individual ants that do climb trees. Thus, numbers of ants climbing up and down different species of forest trees were determined. Numbers varied with both tree species and trunk diameter. Some oaks, plus hickories, tended to have the most ant traffic. These trees were also the most likely to have trunk diameters positively correlated with ant activity. Ants appeared to obtain honeydew or perhaps nectar from the trees, as the crop contents of some ants tested positive for sugar. A possible way to induce more ants to climb trees, and thus to attack caterpillars in trees more frequently, would be to increase numbers of honeydew-producing insects in trees. It should also be possible to encourage ants by spraying trees with sugar solutions or other materials.

The spatial distribution of the eulophid Sympiesis marylandensis Girault was examined in Connecticut in October 1988 and 1989 by vacuum-sampling apple trees in three zones of two apple orchards infested by its gracillariid host, the apple blotch leafminer, Phyllonorycter crataegella (Clemens). The abundance of females of S. marylandensis decreased with increasing distance of the zone or the sampled apple tree from the forest. The abundance of males in different regions of the orchard was similar. In two of three samples, the density of mines of leafminers was significantly higher near the edge than in the center of orchards. Parasitization of leafminers of the second generation and the number of female parasitoids vacuum-sampled during the third generation did not have a similar distributional pattern. We suggest that the amount of parasitism by S. marylandensis would be affected negatively by spraying trees at the border of orchards to kill immigrating pests.

Adult Calosoma sycophanta L. (Carabidae: Coleoptera) male and female pairs in a laboratory arena were observed for up to 30 days with a video recorder. Beetles were visible (i.e. not hiding) or in soil (i.e. female ovipositing) especially during night hours. Feeding on gypsy moth larvae occurred any time of the day or night. Male and female beetles were most active during the time when female beetles were ovipositing. Females spent more time eating and staying in soil than did males, but males tended to move around the arena more than did females. Based on results from this study, it is expected that, in the forest, C. sycophanta females will spend most of their time hidden in leaf litter or ovipositing. Males are more likely to be seen because they spend more time moving about, probably seeking mates.

Observations of behavior and dissections of hosts were carried out to investigate the ability ofApanteles melanoscelusRatzeburg (Hymenoptera: Braconidae) to distinguish between parasitized and nonparasitized gypsy moth larvae,Porthetria dispar(L.) (Lepidoptera: Lymantriidae). Fewer host examinations occurred and fewer eggs were laid in hosts which had been parasitized 0–9 days previously than in those which had never been parasitized. However, superparasitism occurred readily especially when few unparasitized hosts were available. By dissecting hosts which were parasitized more than once it was possible to investigate competition between supernumerary parasitoids. First instars are eliminated by some mechanism (possibly active combat), and older parasitoids eliminate younger ones.

In feeding choice tests, first- and second-instar larvae of Calosoma sycophanta L. preferred gypsy moth, Lymantria dispar (L.) (Lepidoptera: Lymantriidae), pupae as prey but third-instar larvae most often consumed caterpillars. All beetle larvae preferred female pupae over male pupae. In non-choice feeding tests, older predator larvae consumed more gypsy moth fifth-instar larvae than the larger sixth-instar larvae, but the total weights of prey eaten in both cases were similar. First-instar larvae of C. sycophanta only partially consumed prey, and caterpillar size did not affect the total numbers eaten. Beetle larvae ate as many female gypsy moth pupae as male pupae, but larger larvae consumed greater weights of the former than of the latter. As a consequence, C. sycophanta larvae fed female pupae were larger than those provided with male pupae. However, for a given increase in size, third-instar larval beetles ingested the same weight of food no matter what the prey size was. Conversely, young beetle larvae seemed to require greater amounts of the body contents of large prey for a given size increase, probably because fluids from large prey were lost during predator attack. The information gained in this study may make it possible to use sizes of field-observed C. sycophanta larvae to predict numbers of prey they have killed.

Tethered gypsy moth larvae, Lymantria dispar (L.) (Lepidoptera: Lymantriidae), placed in various tree microhabitats were most heavily parasitized by Compsilura concinnata (Meigen) (Diptera: Tachinidae) near the ground especially on leaves. In laboratory experiments, hosts were parasitized primarily between 6:00 AM and 6:00 PM (E.S.T.), with little parasitism at night. These data suggest that in the field, this tachinid will most efficiently attack young gypsy moth caterpillars, as instars 1 to 3 are the only ones consistently on or near foliage during daylight. C. concinnata females successfully parasitized young hosts, but larval development on 2nd instars was twice as long as that on 4th instars. Thus, only one generation of parasitoids on gypsy moths is likely per year. Results indicate that methods for improving the effectiveness of this parasitoid should emphasize increasing adult numbers early in the season.

The impact of predation by Calosoma sycophanta L. on an increasing prey population was assessed by recapturing marked adult beetles, periodically observing tagged gypsy moth pupae, and examining gypsy moth pupal remains in different microhabitats. Adult beetles dispersed in random directions but many tended to remain near the trap at which they were originally caught, suggesting a low dispersal potential. About 75% of the adult beetles present in the plot on one day were still present the next day. Capture–recapture estimates suggested that there were at most about 250 male beetles and half as many females/ha in the plot. Calosoma larvae destroyed 70% of tagged gypsy moth pupae under burlap bands on tree trunks near ground level, which was much more than any other mortality factor. Although this percentage was the same when mortality was assessed by looking at pupal remains within 5 m of the ground on tree trunks, pupae higher in trees and on leaves were not attacked as frequently. On average, about 40% of the pupae present in the entire study area were destroyed by Calosoma larvae. Each female beetle in the site would have had to produce about 30 progeny to have this effect. These data suggest that a relatively low number of adult beetles can have a substantial impact on gypsy moth populations.

A variety of field sampling procedures were used to estimate population levels of the gypsy moth, Porthetria dispar (L.) (Lepidoptera: Lymantriidae), and the following natural enemies: Apanteles melanoscelus (Ratzeburg) (Hymenoptera: Braconidae), Blepharipa scutellata (Robineau-Desvoidy) (Diptera: Tachinidae), and Calosoma sycophanta (L.) (Coleoptera: Carabidae). Regression analyses indicated, among other things, that gypsy moth egg mass counts were not good indicators of tree defoliation, but that defoliation and number of gypsy moth larvae on branch terminals were correlated. Estimates of adult abundance of A. melanoscelus and B. scutellata were negatively correlated with estimates of numbers of immature parasitoids. Numbers of gypsy moth larvae parasitized by A. melanoscelus were positively correlated with numbers of A. melanoscelus cocoons sampled. Numbers of adult C. sycophanta were not correlated with larval numbers of this insect. It was concluded from these results that the procedures used to estimate numbers of natural enemy adults were not entirely adequate, but may be useful for supplementing other sampling methods.

Two-day-old females of Compsilura concinnata (Meigen) were exposed to hosts for several days after which their host-related behavior was observed. Parasites retained their preference for gypsy moth, Lymantria dispar (L.) (Lepidoptera: Lymantriidae), larvae over greater wax moth larvae, Galleria mellonella (L.) (Lepidoptera: Pyralidae), whether conditioned to gypsy moths, wax moths, or no hosts. However, parasites conditioned to gypsy moth larvae examined and attacked hosts less frequently than those conditioned to wax moths or to no hosts. By exposing female flies to gypsy moth larvae for short times before tests and by dissecting them it was found that the number of progeny a female was capable of producing was not closely related to subsequent levels of parasite activity. Thus the activity differences appear to be behavioral rather than physiological in origin. The explanation appears to be that C. concinnata is unusually active when it first encounters a preferred host such as the gypsy moth. The invariance of the preference for gypsy moth larvae despite the exposure history of adult females means that C. concinnata probably could be reared on wax moths in the laboratory without concern that newly-emerged parasites might contact wax moths. They would still successfully attack gypsy moths in the field.

Predation of gypsy moth larvae, Lymantria dispar L. (Lepidoptera: Lymantriidae), by ants was observed by placing caterpillars on the forest floor and waiting for ants to find them or by placing caterpillars very close to foraging ants. Over 80% of contacts with caterpillars were made by Formica spp. The rate of successful capture varied with caterpillar instar, generally becoming lower as larvae became larger. However, neonates were successfully attacked by ants less often than first-instar larvae that had fed. Neonates probably have developed defenses that prevent excessive predation because many fall to the forest floor when dispersing. The distribution of time intervals between encounters of ants with larvae was adequately fit by an exponential distribution having a mean waiting time of 20 min. This distribution was used to construct a simulation model of gypsy moth larval predation by ants. Based on the model results, ant success rate, ant foraging density, and residence time of larvae on the forest floor were important determinants of mortality caused by ants.