PAUL A. GODWIN’s research while affiliated with United States Department of Agriculture and other places

Competition between two tachinid parasites, Parasetigena silvestris (Robineau-Desvoidy) and Blepharipa pratensis (Meigen), initiated in instar 4 of Lymantria dispar L., resulted in a significant, 65% reduction in B. pratensis survival as measured by maggot emergence. When multiparasitism is initiated in instar 5 or 6, competitive advantage is held by the species that infests the host first. In instars 5 and 6, P. silvestris survival is reduced by about 67% when B. pratensis infests first. In instar 5, B. pratensis survival is reduced by about 50%, and in instar 6 by about 73% when P. silvestris infests first. In addition, depending upon host instar and sequence of parasite attack, significant numbers (10-50%) of host larvae died without parasite emergence.

The host selection process ofBlepharipa pratensis (Meigen), a tachinid parasite of the gypsy moth,Lymantria dispar L., was investigated. Once in the host's habitat, and following contact with a recently damaged leaf edge (cut, torn, eaten), the fly orients perpendicular to the edge and moves back and forth with the front tarsi grasping the damaged edge. Oviposturing (oviposition intention) may occur. Leaf exudates appear to arrest the fly on the leaf and increase tarsal examination (searching). If an edge of a gypsy moth-eaten leaf is contacted, oviposition usually occurs. Significantly more eggs are laid when host-browsed foliage is encountered, compared to mechanically cut or damaged foliage, indicating response to a cue left by the host during feeding. The number of host-damaged leaf clusters in an area significantly enhances oviposition there; in field-cage tests, significantly more eggs (7911) were laid in simulated-crown areas with all clusters browsed, compared to the adjacent areas containing 1/2 browsed (4200 eggs) and undamaged clusters (2209 eggs). A host selection sequence is suggested and discussed.

Among the bark weevils of eastern North America, Pissodes strobi (Peck), P. approximatus Hopkins, and P. nemorensis Germar have the greatest impact on the silviculture of conifers. They share a number of behavioral and morphological attributes that make their identification uncertain. Therefore, we made a discriminant analysis of eight morphological variables and one meristic variable on 97 insects of each species. Each weevil in the sample satisfied three attributes of its respective species: karyotype, breeding site, and key characters established by Hopkins. We developed linear discriminant functions to discriminate between P. strobi and P. approximatus, and between P. strobi and P. nemorensis. These functions can be used when, on the basis of other geographical or biological information, the unknown is thought to be one of just two species.

Laboratory-reared 5th and 6th stage gypsy moth larvae were fed Blepharipa pratensis (Meigen) eggs placed on gypsy moth diet to induce parasitization. Laboratory-reared B. pratensis laid an avg of 900 eggs/female. Utilizing survival estimates for each life stage, the ratio of increase in egg laying females for a generation reared in the laboratory was 1:34. Some eggs retained viability when stored at 0°-2°C and 40% RH for up to 4 wk. Pupae stored at 0°-2°C and 100% RH were held successfully for 3 mo beyond the normal adult eclosion period. By proper timing of adult eclosion and egg feeding, the period for biological study of the parasite was extended for 3—4 mo.

The synchrony and interaction of the tachinid parasite, Parasetigena silvestris (Robineau- Desvoidy), with the gypsy moth, Lymantria dispar (L.), were studied in Connecticut in 1973 and 1974. Once in the host habitat the primary method for host location was visual. Each year, the number of P. silvestris attacks (eggs laid) was related directly to the number of large larvae available at any particular time. The number of P. silvestris adults caught on sticky tubes followed the pattern of occurrence of large larvae and attacks. Both the number of larvae attacked (with at least one egg) and the proportion of those with multiple attacks were inversely proportional to the number of large larvae. In 1973, there were ca. 8 times as many larvae, at peak count, as in 1974. The proportion of larvae attacked in 1973 was 17% (N=2237), compared with 54% (N=868) in 1974; in 1973, 14.7% of those attacked had multiple attacks, compared to 48.5% in 1974.s

Feeding response of larvae of the gypsy moth (Lymantria dispar L.) to 30 plant leaf extracts is reported. Plant extract is incorporated into a basal diet of cellulose powder, agar, and water. The amount of feeding was measured by dry weight of frass produced in 24 h. Extracts were tested alone and in combination with a stimulatory plant residue. This allowed classification of an extract into one of 4 categories: stimulant; neutral (no feeding effect); deterrent; and synergist.

A current tactic for biological control of the gypsy moth, Lymantria dispar Linnaeus, is to release its parasites in forests suscepti- ble to gypsy moth damage before the gypsy moth arrives. The basic assumption in these anticipatory releases is that the parasites can find and utilize native insects as hosts in the interim. Blepharipa pmtensis is being used in this way.