Foraging Behavior of Field Populations of Diadegma Spp. (Hymenoptera: lchneumonidae):Testing for Density-Dependence at Two Spatial Scales

The foraging behavior of populations of Diadegma spp. (Hymenoptera: Ichneumonidae) attacking the diamondback moth, Plutella xylostella L. (Lepidoptera: Plutellidae), was studied in the field. The effect of host density on percentage parasitism was investigated at two spatial scales: that of the individual plant, as well as a “cluster of plants” at low, medium and high densities. Using binoculars, parasitoid searching was observed on host plants at different host densities over an 8-h period. Behavior was compared to that predicted under the Patch Selection Theory. Percentage parasitism was independent of host density at both spatial scales. However, the behavioral studies showed parasitoid aggregation behavior at higher host densities. The population displayed an imperfect preference for higher host densities in the first 4 h of foraging. In the second 4-h period, no preference was observed.

Behaviour and development of Elasmosoma sp. (Neoneurinae: Braconidae: Hymenoptera), an endoparasite of Formica ants (Formicidae: Hymenoptera)

The behaviour and development of Elasmosoma sp., near pergandei Ashm. (Neoneurinae: Braconidae: Hymenoptera), a parasite of the ant, Formica obscuriventris clivia Creighton, was studied in a coastal sand dune habitat in central Oregon over a 2-year period. Female wasps oviposited into the abdomen of major worker ants after alighting briefly on the host. Embryonic development of the wasp occurred inside the serosal membrane or trophamnion of the egg in the abdomen of the ant host. First instar wasp larvae possessed a large head capsule with falcate mandibles, 11 ventral body lobes, an elongate tail and a dorsally located anus. Second instar larvae were unspecialized and lacked the large head capsule, elongate tail and paired ventral body lobes. Third instar larvae were hymenopteriform with a distinct head capsule. Cocoon formation and adult emergence is described. Observations on the percentage parasitism and altered behaviour of parasitized ants are presented. The association between neoneurine wasps and ants is a well-balanced system that has been in existence for at least 40 million years.

PARASITISME HEMIPTARSENUS VARICORNIS (GIRAULT) (HYMENOPTERA: EULOPHIDAE) TERHADAP LALAT PENGOROK DAUN LIRIOMYZA HUIDOBRENSIS (BLANCHARD) (DIPTERA: AGROMYZIDAE) PADA TANAMAN KACANG ENDUL (PHASEOLUS VULGARIS L.) DI CILOTO, JAWA BARAT

Parasitism of Hemiptarsenus varicornis (Girault) (Hymenoptera: Eulophidae) on leafminer fly Liriomyza huidobrensis (Blanchard) (Diptera: Agromyzidae) on kacang endul (Phaseolus vulgaris L.) in Ciloto, West Java. The objective of this research was to elucidate the relationship between leafminer and its parasitoid abundants. The research was conducted in Ciloto (Cianjur), West Java in 1999. The miner infested leaves of kacang endul were collected and placed in plastic bowls. The emerged parasitoids from those leaves were counted. The result indicated that the level of parasitism of H. varicornis during the plant growth stage ranged from 39 to 50%. The perfect density dependent between percentage parasitism and the leafminer abundance was experimentally proved.

Parasitism Rates in European Corn Borer (Lepidoptera: Crambidae) Larvae Collected from Six Maize Hybrids

The parasitoid complex and level of parasitism of European corn borer, Ostrinia nubilalis (Hübner), larvae in six maize, Zea mays L., hybrids was determined in Nebraska during 1995 and 1996. Three parasitoids, Eriborus terebrans (Gravenhorst), Macrocentrus grandii Goidanich, and Lixophaga sp., were reared from field-collected European corn borer larvae. Larvae collected from Hoegemeyer 2626 exhibited the highest percentage parasitism for the 1995 first generation in Lancaster (37.2%) and Dixon (28.6%) counties. No significant differences were identified for the 1995 second generation at both sites because of reduced sample size and high larval mortality caused by naturally-occurring entomopathogens. During 1996, there were several significant differences in percentage parasitism of larvae collected from the hybrids. Larvae collected from Northrup King N7070 exhibited the highest first-generation parasitism (23.8%), while larvae collected from Hoegemeyer 1125W exhibited the highest second-generation parasitism (46.0%) in Dixon Co. In Lancaster Co., parasitism of first-generation larvae collected from Hoegemeyer 1125W (10.3%) was only significantly greater than parasitism of larvae collected from Hoegemeyer 2626 (1.1%). Results indicate that European corn borer larval parasitism is significantly affected by the maize hybrid planted in the field; however, differences may vary among years and generations as environmental factors affect the maize phenology.

Inundative Release of Archytas marmoratus (Diptera: Tachinidae) Against the Corn Earworm and Fall Armyworm (Lepidoptera: Noctuidae) in Whorl-Stage Corn

A 3-yr pilot test was conducted to determine the feasibility of controlling early-season populations of corn earworm, Helicoverpa zea (Boddie), and fall armyworm, Spodoptera frugiperda (J. E. Smith), by augmentative releases of the tachinid parasitoid Archytas marmoratus (Townsend). Percentage parasitism of corn earworm larvae was increased to 42% in non-isolated fields of whorl-stage corn and >90% in isolated fields by inundative releases (≈1500 A. marmoratus ♀♀ per ha per week). Fall armyworm larvae were parasitized at a much lower level than corn earworm larvae. In a contiguous corn growing area, there was a positive correlation between density of corn earworm larvae and percentage parasitism within 0.8 km of the release field. The field with the greatest larval density and percentage parasitism of corn earworm larvae was the one farthest from the release site, indicating good host finding capability by A. marmoratus. These results show that inundative releases of this parasitoid could become an important component of integrated management strategies against early-season populations of corn earworm and fall armyworm. The high percentage of superparasitism in corn earworm larvae suggests that the release rate of A. marmoratus will need to be adjusted to host larval density.