Evaluation of the potential of Pteromalus puparum (L.) (Hymenoptera: Pteromalidae) for suppression of the imported cabbageworm and parasitism of the diamondback moth

The seasonal abundance of the imported cabbageworm, Artogeia rapae (L.)), cabbage looper Trichoplusia ni (Hubner)) and diamondback moth (Plutella xylostella (L.)) was determined in 1982 to 1984 on cabbage in southwest Virginia. The imported cabbageworm was the most important pest. It had one and a partial second generation in 1982 and 1983, and two and a partial third generation in 1984. Market Prize and Green Winter varieties had lower A. rapae infestations than Abbott & Cobb #5 or Rio Verde. Two generations of the diamondback moth, which preferentially fed on cabbage leaves versus heads, were seen in 1983 and 1984. Diadegma insularis (Meus.) (Hymenoptera: Ichneumonidae) parasitized 46% and 69% of the diamondback moth in 1983 and 1984, respectively. Higher parasitization of P. xylostella was found in pupae collected from Abbott & Cobb #5. Two generations of the cabbage looper were seen in 1983 and a single generation in 1984.

Pteromalus puparum (L.) (Hymenoptera: Pteromalidae) parasitized 64.1% and 32.5% of imported cabbageworm pupae in 1983 and 1984; parasitism was most pronounced in the latter part of the season. High percentages of parasites successfully emerged as adults, indicating efficient host utilization. Most parasite mortality within the host occurred in the larval stage; mean adult parasite emergence per host for 1983 and 1984 was 52.3 with a 1:1 sex ratio. P. puparum parasitized either host sex, producing equal proportions of male and female parasites. Adult female P. puparum were not adversely affected by residues of methomyl (Lannate®), permethrin (Pounce®) and fenvalarate (Pydrin®), but males showed significantly higher mortality than controls following exposure to methomyl after 12 h, and methomyl and permethrin after six days. <P. puparum adults were successfully refrigerated for up to 15 days at 3°C in individual gelatin capsules. Survival beyond 15 days was better at l5°C and 23°C.

A. rapae larvae could be reared at densities of 30 to 60 larvae per 70±10 g on a high wheat germ artificial diet. Pupae from the lowest density were larger in length and weight than those reared at the two higher densities, and all laboratory-reared pupae were smaller than either normal or parasitized field pupae.