Impact of the microbial pesticide Bacillus thruingiensis Berliner subsp. kurstaki on Hymenopterous parasites of the imported cabbageworm, Pieris rapae (L.) (Lepidoptera: Pieridae)

Three formulations of Bacillus thuringiensis Berliner subsp. kurstaki (Dipel 4L, Dipel 2X, and ABG-6167) were compared with the synthetic pyrethroid perrnethrin ( common name Pounce 3. 2 EC) for insecticidal activity and impact upon parasitism of the imported cabbageworrn, Pieris rapae (L.) (Lepidoptera: Pieridae) in field broccoli (CV Packrnan) from fall 1986 to spring 1988. Perrnethrin, Dipel 4L, and ABG-6167 were not significantly different in their efficacy towards imported cabbageworm larvae. Parasitization of P. rapae by the larval parasite Cotesia glomerata (L.) (Hymenoptera: Braconidae) and the pupal parasite Pteromalus puparum (L.) (Hyrnenoptera: Pteromalidae) continued after spraying in the B. thuringiensis plots, but was not significantly different from perrnethrin. However, 100% of the P. rapae chrysalids recovered were parasitized by P. puparum. The impact of seasonal hyperparasitism was compared between .Q. glomerata, and a Yugoslavian strain of Cotesia rubecula (Marshall), an exotic larval parasite of the imported cabbageworm. Four hyperparasites, two of them attacking both~. glomerata and~. rubecula, were found in field plots from 1986-1988. The level of hyperparasitization for the two primary parasites was significantly different. Hyperparasitization averaged only 8.1% for C. glomerata from 1986-1988, but was 37. 9% for C. rubecula from 1987-1988. During the early- to mid-season of 1988, hyperparasite activity was not detectable and C. rubecula outcompeted C. glomerata for hosts; but by mid-season, hyperparasite activity against C. rubecula increased to 100%, causing its populations to crash. C. glomerata then became the dominant parasite of P. rapae. C. rubecula was not recovered in 1989. Hyperparasites may be a limiting factor in establishing C. rubecula in southwestern Virginia. Mortality and successful pupation of P rapae fourth instars parasitized by C. rubecula to B. thuringiensis endotoxin at dosages of 850, 85, and 8.5 I.U./ml was examined. After day two, the LC₅₀'s of parasitized fourth instars were approximately thirty times higher than that of unparasitized larvae and by day four, the LC₅₀ response of parasitized fourth instars was 180 times higher than unparasitized larvae. Twenty-five percent of parasitized fourth instars exposed to a concentration of 850 I.U./ml successfully pupated, compared to 76% at 85 I.U./ml and 69% at 8.5 I.U./ml. Parasitized fourth instar P. rapae consume less food and are therefore less susceptible to B. thuringiensis than unparasitized larvae at the same dosages.

Name thesis:degree_name

Ph. D.

Level thesis:degree_level

doctoral

Discipline thesis:degree_discipline

Entomology

Department dc:contributor.department

Entomology

Grantor dc:publisher

Virginia Tech

Year dc:date.issued

1990

Author dc:creator

• McDonald, Richard C.

Chair dc:contributor.committeechair

• Kok, Loke T.

Committee members dc:contributor.committeemember

• Eaton, Judith L.
• O’Dell, Charles R.
• Pienkowski, Robert L.
• Ravlin, F. William
• Yousten, Al A.

Statement dc:rights

• In Copyright

Licence dc:rights.uri

• http://rightsstatements.org/vocab/InC/1.0/

Language dc:language.iso

en

Dc Identifier Other

etd-10192005-113246

OAI identifier oai:identifier

oai:vtechworks.lib.vt.edu:10919/39942