DIFLUBENZURON: DIFFERENTIAL TOXICITY TO LARVAE OF THE COLORADO POTATO BEETLE (COLEOPTERA: CHRYSOMELIDAE) AND ITS INTERNAL PARASITE, DORYPHOROPHAGA DORYPHORAE (DIPTERA: TACHINIDAE)

Abstract

Can. Ent. 1 16: 197-202 (1984) An insecticide, diflubenzuron, suppressed 3rd-and 4th-instar larvae of the Colorado potato beetle, Leptinotarsa decemlineata (Say), with reduced effect on the tachinid parasite, Doryphorophaga doryphorae (Riley), developing within the larvae. Concentrations applied to potato foliage were 50, 100, 300, and 500 mglL. In laboratory and greenhouse tests, parasite survival was not adversely affected when the 3rd instars were treated with 50 mg/L diflubenzuron but survival decreased to 0 and 4% at 300 and 500 mg/L. Survival and emergence of the parasite from treated 4th instars were not adversely affected at any concentration tested. Fourth-instar beetle larvae were much more tolerant of diflubenzuron than were the 3rd instars. Neither fertility nor the ability to parasitize beetle larvae was adversely affected in adult parasites emerging from treated 3rd or 4th instars. Adult beetles developing from treated larvae mated normally and laid fertile eggs. Foliage consumption by the beetle larvae decreased progressively as dosage of diflubenzuron increased but only slowly once the dosage increased beyond 100 mg1L.

Toxicity of the insect growth regulator diflubenzuron to the rove beetle Aleochara bilineata, a parasitoid and predator of the cabbage maggot Delia radicum

“…When applied in a water-based suspension, the chitin synthesis inhibitor did not affect the hatching capacity of eggs, the survival capacity of larvae (first instars and parasitoid stages) and adults, or the fecundity of beetles. Such a differential toxicity of diflubenzuron has been demonstrated for parasitoids of several insect pests (Ables et al, 1975(Ables et al, , 1977Wilkinson et al, 1978;Westigard, 1979;Zungoli et al, 1983;Tamaki et al, 1984). In a number of associations, however, the susceptibility of the parasitoid to diflubenzuron was shown to be close to that of the host (Granett & Weseloh, 1975;McWhorter & Shepard, 1977;Madrid & Stewart, 1981).…”

“…In a number of associations, however, the susceptibility of the parasitoid to diflubenzuron was shown to be close to that of the host (Granett & Weseloh, 1975;McWhorter & Shepard, 1977;Madrid & Stewart, 1981). The fact that Dimilin, applied topically in DMSO to infected host puparia, suppressed larval development of A. bilineata, whereas treatment with a water-based suspension of the IGR was without effect, suggests that the staphylinid, like certain other Coleoptera (McLaughlin, 1976;Peleg, 1983;Rajendran & Shivaramaiah, 1983;Tamaki et al, 1984) is physiologically sensitive to the compound. When suspended in distilled water, however, the IGR is not absorbed across the insect's cuticle in concentrations sufficient to cause harmful effects; the higher penetrating capacity of DMSO provides access to diflubenzuron across the exoskeleton of the parasitoid (and host).…”