No abstract

Potato tuber worm (PTW), Phthorimaea operculella (Zeller), is a world-wide pest of potato. In rustic stores, PTW larvae can infest 100% of stored tubers. Treatment of tubers in rustic stores with the PTW granulovirus (PoGV) has been demonstrated to protect stored tubers. This is the first study to show the effects of PoGV for protection of tubers stored in refrigerated warehouse conditions. Tubers were treated by dipping in aqueous suspensions of PoGV or water. An estimated 0.0819 larval equivalents of virus or 1.88 )10 9 viral occlusion bodies were deposited on each kilogram of tubers. They were held at 168C for 11 days before lowering the temperature by 0.58C per day until 108C was reached. The tubers were stored at this temperature for 53 days. Mean numbers of infested tubers at the end of the assay was affected by both pre-infestation rate and virus treatment. Mean numbers of infested tubers in the control treatment was 3 tubers per chamber higher than in the virus treatment providing strong evidence that PoGV controlled larvae and minimized spread into un-infested tubers. Of the larvae that were retrieved in virus-treated infested tubers, the mean mortality was 87% compared to 37% in controls.

From 1988 to 1994, adult vial bioassays were conducted on bollworms, Helicoverpa zea (Boddie), collected from pheromone traps in Missouri to determine their susceptibility to pyrethroids. Although most moths were susceptible to cypermethrin, many assays contained individuals that survived concentrations of 5 and 10 μg per vial. The number of individuals that survived these concentrations increased each of the first 3 yrs, and then fluctuated from year to year. In some cases, moths with increased tolerance to cypermethrin occurred in locations where little or no pyrethroid insecticides were used for bollworm control. A likely explanation for tolerant bollworms in Missouri is immigration from more southerly locations, and evidence for long range dispersal of these insects is presented. Implications for regional resistance monitoring also are discussed.

No abstract

Control failures of many insecticides used against the western flower thrips (WFT), Frankiniella occidentalis (Pergande), have been reported from several locations by greenhouse operators. To document resistance, thrips were bioassayed by placing them in vials coated with doses of diazinon, methomyl, bendiocarb, dimethoate, azinphosmethyl and cypermethrin at (100, 50, 10, 5, 1, 0.5 and 0.1 g/vial). Adult female WFT were collected from a colony exhibiting control failures using organophosphate, carbamate and pyrethroid insecticides. A colony showing no resistance was used as a control. The LC50's of the resistant and susceptible strains were diazinon 49.3 and 4.6 g/vial, cypermethrin no mortality and 3.7 g/vial, and azinphosmethyl 20.2 and 2.l g/vial respectively. Results show resistance is present as well as cross resistance to diazinon and cypermethrin because the resistant population was never exposed to these compounds.