Candidate Fumigants for Control of Caribbean Fruit Fly, 1981-1982

The chemical compounds listed below were tested for effectiveness as fumigants against mature fruit fly larvae. Ethylene dibromide was used as the standard for comparison. All compounds were reagent grade (99% pure) or better. Fumigation containers were 3.8 liter widemouth glass jars with teflon-lined, screw-cap lids. An open petri dish containing 200 naked larvae was placed in each jar. Test chemicals were then pipetted onto 11-cm filter papers, placed in the jars with the insects. The lids were fastened in place. Jars were placed on their sides to minimize settling effects. All tests were conducted at 24°C and 50% RH. After exposure, larvae were placed in moist vermiculite, held at 27°C, and allowed to complete development. Survival was based on the number of insects that reached the adult stage. A two-phase testing procedure was used to evaluate the chemicals. The first phase was designed to eliminate compounds that were not effective at high dosage-time combinations, and involved exposure of larvae to 16, 32, and 64 g/m3 for 4 h. High mortality in the initial tests qualified compounds for second-phase testing. This involved exposing larvae to a series of lower dosages for only 2 h, so LD values could be determined. Data were first corrected for natural mortality in the controls by Abbott’s formula. Then probit mortality was plotted against the logarithm of dosage and examined by eye to determine that linear regression was appropriate. Data were subjected to a computer programmed probit analysis to estimate LD50, LD95, and LD99 dosages.