A REFINED METHOD OF HANDLING ROOT MAGGOT LARVAE (DIPTERA: ANTHOMYIIDAE) FOR BIOASSAY

Abstract

A method is described for rearing and selecting strong, robust populations of first-stage root larvae for bioassay of insecticide toxicants in soil and host plant tissue. Oviposition dishes are placed in cages with flies for a 6-hour period 3 times a week. The eggs are then incubated on silk cloth over moist blotting paper in petri dishes at 21° to 22 °C until they hatch. When the larvae move away from the empty egg cases to a food supply, they are transferred to the centre of another piece of silk cloth lying fiat on a wet sponge. The strongest of the larvae move most quickly outward from the central mass and are transferred to holding trays and later set up for bioassay with plant tissue or treated soil. The weaker larvae are discarded. In 24- to 48-hour tests with larvae obtained by this method, there was no mortality in untreated samples. When larvae were reared to maturity, mortality in untreated media averaged approximately 6% in several hundred tests conducted from 1969 to 1971.