BIOASSAY SYSTEMS FOR THE PYRETHRINS I. WATER‐BASE SPRAYS AGAINST AXDËS AEGYPTI L. AND OTHER FLYING INSECTS

Abstract

A bioassay system for the pyrethrins is discussed in which the quantity of toxicant that flying insects accumulate is measured, as well as the responses of the insects. T h e determination of spray pick-up from water-base sprays is described, and the use of primary responses, such as activation and paralysis, in biological assays is advocated. T h e test system is discussed in detail for Aedes aegypti L. and the special characteristics of some other species of flying insects noted. I t is considered that the location of the site of action of the pyrethrins under these conditions is at the peripheral nervous system of the test insects. WATER-BASE SPRAYS AND AIDES AEGYPTI L. Relation between toxicity and pick-up of insecticides applied as aqueous spraysMuch published work has been based on the tacit assumption that the quantity of insecticide accumulated by an insect flying in a spray is proportional to the concentration of insecticide in the spray fluid and to the volume sprayed into the air space occupied by the insects. Published statements that wasps, horseflies and blowflies are more sensitive than houseflies to pyrethrins, based on the concentrations used, ignore the fact that the first-mentioned insects, which are hairy, pick up far more spray liquid in flight or when stationary than the houseflies. We have shown that the weight of insecticide acting on the insect is proportional to the product of the volume of spray liquid accumulated by the insect and the concentration of insecticide in the liquid.If the volume of liquid picked up by the insect is plotted against the concentration of insecticide in the spray liquid, the points representing the acquisition of a constant quantity of insecticide by the insect should then lie on arectangular hyperbola. This has been shown to be true for a number of insects, using their responses to the weights of pyrethrins accumulated. Any variation of the conditions which alters the quantity of spray liquid accumulated, such as a change of nominal spray dosage, or humidity, also alters the concentration at which any particular response occurs and alters it in such a way that the threshold weight of the insecticide causing the response is maintained.

Bioassay Systems for the Pyrethrins: Iv. Stoichiometric Relations With Pyrethrum Synergists*

“…This resting potential probably occurs across a lipoidprotein interface. Page, Stringer & Blackith (1949) found that, at concentrations slightly higher than the minimum required to paralyse the flying insects they used, within the fixed exposure period, the weight of pyrethrins accumulated by the paralysed insects is consistently less than at the minimum concentration. This difference implies an increase in absolute toxicity of the pyrethrins, and applies to all the flying insects used in that investigation.…”

Tests of Motor Stimulants for Eastern Spruce Budworm Moths (Lepidoptera: Tortricidae)

“…), in New Brunswick in 1977, indicated that most of the females killed in these experiments had laid more than 50% of their eggs (Thomas 1976).2 This result suggests that fully gravid female moths which rest in the foliage are never exposed to a lethal dose of insecticide. If these moths could be induced to fly, they would be more likely to accumulate a lethal dose as has been suggested by Page et al (1949) for insects flying through an aerosol cloud of pyrethrin.…”