Relation of lipid adsorptivity of powders to their suitability as insecticide diluents

Abstract does not appear. First page follows.

Introduction

It has been well established that sorptive powders can cause the death of insects, sometimes with remarkable rapidity, by removing a portion of the very thin layer of lipid, averaging about 0.25 ? in thickness, that covers the insect epicuticle and normally prevents desiccation (Alexander et al., 1944);4(Hurst, 1948); (Helvey, 1952); (Glynne Jones, 1955); (Nair, 1957); (Ebeling and Wagner, 1959); (Wagner and Ebeling, 1959); (Tarshis, 1959), (1960), (1961); and (Micks, 1960).

It thus might be assumed that sorptive diluents should increase the insecticidal effectiveness of toxicants by adding their independent effect as lipid removers. However, preliminary tests showed that this is not always the case; with some toxicants, the sorptiveness of the diluent proved to be highly detrimental. Obviously, if an inert powder having the ability to cause the death of an insect is to be less effective as a diluent than one without insecticidal effect, some adverse action must take place when that powder is combined with the toxicant.

The purposes of the present investigation were (1) to determine the independent influence of sorptive and nonsorptive powders on the ultimate effects of the toxicants by applying them to insects for brief periods before the latter were treated with the toxicants; (2) to determine the effects of these same powders when used as diluents for the toxicants; and (3) to find an explanation for the differences in insecticidal effectiveness of toxic dusts that might be caused by the different types of diluents.

Materials and Methods

The insect species used in this investigation were adult Drosophila pseudoobscura; adult males of the German cockroach, Blattella germanica, and of the brown-banded cockroach, Supella supellectilium; full-grown nymphs of the drywood termite, Kalotermes minor, and of the dampwood termite, Zootermopsis angusticollis.

Drosophila pseudoobscura is much larger than the familiar D. melanogaster and much more resistant both to the effects of toxicants and to the desiccating effect of sorptive powders. The flies used in the present investigation were obtained from the laboratory of Dr. Carl C. Epling, who rears them in large numbers throughout the year in connection with genetics investigations. The flies are reared in a uniform manner in half-pint milk bottles, and