Raimon L. Beard

Kojic acid as an insecticidal mycotoxin

Abstract Kojic acid was isolated as one insecticidal metabolic product of Aspergillus flavus var. columnaris grown in synthetic media. Kojic acid differs from mycotoxin(s) sought in fly-rearing media, but in many respects in mimics the insecticidal properties of the unknown toxin(s). Kojic acid is low in acute toxicity, but it acts to retard insect development and can be insecticidal by virtue of its presence in high concentrations.

OVARIAN SUPPRESSION BY DDT AND RESISTANCE IN THE HOUSE FLY (MUSCA DOMESTICA L.)

Suggested by immunological theory, this study was initiated to test an hypothesis on physiological induction of resistance to insecticides. The hypothesis was proved untenable in the test system, but from the experimentation emerged evidence for a chronically toxic action of DDT expressed in reduced fecundity in female house flies fed sub‐lethal amounts of this insecticide. This action can be a strong selective force, promptly revealing tolerant genotypes in the population. The usual selection for resistance does not necessarily also select for ovarian tolerance; even DDT‐resistant flies can show ovarian suppression when fed DDT‐contaminated food.

SECONDARY PHYSIOLOGICAL EFFECTS OF DDT IN GALLERIA LARVAE

Secondary physiological effects of DDT leading to death in Galleria larvae do not follow a constant pattern. At least three courses have been observed: (1) In the usual toxication, muscular activity is continuous until the insect dies of exhaustion. This is confirmed by the evidence that DDT does not hasten death if muscle action is blocked by braconid venom. Adenosine triphosphate (ATP) is not depleted until after death. (2) DDT‐induced hyperactivity predisposes the insect to non‐specific “natural” mortality. (3) DDT induces regurgitation. Under special environmental conditions that permit larvae to become covered with regurgitated fluids, they quickly become prostrate. Prostrate larvae show a loss of ATP. With different treatments, prostrate larvae may (a) die with no further activity, (b) become active and follow the usual course of DDT toxication, or (c) dramatically recover from prostration and the effects of DDT. The nature of these events is discussed, but not fully explained.