Insect-derived compounds affect the behaviour of Liposcelis bostrychophila: Effects of combination and structure

Abstract

A methanol fraction (MFr), prepared from 80% methanol extracts of whole Liposcelis bostrychophila, repels conspecifics when presented to groups of insects at 8000 ppm. To examine the reason for this repellent effect, bioassays tested a mixture of fatty acids and fatty acid methyl esters that are present in the MFr at concentrations ranging from 0.02 to 1.2 mM. This mixture of compounds contributes significantly to the repellence of the MFr. Therefore, an interaction among compounds can affect the settling behaviour of L. bostrychophila, even though the individual compounds do not have any effect. Other experiments further investigated the repellence of C 16 and C 18 fatty acids. In the majority of instances groups of insects consistently settled on the disc impregnated with either stearic acid or the compound with the most saturated bonds. The one exception was C 18:2 versus C 18:3 where more insects settled on C 18:3. This repellent effect of unsaturated fatty acids was also evident in five-way choice tests using a series of C 18 fatty acids, where stearic acid (10 mM) was consistently selected by groups of L. bostrychophila instead of oleic, linoleic and linolenic acid. The discrimination between and among fatty acids could be due to the differences in their physical properties which affect how the compounds are perceived by the insects. The fact that the most unsaturated fatty acids repel the insects presents the possibility that volatile insect-derived compounds could be utilised as repellents for this increasingly important pest.