The Effects of Insect Extracts and Some Insect-Derived Compounds on the Settling Behavior of Liposcelis bostrychophila

Extracts of whole booklice (Liposcelis bostrychophila)—sequentially extracted in hexane and aqueous 80% methanol (80%MeOH)—repel conspecifics. A methanol-soluble fraction (MFr) of the 80% methanol extract was more repellent than either its corresponding water fraction (WFr) or the hexane extract. The repellent effect of the MFr was repeatable across extracts prepared on different occasions over a 1 month period. Gas chromatography, mass-spectrometry (GC-MS) analyses showed that saturated (C₁₆; C₁₈) monoenoic (C₁₆:₁; C₁₈:₁) and a dienoic fatty acid (C₁₈:₂) and the corresponding methyl esters of all but C₁₆:₁ and C₁₈ constituted approximately 95% and 30%, of the detected compounds in the methanol fractions and the hexane extract, respectively. Qualitative thin layer chromatography showed that cholesterol was present in methanol fractions and the hexane extract, and also enabled tentative identification of triacylglycerols and phospholipids in the methanol fractions. Extracts of wheatgerm, dried skimmed milk powder, active yeast, and wholemeal flour—L. bostrychophila dietary components—were analyzed by GC-MS, and C₁₆, C₁₈:₁ and C₁₈:₂ were detected, indicating that C₁₈ and the methyl esters were not directly extractable and/or that they were products of booklice metabolism. A fatty acid amide (stearamide) previously identified in cuticular extracts of L. bostrychophila was not detected, and therefore was not responsible for the observed biological activity. Pure fatty acids and fatty acid methyl esters repelled settling of L. bostrychophila at 10 mM, with the exception of palmitic and stearic acids, indicating, among other things, a difference between the efficacy of saturated and unsaturated fatty acids. The effect of concentrations <10 mM was less significant, although palmiteoleic acid appeared to be attractive to L. bostrychophila at 0.1 mM. Fatty acids and fatty acid methyl esters were at a much lower concentration than 10 mM in the repellent methanol fractions, indicating that an interaction between known and as yet unidentified compounds is likely. The significance of fatty acids in relation to the biology and behavior of L. bostrychophila and their potential for use in traps and monitoring are discussed.