Feeding deterrence of barley seedlings against the migratory locust Locusta migratoria (Orthoptera: Acrididae)

Abstract

Barley seedlings strongly deterred feeding of the migratory locust Locusta migratoria. Analysis of feeding-related behavior revealed that approach to barley seedlings and palpation occurred just as with palatable plants, but rejection of the plant occurred immediately after biting. Excision of the maxillary and labial palps had no effect on the rejection of barley seedlings, and feeding of palatable plants occurred as with intact insects. Removal of compounds on the surface of the barley leaves also had no effect, while ethanol extraction of the leaves diminished the deterrence of the barley seedlings. These results indicated that feeding deterrent(s) are localized inside the seedlings. An ethanol extract of barley seedlings exhibited strong deterrence in a feeding assay using a piece of sucrose-impregnated filter paper as the feeding substrate. Fractionation of the ethanol extract revealed that the strongest feeding deterrence was observed with the basic fraction, which contains alkaloids such as gramine. The other fractions also showed weak feeding deterrence. A crude alkaloid extract equivalent to 100 mg of barley leaf inhibited feeding of the locusts by 90%.