Pestic. Sci. 1988, 22, 17-30 Structure/Activity Studies on Aphid Alarm Pheromone Derivatives and their Field Use Against Transmission of Barley Yellow Dwarf Virus Glenn W. Dawson, David C. Griffiths, John A. Pickett,* Roger T. Plumb, Christine M. Woodcock and Zhang Zhong-Ning AFRC Institute of Arable Crops Research, Rothamsted Experimental Station, Harpenden, Hertfordshire AL5 2JQ, UK (Revised manuscript received 2 March 1987; accepted 23 March 1987) ABSTRACT Derivatives produced by 1,4-cycloaddition reactions between acetylene- carboxylic acid esters and the aphid alarm pheromone, (E)-P-farnesene, and analogues in which other features of the pheromone molecule were modified, were tested for activity against aphid colonisation. The most active compound, formed from (E)-P -famesene and diundecyl acetylenedicarboxylate, decreased aphid-transmitted barley yellow dwarf virus infection of autumn-sown barley. 1 INTRODUCTION For most of the aphid species which have been studied, the main component of the alarm pheromone is (E)-P-farnesene (I, Fig. 1). The synthetic material can be used in crops to increase the movement of aphids and thereby improve control by contact insecticides and biological agents. However, (E)-P-farnesene is too volatile and too readily oxidised to be effective in preventing colonisation of plants and virus transmission by aphids. Derivatives (e.g. 11, Fig. 1) produced by 1,4-~ycloaddition reactions between electron deficient dienophiles and the conju- gated diene system in (E)-P-farnesene are more stable and can be used to protect plant^.^.^ In these early studies, didecyl 4-(4,S-dimethylnona-3,7-dienyl)- cyclohexa-1 ,4-diene-l,2-dicarboxylate (IIe, Table 1) was the most active com- pound, but the structure/activity relationships were not explored. *To whom all correspondence should be addressed. 17 Pestic. Sci. 0031-613X/88/$03.50 0 Society of Chemical Industry, 1988. Printed in Great Britain