Effect of epicuticular waxes of poplar hybrids on the aphid Chaitophorus leucomelas (Hemiptera: Aphididae)

Abstract:  Insect response to plant surface features is a critical step in host-finding and acceptance of herbivorous insects. The plant surface is usually covered with epicuticular waxes (EWs), which are not only involved in water physiology, but also provide resistance to insects. In the present work the probing behaviour and performance of the aphid Chaitophorus leucomelas Koch (Hemiptera: Aphididae) on dewaxed and waxed leaves of two poplar hybrids, [( Populus trichocarpa Torr. & Gray ×  Populus deltoides Bartram ex Marshall) ×  P. deltoides ] (TD × D) and [( P. trichocarpa  ×  Populus maximowiczii Henry) × ( P. trichocarpa  ×  P. maximowiczii )] (TM × TM), previously reported as susceptible and resistant, respectively, are described. Laboratory experiments showed that in naturally waxed leaves of the resistant hybrids, aphids devoted less time to probing and more time to non-probing behaviour when compared with their behaviour on susceptible hybrids. These differences were not present when leaves of these hybrids were experimentally dewaxed. A field experiment demonstrated that aphid reproductive performance was affected by hybrid genotype (higher in the TD × D) but not by EWs, although a trend of lower performance on dewaxed leaves in both hybrids was apparent. SEM analysis of EWs revealed micromorphological differences between both hybrids. These results support the idea that EWs affect aphid behaviour in poplars, with a rather slight impact on reproductive performance.