Does foliar trichome density affect walking activity and speed of Aphidius colemani,and its rate of parasitism of Aphis gossypii on chrysanthemum?

Abstract: The parasitoid Aphidius colemani is one of the major biological control agents ofAphis gossypii and plays an important role in the regulation of aphid populations onchrysanthemum under protected cultivation. The high density of foliar trichomes of the aphidresistant chrysanthemum cultivar White Reagan (WR) reduces the survivorship and fecundity ofA. gossypii. The objective of this study was to evaluate the influence of chrysanthemum foliartrichome densities on the walking speed, walking activity and rate of parasitism of A. colemanion A. gossypii. Leaf discs of the aphid susceptible cultivar Yellow Snowdon (YS) or the resistantcultivar WR were put in Petri dishes to evaluate the walking activity and walking speed of A.colemani in the absence of hosts. The parasitism of the 2nd and 3rd instar nymphs of A. gossypii,reared on the two cultivars, was evaluated by counting the number of hosts containing parasitoidlarvae. Parasitoid walking activity (= % time active of total time on leaf) was higher on WR(64%) than on YS (47%). No significant differences were observed in the walking speed of andthe rate of parasitism by A. colemani on A. gossypii on the two cultivars, so in this case thecharacteristic of aphid resistance of WR may positively influence the reduction of the aphidpopulation by A. colemani.