Host preference and suitability of two aphelinid parasitoids (Hymenoptera: Aphelinidae) for aphids (Homoptera: Aphididae) on citrus

Laboratory tests were conducted to estimate the host preference and suitability of the aphelinid parasitoids, Aphelinus spiraecolae Evans & Schauff and Aphelinus gossypii Timberlake, for the melon aphid, Aphis gossypii Glover; the spirea aphid, Aphis spiraecola Patch; and the black citrus aphid, Toxoptera aurantii (Boyer de Fonscolombe). Both parasitoids attacked all 3 host aphids in choice tests, but A. spiraecolae showed a preference for the spirea aphid; whereas Aphelinus gossypii preferred the melon aphid. Results were similar in no-choice tests. Adult emergence rate of A. spiraecolae was substantially higher when the spirea aphid and the black citrus aphid were hosts compared with when the host was the melon aphid. A. spiraecolae female sex ratios were higher when the host was the spirea aphid than with the black citrus aphid or the melon aphid. Aphelinus gossypii adult emergence rates were higher on the melon aphid than on the spirea aphid or the black citrus aphid. Female sex ratios of Aphelinus gossypii were 70.2, 54.5, and 62.3% when reared on the melon aphid, spirea aphid, and the black citrus aphid, respectively, but these differences were not statistically significant. Development times of the aphelinids reared on the 3 aphid hosts were not significantly different. Adult biomass of A. spiraecolae was higher when reared on the spirea aphid (30.3 and 22.2 micrograms for females and males, respectively) than on the melon aphid (23.1 and 17.9 micrograms) or the black citrus aphid (28.8 and 22.0 micrograms). Biomass of Aphelinus gossypii were higher when reared on the melon aphid (33.6 and 22.1 micrograms for females and males, respectively) and the black citrus aphid (32.6 and 22.3 micrograms) than on the spirea aphid (27.9 and 18.3 micrograms). Based on these studies, we conclude that the spirea aphid was a preferred and suitable host for A. spiraecolae, whereas the melon aphid was a preferred host of Aphelinus gossypii under our test conditions. These aphelinids, therefore, may have potential to act in concert as natural enemies of aphids on citrus.