The role of nutrients and parasitoid on the interaction between the cotton aphid and the parasitoid wasp Aphidius matricariae

To have a better understanding of sustainable management strategies of Aphis gossypii Glover (Hemiptera: Aphididae), it is necessary to determine the role of bottom-up vs. top-down forces on its population dynamics. The present study examined the effect of fertilization (bottom-up force) and parasitoid release (top-down force) on population fluctuations of A. gossypii and its parasitoid (Aphidius matricariae Haliday (Hymenoptera: Braconidae)). A factorial experiment was carried out with two factors: fertilization (0, 0.5 and 1.0 g per plant per time with a fertilizer consisted of macro- and microelements) and initial parasitoid release (0, 2 and 10 1-day-old mated females of A. matricariae per cage). The experiment was started with a 5-week-old cucumber and 10 newly emerged A. gossypii adults. After one generation of A. gossypii, A. matricariae females were introduced into cages. The treatments replicated four times in a randomized complete block design, and maintained under a standard constant environment. The number of live A. gossypii and A. matricariae adults was weekly recorded until two generations of the parasitoid had been completed. The results indicated that an increase of nutrition increased aphid density and its percentage parasitism but did not affect the parasitoid population size. In addition, parasitoid release resulted in higher parasitoid density and percentage parasitism but a reduction of aphid population size. The interaction between factors influenced the aphid population only. These findings indicated that bottom-up and top-down forces play an important role in population regulation of A. gossypii, and hence, must be considered in the pest management.