Natural enemy impacts on bemisia tabaci dominate plant quality effects in the cotton system

Authors: ASLIMWE, PETER - Monsanto Corporation; ELLSWORTH, PETER - University Of Arizona; Naranjo, Steven

Submitted to: Ecological Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/2016
Publication Date: 9/8/2016
Citation: Aslimwe, P., Ellsworth, P.C., Naranjo, S.E. 2016. Natural enemy impacts on bemisia tabaci dominate plant quality effects in the cotton system. Ecological Entomology. 41:642-652.

Interpretive Summary: The sweetpotato whitefly is a key pest of cotton and a number of other agronomic and horticultural crops worldwide. We know that populations of this insect can be influenced by the quality of the plant material upon which it feeds and by the activity of natural enemies that attack and feed on this pest. We generally understand how each of these factors affect pest population dynamics alone, but no information is available as to how these factor might interact to regulate pest abundance. Over three cotton seasons, we manipulated plant quality via differential irrigation and manipulated natural enemy abundance with insecticides. We then used life tables (a way to measure the source and rate of mortality) to evaluate the relative impact of these factors on mortality of immature B. tabaci. Natural enemies consistently affected marginal B. tabaci mortality and this response was not affected by plant quality. High levels of predation, which was determined to be the key factor, the factor associated with changes in generational mortality, drove this pattern. Dislodgement from chewing predation and weather and parasitism contributed as key factors in some cases. Natural enemies but not plant quality affected irreplaceable mortality, or that mortality that can only be supplied by a specific factor. The highest levels of irreplaceable mortality were supplied by predation and dislodgement. The top-down effects of natural enemies had dominant effects on B. tabaci populations relative to the bottom-up effects of plant quality. Our findings demonstrate the important role of arthropod predators in population suppression and validate the importance of conservation biological control in this system for effective pest control. These findings further support the current recognition by cotton growers in Arizona that the preservation of natural enemies is important to their success in managing pest populations and their associate damage.

Technical Abstract: Plant quality (bottom-up effects) and natural enemies (top-down effects) affect herbivore performance and population dynamics; plant quality can influence the impact of natural enemies. Lower plant quality through reduced irrigation generally increases the abundance of Bemisia tabaci Gennadius (Aleyrodidae) on cotton. We predicted that lower plant quality would diminish the impact of natural enemies in regulating this herbivore. Over three cotton seasons, we manipulated plant quality via differential irrigation and natural enemy abundance with insecticides. We used life tables to evaluate the relative impact of these factors on mortality of immature B. tabaci. Natural enemies but not plant quality consistently affected marginal B. tabaci mortality. High levels of sucking predation drove this pattern and predation was the primary key factor associated with changes in generational mortality across all irrigation and natural enemy treatments. Dislodgement (chewing predation and weather) and parasitism contributed as key factors in some cases. Natural enemies but not plant quality affected irreplaceable mortality rates. The highest levels were supplied by sucking predation and dislodgement. The top-down effects of natural enemies had dominant effects on B. tabaci populations relative to the bottom-up effects of plant quality. Effects were primarily due to native generalist arthropod predators and not more host-specific aphelinid parasitoids. Our findings demonstrate the important role of arthropod predators in population suppression and validate the importance of conservation biological control in this system for effective pest control.