Influence of prey availability and induced host-plant resistance on omnivory by western flower thrips

Theory predicts that the balance of nutritional needs, food availability, a nd the quality of particular food items are important factors in the feedin g decisions of omnivorous animals. In this study we investigate factors tha t affect the feeding decisions of an omnivorous thrips (Frankliniella occid entalis) that eats both animal prey and plant foliage. Ln the presence of p rey (mite eggs), adult and larval thrips consumed nearly half the amount of plant. tissue as did thrips without prey. We manipulated host-plant qualit y by exposing plants to spider mite feeding. in the absence of prey, system ically induced plant responses following herbivory reduced the amount of fe eding by thrips compared to that on uninduced control plants. In the presen ce of prey, induced responses caused a shift in the feeding preferences of thrips: thrips consumed half the amount of plant material and twice the num ber of prey on induced plants as did thrips on uninduced control plants. Ou r findings are relevant to understanding the complex factors that shape foo d-web interactions in nature. Variation in host-plant quality and availabil ity of prey can exert a strong influence on the feeding preferences of omni vores. In addition, induced resistance may be a particularly useful biologi cal-control strategy because it reduces herbivorous pest populations direct ly, and indirectly by causing a shift toward predation in naturally occurri ng omnivores.