Plant genotype shapes the feeding decisions of an omnivore

Background/Question/Methods

Omnivores that feed on plant material as well as animal prey have been shown to shift their diet depending on availability of prey and quality of plant material.  For example, in the presence of prey (mite eggs), omnivorous thrips consumed nearly half the amount of plant tissue as did thrips without prey, and the amount of prey items consumed increased on low-quality host plants compared to prey consumed on high-quality host plants. It has also been shown that genotypic variation in plants can affect the interactions of arthropods at multiple levels of community organization.  In this study, we investigate the influence of plant genotype and availability of prey on the feeding decisions of an omnivorous thrips (Franliniella occidentalis).  In no-choice experiments, individual thrips (adult female or immature) were offered one cotton cotyledon with or without five mite eggs placed on the cotyledon.  The total area (mm²) of feeding scars on cotton leaves was quantified, and the number of mite eggs consumed on treatment leaves was counted.  

Results/Conclusions

Plant genotype had a significant influence on the feeding decisions of an omnivorous thrips. Without mite eggs, plant feeding varied significantly among genotypes (P<0.0001, respectively) and this variation was similarly expressed by each life-history stage (P=0.05, R²=0.65).  The number of prey consumed was significantly influenced by the genotypic identity of the plant for immature (P=0.0001) but not adult female (P=0.25).  The availability of prey caused unexpected affects on the ecological interaction between the plant and omnivore.  Across genotypes, the presence of prey did not cause a consistent affect on the amount of plant feeding for either adult (P=0.66), or immature (P=0.77).  For immature thrips, the presence of prey on one genotype resulted in an increase (P = 0.055) in the amount of plant feeding compared to that without prey.  Our results are important by showing that genotypic variation in plants can affect food-web dynamics through altering an omnivores consumption of both plant material and frequency of predation on other herbivores.