Multitrophic Manipulation of Herbivore Perception by Plants

Plants are under constant attack by insect herbivores. While plants can protect themselves using a wide-array of defensive responses, they can also receive protection from the natural enemies of insect herbivores, including parasitoids and pathogens. The project investigates the three-way interaction between plants, insect herbivores and their natural enemies using two economically valuable crop plants (tomato and corn), two of the most devastating insect pests in the New World (fall armyworm and corn earworm) and two key groups natural enemies of the pests (parasitoids and baculoviruses). Parasitoids and baculoviruses occur in nature and are also used as biological control agents to control pest insects in agriculture. Knowledge gained from this project may have widespread impacts on informing sustainable pest management by improving the integration of biological control agents with the development of pest resistant crop plants. The PIs will mentor a diverse group of students, incorporate concepts of multitrophic interactions into college teaching materials, develop cost-free online modules on multitrophic interactions for homeschoolers and the educational community at large, and reach thousands of elementary school children each year in the Great Insect Fair with these concepts.

Plants recognize insect herbivores through elicitors or herbivore-associated molecular patterns (HAMPs) in their oral secretions, which triggers plant defensive responses. These studies have been conducted without considering that insects in the field are often parasitized or infected by baculoviruses. Plant defenses can reduce the quality of insects as a resource for the third trophic level. While parasitoids (and their symbiotic polydnaviruses) and baculoviruses can manipulate the immune systems of their hosts, whether they can also alter the host's production of salivary HAMPs and effectors has never been investigated. The aims of this project are (1) to determine if parasitoids/polydnaviruses and baculoviruses modulate the synthesis and activity of caterpillar salivary HAMPs and effectors and (2) determine whether baculoviruses and parasitoids/polydnaviruses manipulate plant defenses to their own benefit. The third trophic level will consist of both specialists and generalists because it has been postulated that specialist natural enemies exert greater control over the physiology and behavior of their hosts than generalist species. Thus specialists may have a stronger influence on the expression of plant defenses. Molecular and biochemical assays and life-history measurements will be used to address the aims. In the Dawkin's model of the extended phenotype, whereby a gene in one organism has phenotypic effects on another organism, the potential of parasitoids and baculoviruses to exert control over not just their host's immune systems, but also control over the plant's immune system could represent one of the most extended phenotypes known.