Submitted to: Florida Entomologist
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/14/2014
Publication Date: 9/29/2014
Citation: Shelby, K. 2014. Induction of antimicrobial peptides in infected tissues of larval Heliothis virescens (Lepidoptera: Noctuidae). Florida Entomologist. 97(3):921-927. Interpretive Summary: Budworm caterpillars are major pests of commodity crops such as maize, cotton, soybeans and vegetables throughout North America and the world. Microbial entomopathogens possess great potential for the biological control of these pests, however the pest’s immune system presents a formidable barrier which must be suppressed, bypassed or breached in order for biopesticides to become dependable alternatives to insecticides in agricultural production. In this first study to identify how budworm antibacterial defense genes are controlled by bacterial infections, six separate genes were found to rapidly switch on in the tissues of infected budworms. The antibacterial defense genes were found to stay switched on high levels of production for several hours and to produce very high quantities of the defense proteins. A new type of budworm blood cell specific defense protein was found. Continued search for viable pest-insect specific immunosuppression targets to kill or sicken insects will help scientists, industry, IPM workers, and State or Federal agencies understand which budworm specific gene targets are most amenable to attack. Overall, this will help scientists interpret laboratory data correctly and allow correct extrapolation of control measures to the field.
Technical Abstract: Resistance of Heliothine pests to microbial entomopathogens and to parasitoids is one barrier to effective control by biological control agents. In order to better understand the immune response of budworms against microbial entomopathogens several orthologs of antibacterial response proteins were identified and extracted from a tobacco budworm, Heliothis virescens (Lepidoptera: Noctuidae) expressed sequence tag database for detailed study of their functional genomics. Transcript sequences corresponding to precursors of three antibacterial peptides (ABPs) previously isolated from H. virescens hemolymph, virescein, heliomicin and heliocin, have been identified and their induction by bacterial elicitation analyzed. Further, a gloverin-like ABP and an H. virescens ortholog of the Lepidopteran hemocyte specific ABP, Spod-X-Tox have been identified. Induction of these selected antibacterial protein transcripts by bacterial infection was quantitated using quantitative RT-PCR in hemocytes and fat bodies. Transcript levels of all antimicrobial peptides were rapidly elevated by bacterial elicitation, usually as early as three hours post-treatment.