Chemoreception in Antheraea assama-Exorista sorbillans complex: role of host plant chemicals

Host plant specificity in phytophagous insects is governed largely by responses to chemicals that are characteristic of certain plant taxa. We examined chemoreception in the Muga silkworm, Antheraea assama with a restricted host range feeding primarily on Litsea polyantha and Persea bombycina. In addition, electroantennogram responses of the Uzi fly, Exorista sorbillans, a notorious parasite of A.assama to host plant and host related chemicals in order to identify compounds that could be used as a trap/bait to lure the parasite. Electrophysioloigical characterization of the medial and lateral sensilla styloconica reveal that they are sensitive to a wide group of chemicals including sugars and sugar alcohols, salts and deterrents. The epipharyngeal sensilla responds to inositol, salts and deterrents such as salicin, nicotine and caffeine. Qualitative and quantitative differences were observed in volatile profiles of day and night time collections as also between undamaged and A.assama damaged P.bombycina. The volatile profile of undamaged plants typically included green leaf volatiles – C6 alcohols, aldehydes and their corresponding acetates. The compounds identified from A.assama damaged P. bombycina include (3Z)-3-Hexanal, Hexanal, 2-Hexenal, 3-Hexen-1-ol, 1-Hexanol, Heptanal, Decane, alpha-Phellandrene, (Z) 3-Hexenyl acetate, para-Cymene, D-Limonene, (Z)-3,7-dimethyl1,3,6-Octatriene, 3-Carene, trans-Caryophyllene, Undecane, alpha-Farnesene and several acids. Electroantennogram responses of the adult female uzi fly to 52 chemicals exhibit concentration dependent response and among the fatty acid derivatives, the alcohols elicit higher responses than aldehydes. Other than myrcene, all other hydrocarbon monoterpenes and oxygenated monoterpenes elicit low responses. Also, odd number of carbon chains elicit higher responses than even chain compounds. Thus, the wide spectrum response of E.sorbillans to a wide group of chemicals belonging to different chemical classes, though varying, nevertheless suggests that using plant information enhances its parasitisation efficiency.