Response of Plutella xylostella and its parasitoid Cotesia plutellae to volatile compounds

The effects of limonene, a mixture of limonene + carvone (1:1, v/v), and methyl jasmonate (MeJA) on diamondback moth (DBM) (Plutella xylostella L.) oviposition, larval feeding, and the behavior of its larval parasitoid Cotesia plutellae (Kurdjumov) with cabbage (Brassica oleracea L. ssp. capitata, cvs. Rinda and Lennox) and broccoli (B. oleracea subsp. Italica cv Lucky) were tested. Limonene showed no deterrent effect on DBM when plants were sprayed with or exposed to limonene, although there was a cultivar difference. A mixture of limonene and carvone released from vermiculite showed a significant repellent effect, reducing the number of eggs laid on the cabbages. MeJA treatment reduced the relative growth rate (RGR) of larvae on cv Lennox leaves. In Y-tube olfactometer tests, C. plutellae preferred the odors of limonene and MeJA to filtered air. In cv Lennox, the parasitoid preferred DBM-damaged plants with limonene to such plants without limonene. C. plutellae females were repelled by the mixture of limonene + carvone. In both cultivars, exogenous MeJA induced the emission of the sesquiterpene (E,E)-alpha-farnesene, the homoterpene (E)-4,8-dimethyl-1,3,7-nonatriene (DMNT), and green leaf volatile (Z)-3-hexenyl acetate + octanal. The attractive effect of limonene and MeJA predicts that these two compounds can be used in sustainable plant protection strategies in organic farming.