Coffee leaf volatiles and egg laying by the coffee leaf miner Leucoptera coffeella

Recent reports of coffee genotypes resistant to one of its key pests in the Neotropical region, the leaf miner Leucoptera coffeella (Lepidoptera: Lyonetiidae), sparked studies trying to recognize the underlying causes of resistance. An association between increased egg laying by the leaf miner and increased caffeine levels in coffee leaves was recently recognized. However, since caffeine is not volatile, its effect on egg laying is likely aided by a volatile compound. This was the hypothesis tested here. Coffee leaf volatiles from 12 coffee genotypes were collected, analyzed (gas chromatograph coupled with a mass spectrometer (CG/MS)) and tested for electrophysiological activity (EAG). The active volatiles thus recognized were subjected to partial correlation against the density of eggs laid by the leaf miner in each coffee genotype. The volatile showing significant positive correlation, p-cymene, was subjected to an attraction test in a four-arm olfactometer confirming its biological activity and providing evidence of its role stimulating egg laying by the coffee leaf miner.