Leaf alkaloids, phenolics and coffee resistance to the leaf miner Leucoptera coffeella (Lepidoptera, Lyonetiidae)

Coffee alkaloids (caffeine and related methylxanthines) and phenolics (caffeic and chlorogenic acids) have recognized pestistatic/pesticidal activity and mediate insect plant interactions. The present investigation aimed to assess the resistance of 12 coffee genotypes to the coffee leaf miner Leucoptera coffeella and correlate such results with the leaf content of coffee alkaloids and phenolics likely to play a role in the interaction between coffee and its leaf miner. The levels of chlorogenic and caffeic acid, caffeine and related methylxanthines were measured and quantified in leaf extracts of these genotypes before and seven days after their infestation by the leaf miner. Some coffee genotypes (Coffea canephora, and C. racemosa and its hybrids with C. arabica) exhibited high pesticidal activity (100% mortality) towards the coffee leaf miner indicating their antibiosis resistance. However there was no correlation between this activity and the leaf levels of coffee alkaloids and phenolics. Curiously though, infestation by the coffee leaf miner leads to a nearly 4-fold decline in the leaf levels of chlorogenic acid, which does not affect this pest-species, but may affect other more generalist species. Indeed, chlorogenic acid sprayed on coffee leaves stimulated locomotory activity of the green scale Coccus viridis (Hemiptera: Sternorrhyncha: Coccidae), thus minimizing their feeding in contrast with the absence of this polyphenol. Therefore, reduction of chlorogenic acid levels in coffee leaves due to leaf miner infestation seems to also favor infestation by generalist insects, such as the green scale.