Changes in melon plant phytochemistry impair Aphis gossypii growth and weight under elevated CO₂

Elevated CO₂ (eCO₂) modifies plant primary and secondary metabolism that subsequently impacts herbivore insect performance due to changes in its nutritional requirements. This laboratory study evaluated interactions between Aphis gossypii Glover (Hemiptera: Aphididae) and melon (Cucumis melo L., Cucurbitaceae), previously acclimated two or six weeks to different CO₂ levels, eCO₂ (700 ppm) or ambient CO₂ (400 ppm). Under eCO₂, melon plants decreased nitrogen foliar concentration and increased carbon to nitrogen ratio, independently of acclimation period, significantly reducing the content of some amino acids (alanine, asparagine, glycine, isoleucine, lysine, serine, threonine, and valine) and increasing the carbohydrate (sucrose) content in melon leaves. The dilution in some essential amino acids for aphid nutrition could have aggravated the reduction in A. gossypii population growth reared on melon previously acclimated two weeks to eCO₂, as well as the loss of aphid body mass from two successive generations of A. gossypii reared under eCO₂ on plants previously acclimated two or six weeks to eCO₂. The response to eCO₂ of phloem feeders, such as aphids, is actually variable, but this study highlights a negative response of A. gossypii to this climate change driver. Potential implications on control of this pest in a global change scenario are discussed.