Insect clip cages rapidly alter photosynthetic traits of leaves

In plant‐insect interaction experiments, a clip cage is frequently used to isolate insects or other small pests on a leaf. Clip cage effects on the physiology of the leaf could possibly confound experimental results. Our objective was to quantitate the effects of an insect clip cage of the type typically used for small pests such as whiteflies ( Bemisia sp.), aphids ( Aphis sp.) and mites ( Urticae sp.) on the photosynthetic traits of cotton ( Gossypium hirsutum L. cv. Coker 100A‐glandless) and muskmelon ( Cucumis melo L. cv. Imperial 45) leaves. Clip cages that enclosed 11.3 cm 2 of both the abaxial and adaxial sides of a leaf were attached to young fully expanded leaves. For the leaf tissue within the clip cage, incident radiation was decreased and leaf temperature was increased. After 24 h, chlorophyll content of tissue within the clip cage was significantly increased compared with non‐caged‐control samples taken from the opposite half of the same leaf. Three days after clip cages were attached to leaves, compared with controls, the tissue within the cage had a lower light‐saturated, steady‐state CO 2 exchange rate (CER) and leaf soluble protein content. The cage effect on CER and soluble protein could be explained, at least in part, by decreased light‐saturated initial Rubisco activity for leaf tissue within the clip cage. We conclude that the clip cages caused physiological and biochemical alterations of leaves that could alter insect nutrition. Thus, it is suggested that clip cage effects on leaf physiology and microenvironment must be considered when interpreting results of plant‐insect interaction experiments.