Effect of the Black Pecan Aphid on Leaf Chlorophyll Pigments and Gas-Exchange Parameters of Pecan Cultivars

The black pecan aphid (BPA) ( Melanocallis caryaefoliae ) is a serious insect pest of pecan crops. Feeding by BPA induces distinct chlorotic lesions on pecan ( Carya illinoinensis ) foliage. These lesions can lead to premature leaflet abscission and affect the overall tree energy reserves. This study quantified the physiological impact of BPA-induced chlorosis on photosynthetic pigments, chlorophyll a and b and carotenoids, and gas-exchange parameters, including net photosynthetic rate (A), transpiration rate (E), and stomatal conductance ( g sw ), across four commercial cultivars: Avalon, Desirable, Lakota, and Sumner. Field evaluations conducted during the 2024–25 growing seasons revealed that BPA feeding significantly impaired both pigment quantity and gas-exchange efficiency across all cultivars. In 2024, chlorophyll a content in ‘Avalon’ declined from 34.34 (noninfested) to 8.48 µg·cm −2 (infested) in July and from 40.87 to 17.68 µg·cm −2 in September. Similarly, ‘Lakota’ exhibited reductions from 33.15 to 11.34 µg·cm −2 and from 32.17 to 6.58 µg·cm −2 during the same intervals. Although pigment degradation was consistent across all cultivars, ‘Lakota’ demonstrated a degree of physiological resilience, maintaining stable E and g sw in 2024, and sustaining A during Jul 2025. Despite these variations in cultivar response, the data collectively indicate that BPA-induced chlorosis causes profound physiological impairment rather than superficial cosmetic injury. These findings suggest that BPA infestations may significantly limit carbon assimilation and, in turn, tree productivity.