Pecan aphids, part i: distribution on pecan leaves

Authors: Cottrell, Ted

Submitted to: Pecan South
Publication Type: Trade Journal
Publication Acceptance Date: 2/14/2019
Publication Date: 3/1/2019
Citation: Cottrell, T.E. 2019. Pecan aphids, part i: distribution on pecan leaves. Pecan South. 52(1):34-38.

Interpretive Summary: Three species of aphids, black pecan aphid (BPA), yellow pecan aphid (YPA) and blackmargined aphid (BMA) attack pecan foliage. BPA populations generally develop on shaded leaves in the interior of the canopy; whereas, the YPA and the BMA typically exploit sun-exposed foliage. During late summer when populations are higher, all three species can be found throughout the canopy. Even on the same compound leaf, the different aphid species will exploit different areas of the leaf. But regardless of their distribution across the leaf, their distribution on the top versus bottom of the leaf reveals that both adults and nymphs of the BMA and the YPA occur primarily on the underside of the leaf. The underside of the leaf provides the aphid protection from numerous abiotic dangers including solar radiation and rain. Locating on the underside of the leaf is also true for adults of the BPA. However, a proportion of the BPA nymphs will move to the top surface of the leaf even in light of the environmental hazards on that surface of the leaf. Facing the environmental hazards of the upper leaf surface is likely a response to predators of aphids predominantly searching the undersides of pecan leaves.

Technical Abstract: Three species of aphids, Melanocallis caryaefoliae, Monelliopsis pecanis and Monellia caryella, attack pecan foliage. Melanocallis caryaefoliae populations generally develop on shaded leaves in the interior of the canopy; whereas, M. pecanis and M. caryella typically exploit sun-exposed foliage. During late summer when populations are higher, all three species can be found throughout the canopy. Even on the same compound leaf, the different aphid species will exploit different areas of the leaf. But regardless of their distribution across the leaf, their distribution on the top versus bottom of the leaf reveals that both adults and nymphs of M. caryella and M. pecanis occur primarily on the underside of the leaf. The underside of the leaf provides the aphids protection from numerous abiotic dangers including solar radiation and rain. Locating on the underside of the leaf is also true for adults of M. caryaefoliae. However, a proportion of M. caryaefoliae nymphs will move to the top surface of the leaf even in light of the environmental hazards on that surface of the leaf. Facing the environmental hazards of the upper leaf surface is likely a response to predators of aphids predominantly searching the undersides of pecan leaves.