Initiation of leaf chlorosis benefits the black pecan aphid

Authors: Cottrell, Ted; Wood, Bruce; Ni, Xinzhi

Submitted to: Pecan Grower
Publication Type: Trade Journal
Publication Acceptance Date: 8/8/2008
Publication Date: 10/1/2008
Citation: Cottrell, T.E., Wood, B.W., Ni, X. 2008. Initiation of leaf chlorosis benefits the black pecan aphid. Pecan Grower. 20(2):15-23.

Interpretive Summary: The black pecan aphid causes economic damage through feeding on pecan foliage that can lead to leaf abscission and tree defoliation when aphid populations are high. Damage symptoms typically appear as yellow (i.e., chlorotic) zones on pecan foliage that eventually turn brown as the leaf tissue dies. We studied the nature of the interaction between the black pecan aphid and the chlorosis it causes to pecan foliage. In laboratory experiments, we found that a significantly higher percentage of black pecan aphid adults and nymphs settled on chlorotic leaf discs than on non-chlorotic leaf discs indicating that the chlorotic zones on leaves are attractive to the black pecan aphid. Indeed, when we tested young aphid nymphs for their ability to develop on leaf discs, nymphs that were allowed to feed on the same leaf disc which had increased chlorosis over time had lower mortality and developed faster than nymphs that were transferred to new leaf discs without chlorosis each day. These results show that black pecan aphid-induced leaf chlorosis plays an important role in the interaction of the black pecan aphid with its pecan host.

Technical Abstract: The interaction between the black pecan aphid, Melanocallis caryaefoliae (Hemiptera: Aphididae), and the chlorosis it causes to foliage of pecan [Carya illinoinensis (Wangenh.) K. Koch)] is poorly understood. Laboratory experiments were conducted on the settling behavior of the black pecan aphid, when provided chlorotic pecan leaf discs resulting from previous black pecan aphid feeding and non-chlorotic leaf discs, under a normal photoperiod and constant dark. Additionally, aphid development from the first instar to the adult stage was examined when nymphs were either allowed to feed on the same leaf disc or moved daily to a new, non-damaged, same age leaf disc. After 24 h a significantly higher percentage of black pecan aphids settled on chlorotic leaf discs than non-chlorotic leaf discs, regardless of photoperiod. When starting from the first instar, nymphs that were prevented from inducing leaf chlorosis by moving daily to new, same-age leaf discs took about five days longer to complete development and had higher mortality than when aphids remained on the same leaf disc. These results show that black pecan aphid-induced leaf chlorosis plays an important role in the interaction of the black pecan aphid with its pecan host.