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Title: Distribution of the black pecan aphid on pecan leaf surfaces: an overview

Author
item Cottrell, Ted
item Wood, Bruce
item PAULSEN, CHRISTIAN - University Of Georgia
item RUBERSON, JOHN - Kansas State University
item Ni, Xinzhi

Submitted to: Acta Horticulturae
Publication Type: Review Article
Publication Acceptance Date: 2/15/2015
Publication Date: 2/15/2015
Citation: Cottrell, T.E., Wood, B.W., Paulsen, C.M., Ruberson, J.R., Ni, X. 2015. Distribution of the black pecan aphid on pecan leaf surfaces: an overview. Acta Horticulturae. 1070:159-165.

Interpretive Summary: Three species of aphids regularly attack the foliage of pecan trees. Two of them, i.e., the blackmargined aphid and the yellow pecan aphid, are predominantly distributed on the lower leaf surface, as are adults and nymphs of most tree-feeding aphid species. Aphids on the lower leaf surface are protected from rain, solar radiation, honeydew dropped by aphids from leaves above and the protruding leaf veins of the lower leaf surface protect from dislodgement by the movement and abrasion of other leaves. However, nymphs of the third species, i.e., black pecan aphid (BPA), do not follow this distribution pattern. Although adult BPA are mostly found on the lower surface, nymphs are distributed about equally between both surfaces. BPA nymphs need to remain stationary to elicit chlorotic feeding lesions and this may explain their movement to the upper surface. Natural enemies spending more time searching the lower surface coupled with BPA nymphs staying in one location to feed provides the best explanation for the observed distribution of BPA nymphs and adults. BPA nymphs that do not remain stationary to elicit chlorotic lesions face higher mortality (in the absence of predators), take longer to develop and result in smaller adults. Thus, BPA nymphs likely move to the upper leaf surface as a predator avoidance strategy.

Technical Abstract: Three species of aphids (Hemiptera: Aphididae) regularly attack pecan, Carya illinoinensis, foliage. Two of these species, i.e., the blackmargined aphid, Monellia caryella and the yellow pecan aphid, Monelliopsis pecanis, are predominantly distributed on the abaxial leaf surface, as are adults and nymphs of most tree-feeding aphid species. This surface provides aphids protection from rain, solar radiation, honeydew dropped by aphids from leaves above and the protruding leaf veins of the lower leaf surface protect from dislodgement by the movement and abrasion of other leaves. However, nymphs of the third species, i.e., black pecan aphid, Melanocallis caryaefoliae, do not follow this distribution pattern. Although adult M. caryaefoliae are mostly found on the abaxial leaf surface, nymphs are distributed about equally between both abaxial and adaxial leaf surfaces. Melanocallis caryaefoliae nymphs need to remain stationary to elicit chlorotic feeding lesions and this may explain their movement to the adaxial leaf surface. Natural enemies spending more time searching the abaxial leaf surface coupled with M. caryaefoliae nymphs staying in one location to feed provides the best explanation for the observed distribution of M. caryaefoliae nymphs and adults. Melanocallis caryaefoliae nymphs that do not remain stationary to elicit chlorotic lesions face higher mortality (in the absence of predators), take longer to develop and result in smaller adults. Thus, M. caryaefoliae nymphs likely move to the adaxial leaf surface as a predator avoidance strategy.