Distribution, Conditioning, and Interspecific Effects of Blackmargined Aphids and Yellow Pecan Aphids (Homoptera: Aphididae) on Pecan

Abstract

Field studies on the yellow pecan aphid Cornplex showed that, among leaves growing from the same bud, the distal younger and larger leaves of pecan, Carya illinoensis (Wang.) K. Koch, were able to support a higher number of blackmargined aphids, Monellia caryella (Fitch), and yellow pecan aphids, Monelliopsis pecanis Bissell, than the proximal older and smaller leaves, before the leaves become unsuitable for further aphid development. Cumulative aphid days (one aphid on one leaf for 1 d = 1 aphid d) required to render foliage unsuitable for further development ranged from 421 on the most distal leaf to 50 on the most proximal leaf of the same shoot for blackmargined aphids during a 2-mo period, and from 15,132 to 1,322 for yellow aphids during a 4-mo period in separate infestations. Results of sequential infestations where foliage was initially subjected to an epidemic of black margined aphids averaging 18,900 aphid-d per 10 leaves showed that the foliage would support 20,345 aphid-d of yellow pecan aphid development; the reciprocal sequential infestation experiment following a yellow pecan aphid epidemic of 100,861 aphid-d per 10 leaves resulted in the foliage supporting 74 aphid-d of black margined aphid development. Foliage conditioned by blackmargined aphid remained suitable for subsequent infestation by substantial numbers of yellow pecan aphids, but the latter species caused substantial defoliation, rendering foliage unsuitable in the reverse situation. The average calendar time of infestation was 64 d for the blackmargined aphid and 114 d for the yellow pecan aphid.