The quantification of blackmargined aphid (Monellia caryella (Fitch)) honeydew production in pecan (Carya illinoinensis (Koch)) in Texas

Field studies of the blackmargined aphid, Monellia caryella (Fitch), were conducted on three cultivars, ‘Cheyenne’, ‘Kiowa’, and ‘Pawnee’, of pecan, Carya illinoinensis (Koch). Aphid density and natural enemy (lacewings, ladybird beetles, and spiders) densities were determined biweekly by direct inspection of 160 leaves per variety during the 2005 and 2006 growing seasons. Honeydew deposition was measured biweekly using water sensitive cards. Aphid phenologies were similar among cultivars; however, ‘Cheyenne’ supported higher densities of aphids than either ‘Kiowa’ or ‘Pawnee’. Honeydew production correlated positively with aphid density. Honeydew produced per aphid differed only between ‘Cheyenne’ and ‘Pawnee’ in 2006; natural enemies per aphid varied in significance during both seasons. Natural enemy densities increased during initial stages of outbreak on all cultivars in 2006. The asymptote reached on ‘Cheyenne’ had a lower natural enemy to aphid ratio than that on the other cultivars, indicating that the functional response of natural enemies to increased aphid densities was exhausted sooner on ‘Cheyenne than on other cultivars’. Honeydew appears to be an attractant for natural enemies and cost-benefit calculations were made to quantify the loss of photosynthates to aphids for each cultivar versus the gain in natural enemies that occurred. ‘Cheyenne’ was the least efficient of the three cultivars in the utilization of this defense mechanism. The energy drain per hectare attributable by adult aphid feeding was, 761,197 – 900,312kcal, 266,397 – 237,709kcal, and 138,790 – 134,223kcal for ‘Cheyenne’, ‘Kiowa’, and ‘Pawnee’, respectively. Calculated nut-loss equivalents were 14 – 16kg for ‘Cheyenne’, 4 – 5kg for ‘Kiowa’, and 2kg for ‘Pawnee’