| dc.description.abstract | 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’. | en |
