|
Description:
|
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' . |