|HONAKER, JESSICA - Texas A&M University|
|SKRIVANEK, SARAH - Texas A&M University|
|LOPEZ, JUAN DE DIOS - Retired ARS Employee|
|Martin, Daniel - Dan|
|LOMBARDINI, LEO - Texas A&M University|
|HARRIS, MARVIN - Texas A&M University|
Submitted to: Southwestern Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/28/2013
Publication Date: 3/1/2013
Citation: Honaker, J., Skrivanek, S., Lopez, J., Martin, D.E., Lombardini, L., Grauke, L.J., Harris, M. 2013. Blackmargined aphid (Monellia caryella (Fitch); Hemiptera: Aphididae) honeydew production in pecan (Carya illinoinesis (Koch)) and implications for managing the pecan aphid complex in Texas. Southwestern Entomologist. 38:19-32.
Interpretive Summary: The blackmargined aphid damages pecan trees by sucking sugars from their leaves; the residue is secreted by the aphids and drips to the ground as honeydew, wasting the food needed by the tree to build leaves, nuts, and shoots. Pecan growers often spray their orchards to kill the aphids, which costs time and money for chemical applications, may kill helpful insects, and increases risks to worker health and food safety. More information about natural resistance to aphids in pecan trees is needed to develop healthier trees, reduce costs, and protect the environment. Water-sensitive cards were used to detect honeydew droplets, and were found to conveniently measure aphid populations in trees. Populations of beneficial insects increased as aphid populations increased and seemed to be attracted to the honeydew. The results confirm that aphids impose an energy cost to pecan trees, and identify the threshold number of aphids that will justify the cost of chemical applications to protect the trees. These methods will help us identify trees that possess aphid resistance and will lead to the development of better pecan cultivars.
Technical Abstract: Field studies of the blackmargined aphid, Monellia caryella (Fitch), were conducted on three cultivars, “Cheyenne,” “Kiowa,” and “Pawnee,” of pecan, Carya illinoinisis (Wang) K. Koch. Aphid and natural enemy (lacewings, ladybird beetles, and spiders) densities were determined twice weekly by direct inspection of foliage on each variety during summer of 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 that either “Kiowa” or “Pawnee.” Honeydew production was directly correlated with aphid density. Natural enemy densities increased during initial stages of aphid outbreak on all cultivars and the asymptote reached on “Cheyenne” exceeded the action level of 25+ aphids/leaf, and 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 where aphid densities did not exceed the action level. 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 was calculated using aphid density and also by using honeydew measurements; these data showed that energy drain on “Cheyenne” far exceeded that of “Kiowa” or “Pawnee,” using either method. These results suggest that moderate densities of blackmargined aphids efficiently attract natural enemies with little risk of economic damage to the crop.