Controlling Aphids with Harmonia Lady Beetle in Pecan Orchards
Yellow pecan aphids are an annual and nearly universal insect pest of pecans for which no sustainable control exists. A number of foliar applied insecticides are registered for yellow aphids, but control is poor and the insects often resurge after insecticides are applied. The soil- applied systemic insecticide Temik is registered and effective but is expensive ($45 and up per acre), can leach into ground water and may produce tolerance in yellow aphids after several years use.
A species of lady beetle, Harmonia axyridis, was imported from Japan and released in Georgia from 1979-81 by USDA entomologists. It has proved to be an excellent predator of aphids that attack trees and ornamentals, especially yellow aphids in pecans. Although the Harmonia lady beetle is now common in Georgia, Florida and some areas of Louisiana, it did not become widespread until 11 years after its release. A few individuals of this species had been found in Texas, and producers were looking for ways to increase Harmonia populations faster in hopes of providing more effective aphid control in pecan groves.
1.) Increase the biological control of yellow pecan aphids in Texas by introducing the Harmonia lady beetle to pecan groves throughout the state.
2.) Increase producer awareness and knowledge of the Harmonia lady beetle and other beneficial insects and inform producers of their use in a biologically intensive IPM program.
3.) Develop and distribute an Extension bulletin outlining the use of the Harmonia beetle in a biologically intensive IPM program.
4.) Distribute a questionnaire to growers involved in the Harmonia release program to determine the level of beetle establishment and if they reduce levels of yellow aphids.
Twelve thousand beetles were collected from congregating sites on walls of buildings in sheltered areas of Georgia. They were swept into one gallon ice cream cartons and transported to Texas where they were stored in refrigerators at the Texas A&M Research and Education Center in Dallas. Later they were shipped to cooperating pecan growers throughout Texas who volunteered their operations as nursery orchards. The orchards were selected on the criteria of location, grower interest, grower commitment to using the least toxic pesticides and grower willingness to plant legumes as cover crops. The beetles became established at eight of the nursery sites in the 1994 growing season. Since then, orchard scouting by cooperators and
Extension entomologists have monitored beetle and aphid population densities.
Vetch or clover was planted in strips throughout test plots in the orchards to attract pea aphids as an early season food source for the beetles and other predators. Total plantings range from 0.5 acres of legumes up to 15 acres per orchard. Lady beetles normally multiply in these legumes in the spring and then move into pecan trees to feed on yellow aphids in early summer.
In 1994, beetles became abundant in both release and non-release orchards by midsummer, apparently from populations in Louisiana. This natural increase made it unnecessary to assist in redistributing Harmonia from the test orchards.
In the spring of 1995, beetles were most abundant in small grains (wheat) and alfalfa. Aphids were abundant in both crops in February and March. Harmonia were uncommon in legumes planted in orchards or in pecan trees at this time. Harmonia did not increase in pecans midsummer as they did in 1994, even though pecan aphids became very abundant. Many pecan producers throughout the state observed that Harmonia were much less common in pecan trees in 1995 than in the fall of 1994. No explanation was found for this decline in numbers.
In conclusion, legumes seemed less attractive to Harmonia beetles in the spring than did wheat or alfalfa, which hosted large numbers of aphids. Harmonia emerged from overwintering in February or March. Possibly aphids were more common earlier in wheat and alfalfa relative to the legumes and as a result these crops were more attractive to Harmonia. Adding wheat to legume plantings may increase attractiveness to beetles in the spring. Wheat alone may be a more reliable host for aphids than legumes, but wheat does not have the benefit of providing nitrogen to subsequent crops. It is not known why Harmonia numbers did not increase midseason in 1995 when pecan aphids became abundant. No theories have been put forth for testing.
Grower interest in beneficial insects has identified the need for a field guide to important beneficial insects in pecans. Education and outreach efforts are now concentrated around a publication to teach growers how to identify and use the Harmonia lady beetle and other beneficial insects in biological control.
The Texas Pecan Growers Association has contributed funds to help the project coordinators publish such a book co-authored by Louis Tedders, a world-recognized pecan entomologist, and Bill Ree, Extension entomologist for pecans in Texas. The 100-page book with 150 color photos is scheduled for publication early in 1997.
Presentations have been made at Extension pecan programs throughout the state and at the annual conference of the Texas Pecan Growers Association. Articles in Pecan South and other publications have kept growers informed about the project.