Recent studies (Dane, et.al; Calif. Agri. Nov. Dec. '93) on the feasibility of leafhopper control in grapes with Chrysoperla spp. (green lacewings) disclosed that although green lacewing larvae are voracious feeders on leafhoppers, presently used "dry" delivery systems cause excessive egg mortality, do not deliver consistent, uniform rates of eggs and many eggs do not remain on the plant until they hatch into larvae. Additionally, the cost of green lacewing eggs ($3 per thousand) was economically prohibitive. Other critical factors were proper timing and management conflicts of releases.
A recently developed liquid release system shows promise in solving the problems of egg mortality and loss as well as uneven distribution. Additionally, the cost of green lacewing eggs has been reduced to $1.50 per thousand (Beneficial Insectary, Redding, CA). This price should improve the economic feasibility of release programs. The new application system is called the Bio-Sprayer and was developed by pecan entomologist Louis Tedders (USDAARSRetired; Byron, GA). It is manufactured by Smucker Mfg., Inc. (Harrisburg, OR 97446).
Together with a newly developed Bio-Carrier, green lacewing eggs are uniformly sprayed onto plant leaves. The carrier rapidly dries and firmly attaches the eggs to the plant. Since fully mature eggs are used, further egg loss is reduced since they rapidly hatch into larvae and begin searching for prey.
Extensive tests were conducted to determine the effects on the eggs of both extended immersion in the Bio-Carrier solution and delivery through the system.
Fully mature green lacewing eggs were held with agitation in the Bio-Carrier solution for one hour and for four hours. Samples were then taken and held for larval emergence. An average of 95% of the eggs held for one hour had successful larval emergence. An average of 94% of the eggs held for four hours had successful larval emergence. An average of 94% of the eggs in the control of this test showed successful larval emergence.
In separate tests, green lacewing eggs delivered through the system showed an average of 91% successful larval emergence. Controls on these tests showed an average of 93% successful larval emergence.
These results show that an improved liquid delivery system for green lacewing eggs is now available. Damage to the eggs during delivery is minimal and since the eggs are attached to the leaf surface, losses due to eggs falling to the ground are virtually eliminated.
This new system, together with the reduced cost of green lacewing eggs should result in a greatly increased biotic and economic effectiveness of this important biological control agent. Use of the system should improve leafhopper control in grapes.
BY : Richard Morrison