Sampling procedures for banded sunflower moth, Cochylis hospes Walsingham (Lepidoptera: Tortricidae), eggs as indicators of economic injury and economic distance for oilseed sunflower

The banded sunflower moth, Cochylis hospes Walsingham, is a serious pest of sunflower. The objectives of this study were (1) to determine if banded sunflower moth (BSM) eggs can be accurately counted in the field; (2) to develop a survey technique to estimate BSM egg numbers; (3) to describe the relationship between BSM egg counts and total seed weight per plant, seed number per plant, oil content, and head area; and (4) to develop an economic injury level (EIL) measured as numbers of BSM eggs. A technique using head-mounted 3.5X magnification that accurately counts the number of BSM eggs on six bracts from a sunflower bud was developed. Sampling six bracts from five buds at plant stage R3 at 6m from the field margin in the center of each 400m section of field edge accurately estimated the BSM egg population within that span. The weight loss per BSM egg ranged between 0.29g and 0.59g per plant over a two-year period. The two-year results were averaged to develop a BSM EIL given below. EIL=TCVx PPx0.00044x0.8,where V=MarketValueper kg,PP=Plant Plant Population per hectare, TC = Treatment Cost per hectare, and 0.00044 is a combined term representing the average weight loss and a treatment efficacy of 0.8.; The relationship between numbers of eggs sampled at sites along field margins and points at variable distances into the field from that site is: EggsD = [1.29 - 0.194 ln(D)] x E; where D is distance into the field and E is the average BSM egg count from five buds at the 6m sample site. If a sample point is above the EIL, the extent of the EIL from the field edge into the field or the economic distance can be determined. Economic distance (ED) can be derived by rearranging the above formula and solving for the natural anti-logarithm of D. ED=eEIL E-1.29-.194 By calculating the EIL and ED, fields can be diagramed to show the extent of expected BSM damage and chemical applications can be restricted to those areas. This will reduce the cost of insect management, reduce the possibility of insecticide resistance in the BSM, and protect biodiversity.