Within-field distribution of the sunflower midge (Diptera: Cecidomyiidae)

The sunflower midge, Contarinia schulzi Gagné (Diptera: Cecidomyiidae), is a pest of cultivated sunflower (Helianthus annuus L.). Larval feeding can cause damage and yield loss to the sunflower head. Adult emergence is extended and larvae are well protected in the sunflower receptacle, making chemical control methods difficult and expensive. Sunflower midge enter sunflower fields at the edges but fieldwide distributions occur, although the dynamics are not fully understood. Two commercial fields in 1999 and one field in 2000 were systematically sampled by dividing each field into fixed sample points. Mean egg and larval densities from each sample point were used to describe sunflower midge populations. The sunflower heads at each sample point were also assessed for damage. Maps of sunflower midge population density, cumulative density, and sunflower head damage ratings were estimated with kriging interpolation. Maps were estimated several times during first generation sunflower midge infestation. Field edges that were initially populated continued to be areas of infestation throughout the sampling period. Damage ratings were related to population densities when infestations were high. In 2000, we tested the larval hatching rate from different-sized egg masses with regression to determine an estimation technique for combining numbers of eggs and larvae.