Within-Field Distribution of the Sunflower Midge (Diptera: Cecidomyiidae)

Abstract

The sunsower midge, Contarinia schulzi Gagne ´ (Diptera: Cecidomyiidae), is a pest of cultivated sunsower (Helianthus annuus L.). Larval feeding can cause damage and yield loss to the sunsower head. Adult emergence is extended and larvae are well protected in the sunsower recep- tacle, making chemical control methods difÞcult and expensive. Sunsower midge enter sunsower Þelds at the edges but Þeldwide distributions occur, although the dynamics are not fully understood. Two commercial Þelds in 1999 and one Þeld in 2000 were systematically sampled by dividing each Þeld into Þxed sample points. Mean egg and larval densities from each sample point were used to describe sunsower midge populations. The sunsower heads at each sample point were also assessed for damage. Maps of sunsower midge population density, cumulative density, and sunsower head damage ratings were estimated with kriging interpolation. Maps were estimated several times during Þrst generation sunsower 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.