Variable phenotype. The most extreme expression shows a small, deformed thorax which is split into two segments by a longitudinal furrow. The eyes are abnormally shaped and the abdominal tergites are split in the dorsal mid-line and abnormally reunited. The wings are slightly divergent. Occasionally one or both palps is abnormal in position or structure. Viability and fertility are slightly reduced in males, and very reduced in females.

RK3. In extreme manifestation, thorax split into two segments by longitudinal furrow; abdominal tergites also split along mid-dorsal line. Eyes deformed. In least abnormal fly, always a hairless stripe along the dorsal midline of thorax. Wings often slightly divergent. Occasionally, one or both palpi abnormal in position or structure. male viability low male fertility low female viability very low female fertility very low