Imprecise excision of the progenitor insertion, resulting in a deletion which removes the entire Gr64a and Gr64b coding regions, as well as part of Gr64c.

The L-type labellar sensilla of homozygous flies show almost no electrophysiological response to either maltotriose, stachyose, raffinose, leucrose or fructose. The response to sucrose, maltose, turanose, maltitol and palatinose is reduced compared to wild type, but not abolished. The response to m-α-glucoside, glucose and melezitose is not reduced in the mutant flies, and the response to glucose may be somewhat elevated.