Figure 4

Disruption of ChomOrco impairs foraging and host-seeking behaviors in screwworm. (A) Representation of the two-choice trap assay arena. Odor (yellow mist) and control traps are offered to groups of flies at opposite sides of the cage. Groups of 15–25 flies (fasted adults of 3-to-4-days-old, sex ratio about 1:1) were tested in foraging trials, while groups of 10–20 flies (fed, matted females of 6-to-9-days-old) were tested in oviposition assays. Attraction experiments were made in replicates (n = 8 to 12; dots in C,D). (B) Details of the trap model used in two-choice assays (see also Supplementary Methods). (C) Honey odors resemble floral nectar, an important nutritional source for screwworm in nature. Orco mutants (Orco¹⁶; n = 11) lost attraction to honey, as ablated flies (n = 9), while wildtype (Orco^wt; n = 12) and heterozygous (Orco^wt/16; n = 12) flies remain strongly attracted. (D) Screwworm females are stimulated to lay eggs on spent larval media in rearing conditions. This bait releases a volatile blend similar to the one found in screwworm-infested wounds. Orco mutants (n = 8) have severely reduced attraction to the oviposition media when compared to wt (n = 10) and heterozygous (n = 8) flies (Supplementary Movie S1). Similar response was observed for ablated flies (n = 9). The results illustrate that OR-mediated olfaction is necessary for foraging and host-seeking behaviors in C. hominivorax. Bars indicate mean ± SD. Genotypes marked with different letters denote significant deviations of attraction index as given by the two-sample Wilcoxon rank-sum test with continuity correction (significant at p-value < 0.001).