The role of insulin signaling in development of wing morphs in the soapberry bug, Jadera haematoloma

Polyphenic traits develop different final states due to environmental cues. However, it is unclear how developmental processes differ to achieve distinct morphs. The red-shouldered soapberry bug Jadera haematoloma exhibits polyphenic wing morphs in both sexes, where adults may develop with complete wings and functional flight muscles or brachypterous wings incapable of flight. This system presents a combination of alternative patterning and growth, especially within the distal membrane region of the wing. We have explored the biology of this polyphenism using studies of growth, endocrine manipulations, and functional genetic tests using RNA interference. Wing morphs are determined are by juvenile food availability. Distal-less is required for growth within the distal region of the wing, which is reduced in short-wing morphs. Knock down of the insulin signaling pathway component encoded by FoxO alters wing morph specification and results in significantly more short-wing individuals. Overall body size and wing allometry require insulin signaling. Knock down of the insulin receptor (InR) by RNAi caused smaller body size. Most appendages maintained normal allometry, scaled proportionally to body size, but wing lengths of J. haematoloma did not change under InR RNAi. Similar results were obtained from a related species without wing polyphenism, the milkweed bug Oncopeltus fasciatus, except that in this species wings scaled with body size after InR RNAi. These findings suggest that insulin signaling mediates growth in true bugs, and that polyphenism in J. haematoloma involves organ-specific modification of the insulin-signaling pathway.