Hormonal control of body-color polymorphism in Locusta migratoria: interaction between [His7]-corazonin and juvenile hormone

The effects of injection of [His7]-corazonin and juvenile hormone (JH) III on the body color in L. migratoria were investigated using albino and normal (pigmented) nymphs. Most albino nymphs turned green in the fourth instar if injected with JH III during the last 2 days of the previous instar. When albino third instar nymphs injected with 10 pmol of [His7]-corazonin on different days were treated with 100 μg of JH III on day 3.5, they developed various body colors in the following nymphal instar: those injected with [His7]-corazonin during the first 2 days developed very dark green or black color, whereas some of those injected after this period turned green and their legs and ventral side of the body were variously pigmented, the coloration being similar to green solitary individuals often found in the field. Field-collected brown solitary nymphs injected with 1 nmol of [His7]-corazonin and kept individually, turned reddish without any black spots in the following nymphal instar when the ecdysis occurred within 1 day after injection. Injection of [His7]-corazonin 2 days before the following ecdysis induced black patterns on an orange background color, the coloration characteristic of gregarious forms. Similar injections into field-collected green solitary nymphs also induced black patterns but the rest of their body remained green. These results may indicate that the temporal changes in the hemolymph titers of [His7]-corazonin and JH play an important role in the control of body-color polymorphism in this locust.