ECDYSTEROIDS CONTROL EYESPOT SIZE AND WING COLOR PATTERN IN THE POLYPHENIC BUTTERFLY BICYCLUS-ANYNANA (LEPIDOPTERA, SATYRIDAE)

The strongly polyphenic African butterfly, Bicyclus anynana, shows con spicuous ventral eyespots and a transverse band in the wet-season form and small eyespots and no band in the dry-season form, These forms ar e produced when larvae are reared at high and low temperatures, respec tively, Truncation selection was applied to a stock population (UNSELE CTED-LINE) to produce lines which, at a constant intermediate temperat ure of 20 degrees C, always produced the dry season form (LOW-LINE) an d the wet-season form (HIGH-LINE) in addition to a line of fast develo pment (FAST-LINE), A relationship between wing pattern and development time was apparent: the FAST-LINE displayed larger eyespots and HIGH-L INE pupae developed faster (mean = 12.5 days) than LOW-LINE pupae (14. 1 days), Differences were found among the lines in ecdysteroid titers after pupation. Hemolymph ecdysteroids in HIGH-LINE pupae increased ea rlier and reached twice the level of those in LOW-LINE pupae during th e first 3 days after pupation, FAST-LINE pupae developed faster (11.7 days) than UNSELECTED-LINE pupae (12.8 days) and ecdysteroids in the F AST-LINE increased more quickly and reached higher levels, In the four LINES, ecdysteroid titers in 3 day old pupae were in the order UNSELE CT approximate to LOW much less than FAST much less than HIGH, Thereaf ter the titers overlapped. An injection of 20-hydroxyecdysone (20E) in hibited pupal development at a dose between 2.5 and 5 mu g when it was injected into pupae within 24 h after pupation, At lower doses (0.25- 0.5 mu g 20E) 22-100% of the pupae in different experimental groups in the LOW- as well as in the HIGH-LINE developed successfully, The pupa l stage was significantly shortened, especially in the LOW-LINE, Addit ionally, 0.25 and 0.5 mu g 20E injected into 0-12 h LOW-LINE pupae shi fted the wing color pattern towards the wet season form: eyespots incr eased in size and the transverse wing band appeared in the more conspi cuous pattern characteristic of the wet season form, The results demon strate that ecdysteroids appearing early in the young pupa produce the wet season form of the wings, The same hormonal system mediates both developmental time and wing pattern determination.