NUMERICAL ALLOMETRIC GROWTH OF THE OMMATIDIA, ANTENNAL SENSILLA, AND TEETH OF FORETIBIAL COMBS IN THE MILKWEED BUG ONCOPELTUS-FASCIATUS DALLAS (HETEROPTERA, LYGAEIDAE)

Oncopeltus fasciatus (Heteroptera : Lygaeidae), the milkweed bug, was bred in captivity. Sampling showed that individuals grow exponentially through their 6 developmental stages with an average linear increase per molt of 42% for the females and 41 % for the males. The number of ommatidia per eye grows with negative allometry from an average of 30 in the first instar to 860 in the male and 820 in the female adult. Th e total number of sensilla on the 2 flagellar segments of an antenna i ncreases with negative allometry during the 5 nymphal stages from a me an of 239 in the first instar to 2462 in the last. At this point, this allometric growth pattern is sharply broken by distinct numerical inc rease to 7163 on the adult flagellum. The number of teeth composing th e foretibial comb, the tool for grooming the distal flagellar segment, grows with negative allometry through all 6 developmental stages. Cal culations using previously published data from the migratory locust, L ocusta migratoria, revealed the same growth pattern of antennal sensil la: uniform allometric growth during the nymphal development, broken b y a conspicuous upward jump to the adult number of sensilla. In the Am erican cockroach, Periplaneta americana, this growth pattern of antenn al sensilla holds only for the male; the female continues the nymphal allometric growth into the adult stage. These observations on allometr ic growth fit three theoretical explanations: 1. Smooth allometric gro wth is evidence for an aut-adaptation to increasing size. 2. Ex-adapta tions to novel ecological niches cause breaks in allometric growth pat terns. 3. Chapman's rule, which states that increased mobility correla tes with greater olfactory sensitivity, correctly predicts the observe d breaks in the allometric growth patterns in the abundance of antenna l sensilla.