BODY-SIZE INFLUENCES MATING SUCCESS OF THE EUCALYPTUS LONGHORNED BORER (COLEOPTERA, CERAMBYCIDAE)

Both sexes of adult Phoracantha semipunctata F (Coleoptera: Cerambycid ae) congregate on stressed Eucalyptus that are the larval hosts. In a field study, 721 adult P. semipunctata captured on host trees varied c onsiderably in body size with the largest individuals being about twic e the length of the smallest. Females that were paired with a mate wer e similar in size to solitary females, suggesting that the probability of a female being mated was not affected by her size, However, large males had greater success than smaller males in obtaining mates. Male P. semipunctata rely on antennal contact to locate and identify female s on the larval host. Therefore, the rate at which males search for ma tes is a function of the area swept by their antennae per unit time. B ecause of their greater antennal spread, large males were able to sear ch for females at double the rate of the smallest males. Large males a lso dominated in aggressive contests for females. The superior abiliti es of large male P. semipunctata in both locating and defending mates account for the influence of body size on mating success.