Biometric discrimination of the larval instars and sexes of maladera matrida (coleoptera: scarabaeidae: melolonthinae)

Maladera matrida Argaman was first reported from Israel in the late 1970's and was subsequently described as a new species. Shortly thereafter, this species has become a serious pest of ornamental plants and agricultural crops. In this study we identified external anatomical features for distinguishing between the three larval instars and between the two sexes of pupae and adults collected in the field. Larval instars may be divided as follows: first instar, head width less than 1.8 mm; second instar, head width above 1.9 mm and ratio of body length to head width below 3; and third instar, body length above 9 mm. Male pupae may easily be recognized by an ampulla covering the developing genitalia on the posteroventral abdominal segments. Males usually had longer antennal laminae (mean = 823 μm, range 750-900 μm) than females (mean = 704 μm, range of 570-790 μm); however, in about 10% of the beetles this length overlapped between the sexes (range 750-790 μm).