Reproduction site preference and performance by sexuparae,and mating behavior of their sexual generation on the primary host plant in a heteroecious aphid,Neothoracaphis yanonis (Homoptera: Aphididae)

We studied reproduction site preference and performance by the sexuparae (autumnal migrants) of Neothoracaphis yanonis and mating behavior of their sexual generation on its primary host plant, Distylium racemosum. The sexuparae preferred younger leaves of D. racemosum for settlement and imbibing leaf sap, and they produced more offspring there than on older leaves. Thus, it is suggested that the sexuparae selected more nutritious younger leaves to increase their own fecundity. The offspring consist of yellowish dark-grey and creamy yellow type nymphs, which develop into small males and large oviparae, respectively. Yellowish dark-grey nymphs were deposited gregariously on the basal part of the abaxial surface of a leaf blade, while creamy yellow nymphs were deposited evenly over the abaxial surface. Such a localized distribution pattern probably resulted from sexuparae's strategy to enhance a possibility for their male offspring to mate with oviparae at the base of leaf blade, over which oviparae crawl to twigs. During mating and sometimes afterwards, the ovipara incidentally carried a male on her back and crawled downward on twig to find an axillary bud for oviposition. This behavior may be advantageous to males, who can guard their mate during this period against other conspecific males. Such mate-guarding behavior seems to be related to the development of dual mate-seeking strategies, in which males try to copulate, first at the basal part of midrib, and second on the axillary bud.