Abstract
In March and April of 1986 and 1987, studies were carried out on the position of Aphis gossypii GLOVER eggs laid on twigs of Hibiscus syriacus L., time of hatching, rate of successful hatching, duration of larval stage, and movement of the first instars. A random sample of 321 twigs measuring 40cm or more was cut from 4 H. syriacus plants maintained outdoors. A. gossypii eggs were detected on 46 twigs (14.3%). The number of eggs per twig averaged 3.2. The haching of the eggs showed a peak in early April in 1986, when normal winter temperatures prevailed. Hatching showed a peak in late March in 1987, when warmer than normal winter temperatures were recorded. The rate of successful hatching was 72% in 1986, and 83% in 1987. Because the fundatrix larval stage (total period of all instars) was 19.2 days, it was assumed that fundatrices normally grow into adults on about April 20 each year in Utsunomiya. Roughly 60% of the newly hatched fundatrix larvae did not immediately settle on buds, but wandered during 1-3 days before settling. Of these, more than half eventually settled on the first, second, or third bud from where they hatched.
