Division of larval instars and its vertical distribution on the Phoenix sylvestris trees of Javeta pallida Baly 1858, a new invasive pest.
Javeta pallida Baly 1858 (Coleoptera: Cassidinae), is a new invasive pest which outbreaks on phoenix species plants in south China recently. The larval instar numbers and its vertical distribution on the tree should be investigated before further studying on occurrence trend, biology and integrated management program. In this study, larval samples of various instars were collected from the field. Their prothoracic plate width and head capsule width were measured. According to frequency histograms, Dyar's law, Crosby law of growth and linear regression, the head capsule width provided the best division of instars, and showed it has 5 instars. The average width of head capsule from 1st to 5th were 0.407±0.004 mm, 0.503±0.003 mm, 0.582±0.002 mm, 0.725±0.002 mm and 0.847±0.001 mm, respectively. The equations of exponential model and polynomial model of the head capsule width against the instar numbers was Y=0.344 × exp (0.181 × X) and Y=0.34+0.061 × X+0.008 × X2, respectively. The different instars of Javeta pallida larvae on the trees at lower, medium, and top position were counted as well, and their density was 2.096, 1.678, and 1.068 individuals on each leaf. The results indicated that most of Javeta pallida larvae were distributed at lower and medium position on the Phoenix sylvestris trees.