新入侵害虫海枣异胸潜甲幼虫的龄数划分及在银海枣树上的垂直分布

Division of larval instars and its vertical distribution on the Phoenix sylvestris trees of Javeta pallida Baly 1858,a new invasive pest

海枣异胸潜甲是一种新入侵并爆发成灾的为害刺葵属植物的害虫,了解幼虫的龄数及其在树上的垂直分布,是进一步研究其发生趋势、生物学习性、预测预报以及制定综合防治技术的基础。本研究采取了田间取样收集野外海枣异胸潜甲各龄幼虫,分别测量了该幼虫的前胸背板宽度和头壳宽度2个形态指标,根据所测量的频次分布图、Dyar定律、Crosby生长法则以及线性回归的方法进行分析,发现以头壳宽度作为标准,幼虫龄期数分为5个龄数是较为合理的。1-5龄幼虫头壳宽度(mm)分别为0.407±0.004、0.503±0.003、0.582±0.002、0.725±0.002和0.847±0.001,头壳宽度和幼虫龄数的线性回归方程均符合指数模型Y=0.344×exp(0.181×X)和多项式模型Y=0.34+0.061×X+0.008×X^2。并以此指标对底部、中部和顶部的为害幼虫数进行了统计,发现幼虫密度分别在2.096头/叶、1.678头/叶和1.068头/叶,表明了该幼虫在银海枣多分布于树的底部和中部。

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 1 stto 5 thwere 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 × X^2,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.