The Effects of Synthetic Pyresroids on Spider Mite Resurgences

在定期喷洒三种拟除虫菊酯(SP)的茄子田中，研究了蜘蛛种群回流的机理。研究表明，无论SP的杀灭效果如何，SP处理小区的甘蔗叶螨峰值密度均比其他农药(S)处理小区和未喷洒处理田的高10倍以上。在整个研究期间，SP样地中的螨类种群存在2~4个不同的高峰，该地区的主要捕食性天敌是植绒螨类Amblyseius Longispinosus和炭疽害虫Orius sp.在SP样地中，这些捕食者的密度保持在低得多的水平，并且随着螨类密度的增加而增加的幅度也小得多。如果将植叶螨从SP样地中人工移除，只留下炭疽天敌，蜘蛛种群密度仍达到峰值，几乎与有植叶螨时的密度一样高。这些都清楚地表明，这一暴发是由于SP喷雾对炭疽捕食者的AdiVerse效应所致。SP喷雾由于对寄主植物的驱避作用，促进了蜘蛛从寄主植物上的扩散。然而，这并没有显著改变叶螨种群的空间分布格局，也从未导致叶螨种群数量的增加。这就提出了拟除虫菊酯诱导的扩散将是造成螨类种群回升的重要因素的假说。

Mechanisms underlying spider mite population resurgences were tested in eggplant fields which were sprayed periodically with each of three Synthetic Pyrethroids (SP). The study showed that regardless of the miticidal effects of the SP's, peak densities of the spider mite, Tetranychus Kanzawai, in the SP Plots were more than 10 times higher than those in plots treated with other pesticide (s) and those in fields that were not sprayed. The mite populations in the SP plots exihibited 2 to 4 distinct peaks throughout the study period.The dominant predators in this field were the phytoseiid mite, Amblyseius longispinosus and the anthcorid bug, Orius sp. In the SP plots, the densities of these predators remained much lower and increaesd much less in response to increases in mite density. If the phytoseiid mites were artificially removed from the SP plots leaving only anthcorid predators, the spider mite populations still reached peak densities which were almost as high as those when the phytoseiids were present. These clearly indicated that the mite outbreaks occurred because of the adiverse effects of the SP sprays on the anthcorid predators.The SP sprays enhanced spider mite dispersal from host plants as a result of their repellent action on the mites. However, this did not change significantly the spatial distribution patterns of the mite populations and never resulted in an increase in the mite populations. This rendered the hypothesis that pyrethroids-induced dispersal will be the important factor responsible for mite population resurgences.