嘉義地區柑橘木蝨消長及其傳播立枯病之研究

Abstract

柑橘木蝨為柑橘立枯病之媒介昆蟲，調查柑橘木蝨在田間之消長規律，顯示成蟲一年出現三個高峰期與柑橘之春芽、夏芽及秋芽期一致。其中以春芽期蟲數最多，夏芽期次之、秋芽期最少。若成蟲空間分布之變化以聚集度值為參考依據，則當新芽長出時，成蟲逐漸聚集產卵，聚集度指標往上攀升，當若蟲大量羽化為成蟲且尚未分散之際，聚集度值達最高峰，之後隨著成蟲的分散，聚集度值往下降。由田間設置黃色枯板誘蟲情形，確知柑橘木蝨飛翔最活躍的時期集中在柑橘新芽出現時，成蟲羽化後的分散則以植株內之爬行為主，並在老葉下停留吸食汁液，不太活躍。木蝨在柑橘園較大量之遷移以三月中旬以後至四月底較多，此段期間離柑橘園數百公尺遠之雜果園、水稻田皆可採到柑橘木蝨成蟲。當木蝨侵入柑橘園後可迅速繁殖並在果園四處分散。因此，三、四月木蝨侵入後若不防治，至八月時可在70％的植株上嶺現木蝨取食，故三至五月是防治木蝨的關鍵時期。以核酸探針配合點漬雜配法偵測植株，研究田間感染生態，立枯病於田間的發生是漸進的擴散方式，鄰近病株周圍的值株最早受感染但不呈現病徵。在田間，一些外表健康的值株其實已帶病原，而且潛伏期很長，需一年以上的時間才會出現病徵。在初受感染局部呈現病徵的罹病株，病原分布不平均，離感染點愈遠，病原含量愈少。整株呈現典型病徵的病株，根、莖、葉、花、果實均有病原分布，但分布量差異不大。病原濃度隨著季節不同會有變化，在春夏交替的五、六月及晚秋的十月是病原濃度的高峰期，冬季則病原濃度低。由核酸探針的偵測也證實柑橘木蝨的確是立枯病的媒介昆蟲，但蟲體個別的帶菌量、帶菌率都低，顯示台灣的柑橘木蝨生態種和立枯病原親和力差。但若讓木蝨族群長時問感染，仍有極高的發病率，而使植株嚴重罹病。 The psyllid, Diaphorina citri Kuwayama has been recognized as a vectorial insect of citrus likubin for a long time in Taiwan. Investigation on population dynamics of the psyllid in citrus orchards was showed that the population of adults had three peaks per year which were coincided with the period of citrus flushing at spring, summer and autumn. The number of adults was most abundance in the first population peak and followed by the second peak appearing in summer and the least in the third peak appearing in autumn. As the space distribution of the adults in the field was referring to the Relative Degree of Aggregation(RDA) the index of RDA went up during the flushing period when the adults aggregated on the new shoots to lay eggs. The index went up to the highest when the adult emerged completely, then it fell down with the dispersion of adults. Newly emer-ging adults were not so active, most of them dispersed by climbing within the same trees and sucked juice from down surface of leaves. Migration of adults around citrus orchard was mostly from March to the end of April. During this period the adults could be trapped by yellow sticky traps set in the rice field or other fruit orchards located in several hundreded meters away from the tested citrus orchard. While the adults immigrated into a new citrus orchard, they multiplicated rapidly and spread to other trees. About 70% of citrus plants could be recorded to be infested by the psyllid four month after if the insect was not control with insecticides during the period from March to May. The incubation period for infected plants to the appearance of likubin symptom was more than one year. The dissemination of likubin in the field from the primarily infected plants to the surrounding plants, which might not show any symptom within one year, could be detected by using dot hybridization (DH) test cooperated with DNA probe. The same technique could be also used to detect the distribution and variation of greening organism, the causal agent of (ikubin, in the infected plants. It was showed that the greening organism distributed unevenly in the partially symptom-appearing plants in the early infected period and their density lowered in the tissues with the distance far from the infection point. However, the greening organism distributed near evenly in all organs of the diseased plant after appearance of typical symptoms. The density of the causal agent varied seasonally with high peaks in late spring (May to June) and late autumn (October) but low in winter. The psyllids on citrus plants was also clarified as a vec-torial insect of likubin by DH test. But the percentage of viruliferous vectors was very low. This indicated that affinity between the biotype of Diaphorina citri in Taiwan and greening organism was low. However, high diseased rate would be expected in the field due to accumulation of natural infection for a long time period.