|Efficacy of Hot-Water Immersion Against the Taro Root Aphid, Hawaii, 1995|
By: A. H. Hara, R.F.L. Mau, T. Y. Hata and B.K.S. Hu
Beaumont Agri. Res. Center University of Hawaii-Manoa 461 W. Lanikaula Street Hilo, Hawaii 96720, Phone (808) 935-2885
HOST: CHINESE TARO: Colocasia esculenta
TARGETED PEST: 'Chinese' Taro root aphid: Patchiella reaumuri (Kaltenbach)
Efficacy trials were conducted from 21 Apr through 24 Apr 95. Taro hulis (0.5 inch cut stem with petiole attached) were harvested from a infested field in Kaiwiki, Hi, (1,500 ft elev.) placed in bags (three hulis per bag) made from Reemay crop cover material, and transported in a cooler to the University of Hawaii at Manoa Waiakea Experiment Station in Hilo, Hi. Roots and soil were left on the hulis to maintain a sufficient test population. Taro hulis (ca. 15 inches long x 2 5 inch base diameter) and Reemay bags were immersed in 49 °C water from 0 to 5.5-min at 30 sec intervals. The bags were used to catch aphids which fall off during treatment. Immediately following treatment, hulis were cooled in a water bath at ambient temperature (26 °C) for a time equal to the heating time then held in a dark room until evaluation. The control was dipped in water at ambient temperature for 30 sec. Three days after treatment, hulis were dissected and the number of live and dead aphids counted.
Hot-water treatment at 49 °C for 5.0 and 5.5 min resulted in 100 % mortality of aphids on the taro petiole and roots, respectively. Survivors were mobile and were usually found in pockets between the dense roots. In actual commercial production. hulis do not contain roots and soil.
Table 1 . Percent mortality of taro root aphids after hot-water treatment at 49 °C.
|No Treatment||5.8 (931)a||9.8 (92)||6.2 (1023)|
|Water Dip (Ambient)||20.3 (989)||9.7 (226)||18.4 (1215)|
|0.5 min||0 4 (767)||2.9 (173)||0.9 (940)|
|1.0 min||35 3 (485)||55.1 (89)||38.3 (574)|
|1.5 min||73.0 (241)||75.0 (80)||73.5 (321)|
|2.0 min||89.0 (374)||90.6 (32)||89.2 (406)|
|2.5 min||64.7 (966)||62.4 (311)||64.1 (1277)|
|3.0 min||87.5 (376)||77.8 (54)||86.3(430)|
|3.5 min||94.7 (636)||96.8 (63)||94.8 (699)|
|4.0 min||99.8 (1112)||100.0 (272)||99.9 (1384)|
|4.5 min||95.8 (288)||99.2 (131)||96.9 (419)|
|5.0 min||99.2 (1705)||100.0 (156)||99.2 (1861)|
|5.5 min||100.0 (1511)||100.0 (244)||100.0 (1755)|
aNumber of aphids recovered.
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