The influence of free-ranging ducks (Indian Runner, Chinese native duck and crossbred duck) on emerging weeds and pest insect infestations in paddy fields

摘要

The objective of this study was to compare the differences in the weeding and pest control roles of Indian Runner(IR), Chinese native duck(CN) and crossbred ducks(Mallard x Khaki Campbell:F_1) free-ranging in paddy fields. During June to September in 1996-1997, weed growth, pest insect infestations, and the number of the insects ingested by free-ranging ducks were examined. 1. It was found that in July 1997 three duck breeds were able to control weed growth significantly. Chinese native duck showed a higher ability to control weeds than F_1 in paddy fields, where a lot of weeds (especially, Echinochloa crus-galli P. Beauv. var. oryzicola Ohwi and Echinochloa crus-galli P. Beauv.) were found in August 1997. 2. It was also found that white-backed and brown planthopper infestations were controlled by 3 duck breeds in the experimental period, however there were no differences in the pest control capabilities among 3 breeds. An experiment in July 1996 measuring the number of pest insects in pseudo-crops, glandular stomachs and gizzards of the ducks after free-ranging in a paddy field for 80 min., showed that F_1, IR and CN ingested 336, 732 and 506 white-backed planthoppers per duck. suggesting a significant effect on pest control. The green rice leafhopper infestations were not controlled by 3 duck breeds. 3. Three duck breeds also significantly suppressed an infestation of big mud snails in the paddy fields, however there was no significant difference in the population of big mud snails among 3 breeds. On the other hand, the abilities of F_1 and CN to supress big mud snail eggmasses were higher than that of IR. These results indicated that CN had a higher ability to control weeds and pest insects in paddy fields comparing with F_1 and IR.