Impact of fish on arthropod communities in irrigated rice in the Philippines
1994
Halwart, M. (University of Stuttgart, Stuttgart 1 (Germany). Inst. of Landscape Planning and Ecology)
For the DVac [sunction sampling device] sampling it was found that abundance of phytophages was relatively constant throughout the season, while predators, parasitoids and transients peaked at about 60 DAT. Of importance were chironomids, whorl maggot (Hydrellia philippina), green leafhopper (Nephotettix virescens), ripple bug (Microvelia douglasi atrolineata), and spiders of the genera Callitrichia and Tetragnatha. No differences among treatments were detected although sticky trap catches at the water surface showed that many arthropods fall off the rice plants. This was especially true for the phytophages in the early season which were mainly composed of Hydrellia philippina. The gut content analysis revealed that all guilds are represented in the diet of both fish species regardless of aquatic, semiterrestial or terrestial life cycle of the arthropod species. Although only few specimen of Scirpophaga incertulas were found in the guts, significant (P0.05) differences between rice-fish and rice treatments were detected for stemborer damage (whiteheads). Whiteheads were reduced by 3 percent in the tilapia and by 5 percent in the carp treatment. Stemborers lay their eggs in masses, but generally only one larva infects one tiller. The most likely mechanism of control is predation by fish on the neonate stemborer larvae. After hatching they often suspend themselves from the rice leaves with a silken thread to disperse to other hills. Stemborer damage is economically important as the yield of the whole panicle is lost. In this experiment the reduced percentage of whiteheads in fish treatments corresponded to a significant increase in rice yield
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