Survey and quantification of natural enemy fauna in the rice ecosystems in Thrissur district
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Date
2000
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Department of Agricultural Entomology, College of Horticulture,Vellanikkara
Abstract
A pilot study was carried out with the objective of identification,
quantification and comparison of the pest and natural enemy complex present in
two different rice ecosystems in Thrissur district of Kerala, viz. non-kole and kole
area. The species composition, abundance and relative occurrence of pests,
parasitoids and predators collected in sweep net samples from six locations each of
non-kole and kole area were studied. Six samples were drawn at weekly intervals
from each location starting from 15 days after transplanting till the emergence of
panicles and the mean data used for analysis. The species richness, diversity and
evenness of all the pests and important natural enemies were also assessed. In situ
count of leaf and planthoppers and associated generalist predators were recorded.
The extent of natural parasitism on the field collected immature stages of stem
borer, leaf folder and gall fly was recorded and identified the important species.
In the sweep net samples taken from 12 rice fields, altogether 29 species
of phytophages representing 19 families of six insect orders could be identified.
Among the 96 species of natural enemies (entomophages) identified, 19 species
were predators and 77 were the hymenopteran parasitoids. Except in the case of
one or two locations, the occurrence of most common and regular pests and the
associated natural enemy fauna were found to be the same in the non-kole and kole
area. The entomophages comprising of parasitoids and predators were found to be
higher than the phytophages in most of the locations. Homoptera comprising of
leaf and planthoppers and Thysanoptera (thrips) were the predominant
phytophages. Nephotettix spp. were dominant among the leaf and planthopper
while it was Sogatella furcifera (Horvath) among the planthoppers.
A significant difference was observed in the mean count of pests as well
as natural enemies within the six locations of each situation. Spiders (8 species)
cocinellid beetles (3 species), mirid bug (Cyrtorhinus Iividepennis Reuter),
damselflies (2 species) and veliid bug [Microvelia douglasi atrolineata (Bergoth)]
were the important predators. The predominant predator species were Tetragnatha
maxillosa Thorell (Aranae), Cyrtorhinus lividipennis Reuter (Miridae), Micraspis
spp. (Coccinallidae) and Agriocnemis pygmea Rambur (Odonata). Highest
diversity was noticed in the case of hymenopteran parasitoids and was the single
largest group of entomophages. In the non-kole area, spiders were most abundant
followed by Odonata, whereas in kole area C. lividipennis was abundant followed
by spiders.
In the case of phytophages, between the two situations studied,
significant difference was noticed only in the case of planthoppers, which was
significantly high in kole lands. Spiders, C. Iividipennis and the total predators
population were significantly high in kole area, whereas Odonata (damselflies)
were significantly high in non-kole area. A highly significant positive correlation
existed between the leaf and planthoppers with predators like C. lividipennis and
spiders. In situ population count of leaf and planthoppers and their associated
natural enemies viz. C. lividipennis and Lycosa indicated a density dependent
relationship.
From the field collected samples, three species of parasitoids VlZ.
Telenomus spp. Tetrastichus spp. and Trichogramma spp. were obtained from the
stem borer eggs. The parasitoids emerged from the leaf folder larvae and pupae
were Cotesia (=Apanteles) spp. Brachymeria excarinata Gahal, Cardiochilus
philippinensis Ashmead, Goniozus spp., Macrocentrus philippinensis Ashmead
and Xanthopimpla spp. Only a single species (Platygaster sp.) was obtained from
gallfly pupae.
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Citation
171776