Insect pest natural enemy- host plant interaction studies with special reference to the brown planthoper nilaparvata lugens(Stal.)
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Date
1999
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Department of Agricultural Entomology, College of Horticulture, Vellanikkara
Abstract
Field surveys were conducted in Kole land and Kuttanad to assess the
population of rice BPH, Nilaparvata lugens (Stal) and its natural enemies. Field
investigations on the population dynamics of BPH and its natural enemies were
carried out on susceptible (Jaya), moderately resistant (Jyothi) and resistant
(Kanakom) rice varieties at the rice fields of Rice Research Station, Moncompu
during 1997-98. The influence of these varieties on the biology of the pest, the
biocontrol efficiency of the major natural enemies and the biology of the mirid
predator Cyrtorhinus lividipennis Reuter was studied in the laboratory.
Histological and chemical investigations were undertaken to evaluate the factors
that contribute to the resistance/susceptibility in them.
Results of field survey in Kole land revealed that the population of BPH
was far below the economic threshold level (ETL). In Kuttanad, in kayal area
during Rabi season and in karappadam tract during Kharif season outbreaks of
BPH occurred in some localities due to the indiscriminate use of insecticides
resulting in the mortality of natural enemies.
The results of the study on population dynamics revealed that the BPH
population was significantly high on the susceptible J aya and low on the resistant
Kanakom with the population reaching a peak from February to March. The
predatory complex of the BPH comprised of the rnirid Cyrtorhinus lividipennis,
Lycosa pseudoannulata, Tetragnatha maxillosa, Atypena formosana, Microvelia
douglasi atrolineata, Pseudogonatopus sp. and Ophionea nigrofasciata. C.
lividipennis was the most predominant predator regulating the hopper population
and there exists a density dependent host-predator relationship.
The population of the mirid predator on Jaya and Kanakom did not
differ significantly. The prey-predator ratio was lowest on the resistant variety and
highest on the susceptible variety. Of the weather parameters studied, the minimum
-.
temperature showed a highly significant negative correlation with the population of
N. lugens in all the varieties.
BPH reared on the resistant variety recorded longer nymphal duration,
decreased nymphal survival and shorter adult longevity indicating the prevalence
of antibiosis in the variety. Lesser number of eggs laid, longer pre-oviposition
period and shorter oviposition period recorded on Kanakom indicate the
antixenosis factor in it. Macrpterous forms of BPH did not develop on the variety .
The predator C. lividipennis and Micraspis sp. fed more BPH when
reared on the resistant variety. The veliid bug M. d. atrolineata, the spider
L. pseudoannulata and the dryinid Pseudogonatopus sp. predated significantly
more BPH nymphs on resistant variety at a higher prey density only. However, the
dryinid parasitoid consumed significantly fewer number of hoppers on Kanakom at
the higher host density.
C. lividipennis recorded longer nymphal duration, shorter adult
longevity and low fecundity when fed on BPH reared on Kanakom which can be
attributed to the low fecundity of N. lugens on Kanakom leading to less availability
of food to the mirid. Nymphal duration and adult longevity of C. lividipennis did
not vary between the varieties Jaya and Jyothi.
Well developed bundle sheath with more frequently distributed
schlerenchyma tissue in the culm of the resistant variety seemed to impart
resistance in Kanakom along with thicker cuticle.
Higher amounts of silica, Zn and Mn and lower amounts of N, K, Ca
and Mg were recorded in the culm of the resistant variety compared to moderately
resistant and susceptible varieties.
The findings strongly suggest the mechanism of antibiosis and
antixenosis in the resistant variety Kanakom.
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171578