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Establishment of Nilaparvata lugens Stal in Rice Crop Nurseries: A Possible Source of Outbreaks
Preap, Visarto,Zalucki, Myron P.,Jahn, Gary C.,Nesbitt, Harry J. Korean Society of Applied Entomology 2002 Journal of Asia-Pacific Entomology Vol.5 No.1
We tested the hypothesis that early-planted seedbeds of rice are more heavily infested with brown planthopper (BPH) than later seedbeds, and that transplanted plants with BPH are a source of subsequent population increase and possible outbreaks. The experiments were conducted at CARDI and Takeo province in wet season 2000 and early wet season 2001. BPH at 0, 25, 50, 100, 200 /$\textrm{m}^2$ were infested onto plants with low and high fertilizer treatments. Rice seeds of varieties moderately and highly susceptible to BPH were sown 3 weeks early, 2 weeks early, at the normal time, and later than normal (5 weeks) and treated with low and high fertilizer rates. At Takeo, the 3 weeks early seedbeds were infested by BPH migration, and both varieties with high fertilizer caught more immigrant insects and subsequently had damaging outbreaks of BPH in the third generation. At CARDI, no seedbeds were infested with immigrant BPH. Seedbeds in areas with continuous cropping of rice have a high risk of BPH attack. Seedlings infested wish 200, 100, and 50 BPH/$\textrm{m}^2$ resulted in death of the plant. Plants with 100 and 200 BPH/$\textrm{m}^2$ were killed sooner. With 25 BPH/$\textrm{m}^2$ plants were not killed, but subsequent population increase caused yield reduction. Yield loss was high in high fertilizer treated plants.
Preap, Visarto,Zalucki, Myron P.,Jahn, C.,Nesbitt, Harry J. Korean Society of Applied Entomology 2001 Journal of Asia-Pacific Entomology Vol.4 No.2
The most abundant natural enemies found in Cambodian rice field are spiders, mostly Araneus inustus and Pardosa pseudoannulata. These two hunting and wolf spider, respectively, are believed to actively contribute to brown planthopper (BPH) population control. However, how much each species attacks prey in Cambodian field condition is unknown. We conducted field experiments in Cambodia during the wet season at two locations, a farmer\`s fields at Takeo and at CARDI, using both field cages and natural conditions. Cages were sprayed with insecticide to remove all pre-existing insects in the cages and then washed after 10 days to reduce insecticide residue. Results confirmed BPH inside the cage were killed by the insecticide. A known BPH population was reared inside the cages starting with 3 pairs of adults. Temporary cages were removed after counting second instar BPH and permanent cages were left in place. Spiders were released into the cages for 15 days. In permanent cages either two individual A. inustus or P. pseudoannulata were allowed to feed on BPH prey. Both spider species have the same killing ability in dense prey populations, but predation is higher for Pardosa at low prey density. In uncaged field environments (where more than just BPH prey are available) with a spider/BPH ratio 1:3 to 1:11 BPH mortality was 78-91%. Within 15 days in permanent cages spiders caused 100% BPH mortality at an average predator/prey ratio of 1:5 to 1:14. At a ratio of 1:18 or higher there was some BPH survival in cages.