Abstract
Prevalence of spiders inhabiting rice ecosystem of Bangladesh Institute of Nuclear Agriculture (BINA), Mymensingh, Bangladesh was investigated to identify predatory spiders of brown planthopper (BPH) during Aman, Boro and Aus season from October 2007 to September 2008. A total of 1677 spiders were recorded which belonged to 10 families, 18 genera and 27 species. Eleven agrobiont spider species were confirmed as predator of BPH of which Pardosa pseudoannulata was identified as most potential predator. The biological features, functional response, predatory interactions and mass rearing of most dominant spider, P. pseudoannulata were studied in the Laboratory from July, 2008 to December, 2010. Survival of P. pseudoannulata spiderling was greatly influenced by prey BPH showing 100 per cent mortality within 5th instar while that declined from 93.33 and 86.67 per cent in 5th instar to 20.0 and 26.67 per cent at adult emergence on Drosophila and mixed diet (BPH+Drosophila), respectively. Spiderling passed through 8 to 9 instars to mature, and the developmental time of male was 74 and 82 days while in female that was 90±3.0 and 100±8.41 days on Drosophila and mixed prey, respectively. Reproductive potential of field collected spiders were compared to laboratory reared ones and found that significantly lowest number of 103.5±7.50 and 117.0±10.02 spiderlings were produced from first egg sac of female fed on Drosophila and mixed diet, respectively while the highest number of 167.9±12.20 spiderlings were obtained from the egg sac of field collected female. P. pseudoannulata male lived for 97 and 100 days but female lived for 124.5±4.50 and 138.7±3.28 days on Drosophila and mixed diet and produced 2.50 and 2.67 egg sacs, respectively. A generation cycle from spiderling to spiderling of P. pseudoannulata was calculated as 112.5 and 123.7 days on Drosophila and mixed diet, respectively. Handling time for 1st prey of 4th instar BPH was 27.06±7.14 minutes and highest for gravid BPH prey. Prey consumption of female P. pseudoannulata in the different prey densities indicated Holling type II functional response and showed significant correlation between consumption and prey density. Consumption peaked at 18 of 35 fourth instar BPH per day per female spider. Investigation of choice feeding test revealed that female P. pseudoannulata showed the highest preference for 4th instar BPH and consumed 10.50±0.52 prey in 24 hours. The order of prey preference of spider was recorded as 4th instar>2nd instar>3rd instar>5th instar>gravid BPH. The predation efficiency of female P. pseudoannulata was significantly highest of 190.8±7.35 of 2nd instar BPH per day, than feeding on other BPH stadia and adult Drosophila in no choice test. Significantly highest biomass consumption (38.41±5.45mg) and resulting weight gain (40.25±6.21%) by female P. pseudoannulata were recorded on fourth instar BPH while those were lowest of 17.30±1.58 mg and 22.64±5.40%, respectively on second instar BPH in 6 days. Weak additive interactive effect on predation of 4th instar BPH was observed at first day due to low consumption rate of prey by female Oxyopes javanus but intraguild predation of O. javanus by female P. pseudoannulata was found to occur at second and successive days and 100 percent Oxyopes were consumed within five days after release without significant reduction in predation rate of BPH by intraguild predator (P. pseudoannulata). Mass rearing of P. pseudoannulata was tried but cannibalism found to occur among spiderlings from very beginning of release and percentage of alive spiderlings decreased to 28 after 35 days. In contrast, only 9 per cent of initial spiderlings survived until 50 days due to cannibal reduction. Mortality of spiderling due to cannibalism in initial developmental stages compelled to terminate mass rearing of P. pseudoannulata after 50 days. It is concluded that due to high prevalence, reproductive capability and bio-potentiality, P. pseudoannulata appeared to be promising in management of brown planthopper.