SAMPLING METHODS FOR ESTIMATING POPULATION DENSITIES OF PLANTHOPPERS AND PREDATORS IN DIRECT-SEEDED AND TRANSPLANTED RICE'

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1 SAMPLING METHODS FOR ESTIMATING POPULATION DENSITIES OF PLANTHOPPERS AND PREDATORS IN DIRECT-SEEDED AND TRANSPLANTED RICE' E. R Ferrer and B. M. Shepard Department of Entomology The International Rice Research Institute P. O. Box 933 Manila, Philippines Ab~'tract: Two sampling methods ( I water pan and carbon dioxide sampler) were compared for estimating populatings of brown plnnlhopper, Mlaparuata lugens (Stal) (Homoptera: Delphacidae), white-backed planthopper, Sogatefla furcifera (Horvath) (Homoptera: Delphacidae), a predatory mirid bug, Cyrtorhi1lus liuidipetlllis (Hemiptera: Miridac) and spiders in directseeded and transplanted rice in the Philippines. Similar populntion trends were observed in direct-seeded and transplanted rice using both methods although a significantly higher number of spiders (p < 0.05) was sampled using the carbon dioxide sampler, especially in direct-seeded rice_ The pan sampler however, required less time and was less expensive than the carbon dioxide sampler. Key Words: Rice. planthoppers. brown planthopper, Nilaparoata lugens whit.e-backed planthopper, Sogatello furcifera mind bug, Cyrtorhinus lividipermi.'l, spider, water pan Saml)ler, carbon dioxide sampler. J.Agric. EntomoL 5(3): (July 1988) A carbon dioxide (C0 2 NE) sampler was found useful in estimating densities of rice arthropods (Aquino and Heinrichs 1986; Shepard et al. 1985). To use this device, a cone-shaped enclosure was placed over each rice hill to prevent mobile arthropods from excaping, then carbon dioxide was discharged to the enclosure. After a few minutes, the arthropods were removed from the water's surface with a small screen scoop. A detailed discription of this sampler was published by Aquino and Heinrichs (1986). The D-vac and FARMCOP are suction type samplers (Dietrick 1961; Carino et al. 1979; Perfect et al. 1983). Comparison of the CO,NE sampler with FARMCOP revealed that in general, FARMCOP yielded higher means of most arthropods except for spiders (Shepard et al. 1985) but coefficients of variation were approximately the same for the two techniques. The C0 2 NE sampler was more practical because it was inexpensive and easier to use. The above methods are useful for research but not practical for making insect management decisions. Thus, there is a need for a simpler but reliable sampling method in direcr seeded and transplanled rice. Boards (18 X 25 cm) covered with sticky matel-ial have been used in sampling brown planthopper (BPH), Nilaparuala lugens (Stal) for pesticide tests in Japan (Nagata and Masuda 1978) and modified for a surveillance program in Malaysia (Ooi 1982). The sampler holds the sticky board horizontally to one side of the rice hill and the hill was struck to dislodge the arthropods onto the sticky surface of the boards. The advantage of this method was that after the insects were collected on the sticky boards, they were caitied to I t\ccepted for publication 20 July

2 200 J. Agric. Entomol. Vol. 5, No.3 (1988) the laboratory for counting and identification, or samples can be stored in the refrigerator for processing later. The major disadvantages were that the sticky material was messy and expensive. The objective of this study was to develop an efficient and reliable method for practical use in surveillance programs, and compare the population estimates obtained witb those using an absolute sampling device (CO,NE sampler) for sampling BPH and white-backed planthopper (WBPH), Sogal lla {urci{era (Horvath), and major predators (spiders and the mirid bug, Cyrtorhinus lividipennis (Reuter)) in rice. MATERIALS AND METHODS This study was conducted in Victoria, Laguna and at the International Rice Research Institute (IRRI) Farm, Los Banos, Laguna, Philippines during the wet season (June to October) A yellow plastic pan (measuring 25 em dia at the top X 15 em at the bottom and 6.5 em high) was used to collect the samples. About 100 ml of water was added to the pan along with 3-5 drops of liquid detergent (Teepoll!l) to reduce the surface tension of the water so that small arthropods would sink. The pan was then placed at the base of the hill and the hill was struck three times to dislodge the arthropods onto the pan. A comparison between C0 2 NE sampler and the pan was made in fields measuring approximately 1,200 m 2 planted to IR1917~3-17 at 25 X 25 em spacings. In each plot, 32 random samples were taken by each method weekly for 11 weeks. At IRRI Farm, comparison was made between the two sampling methods in 1,200 m 2 plots which were established by direct~seeding and transplanting. The sampling unit was the hill for transplanted rice and 25 cm 2 area for direct-seeded rice. The area was delineated by using a wire frame which approximated the number of tillers in a hill at seeding rates used in the study. Arthropods collected were placed in glass vials containing 70% ethyl alcohol and taken to the laboratory for sorting and identification. Average weekly densities were estimated and correlation coefficients and coefficients of variability were compared. Tests of homogeniety of correlation coefficients were conducted and Student's T-test (p < 0.05) was used to detennine significant differences between means. RESULTS AND DISCUSSION The predominant arthropod populations during the season (June to October, 1985) in Victoria, Laguna and at!rri Farm were BPH, WBPH, C. lividipennis and spiders. Because BPH and WBPH occur together in mixed colonies on the rice plant, we combined the counts of the adults of these species. Nymphal forms of both species were categorized as delphacid nymphs. Likewise, all spider species were combined but they were predominantly Atypena (Callitrichia) formosana (000 and Lycosa pseudoannulata (Boesenberg and Strand). Comparison between seasonal mean (± S.E.) numbers of arth.ropods per hill estimated by water pan and C0 2 NE sampling devices in transplanted rice in

3 FERRER and SHEPARD: Sampling Planthoppers and Predators in Rice 201 Victoria and at TRRI Fann are presented in Figs. land 2. In both locations, the same population trends were observed for BPH + WBPH adults, delphacid nymphs, C. lividipennis and spiders. In Victoria, for BPH + WBPH adults, delphacid nymphs and C. liuidipennis the average number of insects caught per sampling occasion was about he same using C0 NE and water pan. For spiders 2 however, in almost all occasions, significantly higher population density was estimated using C0 2 NE. At IRRI Farm, there were no significant differences between etimates of population densities using both devices for most of the arthropods sampled except for C. lividipennis. For this predator, higher numbers were estimated using the water pan when populations were denser (at days after transplanting). I\ fean numbcrlhill Menn number/hill u"a,------' , "",: "...c,.,r-;:, , c o o,.,~ec.~.~.~.-;.~,-:,,:-;,,~!_o;:._~,-:_~.~.t,-±~ Days after transplanting -.C-,_;.~._;":--:,,:--:,,:--:.,,,----:.,,:--:."',----:. Days after transplanting..-=.~~ Fig. 1. Seasonal populations of brown- and white-backed planthoppers (BPH + WBPH) adults (A), delphacid nymphs (B), C. liuidipennis (C) and spiders (0) sampled by water pan and C0,NE devices in transplanted rice. Victoria, Laguna, Philippines, For direct-seeded rice (Fig. 3), the same population trends were observed using both sampling devices. On most occasions, no significant differences between estimates of means were observed for BPH + WBPH adults, delphacid nymphs and C. liuidipennis. Significantly higher densities of spiders were estimated using CO,NE sampler.

4 202 J. Agric. EnlomoL Vol. 5, No.3 (1988) "~I,. Mean numher/hili A -".,... -+c... {""" "".""~'" ",. c o 'I,1 0 ~ n» ~ ~3 ~ U ~ l' 18 " ~ n» ~ <3 ~ '1 ~ r, Ie» Days aner transplantin~ Days llncr transplanting Fig. 2. Seasonal populations of brown- and white-baked planthoppers (BPH + WBPH) adults (A), delphacid nymphs (B), C. Iiuidipellllis (C) and spiders (D) sampled by water pan and CO,NE devices in transplanted rice. IRRI Farm, Los Banos, Laguna, Philippines, In general, the two techniques were highly correlated (Table 1). At Victotia, the correlation coefficients for BPH + WBPH adults, delphacid nymphs and C. liuidipennis were similar (91-94) regardless of the sampling devise used as detennined by a test of homogeniety. In general, correlation coefficients were lower for spiders and the C0 2 NE sampler yielded higher estimates of spider populations. At IRRI Farm, high correlation coefficients were obsel ved for delphacid nymphs, C. liuidipennis, and spiders while they were relatively lower for BPH + WBPH adults. Comparisons of coefficient of variability (CV) were similar for all arthropods regardless of the sampling technique used both in Victoria and at IRRI Farm (Table 2). CVs were high at both locations ( ). This is likely due to the low arthropod population densities during the season. C0 2 NE sampling can only be carried out in flooded fields but sampling by the water pan can be made even in dry fields. Also, while C0 2 NE sampling requires that arthropods be transferred to vials and counted later, counting can be carried out more easily in the field using water pan. Considering the ease of use and favorable comparison of population estimates with the CO?NE sampler, the water pan would be more practical in an insect pest managem~nt program for rice.

5 FERRER and SHEPARD: Sampling Planthoppers and Predators in Rice 203,.,~M~.",a~n-,n",u~n~, I",)e~r,-,/pl"l",a~nl~ ----,.;:.~'.::I.::a.::n-,n::u::m=b.::r::/"pl.::".::n:.t _ A,.. c...u H " ~ 11 '0.1 W _.,.~,=.':',::::::,;,---:,'-,---:":--:,,;--:,,;--:..,,...:::o'j Days after seeding Days after seeding..~., Fig. 3. Seasonal populations of brown- and white-backed planthoppers (BPH + WBPH) adults (A), delphacid nymphs (B), C. liuidipennis (C) and spiders (D) sampled by water pan and C0 2 NE devices in direct-seeded ricc. IRRI Farm, Los Banos, Laguna, Philippines, Table 1. Correlation coefficients between C0 2 NE and water pan sampler. Wet season (June-October), Victoria, Laguna and IRRI Fann, Philippines, Arthropods sampled Victoria IRRI' Farm BPH + WBPH adults Delphacid nymphs C. liuidipennis Spiders The Intem{lLional Rice Reseurch Instihlte. Table 2. Coefficients of variability of C0 2 NE and water pan sampler. Wet Season (June-October), Victoria, Laguna and IRRI Farm, Philippines I Victoria IRRI' Farm Arthropods sampled Water pan CO,NE Water pan CO,NE BPH + WBPH adults Delphacid nymphs C. Jividipennis Spiders The Intemational Rice Rcscnrch Inst.ilutC.

6 2M J. Agric. Entomol. Vol. 5, No.3 (1988) REFERENCES CITED Aquino, G. B., and E. A. Heinrichs A carbon dioxide-cone (CO.,NE) sampler for arthropods in flooded rice. The International Rice Research Newslett~r 2(1): Carino, F. A., P. E. Kenmore, and V. A. Dyck A FARMCOP suction sampler for hoppers and predators in flooded rice fields. The International Rice Research Newsletter 4(5), Dietrick, E. J An improved back-pack motor fan for suction sampling of insect populations. J. Eeon. Entomol. 54: Nagatn, T., and T. Masuda Efficiency of sticky boards for population estimation of the brown planthoppcr Nilaparvala lugens (Stal) (Hemiptera: Delphacidae) in rice hills. App!. Ent. Zool. 13: Dai, P. A. C A surveillance system for planthoppers in Malaysia, Proc. lnt. Conf. PI. in Tropics. pp Perfect, T. J" A. G. Cook, and E. R. Ferrer Population sampling of planthoppers, leafhoppers (Hemiptera: Delphacidae and Cicadellidae) and their predators in flooded rice. BulL Ent. Res. 73: Shepard, M., G. B. Aquino, E. R. Ferrer, and E. A. Heinrichs Comparison of vacuum and carbon dioxide-cone sampling devices for arthropods in flooded rice. J. Agric. EntomoL 2: