Long-Term Monitoring of Arthropod Community

in Paddy Fields in Korea

Joon-Ho Lee and Hong-Hyun Park

Entomology Program, School of Agricultural Biotechnology,

Seoul National University, Suwon 441-744, Korea

Abstract

Long-term monitoring study has been conducted to understand structure of arthropod community, find the effect of conventional practices on arthropod community and enhance rice IPM in paddy fields. The arthropod community was analyzed using guild categories. The arthropods were found in the order of non-pests>natural enemies>pests in their density in unsprayed site in Baran, Kyonggi Province, 1996. But the order could be changed dependent upon immigration rates of pests, regional characteristics, cultural practices, and sampling methods. The pest were mainly Homoptera and dominated by Delphacidae(Nilaparvata lugens Stål, Sogatella furcifera Horvath and Laodelphax striatellus Fallen) and Cicadelidae (Nephotettix cincticeps Uhler). They constituted>80% of pest abundance. Spiders were the most dominant group in the natural enemy and constituted >90% of natural enemy abundance. Non-pests group was mainly chironomids and occurred abundantly in early growing season and gradually decreased as rice development proceeded. Pests and natural enemies groups all occurred abundantly in mid and late growing season.

The results of irrigating water quality study showed the densities of spiders were 2 or 3 times higher in the clean water field than in the other fields (life sewage and animal sewage). The difference was apparent in webbing spiders. Through all the growth stage of rice plants, the density of spider population in clean water field increased as rice plants grew, however the other two sites didn’t. Arthropod community patterns in small rice fields associated with different planting methods (transplanting, water seeding, and drill seeding) in Suwon showed that differences in pest abundance were not found among rice fields associated with different planting methods. No difference was found in species richness and diversity in spider community among rice fields associated with different planting methods. Different cultural methods (Conventional and Low Input Sustainable Agriculture (LISA)) showed no differences in arthropod abundance and species composition between two differently practiced fields.

Key Words; Long-term monitoring, arthropod community, paddy fields

Introduction

Pesticides centered pest control have caused problems such as insecticide resistant, secondary pests, pesticide residue in environment, and water and soil pollution. These problems also have occurred in Korea without exception. Even though there have been many studies to reduce insecticide overuse or abuse (Uhm et al. 1991), most of the studies were focused on timely treatment of insecticides or establishing pest control strategy using pesticides. Therefore, There have not been many studies trying to develop comprehensive pest management strategy based on insect community characteristics in paddy fields (Lee et al. 1997). These approaches might have achieved partial success in controlling individual pest species, but have exhibited several limits in solving pest problems with comprehensive understanding of ecological structure in paddy fields. Occurrence of rice insect pests is closely related to cultural methods such as cropping system, sanitation and rotation and biological and environmental factors such as natural enemies, rice variety, weather, and morphological structure of rice plants. Therefore, to maintain stable rice ecosystem and to manage insect pests, the management strategy should be developed based on comprehensive understanding of characteristics of arthropod community structure in paddy fields.

Studies presented in this paper have been conducted to understand arthropod community structures in various rice paddy fields located in Kyunggi province. Effects of different cultural methods, irrigating water quality, pesticide application, and conventional and low input practice on arthropod community have been studied (Lee et al. 1997, Park et al 1997, Park and Lee 1997, Lee et al. 1998). A common objective of these studies was to understand the arthropod community in paddy fields and reveal the strength of interactions among pest, natural enemy and non-pest groups. Based on these understandings, our aims are to develop integrated pest management strategies harmonized with environment.

Materials and Methods

Community Structure and Occurrence of Arthropod

This study was conducted in the rice paddy fields located in upstream and downstream paddy fields neighboring Baran reservoir, Kyunggi province in 1996. On May 20, rice seedlings were transplanted to the experimental plots. Insecticides were treated twice to the sprayed plot. To control rice water weevil (Lissorhoptrus oryzophilus Kuschel) pyrethroid insecticide was applied (1kg/10a) 10 days after transplanting and carbamate group insecticide was treated (150l/10a) 75 days after transplanting. Electric powered sucking device was used to sample arthropods in the rice paddy fields. Rectangular -shape acrylic cage (0.5 x 0.5 x 0.7m) was covered to prevent arthropods from escaping from the sampling rice plants while sampling was conducted. Each experimental plot was replicated 10 times and sampling was conducted 13 times through rice growth periods with one week interval between each sampling.

Arthropod Community According To Irrigating Water Quality

This study was conducted in three different rice paddy fields irrigated with three different water quality types (clean water, life sewage and animal sewage) from 1994 to 1996. The experimental fields were located in Banwol, Kyunggi province. The quality of water irrigated to clean water rice field and two other sites was classified as acceptable and slightly polluted, respectively, according to the water quality classification test. To collect arthropods on a rice plant, mesh cloth cage (1 x 0.5 m) was covered on a sampling rice plant then bottom of the plant was cut with a large scissors. The experimental plots were replicated 10 times and sampling was conducted with two weeks interval.

Effect of Different Seeding Methods

This study was conducted in rice paddy fields in the experimental station of Seoul national university located in Suwon, Kyunggi province in 1994. Each plot (18.5 m x 18 m) was planted with three different methods (transplanting, water seeding and drill seeding). Electric powered sucking device was used to sample arthropods in the rice paddy fields. Rectangular -shape acrylic cage (0.5 x 0.5 x 0.7m) was covered to prevent arthropods from escaping while sampling was conducted. There were 10 replications of the experimental plots and sampling was conducted with 15 days interval.

Conventional Cultural Method and Low Input Sustainable Agriculture (LISA)

This experiment was conducted in 1995 and 1996. The experimental plots were located in Top-dong, Suwon, Kyunggi province. Two rice paddy fields that were cultivated by two farmers were selected and one rice field was designated to conventional cultural practice plot and the other was designated to low input practice plot (LISA). Each plot was treated with pesticides and fertilizers as shown in table 1. To sample arthropods on a rice plant, mesh cloth cage (1 x 0.5 m) was covered on a sampling rice plant then bottom of the plant was cut with a scissors. Each experimental plot was replicated 10 times and sampling was conducted with 2 weeks interval.

Table. 1. Fertilizer and pesticides applications for conventional and LISA plots

Item	Conventional	LISA
Fertilizer application(kg/10a)	11.8 : 5.3 : 5.3 (N: P: K)	5.3 : 2.5 : 2.5 (N: P: K)
Pesticide applications(no.)
Herbicides	1	1
Insecticide & Fungicide	5	2

Results and Discussion

Community Structure and Occurrence of Arthropod

Table 2 showed the mean density of arthropods by taxa in guilds sampled in control plots in Baran, Kyonggi province. The occupancy pattern of each guild appeared in the order of non-pests > natural enemies > pests. The mean density of non-pests was much higher than that of other guilds and there was little difference between the mean densities of the natural enemies and the pests. This occupancy pattern is different from other previous studies. The pattern appeared in the order of pests > non-pests > natural enemies in Jinju (Song and Choi 1993) and natural enemies > pests > non-pests in Ichon (Lee et al. 1997). It is suspected that these differences were resulted from the differences of immigration rates of pests, regional characteristics, cultural practices, and sampling methods.

Dominant species of the pests were brown planthopper (Nilaparvata lugens Stål), white-backed planthopper (Sogatella furcifera Horvath), and small brown planthopper (Laodelphax striatellus Fallen) in Delphacidae, and Nephotettix cincticeps Uhler in Cicadelidae. These dominant species were over 80 % of total pest species. In natural enemy guild, spiders were dominant group occupied over 90 %. Parasitic wasps and heteropterans were two distinctive minor groups in this guild. In non-pests group, chironomids and flies in Diptera, and collembolans were dominant groups. Chironomids and flies appeared in high density level during early rice growing season while collembolans reached high density level late in the season. Lavae and adults of chironomids and flies, as well as collembolans were preys of generalist predators like spiders (Settle et al. 1996).

Table. 2. Mean density of arthropods by taxa in guilds sampled at paddy fields in Baran, Kyonggi Province, 1996 (Sample unit = 6 hills (0.5 x 0.5m)).

Guilds	Order	Common name	Mean density
Pests	Homoptera	Aphids	1.61
		Leafhopper	0.59
		Planthopper	5.40
	Hemiptera	Phytophagous bug	0.84
	Lepidoptera	Rice stem borer	0.02
		Rice leaf roller	0.01
		Others	0.02
	Coleoptera	Rice water weevil	0.11
		Rice leaf beetles	0.05
	Subtotal		8.72
Natural Enemies	Araneae	Spiders	8.50
	Coleoptera	Carabids	0.47
	Hemiptera	Predatory bug	0.51
	Others		0.21
	Subtotal		9.72
Non-pests	Collembola	Collembola	0.85
	Diptera	Chironomides	24.84
		Flies	3.6
	Subtotal		29.36
	Total		47.80

Figure 1 showed the changes of occupancy rate of each guild during the rice growing season. In early growing season, non-pests guild showed over 90 % occupancy rate in both experimental plots, and pests and natural enemy guild showed low occupancy rate. However, in the middle of the season the occupancy rate of the natural enemies gradually increased and at the late in the season, natural enemies showed highest occupancy rate among three guilds. These patterns which were well coincided with results of previous studies (Song and Choi 1993, Yun 1997) were assumed to be a general trend of arthropod community structure in paddy fields in Korea. And no differences were found in changes of percentage of each guild between unsprayed plot and sprayed plot (fig. 1)

Figure 1. Proportion(%) of three guilds (pests(·), natural enemies(○), non-pests(▼)) in two paddy fields, Baran, Kyonggi province, 1996. (a) Unsprayed field, (b) Sprayed field.

Arthropod Community According To Irrigating Water Quality

Figure 2 shows the changes in the densities of arthropods with rice developmental stages (early, middle and late growing stages) with three irrigating water qualities. . The same fluctuation patterns in total arthropod density didn’t repeat annually. In 1994, the density levels were almost the same thought out the developmental stages of rice in all three plots. The density level in life sewage irrigating fields was higher in early season in 1995 and, the density level increased as time passed in rice fields irrigated with three different water qualities in 1996. Without the outbreak of immigrating pests such as brown planthopper, occurrences of arthropods in normal year had high variances in densities among samples at the early season but the variances decreased at the late (Park and Lee 1997). But life sewage irrigated fields showed the density variance increased with time in 1996.

Figure 2. Changes in the density (no. / hill) of arthropods in the rice fields with different irrigating water quality at Banwol, Kyonggi province, 1994 –1996.

Table 3 showed the mean densities of spiders classified by their life strategy in rice paddy fields with different irrigating water qualities. The density level of spiders was 2 – 3 times higher in clean water irrigating field than in life sewage or in animal sewage irrigating fields. The density levels of hunting spiders showed no differences among all three types of fields. However orb webbing spiders and space webbing spiders showed higher density levels in clean water irrigating fields than in the other two types of fields.

Table. 3. Densities (No./hill) of spiders in rice paddy fields with different irrigating water quality at Banwol, Kyonggi Province, 1995

Type	Clean water	Life sewage	Animal sewage
Hunting spiders	2.50	2.56	2.11
Orb webbing spiders	2.72	0.28	0.50
Space webbing spiders	4.61	2.06	1.11
Total	9.83	4.89	3.72

Figure 3 showed the changes of the densities of spider in three different qualities of water irrigating rice fields with three rice developmental stages. During the early rice developmental stage, the density levels were the same in all three water qualities irrigating fields. However, the density level difference between the clean water irrigating rice fields and the life sewage and animal sewage irrigating fields increased with rice developmental stages. The density of spider was low at the early stage and increased in the mid-stage, then maintained in high level until the late developmental stage (Okuma et al 1978, Park and Lee 1997). In this study, there was no rapid increase of the density at the middle of the rice developmental stage in the life sewage and the animal sewage irrigating fields. This result might be resulted from the negative effect of low water quality on spider community.

Figure 3. Changes in the densities (No. / hill) of spider in the rice fields with different irrigating water quality at Banwol, Kyonggi province, 1995.

Effect of Different Seeding Methods

Seeding methods have greatest effect on the development of arthropod community in rice paddy fields at the early in the season. Seeding methods also influence the cultural practice applied in early rice growing season and this could result in changes in early rice ecosystem. These changes will affect the development and the density of arthropod community on rice plants. Figure 4 shows the temporal density fluctuation of three arthropod guilds in rice paddy fields seeded with 3 different methods. Delphacidae and Cicadelidae in Homoptera constituted over 90 % of the pest guild. There was almost no occurrence of brown planthoper and white- backed planthopper. Green rice leafhopper started to occur in early August, and then at the end of August the density of Green rice leafhopper reached the highest level. However, the highest density level was only 2 ind. /6 hills. The density level of spiders that constituted over 90 % of natural enemy guild rapidly increased since August.

Figure 4. Temporal fluctuation of main pest and natural enemy in differently planted rice paddy fields in Suwon , 1994.

On the other hand the seasonal patterns that the density of major pests, brown planthopper and white-backed planthopper occurred at low density in early growing season and thereafter showed slightly increase could be explained by huge decreases of migration of these pests from China recently. Green rice leafhoppers are not migration pest from China, they also showed same population dynamics patterns as planthoppers. At early growing season non-pest group including chironomids and flies showed higher density in drill seeding plot than transplanting plot (Lee et al. 1997). And since mid rice growing season the structural difference of arthropod community by seeding method didn’t appear in our study, so we assumed that these different methods could not cause occurrence of arthropod in paddy field.

Table 4 shows the result of analysis of spider community in rice paddy fields seeded with different methods. There was no difference in the number of spider species sampled (16 – 7 species) and in diversity indices among different seeding methods.

Table. 4. Diversity indices of spider community in small rice paddy field in 1994

Indices	Water Seeding	Drill Seeding	Transplanting
No. of species	16	16	17
No. of individuals	178	183	376
Shannon index (H’)	2.435	2.363	2.389
Dominance index (D)	0.123	0.129	0.127
Evenness index (J’)	0.878	0.852	0.843

Conventional Cultural Method and Low Input Sustainable Agriculture (LISA)

Figure 5 shows the occurrence of arthropods in guilds in rice paddy fields cultivated with two different cultural practices. There was no significant difference in the occurrence of arthropods between the two differently cultivated rice fields. Chironomids were the dominant species in the early season and decreased in density after July. Then, the density of pest guild consisted mainly of Delphacidae and Cicadelidae and natural enemy guild consisted mainly of spiders increased. The density of natural enemy and pest guild started to increase in mid-July. It is thought that increased fitness and reproductive capacity of arthropods of the guilds resulted from increased humidity, temperature and canopy and increased prey populations in rice paddy fields could be the reason. This result agreed with previous studies (Song and Choi 1993, Yun 1997, and Lee et al. 1997).

Figure 5. Temperal abundance of arthropods of three guilds(pest, natural enemy and non-pest) in rice fields managed by different cultural methods, Suwon, 1995 and 1996.

Only 51.3 % of pesticides and fertilizers were applied in low input plots in this study compared to conventionally cultivated plots (Table 5). However, no difference was found in the community structures and the density of arthropods in the rice paddy fields regardless the cultivating practice used. This result showed that even though conventional cultural practice inputs more energy into the field than low input practice, rice development might not be affected by higher energy inputs in conventional practice. Therefore, it is possible that with conventional cultural practice more energy was input into the rice fields than necessary.

Table. 5. Total energy of fertilizer and pesticides applied in rice fields

Source		Energy Equivalents	Input energy(kcal/10a)
			Conventional	LISA^a
Fertilizer	Nitrogen	14,700 kcal/kg	161,700	88,200
	Phosphate	14,700 kcal/kg	24,000	24,000
	Potash	14,700 kcal/kg	12,800	12,800
Herbicides		14,700 kcal/kg	12,990	13,828
Other pesticides		14,700 kcal/kg	86,665	14,501
Total			298,155 (100%)	152,829 (51.3%)

^a Low input sustainable agriculture.

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