Journal of Tropical Agriculture 45 (1-2): 1–8, 2007 1 Aboveground arthropod pest and predator diversity in irrigated rice (Oryza sativa L.) production systems of the Philippines Sarwshri Gangurde* Institute of Plant Production and Agroecology in the Tropics and Subtropics, University of Hohenheim, Garbenstrasse 13, 70593 Stuttgart, Germany. Received 12 January 2007; received in revised form 15 May 2007; accepted 20 May 2007. Abstract Abundance and diversity of pest and predator species at different stages of crop growth were studied in chemical insecticide- treated and untreated irrigated rice production systems of the Philippines in a single season. Immigration of pest and predator species to the rice fields from the adjoining vegetated patches was also monitored for assessing the potential role of the latter group in natural biological control. Dominant pest species during the tillering stage were plant and leafhoppers belonging to the Hemipteran families of Cicadellidae and Delphacidae. Higher pest species diversity was recorded during the milk stage of the crop in both treatments compared to other pheno-phases. Among the predator species, Micraspis crocea, Conocephalus longipennis, Metioche vittaticollis, Agriocnemis spp., and Cyrtorhinus lividipennis were abundant. Malaise trap catches indicated the movement of pests, namely Recilia dorsalis, Cofona spectra, Nephotettix spp., Nilaparvata lugens, and Eysarcoris spp. and predator species such as M. crocea, Agriocnemis spp., and M. vittaticollis from the adjoining areas. Diversity and richness indices of pest and predators were higher in the untreated fields compared to the insecticide-treated fields. Highest pest species richness was found during the tillering stage, while predator species richness was highest during the milk stage. Implicit in this is that as the pest species increased, the predator diversity followed. Keywords: Biological control, Immigration, Shannon index, Species richness, Evenness, Dominance. Introduction interested both agroecologists and conservation biologists alike (Bambaradeniya et al., 2004). Arthropod pest and predator populations in rice (Oryza sativa L.) fields are intimately associated with each The Philippines is one among the chief rice growing other (Settle et al., 1996). A lot of ecological research and consuming countries in the world. Among the major has been done on this and many scientific publications constraints of Philippine rice production are the high brought out on the occurrence, abundance, and diversity incidence of pests and the consequent over-use of of arthropods, besides the variations due to topography, chemical insecticides (Rola and Pingali, 1993), which geographical conditions, and weather conditions (e.g., disrupts the natural balance between insect pests and Landis et al., 2000; Juen et al., 2003). Yet there have their natural enemies. In particular, spray formulations been few studies demonstrating how the abundance and of monocrotophos, chloropyrifos, and quinalphos have diversity of arthropod pests and predators contribute adversely affected the predators and parasitoids of major to the biological control of crop pests at different stages rice pests (Patel et al., 1997). However, some workers of growth. The tropical rice fields offer a biologically have argued that Acephate, chloropyriphos, and diverse and dynamic environment for invertebrate and monocrotophos are relatively safe to the predator vertebrate populations (Settle et al., 1996). The species such as Lycosa pseudoannulata, Tetragnatha biodiversity in irrigated rice agroecosystem has javanica and Paederus fuscipes (e.g., Kumar and *Author for correspondence: Telephone +49 711 459 23605; Fax +49 711 459 23843; Email <[email protected]>. Aboveground arthropod pest and predator diversity in irrigated rice 2 Velusamy, 2000). It thus necessitates further and more treated once in 10 weeks of crop growth with Rador systematic efforts to evaluate the effects of insecticidal (Chloropyrifos–250 g L–1, Betacyfluthrin–12.5 g L–1, and applications on the pest complex of rice and the natural Solverro150–633.5 g L–1 active ingredients). Three plots abundance and diversity of predators. This paper of size 100 m2 (10 x 10 m) were selected at both sites focuses on the diversity and abundance of pests and during March 2004. Rice (var. RC-18) was planted in predators in insecticide-treated and control (no insect- both sites at a spacing of 20 x 20 cm. icide) fields and correlates the effects of insecticidal application on arthropod species diversity, besides Aboveground arthropod pest and predator species at analyzing the immigration pattern of arthropod pests and different stages of rice growth, which can be easily predators to the rice fields from adjoining patches of trapped in sweep nets (32 cm dia) and malaise traps, natural vegetation. The community structure of the were monitored. Sampling was done by sweep netting selected taxa and species diversity in different stages of in established plots during various stages of rice growth. rice growth were also monitored. Twenty sweeps per plot was used as the standard. Weekly data on the number of individuals of each Materials and Methods species obtained by net sweeping from both sites for the whole rice-cropping season was used to calculate The study was conducted in the Baybay municipality in the indices of diversity and to describe the community Western Leyte, one of the Visayas group islands (124o17’ structure of arthropods. The malaise trap was installed E longitude and between 9o55’ and 11o48’ N latitude) in at both sites along the border of the rice field to study the Philippines. Two sampling sites were established: the immigration of insects from weedy vegetation and one near the Leyte State University (LSU) campus in agroforest to the rice fields. The trap was kept open the rice fields adjacent to the Agroforestry Demo Farm only in one direction. Collection jars filled with 70% (AF site) and the second in Barangay Pangasugan about ethyl alcohol were attached to the traps in the morning 2.3 km north from the LSU administrative headquarters (9 a.m.) and maintained until 9 a.m. the next day. (BP site). The AF site was near an upland contour demo Observations were made every 24 h and once every farming system planted with leguminous hedgerows and week the samples were identified to its lowest alleys planted with annual crops. Stands of Carica taxonomic category. Shannon’s index of diversity (H’), papaya, Mangifera indica, Musa paradisiaca, Ficus spp., Menhinick index (ES) for species richness, species Ananas comosus, Ipomoea batata, Leucaena evenness index (Magurran, 1988), and index of leucocephala, Mallotus barbatus exist in this area. Weed dominance (Odum, 1971) were computed to assess the flora including Pseudoelephantopus spicatus diversity of arthropods at both sites. ANOVA and (Asteraceae), Ipomoea pescaprae (Convolvulaceae), regression analysis were done to compare the Colocasia esculenta (Araceae), Commelina diffusa insecticide effect on pest and predator abundance and (Commelinaceae), Hyptis capitata (Lamiaceae), Wedelia diversity. trilobata (Asteraceae), Axonopus compressus (Poaceae), Mimosa pudica (Mimosaceae), and Mikania cordata Results and Discussion (Asteraceae) were found at both sites. The rice sampling areas lay adjacent to the demo farm at the lower slope at Arthropod pest diversity an elevation of around 10 to 15 m above sea level. The BP site was situated in a communal farmer’s rice field Seventeen (AF site) and 14 (BP site) species were and was not treated with insecticides during the whole recorded by net sweeping (Table 1). They belonged to duration of the crop. This is part of an organic farm of three major orders (Homoptera, Hemiptera, and LSU and was always kept free of insecticides and the Coleoptera) and five major families (Cicadellidae, surrounding areas are all rice fields compared to the AF Delphacidae, Alydidae, Pentatomidae, and site surrounded by an agroforest. The AF site was also Chrysomelidae). In general, the results indicate that Sarwshri Gangurde 3 Table 1. Occurrence and abundance of arthropod pest species at treated (AF) and an untreated (BP) site in the Leyte Island of Philippines. Name of the species, Family, and Order Weekly catch (no.) AF site BP site Total Total Mean SE Range Total Total Mean SE Range (S) (M) (S) (S) (S)1 (S) (M) (S) (S) (S)1 Chaetocnema basalis – Chrysomelidae (Coleoptera) NO 1 - - - 1 NO 0.08 0.27 1 Dicladispa armigera – Chrysomelidae (Coleoptera) NO NO - - - NO NO - - - Oulema oryzae – Chrysomelidae (Coleoptera) NO NO - - - NO NO - - - Monolipta spp. – Chrysomelidae (Coleoptera) 2 2 0.15 0.37 1 3 2 0.23 0.59 2 Leucopholis irrorata – Scarabidae (Coleoptera) NO NO - - - NO NO - - - Holotrichia mindanaoana – Scarabidae (Coleoptera) NO NO - - - NO NO - - - Phyllophaga spp. – Scarabidae (Coleoptera) NO NO - - - NO NO - - - Anomala pallida – Scarabidae (Coleoptera) 1 NO 0.07 0.27 1 NO NO - - - Scotinophara coarctata/lurida – 16 2 1.23 2.27 7 1 1 0.07 0.27 1 Pentatomidae (Hemiptera) Nezara viridula – Scarabidae (Hemiptera) 7 NO 0.54 1.94 7 NO NO - - - Pygomenida varipennis – Coreidae (Hemiptera) 7 NO 0.54 1.45 5 2 NO 0.15 0.37 1 Eysarcoris spp./cletus spp.– Coreidae (Hemiptera) 119 3 9.15 12.4 32 67 1 5.15 11.02 34 Nephotettix spp. – Cicadellidae (Hemiptera) 434 6 33.38 34.31 96 407 17 31.3 43.67 116 Recilia dorsalis – Cicadellidae (Hemiptera) 53 21 4.07 3.7 12 20 22 1.53 2.1 7 Cofona spectra – Cicadellidae (Hemiptera) 12 12 0.92 1.32 4 4 3