Insect Biodiversity in Organic and Non-Organic Rice Ecosystem in the District of Bantul

Measuring biodiversity of insects is an essential part in management concept of insect pest populations based on ecology. This study examined the index of insect biodiversity by measuring species richness, species evenness and heterogeneity in organic and non-organic rice farming ecosystem. The sampling was conducted during the planting season of April–May 2015 and October–November 2015 at 44, 52 and 66 days after rice transplanting (DAT). High number of species richness (7 to 13 species) was found in the non-organic rice field (April–May 2015). In contrast, high number of species richness (22 to 33 species) was found in the organic rice field (October–November 2015). The species evenness and heterogeneity in the organic farming were generally higher than these in the non-organic rice in the both of planting season April–May 2015 and October–November 2015. Overall, the organic rice farming ecosystem can increase species richness, species evenness and heterogeneity of insect. INTISARI Mengukur biodiversitas serangga adalah salah satu bagian penting dalam konsep pengelolaan populasi serangga hama berbasis ekologi. Penelitian ini mengkaji indeks biodiversitas serangga dengan mengukur kekayaan spesies (species richness), kemerataan spesies (species evenness), dan keanekaragaman/kelimpahan spesies (heterogenity) pada sistem budidaya padi organik dan non-organik. Pengambilan sampel diperoleh pada saat musim tanam April–Mei 2015 dan musim tanam Oktober–November 2015 di 44, 52, dan 66 hari setelah tanam. Total kekayaan spesies tertinggi (7–13 spesies) ditemukan di lahan padi non-organik (April–Mei 2015). Sebaliknya, total kekayaan spesies (22–33 spesies) ditemukan di lahan padi organik (Oktober–November 2015). Kemerataan spesies dan heterogenitas di lahan padi organik secara umum lebih tinggi dibanding di padi non-organik pada kedua musim tanam April–Mei 2015 dan Oktober–November 2015. Secara keseluruhan, sistem budidaya di ekosistem padi organik dapat meningkatkan kekayaan spesies, kemerataan spesies, dan heterogenitas serangga.


INTRODUCTION
Rice farming ecosystem is one of the unstable ecosystems because there were rapid and ever changing conditions in rice farmers cultivation. For example, rice cultivation system using conventional methods causes low biodiversity (Loreau et al., 2002). While, organic farming used more environmentally friendly materials for fertilizers and pesticides, which can reduce the leaching of nutrients, store more carbon (Drinkwater et al., 1995) and reduce pesticide in the irrigation system. Organic farming is reported to increase the population of natural enemies, such as carabid beetles (Pfinner et al., 1996).
Insect is one of the components of agricultural ecosystems which play an important role as herbivores, pollinators, predators and parasitoids. Changes in the abundance and diversity of these insects could potentially alter the ecosystem services (Hillstrom et al., 2008). Herbivorous insects in the rice field tend to be more dominant than the non-herbivore guild (Settle et al, 1996). However, herbivorous insects live together with other insects (predators, parasitoids, and decomposers, pollinators), which can control the population of herbivorous insects (Untung, 2006;Foottit et al., 2009). Insect biodiversity is one of the important information in insect management concept based on ecology (SARE, 2012).
Biodiversity or biological diversity is defined as the number and variety of species or other taxa present in a location, ecosystems, or biosphere region (Price et al., 2011). As a system of cultivation, giving a preferred treatment to ascertain the biodiversity that will affect populations of insects (herbivores, predators, parasitoids, and detrivors, pollinators). Some studies showed that organic farming system has able to suppress the growth rate of the abundance of herbivores and carnivores keep groups of arthropods (Padmavathi et al., 2007;Mukerji, 2009). David et al. (2005) reported that organic rice cultivation systems can suppress thrips abundance. While several studies have reported that conventional rice system that adds a lot of synthetic inputs would trigger an explosion of insect pests (Hepperly et al., 2009), for example increment the abundance of Nilaparvata lugens (Ravi et al., 2007).
Index biodiversity is generally measured by including the approach of species richness, evenness, and heterogeneity. Species richness has the number of species in a community or a region (McIntosh,1967). Species evenness is trying to measure the unequal representation of the hypothesis community where all species are generally the same (Lloyd & Ghelardi, 1964). Heterogeneity measure the incorporation of species richness and abundance in the diversity index (Good, 1953) and for the ecological, this concept is the same as diversity (Hurlbert, 1971). There are many formulation to measure the biodiversity index and there interpretation of the index value (Magurran, 1988;Krebs, 1999;Magurran, 2004).
The aims of this study was to examine the index of insect biodiversity by measuring species richness, evenness, and heterogeneity. To address the aim, we conducted a field study in an organic and non-organic rice farming ecosystem was conducted during the planting season April−May 2015 and October− November 2015.

Location and Time Sampling
Insect samples were collected from rice ecosystem in The Village of Kebonagung, the District of Bantul (6.9932 o S, 110.7003 o E) to determine the effect of different management of rice cultivation (organic vs. non-organic) on biodiversity of insects. Observation time lasted for two planting seasons, April−May 2015 by using rice varieties Mentik Wangi, and planting season October−November 2015 by using rice varieties Inpari 23. Rice cultivation with organic systems had begun in 2008, and has a certificate from the Institute of Organic Agricultural Production Quality Certification Persada, Yogyakarta. Management of organic and non-organic rice ecosystem difference used of fertilizers, pesticide and plant refuge ( Table 1).

Method of Sampling
Insect samples were collected using a modified D-Vac Vacuum (IL-130 with rated voltage AC 220− 240V and rated frequency 50Hz) at 44, 52, and 66 days after transplanting (DAT). In each sampling time, 40 different hills of rice plants were taken randomly in the organic and non-organic field. The insect samples were identified in the laboratory until the species and they were classified according to the insect's trophic level.

Measure the Biodiversity of Insects
Measuring the spesies richness, species evenness and heterogeneity of the insect samples was conducted to determine the insect biodiversity. Species richness was determined by counting the number of many species of insects found in each plot observations. Species evenness was measured using the Shannon-Wiener index, species evenness interpretation value ranges from 0 to 1 (Magurran, 2004;Krebs, 2009). Heterogeneity measured by Simpson index (D) (Simpson, 1949); the interpretation of Simpson index values range from 0 to 1; zero was the lowest and one was the highest value of diversity (Krebs, 1999;Krebs, 2008).

Species Richness
Non-organic rice ecosystem had the higher value of species richness during the planting season April− May 2015, on rice variety Mentik Wangi ( Figure  3A). From the total of 13 species, 12 of them were herbivores (Nilaparvata lugens, Nezara viridula, Sogatella furcifera) while the other 1 species was a predator Micraspis frenata. The species richness in organic rice ecosystem was low in the planting season April−May 2015, we found only 3 species of herbivores insect and 4 species of predators. In contrast, in the organic rice field we found 22 to 33 insects species during the planting season October− November 2015 ( Figure 3B). In contrary, in the nonorganic rice field planting season October−November 2015 we only found 10−15 species, consisting of herbivores, predators and detrivores.

Species Evenness
The species evenness in the organic rice ecosystem was higher than that of in the non-organic rice ecosystem in both planting seasons ( Table 2). The highest value (0.9 to 1) of insect species evenness in the organic rice field at 66 DAT and low value (0 to 0.5) in the non-organic rice field at 52 DAT October −November 2015. The number of arthropod found in organic plots were 33 species comprising of 54% predators, 9% parasitoids, 13% detrivores, 2% pollinator, and 21% insect herbivores. The number of individuals in the non-organic rice field at 52 DAT during the planting season October−November 2015 was 113, but most of the individuals were Chirothrips sp. as herbivore insects with a few Paederus fuscipes, Micraspis frenata, Polyrachis sp. as predators, and no parasitoid.

Heterogeneity
The insect diversity in organic rice field was consistently higher than that in non-organic field in both seasons (Table 3). The highest value (0.9) of Simpson's index of insect occurred in the organic rice field during the planting season October−November 2015 and low value (0 to 0.5) occurred in the nonorganic rice field during the planting season October− November 2015. The medium value (>0.5 to 0.8) occurred in the organic and non-organic rice field during the planting season April−May 2015 (Table 3). The number of species richness and distribution abundance of individual insect was in balance in the organic rice field during the planting season October− November 2015. However, in the non-organic rice field was dominance by Chirothrips sp. as a herbivorous insects (73%) during the planting season October− November 2015.
The abundance of insect herbivores were higher than the carnivores (predators and parasitoids) in non-organic fields, and otherwise in organic rice fields both in the both of planting seasons (Figure 1 and 2). Organic farmers used compost as a soil fertility (7.5 ton/ ha) and Bacillus subtilis as a pest control biological agent to controlling plant pests ( Table 1).
Application of organic fertilizer was safe for beneficial organisms than non-organic fertilizers that tend toxic. Birkhofer (2008) reported that organic fertilizers on crops have a positive impact on the activity of generalist predators such as spiders and Carabidae. Thus, the condition of the soil and healthy plants was favorable to the growth rate of carnivorous insects (predators and parasitoids). Moreover, it will also increased the number of species richness in organic fields (Figure 3) as well as the higher index value of species evenness and heterogeneity of Simpson index (Table 2 and 3).
Meanwhile, in the non-organic rice fields, farmers still used chemical fertilizers (NPK Phonska) as well as pesticides (Providor 30 WP) to control pests (Table 1). Heong et al. (2007) proved that reduction of pesticide use more than 95% during the year 1994−2007 at IRRI rice fields can increase species richness of natural enemies from 17 to 38. Some studies also reported that the application of pesticides such as deltamethrin may reduce biological potential parasitoids of Anagrus nilaparvatae (Meilin, 2012), and abamectin applications led to increased fecundity of Nilaparvata lugens (Wisuda, 2014). Application of insecticides on non-organic rice was not favorable for carnivorous insects, and thus can reduce the pressure on the growth rate of insect herbivorous. That's why the composition of herbivorous insects was higher than carnivores (predators and parasitoids) in non-organic field in both of planting seasons. The use of chemical fertilizers and insecticide applications in non-organic field affected the abundance of individuals, which will also have an impact on the value of species richness non-organic rice field (7−13 species) which was higher than on organic field during April− Mei 2015 (Figure 3). The value of species evenness and heterogeneity of Simpson index were also lower in non-organic field at 52 DAT during October− November 2015 (Table 2 and 3). Figures 1 and 2 also explained that the composition of insects in the planting season April−May 2015 and October−November 2015 was differed. The percentage of the number of individual abundance of herbivorous insects in organic field April−May 2015 was lower than in rainy season (19% vs 23%) and was dominated by Chirothrips sp.. Heinrichs (1994) reported that Rice Thrips in northern India began to emerge early at August and peaked at late August to early September. Meanwhile, the percentage abundance of herbivorous insects in non-organic rice field during April−May 2015 was higher than in October− November 2015 (81% vs 62%), which was dominated by Nilaparvata lugens. April− May 2015 farmers used local rice varieties (Mentik Wangi) were susceptible to plant pests, but in the planting season October−    (Suputa et al., 2015). The highest species richness (22−33 species) was found in the organic field during October−November 2015 ( Figure 3). Besides predators and parasitoids, beneficial insects as pollinators (Eristalis sp., Anthrax sp., Sphaerophoria sp., and Xylocopa sp.) was also found in this rice field. Flower plant as refuge was planted by farmers during October−November 2015 (Table 1) and invites the presence of insects. Usyati (2012) reported that the addition of flowering plants in the fields of agro-ecosystem can attract useful insects and suppress pest. Study by Kurniawati (2014) also showed that the flowering plants, sesame (Sesamum indicum L.) family Pedaliaceae and Wedelia spp. family Asteraceae, increasing the diversity and abundance of arthropods in rice field.

CONCLUSION
Organic rice ecosystems increased the biodiversity of useful insects (predators, parasitoids, pollinators, and decomposers) in both of planting seasons (April− May 2015 and October−November 2015). The higher species richness (22−33 species) was occurred in the organic rice fields during October−November 2015, and during April−May 2015 the highest species richness (7−13 species) was occurred in non-organic rice fields, that dominated by insects herbivorous. The higher of species evenness and heterogeneity of Simpson index,were found in organic rice fields during both of planting seasons. Overall, the organic farming ecosystem increased species richness, species evenness, and heterogeneity of insect.