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BACKGROUND Spiders are effective biological control agents in rice ecosystems, but the comparative study of predations among main spider species under field conditions has not been fully explored owing to a lack of practical methodology. In this study, more than 6000 spiders of dominant species were collected from subtropical rice ecosystems to compare their predations on Sogatella furcifera (Horvath) (white-backed planthopper, WBPH) using DNA-based gut content analysis. RESULTS The positive rates for all spider taxa were closely related to prey densities, as well as their behaviors and niches. The relationships of positive rates to prey planthopper densities for Pardosa pseudoannulata (Boes. et Str.), Coleosoma octomaculata (Boes. et Str.), Tetragnatha maxillosa Thorell and Ummeliata insecticeps (Boes. et Str.) under field conditions could be described using saturated response curves. Quantitative comparisons of predations among the four spider species confirmed that P. pseudoannulata and C. octomaculata were more rapacious than U. insecticeps and T. maxillosa under field conditions. A comparison of ratio of spiders to WBPH and positive rates between fields revealed that biological control by spiders could be effectively integrated with variety resistance. CONCLUSION Generalist spiders could follow up WBPH population timely, and assemblages of spiders coupled with variety resistance could effectively suppress WBPH population. © 2016 Society of Chemical Industry.

Reduction of noncrop habitats, intensive use of pesticides and high levels of disturbance associated with intensive crop production simplify the farming landscape and bring about a sharp decline of biodiversity. This, in turn, weakens the biological control ecosystem service provided by arthropod natural enemies. Strategic use of flowering plants to enhance plant biodiversity in a well-targeted manner can provide natural enemies with food sources and shelter to improve biological control and reduce dependence on chemical pesticides. This article reviews the nutritional value of various types of plant-derived food for natural enemies, possible adverse effects on pest management, and the practical application of flowering plants in orchards, vegetables and field crops, agricultural systems where most research has taken place. Prospects for more effective use of flowering plants to maximize biological control of insect pests in agroecosystem are good but depend up on selection of optimal plant species based on information on the ecological mechanisms by which natural enemies are selectively favored over pest species.

Despite over 30 years of deployment, varieties with the Bph3 gene for resistance to the brown planthopper (BPH), Nilaparvata lugens (Stal) (Hemiptera: Delphacidae), are still effective in much of the Philippines. In the present study, we determined the effects of adaptation to one resistant variety, IR62 – assumed to possess the Bph3 gene – on (1) resistance against a series of varieties with similar biotypical responses (presumed to contain the same major resistance genes), and (2) a differential variety with the bph4 gene that occurs at the same chromosome position as Bph3. We also examined the effects of high soil nitrogen on the effectiveness of Bph3. Feeding, planthopper biomass, and development times were reduced in a wild BPH population when reared on IR62 compared with the susceptible standard variety TN1. However, nitrogen application increased the susceptibility of IR62. After 13 generations on IR62, BPH had adapted to the plant’s resistance. Virulence of the adapted BPH against the variety ‘Rathu Heenati’ supports the idea that Bph3 is present in IR62. Across similar IR varieties (IR60, IR66, IR68, IR70, IR72, and IR74), feeding, planthopper biomass, and development rates were generally higher for IR62-adapted than for non-adapted BPH; however, contrary to expectations, many of these varieties were already susceptible to wild BPH. Fitness was also higher for IR62-adapted BPH on the variety ‘Babawee’ indicating a close relation between Bph3 and bph4. The results indicate that the conventional understanding of the genetics behind resistance in IR varieties needs to be readdressed to develop and improve deployment strategies for resistance management.

The brown planthopper (BPH) Nilaparvata lugens, whitebacked planthopper (WBPH) Sogatella furcifera and smaller BPH Laodelphax striatellus increasingly exhibit resistance to insecticides and adaptation to resistant varieties, so they threaten food security. This review draws together, for the first time, information on the parasitoids of planthopper pests of rice from the non-English literature published in Asia. This is integrated with the English language literature to provide a comprehensive analysis. Planthopper pests of rice are attacked by a large range of parasitoids from Strepsiptera, Diptera and, especially, Hymenoptera. Levels of field parasitism vary widely between parasitoid species and locations. For many taxa, especially within Mymaridae, there is evidence that non-crop habitats are important as overwintering habitat in which alternative hosts are available. These source habitats may promote early season parasitism of pest Hemiptera in rice crops, and their movement into crops could be manipulated with applications of herbivore-induced plant volatiles. Non-crop plants can also provide nectar to improve parasitoid longevity and fecundity. Despite evidence for the importance of environmental factors affecting parasitoids of rice pests, the use of habitat manipulation to enhance biological control in the world's most important crop is surprisingly underrepresented in the literature. Current research in China, Vietnam and Thailand on ecological engineering, carefully selected vegetation diversity introduced without disrupting profitable farming, is briefly reported. Although the most important pest, BPH (N. lugens), is a migratory species, maintaining local communities of parasitoids and other natural enemies offers scope to prevent even r-selected pests from reaching damaging population densities.

Summary 1. Fallowing, a type of rotation where no crop is grown, deprives insect pests of food. In tropical irrigated rice, it is not known whether fallow periods deplete natural enemy populations and reduce their pest control effectiveness in post-fallow crops. We tested the null hypothesis that small-scale synchronous cropping (embedded in asynchronously planted rice landscapes) does not significantly increase pest densities during post-fallow periods in the presence of a large, diverse natural enemy complex undisrupted by insecticides. We tested this null hypothesis by comparing the invertebrate fauna before and after fallowing. 2. In six molluscicide-only fields at the International Rice Research Institute (IRRI) in southern Luzon and at Zaragoza in central Luzon, Philippines, canopy and floodwater invertebrates were vacuum-sampled over two cropping seasons, dry and wet. 3. Thirty-three of the ubiquitous common taxa dominated the samples in both seasons at each site. Most species were natural enemies of rice pests and recyclers of organic matter in the floodwater and waterlogged sediments; some were rice pests. 4. Fallowing depleted populations of more ubiquitous taxa at Zaragoza (four natural enemies, one detritivore) than at IRRI (one herbivore, one natural enemy). At both sites, only green leafhoppers, Nephotettix virescens and Nephotettix nigropictus, had consistently higher post-fallow densities than pre-fallow densities. 5. At both sites, fallowing did not affect rice-invertebrate faunas differently between seasons with regard to community structure, trajectories and accumulation rates of guild members. 6. Synthesis and applications. In tropical irrigated rice fields, small-scale synchronous fallowing combined with low-pesticide inputs and pest-resistant rice varieties did not induce pest outbreaks or notably diminish populations of natural enemies when embedded in asynchronous cropping on larger, regional scales. Our results suggest that small-scale synchronous fallowing, when embedded in asynchronously planted landscapes, does little harm to biological regulation of the invertebrate faunal community and may be adopted as part of integrated pest management when it serves other

1. Determining the functional significance of species diversity in natural enemy assemblages is a key step towards prediction of the likely impact of biodiversity loss on natural pest control processes. While the biological control literature contains examples in which increased natural enemy diversity hinders pest control, other studies have highlighted mechanisms where pest suppression is promoted by increased enemy diversity. 2. This study aimed to test whether increased predator species diversity results in higher rates of predation on two key, but contrasting, insect pest species commonly found in the rice ecosystems of south-east Asia. 3. Glasshouse experiments were undertaken in which four life stages of a planthopper (Nilaparvata lugens) and a moth (Marasmia patnalis) were caged with single or three-species combinations of generalist predators. 4. Generally, predation rates of the three-species assemblages exceeded expectation when attacking M. patnalis, but not when attacking N. lugens. In addition, a positive effect of increased predator species richness on overall predation rate was found with M. patnalis but not with N. lugens. 5. The results are consistent with theoretical predictions that morphological and behavioural differentiation among prey life stages promotes functional complementarity among predator species. This indicates that emergent species diversity effects in natural enemy assemblages are context dependent; they depend not only on the characteristics of the predators species, but on the identity of the species on which they prey.

The effect of nitrogen content in rice plants on the tolerance of brown planthopper (BPH), Nilaparvata lugens Stal to high temperature, starvation and insecticide, was studied in the laboratory at International Rice Research Institute (IRRI), Philippines. Survival of nymphs and adults, fecundity and egg hatchability were significantly increased by the increase of nitrogen content in host plants at 38. Moreover, the survival of nymphs, fecundity and egg hatchability were significantly higher in BPH populations on rice plants with a high nitrogen regimen than those on rice plants with a low nitrogen regimen. Meanwhile, the tolerance of female adults to starvation and nymphs to growth regulator buprofezin on rice plants with a high nitrogen regimen were slightly increased. This indicates that the tolerances of BPH to adverse environmental stresses were positively increased by the application of nitrogenous fertilizer. The outbreak potential of BPH induced by the excessive application of fertilizer in rice fields was also discussed.

The functional response ofCyrtorhinus lividipennis Reuter attacking the brown planthopper(Nilaparvata lugens (Stal.), BPH) eggs on rice was determined at six constant temperatures of 20°C, 23°C, 26°C, 29°C, 32°C and 35°C. Rogers’ (1972) random predator equations were fitted to the data for each temperature separately. The equation model adequately described a Holling’s Type II functional response forC. lividipennis and produced biologically realistic estimates of attack rates and handling times at five experimental temperatures between 20°C and 32°C. However, at 35°C, a negative handling time(Th = - 0.0029) was produced. The effect of temperature was incorporated in to Rogers’ equation by making the attack rate(a) and handling time(Th) functions of temperature within the range 20°C to 32°C. The attack rate and handling time were fitted as hyperbola and reciprocal hyperbola functions of temperature respectively. The temperature incorporating fourparameter composite model fitted the combined data as well as did separate Rogers’ equations based on the parameter estimates.

Functional responses of the wolf spider,Pardosa pseudoannulata (Boesenberg et Strand) attacking the rice brown planthopper,Nilaparvata lugens (Stal.), and the mirid predatorCyrtorhinus lividipennis Reuter were both those of Holling Type II. The attack rate was higher and handling time lower forC. lividipennis. However, when caged with the two prey, the wolf spider showed a significant preference forN. lugens at a lower prey proportion. Proportions of prey attacked were significantly different from the expected ratios of prey available as well as from the predicted preferences derived from the functional response parameters. As proportions ofN. lugens attacked changed from greater to less than expected as the proportions ofN. lugens available increased, a “reverse switch” behaviour seems to be evident.