Landscape structure influences natural pest suppression in a rice agroecosystem

Agricultural landscapes are constantly changing as farmers adopt new production practices and respond to changing environmental conditions. Some of these changes alter landscape structure with impacts on natural pest control, pesticide use, and conservation of biodiversity. In rice agroecosystems the effect of landscape structure on natural enemies and pest suppression is often poorly understood. Here we investigate the effect of landscape composition and configuration on a key pest of rice, the brown planthopper (Nilaparvata lugens). Using N. lugens as sentinel prey coupled with predator exclusions, we investigated landscape effects on herbivore suppression and rice grain yield at multiple spatial scales in two regions of Bangladesh. Ladybird beetles and spiders were the most abundant natural enemies of N. lugens with landscape effects observed at all scales on ladybird beetles. Specifically, ladybird beetles were positively influenced by road edges, and fallow land, while spiders were strongly influenced only by rice phenology. Predator exclusion cages showed that N. lugens abundance significantly increased in caged plots, reducing rice gain yield. We also used an estimated biocontrol service index that showed a significant positive relationship with landscape diversity and a significant negative impact on pest density and yield loss. These results suggest that promoting fallow lands and fragmented patches between rice fields could lead to more sustainable insect pest management in rice agroecosystems, potentially reducing the practice of prophylactic insecticide use.

Salinity Influences Plant-Pest-Predator Tritrophic Interactions

Climate change-induced salinity intrusion into agricultural soils is known to negatively impact crop production and food security. However, the effects of salinity increase on plant-herbivore-natural enemy systems and repercussions for pest suppression services are largely unknown. Here, we examine the effects of increased salinity on communities of rice (Oryza sativa), brown planthopper (BPH), Nilaparvata lugens, and green mirid bug (GMB), Cyrtorhinus lividipennis, under greenhouse conditions. We found that elevated salinity significantly suppressed the growth of two rice cultivars. Meanwhile, BPH population size also generally decreased due to poor host plant quality induced by elevated salinity. The highest BPH density occurred at 2.0 dS/m salinity and declined thereafter with increasing salinity, irrespective of rice cultivar. The highest population density of GMB also occurred under control conditions and decreased significantly with increasing salinity. Higher salinity directly affected the rice crop by reducing plant quality measured with reference to biomass production and plant height, whereas inducing population developmental asynchrony between BPH and GMB observed at 2 dS/m salinity and potentially uncoupling prey-predator dynamics. Our results suggest that increased salinity has harmful effects on plants, herbivores, natural enemies, as well as plant-pest-predator interactions. The effects measured here suggest that the bottom-up effects of predatory insects on rice pests will likely decline in rice produced in coastal areas where salinity intrusion is common. Our findings indicate that elevated salinity influences tritrophic interactions in rice production landscapes, and further research should address resilient rice insect pest management combining multipests and predators in a changing environment.

Response of a rice insect pest, Scirpophaga incertulas (Lepidoptera: Pyralidae) in warmer world

Background

Increases in global mean temperature, changes in rainfall patterns, and extreme climatic events are expected results of climate change. The individual effects of elevated temperature and precipitation on insect pests due to the impact of climate change have been widely modeled individually but their combined effects are poorly understood.

Results

Ten years of monthly abundance of an important economic rice insect pest, the rice yellow stem borer (YSB), Scirpophaga incertulas Walker (Lepidoptera: Pyralidae), was modeled in relation to temperature and rainfall using cross-correlation functions, general linear models, ARIMA models and simple linear regressions. The results suggested that increasing temperature and rainfall separately had a positive effect on growth rate of YSB. However, the combined effect of high temperature and rainfall was negative Temperature affected abundance of YSB negatively at high rainfall, but positively at intermediate to low rainfall level. The growth rate of YSB was found to be high at relatively low temperature and abundant rainfall.

Conclusion

The combined effects of temperature and rainfall showed a quadratic response of YSB abundance, which indicated that outbreak risk of YSB may be reduced if climate change results in increasing temperature and rainfall. It should be noted that we could address only a few of the important factors which could influence our model prediction.

Mapping QTLs underpin nutrition components in aromatic rice germplasm

As rice is an important staple food globally, research for development and enhancement of its nutritional value it is an imperative task. Identification of nutrient enriched rice germplasm and exploiting them for breeding programme is the easiest way to develop better quality rice. In this study, we analyzed 113 aromatic rice germplasm in order to identify quantitative trait loci (QTL) underpinning nutrition components and determined by measuring the normal frequency distribution for Fe, Zn, amylose, and protein content in those rice germplasm. Comparatively, the germplasm Radhuni pagal, Kalobakri, Thakurbhog (26.6 ppm) and Hatisail exhibited the highest mean values for Fe (16.9 ppm), Zn (34.1 ppm), amylose (26.6 ppm) and protein content (11.0 ppm), respectively. Moreover, a significant linear relationship (R2 = 0.693) was observed between Fe and Zn contents. Cluster analysis based on Mahalanobis D2 distances revealed four major clusters of 113 rice germplasm, with cluster III containing a maximum 37 germplasm and a maximum inter-cluster distance between clusters III and IV. The 45 polymorphic SSRs and four trait associations exhibited eight significant quantitative trait loci (QTL) located on eight different chromosomes using composite interval mapping (CIM). The highly significant QTL (variance 7.89%, LOD 2.02) for protein content (QTL.pro.1) was observed on chromosome 1 at 94.9cM position. Also, four QTLs for amylose content were observed with the highly significant QTL.amy.8 located on chromosome 8 exhibiting 7.2% variance with LOD 1.83. Only one QTL (QTL.Fe.9) for Fe content was located on chromosome 9 (LOD 1.24), and two (QTL.Zn.4 and QTL.Zn.5) for Zn on chromosome 4 (LOD 1.71) and 5 (LOD 1.18), respectively. Overall, germplasm from clusters III and IV might offer higher heterotic response with the identified QTLs playing a significant role in any rice biofortification breeding program and released with development of new varieties.

Establishing next-generation pest control services in rice fields: eco-agriculture

Pesticides are commonly used in food crop production systems to control crop pests and diseases and ensure maximum yield with high market value. However, the accumulation of these chemical inputs in crop fields increases risks to biodiversity and human health. In addition, people are increasingly seeking foods in which pesticide residues are low or absent and that have been produced in a sustainable fashion. More than half of the world’s human population is dependent on rice as a staple food and chemical pesticides to control pests is the dominant paradigm in rice production. In contrast, the use of natural enemies to suppress crop pests has the potential to reduce chemical pesticide inputs in rice production systems. Currently, predators and parasitoids often do not persist in rice production landscapes due to the absence of shelter or nutritional sources. In this study, we modified the existing rice landscape through an eco-engineering technique that aims to increase natural biocontrol agents for crop protection. In this system, planting nectar-rich flowering plants on rice bunds provides food and shelter to enhance biocontrol agent activity and reduce pest numbers, while maintaining grain yield. The abundance of predators and parasitoids and parasitism rates increased significantly in the eco-engineering plots compared to the insecticide-treated and control plots. Moreover, a significantly lower number of principal insect pests and damage symptoms were found in treatments where flowering plants were grown on bunds than in plots where such plants were not grown. This study indicates that manipulating habitat for natural enemies in rice landscapes enhances pest suppression and maintains equal yields while reducing the need for insecticide use in crop fields.

Variability Assessment of Aromatic Rice Germplasm by Pheno-Genomic traits and Population Structure Analysis

While the pleasant scent of aromatic rice is making it more popular, with demand for aromatic rice expected to rise in future, varieties of this have low yield potential. Genetic diversity and population structure of aromatic germplasm provide valuable information for yield improvement which has potential market value and farm profit. Here, we show diversity and population structure of 113 rice germplasm based on phenotypic and genotypic traits. Phenotypic traits showed that considerable variation existed across the germplasm. Based on Shannon-Weaver index, the most variable phenotypic trait was lemma-palea color. Detecting 140 alleles, 11 were unique and suitable as a germplasm diagnostic tool. Phylogenetic cluster analysis using genotypic traits classified germplasm into three major groups. Moreover, model-based population structure analysis divided all germplasm into three groups, confirmed by principal component and neighbors joining tree analyses. An analysis of molecular variance (AMOVA) and pairwise FST test showed significant differentiation among all population pairs, ranging from 0.023 to 0.068, suggesting that all three groups differed. Significant correlation coefficient was detected between phenotypic and genotypic traits which could be valuable to select further improvement of germplasm. Findings from this study have the potential for future use in aromatic rice molecular breeding programs.

Diversity and population structure of red rice germplasm in Bangladesh

While the functionality and healthy food value of red rice have increased its popularity, such that market demand for it is expected to rise, most strains suffer from low grain yield. To perform diversity and population structure analyses of red rice germplasm, therefore, becomes essential for improving yields for commercial production. In this study, fifty red rice germplasm from the Bangladesh Rice Research Institute (BRRI) genebank were characterized both morphologically and genetically using fifty simple sequence repeat (SSR) markers. Overall, 162 alleles were detected by the markers with the detected allele number varying from two to seven. Additionally, 22 unique alleles were identified for use as a germplasm diagnostic tool. The highest and lowest polymorphic information content (PIC) indices were 0.75 and 0.04 found in markers RM282 and RM304, respectively, and genetic diversity was moderate, varying from 0.05 to 0.78 (average: 0.35). While phylogenetic cluster analysis of the fifteen distance-based agro-morphological traits divided the germplasm into five clusters (I, II, III, IV and V), a similar SSR analysis yielded only three major groups (I, II, and III), and a model-based population structure analysis yielded four (A, B, C and D). Both principal component and neighbors joining tree analysis from the population structure method showed the tested germplasm as highly diverse in structure. Moreover, an analysis of molecular variance (AMOVA), as well as a pairwise FST analysis, both indicated significant differentiation (ranging from 0.108 to 0.207) among all pairs of populations, suggesting that all four population structure groups differed significantly. Populations A and D were the most differentiated from each other by FST. Findings from this study suggest that the diverse germplasm and polymorphic trait-linked SSR markers of red rice are suitable for the detection of economically desirable trait loci/genes for use in future molecular breeding programs.

Higher Fertilizer Inputs Increase Fitness Traits of Brown Planthopper in Rice

Rice (Oryza sativa L.) is the primary staple food source for more than half of the world's population. In many developing countries, increased use of fertilizers is a response to increase demand for rice. In this study, we investigated the effects of three principal fertilizer components (nitrogen, phosphorus and potassium) on the development of potted rice plants and their effects on fitness traits of the brown planthopper (BPH) [Nilaparvata lugens (Stål) (Homoptera: Delphacidae)], which is a major pest of rice in Bangladesh and elsewhere. Compared to low fertilizer inputs, high fertilizer treatments induced plant growth but also favored BPH development. The BPH had higher survival, developed faster, and the intrinsic rate of natural increase (r _m ) was higher on well-fertilized than under-fertilized plants. Among the fertilizer inputs, nitrogen had the strongest effect on the fitness traits of BPH. Furthermore, both the "Plant vigor hypothesis" and the "Plant stress hypothesis" were supported by the results, the former hypothesis more so than the latter. These hypotheses suggest that the most suitable/attractive hosts for insect herbivores are the most vigorous plants. Our findings emphasized that an exclusive focus on yield increases through only enhanced crop fertilization may have unforeseen, indirect, effects on crop susceptibility to pests, such as BPH.

Host Egg Age and Supplementary Diet Influence the Parasitism Activity of Trichogramma zahiri (Hymenoptera: Trichogrammatidae)

Mass production of egg parasitoids mostly depends on the age of the host. Generally old eggs are less preferred by egg parasitoids, which can discriminate between eggs of different ages by using chemical cues. This study was designed to determine the preference, development, and arrestment of Trichogramma zahiri Polaszek (Hymenoptera: Trichogrammatidae) parasitizing eggs of its native host, the rice hispa, Dicladispa armigera (Olivier) (Coleoptera: Chrysomelidae). Eggs of different ages, in addition, with or without supplementary foods were evaluated. T. zahiri preferred to parasitize 1-d-old eggs rather than 2-, or 3-d-old eggs by no-choice assays. However, although the percentage emergence of parasitoids is significantly lower from 2- and 3-d-old eggs, the sex ratio is unaffected. Parasitoids lived longer when 25% honey solution was provided with the host food. Significantly higher fecundity (38.5 eggs per female) and parasitoid emergence (94.6%) occurred when 25% honey solution was provided in the diet with host food, followed by 25% sugar solution, as compared to the control (only water as food). An average of 7.9 eggs were parasitized when one parasitoid was released per 10 rice hispa eggs. Ability of T. zahiri to parasitize egg increased with an increase in the number of eggs offered. We also found that inclusion of a fresh host egg with the supplementary diet improves the mass rearing of T. zahiri for commercial purposes.

Will climate change affect outbreak patterns of planthoppers in Bangladesh?

Recently, planthoppers outbreaks have intensified across Asia resulting in heavy rice yield losses. The problem has been widely reported as being induced by insecticides while other factors such as global warming that could be potential drivers have been neglected. Here, we speculate that global warming may increase outbreak risk of brown planthopper (Nilaparvata lugens Stål.). We present data that demonstrate the relationship between climate variables (air temperature and precipitation) and the abundance of brown planthopper (BPH) during 1998-2007. Data show that BPH has become significantly more abundant in April over the 10-year period, but our data do not indicate that this is due to a change in climate, as no significant time trends in temperature and precipitation could be demonstrated. The abundance of BPH varied considerably between months within a year which is attributed to seasonal factors, including the availability of suitable host plants. On the other hand, the variation within months is attributed to fluctuations in monthly temperature and precipitation among years. The effects of these weather variables on BPH abundance were analyzed statistically by a general linear model. The statistical model shows that the expected effect of increasing temperatures is ambiguous and interacts with the amount of rainfall. According to the model, months or areas characterized by a climate that is either cold and dry or hot and wet are likely to experience higher levels of BPH due to climate change, whereas other combinations of temperature and rainfall may reduce the abundance of BPH. The analysis indicates that global warming may have contributed to the recent outbreaks of BPH in some rice growing areas of Asia, and that the severity of such outbreaks is likely to increase if climate change exaggerates. Our study highlights the need to consider climate change when designing strategies to manage planthoppers outbreaks.