Rice Insect Research Articles

Control of Rhyzopertha dominica in stored rough rice through a combination of diatomaceous earth and varietal resistance

AbstractAdults of Rhyzopertha dominica (F.), the lesser grain borer, were exposed on four varieties of rough rice with Dobie indices of susceptibility of 1.1 to 1.1 (low), and four varieties with Dobie indices of susceptibility of 3.4 to 3.8 (high). The varieties with low and high Dobie indices were classified as resistant and susceptible, respectively, to R. dominica. The purpose of the study was to evaluate control of R. dominica through the use of diatomaceous earth (DE) in combination with rice varieties that were either susceptible or resistant to R. dominica. The rice was treated with varying rates of the commercial DE Insecto®, up to a maximum of 1 000 mg DE/kg of rice. Adult mortality at each application rate of DE was generally greater on three of four resistant varieties compared to three of four susceptible varieties. Progeny production from the parental generation exposed on the rice was also greater in 3 of the 4 resistant varieties compared to 3 of the 4 susceptible varieties at DE rates of 500 mg/kg or more. Progeny production in rice treated with a maximum rate of 1 000 mg/kg DE ranged from 7‐44 adults on the resistant varieties compared to 75‐155 adults on the susceptible varieties. At DE rates of 500, 750, and 1 000 mg/kg, the percentage of insect‐damaged kernels (IDK) was also greater in 3/4 resistant varieties than in the susceptible varieties. Results show combining the use of DE with varietal resistance of rough rice to R. dominica could be used to limit populations of this insect in stored rice and help prevent economic damage.

Elucidation of the genomic basis of indirect plant defense against insects

Using airborne signals to attract herbivore predators and parasitoids is an important strategy that plants use in defense against herbivorous insects. The volatiles involved in this indirect plant defense are often chemically complex and variable across species. We recently established rice as a model for studying the molecular and genomic basis of volatile-mediated indirect plant defense. Rice plants when damaged by fall armyworm larvae become highly attractive to parasitic wasps. The volatiles potentially responsible for parasitoid attraction were determined to be a blend of compounds predominated by terpenoids, of which S-linalool is the most abundant. Racemic linalool alone was shown to be effective in attracting parasitic wasps. By combining volatile profiling and microarray analysis, a catalog of candidate genes for volatile biosynthesis was identified. Three genes encoding terpene synthases were biochemically characterized. They are responsible for the production of the majority of volatile terpenes released from insect-damaged rice plants. Additional candidate genes are being currently characterized for their role in production of other insect-induced volatiles from rice plants. Identification of a complete set of key genes for synthesizing herbivory-induced volatiles in rice will provide an important reference for comparative study of this important defense trait across a variety of plant species.Addendum to: Yuan JS, Köllner TG, Wiggins G, Grant J, Degenhardt J, Chen F. Molecular and genomic basis of volatile-mediated indirect defense against insects in rice. Plant J 2008; In press.

Molecular and genomic basis of volatile‐mediated indirect defense against insects in rice

Rice plants fed on by fall armyworm (Spodoptera frugiperda, FAW) caterpillars emit a blend of volatiles dominated by terpenoids. These volatiles were highly attractive to females of the parasitoid Cotesia marginiventris. Microarray analysis identified 196 rice genes whose expression was significantly upregulated by FAW feeding, 18 of which encode metabolic enzymes potentially involved in volatile biosynthesis. Significant induction of expression of seven of the 11 terpene synthase (TPS) genes identified through the microarray experiments was confirmd using real-time RT-PCR. Enzymes encoded by three TPS genes, Os02g02930, Os08g07100 and Os08g04500, were biochemically characterized. Os02g02930 was found to encode a monoterpene synthase producing the single product S-linalool, which is the most abundant volatile emitted from FAW-damaged rice plants. Both Os08g07100 and Os08g04500 were found to encode sesquiterpene synthases, each producing multiple products. These three enzymes are responsible for production of the majority of the terpenes released from FAW-damaged rice plants. In addition to TPS genes, several key genes in the upstream terpenoid pathways were also found to be upregulated by FAW feeding. This paper provides a comprehensive analysis of FAW-induced volatiles and the corresponding volatile biosynthetic genes potentially involved in indirect defense in rice. Evolution of the genetic basis governing volatile terpenoid biosynthesis for indirect defense is discussed.

Effect of Transgenic <I>Bacillus thuringiensis</I> Rice Lines on Mortality and Feeding Behavior of Rice Stem Borers (Lepidoptera: Crambidae)

Ten transgenic Bacillus thuringiensis Bt rice, Oryza sativa L., lines with different Bt genes (two Cry1Ac lines, three Cry2A lines, and five Cry9C lines) derived from the same variety Minghui 63 were evaluated in both the laboratory and the field. Bioassays were conducted by using the first instars of two main rice lepidopteran insect species: yellow stem borer, Scirpophaga incertulas (Walker) and Asiatic rice borer, Chilo suppressalis (Walker). All transgenic lines exhibited high toxicity to these two rice borers. Field evaluation results also showed that all transgenic lines were highly insect resistant with both natural infestation and manual infestation of the neonate larvae of S. incertulas compared with the nontransformed Minghui63. Bt protein concentrations in leaves of 10 transgenic rice lines were estimated by the sandwich enzyme-linked immunosorbent assay. The cry9C gene had the highest expression level, next was cry2A gene, and the cry1Ac gene expressed at the lowest level. The feeding behavior of 7-d-old Asiatic rice borer to three classes of Bt transgenic rice lines also was detected by using rice culm cuttings. The results showed that 7-d-old larvae of Asiatic rice borer have the capacity to distinguish Bt and non-Bt culm cuttings and preferentially fed on non-Bt cuttings. When only Bt culm cuttings with three classes of different Bt proteins (CrylAc, Cry2A, and Cry9C) were fed, significant distribution difference of 7-d-old Asiatic rice borer in culm cuttings of different Bt proteins also was found. In the current study, we evaluate different Bt genes in the same rice variety in both the laboratory and the field, and also tested feeding behavior of rice insect to these Bt rice. These data are valuable for the further development of two-toxin Bt rice and establishment of appropriate insect resistance management in the future.

Effect of Transgenic Bacillus thuringiensis Rice Lines on Mortality and Feeding Behavior of Rice Stem Borers (Lepidoptera: Crambidae)

Ten transgenic Bacillus thuringiensis Bt rice, Oryza sativa L., lines with different Bt genes (two Cry1Ac lines, three Cry2A lines, and five Cry9C lines) derived from the same variety Minghui 63 were evaluated in both the laboratory and the field. Bioassays were conducted by using the first instars of two main rice lepidopteran insect species: yellow stem borer, Scirpophaga incertulas (Walker) and Asiatic rice borer, Chilo suppressalis (Walker). All transgenic lines exhibited high toxicity to these two rice borers. Field evaluation results also showed that all transgenic lines were highly insect resistant with both natural infestation and manual infestation of the neonate larvae of S. incertulas compared with the nontransformed Minghui63. Bt protein concentrations in leaves of 10 transgenic rice lines were estimated by the sandwich enzyme-linked immunosorbent assay. The cry9C gene had the highest expression level, next was cry2A gene, and the cry1Ac gene expressed at the lowest level. The feeding behavior of 7-d-old Asiatic rice borer to three classes of Bt transgenic rice lines also was detected by using rice culm cuttings. The results showed that 7-d-old larvae of Asiatic rice borer have the capacity to distinguish Bt and non-Bt culm cuttings and preferentially fed on non-Bt cuttings. When only Bt culm cuttings with three classes of different Bt proteins (Cry1Ac, Cry2A, and Cry9C) were fed, significant distribution difference of 7-d-old Asiatic rice borer in culm cuttings of different Bt proteins also was found. In the current study, we evaluate different Bt genes in the same rice variety in both the laboratory and the field, and also tested feeding behavior of rice insect to these Bt rice. These data are valuable for the further development of two-toxin Bt rice and establishment of appropriate insect resistance management in the future.

Induced resistance in rice against insects

Vaccinations are the mainstay of western preventive medicine, and they have been used to protect some crops against disease and insect pests. We consider rice as a model for protection using induced resistance since it is one of the most important staple crops and there have been significant new developments in: cross-resistance among rice insects, chemical pathways involved in induced resistance, sequencing the rice genome and expression of genes conferring resistance against rice insect pests. Insect attack has been found to cause lesions that kill planthopper eggs and early stages of gall midges. Damaged plants released volatiles that made them less likely to be chosen by planthoppers and more attractive to parasitoids. Chemical elicitors have been developed for dicotyledonous plants and these can induce resistance in rice, although rice does not fit models developed to explain signalling in dicots. For example, salicylic acid did not increase in rice after infection by pathogens and did not appear to be the mobile signal for induced resistance against pathogens although it was involved in induced responses to phloem-feeding insects. Jasmonic acid acted as a signal in some induced responses to pathogens as well as chewing insects. Many of the genes associated with induced resistance in rice have recently been mapped, and techniques are being developed to incorporate them into the genome of cultivated varieties. Attempts to control insect pests of rice will affect interactions with pathogens, predators and parasites, and other organisms in this agroecosystem.

Susceptibility of rice insect pests and their natural enemies to commonly used insecticides

The Journal of the National Science Foundation of Sri Lanka publishes the results of research in all aspects of Science and Technology. The journal also has a website at http://www.nsf.gov.lk/. 2021 Impact Factor: 0.682The JNSF provides immediate open access to its content on the principle that making research freely available to the public supports a greater global exchange of knowledge.

Involvement of metabolic and insensitive acetylcholinesterase mechanisms in insecticide resistance of rice insect pests and predatory populations from Batalagoda, Sri Lanka

Mechanisms of insecticide resistance were studied in five rice insect pests (brown planthopper Nilaparvata lugens; green leafhopper Nephotettix virescens; paddy bug Leptocorisa oratorius; white leafhopper Cofana spectra and white- backed planthopper Sogatella furcifera), and four of their predators (ladybird beetle Micraspis discolor; ground beetle Ophionea indica; mired bug Cytorhinus lividipennis and spider Tetragnatha sp.). Insects were collected from the rice fields at Batalagoda, Kurunegala, during 2001 - 2003 and stored at -20°C Biochemical assays were carried out within one week of storage to determine the activity levels of major enzyme groups (i.e carboxylesterases, glutathione S-transferases and mono- oxygenases), which are involved in insecticide metabolism. Native polyacrylamide gels were run with crude homogenates to resolve carboxylesterase isozymes. Sensitivity of the organophosphate and carbamate target site acetylcholineesterase was tested by inhibiting the enzyme with propoxur. N. lugens, S. furcifera and N. virescens showed high insecticide resistance, especially to organophospha tes and pyrethroids due to higher activity levels of metabolic enzymes. All the species were susceptible to malathion mainly because of the absence of malathion carboxylesterase mechanism. Resistance to permethrin in the populations of N. lugens, C. lividipennis, M. discolour, O. indica and Tetragnatha sp. may be due to their higher mono-oxygenase activities. Presence of insensitive acetylcholinesterases could be detected among the populations of N.lugens, C. spectra, C. lividipennis and Tetragnatha sp. It appears that multiple resistance mechanisms are present in the populations tested. Higher susceptibility levels of L. oratorius and C. spectra could be attributed to the absence of resistance mechanisms in these two species.

Effect of nitrogenous fertilizer on the incidence of rice insect pests and their natural enemies

Key words: nitrogen; fertilizer; urea; rice insect pest; natural enemies Univ. j. zool. Rajshahi Univ. Vol.21, 2002. pp. 13-15

SIKey: A tool to generate secondary identification keys for targeted diagnosis

Secondary identification key (SIK) is a new tool for species identification which enables users to identify possible specimens from a particular group of species (as rice insect pests). The SIK has proved more efficient and easier to be adapted than traditional keys for targeted diagnosis. Since it is hard and time-consuming for taxonomists to design SIK manually, a Web-based tool, SIKey, was developed for both experts and non-experts to acquire or revise SIK rapidly and conveniently. SIKey operates on secondary use of existing identification keys with logical reasoning and involves construction of computerized taxonomic knowledge base, tree-tracing for crossing nodes and generation of sub-keys. Currently a software called InsectID has been developed for the computerization of dichotomous keys while SIKey offers online, real-time auto-generation of SIKs for user-defined group of taxa. The principles, construction methods and testing of SIKey were described in this paper.

Effects of N-fertilization and spacing on african rice gall midge <i> Orseolia oryzivora </i> harris and gagn&eacute i a sub-humid area of southeastern Nigeria

Nitrogen fertilization and spacing hold a strong promise in the integrated management of rice insect pest problem. Therefore, three levels of urea: 0, 80 and 160 kg N ha -1 and three spacings: 10-cm x 10-cm, 20-cm x 20-cm and 30-cm x 30-cm were evaluated for two years in Abakaliki, Nigeria, for the control of rice gall midge. The experiment was set up using split-plot arrangement in a randomized complete block design (RCBD) with three replications. Results of the trial showed that nitrogen significantly increased incidence by gall midge (P<0.05) with 160 kg N ha -1 recording the highest incidence of 50.95% and 36.01% in 2002 and 2003 trials, respectively. Similarly, incremental doses of urea n-fertilizer increased the grain yield of rice but only up to 80 kg N ha -1 . Beyond this level further n-fertilization had no effect. Generally, increasing plant population significantly increased the incidence by the midge (r = 0.93 and 0.99 in both years). Conversely, grain yield was significantly reduced with increasing population. Differences among treatment combinations between nitrogen and spacing however did not produce any significant effect.

Differential susceptibilities to pyrethroids in field populations of Chilo suppressalis (Lepidoptera: Pyralidae)

To assess the feasibility of pyrethroids for rice insect control, we examined susceptibilities of six field populations of rice stem borer Chilo suppressalis (Walker) to 10 pyrethroids using the topical application method in laboratory in 2004 and 2005. Our results showed that the seven pyrethroids with high fish-toxicity (i.e., β-cyfluthrin, λ-cyhalothrin, β-cypermethrin, deltamethrin, S-fenvalerate, α-cypermethrin, and fenpropathrin) were more effective against C. suppressalis than the three compounds with low fish-toxicity (i.e., cycloprothrin, etofenprox, and silafluofen). The results also showed that all 10 of the pyrethroids were much more effective than methamidophos and monosultap for C. suppressalis control. In addition, we found that susceptibilities of some field populations of C. suppressalis to some high fish-toxicity pyrethroids were significantly reduced, and our results indicated that a Ruian (RA) field population showed a year-to-year variation in susceptibility to most tested pyrethroids between 2004 and 2005. Our data indicated that the tolerance levels increased dramatically in RA population, especially to β-cyfluthrin and deltamethrin. This study provided the first assessment of resistance to pyrethroids in field populations of C. suppressalis. In addition, a close correlation between resistance ratios to the 10 compounds and differences of the structures of these compounds was established in the RA05 population, which was resistant to most of the pyrethroids tested while it was still very susceptible to fenvalerate with no cross resistance. Finally, the feasibility and precaution were discussed in selecting pyrethroids as alternatives to replace high toxicity organophosphates for C. suppressalis control and insecticide resistance management.

Survey of rice diseases and insect pests in Northern Ghana

Survey of rice diseases and insect pests in Northern Ghana

Evaluation of action thresholds for chronic rice insect pests in the Philippines. IV. Stemborers

Action thresholds (ATs) as insecticide application decision tools were developed and tested against mainly yellow Scirpophaga incertulas (Walker) and white S. innotata (Walker) rice stemborers in four sites in the Philippines over 68 crops. Damage incidence was low with a mean over all crops and sites of 2% deadhearts (DH) and 3% whiteheads (WH) based on weekly sampling. Highest incidence reached 19% WH as a mean of one crop and 31% WH in an individual field in 1 week. AT characters were based on deadhearts, egg masses, or flushed moths. A mean of 9% fields exceeded ATs in the vegetative, 5% in the reproductive, and 4% in the ripening stages. The most effective AT character in each of the three growth stages was percentage DH with 5% being optimal in the vegetative, 25% in the reproductive, and 10% in the ripening stages. These ATs resulted in 96 – 99% correct decisions based on criteria involving DH and yield loss benchmarks set from earlier studies on economic loss. Insecticide response to the highly accurate ATs was a disappointing <40% control, with chlorpyrifos + BPMC mixture being superior to chlorpyrifos or endosulfan alone. Despite this low level of control and the noted high tolerance of modern rices to stemborer damage, the AT treatments resulted in significant 0.2 – 0.3 t/ha yield gains over the untreated check in each growth stage. This yield response is explained in part by control of coterminous nontarget chronic pests and in part to a synergistic compensatory yield response when a crop under multiple stress is even partially released. It is hypothesized that under such conditions, even low levels of control allow greater compensatory capacity to tolerate stemborer injury but also from other causes, thus accentuating yield responses, particularly if the nutrient supply is adequate and the variety is longer maturing. Stemborer IPM is seen as a two-pronged strategy, the first is couched in integrated crop management as a preventative measure to bolster the crops' ability to compensate from stemborer injury or other crop stress and the second to regularly monitor the crop using ATs. Crop monitoring protocols were seen to be improved if adjustments were made for crop maturity and damage pattern. The typical damage pattern over a crop showed DH initially increasing in the vegetative stage, then leveling off during the reproductive stage (indicating a period of natural plant resistance) before a late peak of WH. Vigilance can be relaxed during the mid-growth stages and heightened during periods of tiller elongation and panicle exsertion. AT levels need to be adjusted for each location, but as a rule of thumb percentage DH could follow the ratio 1:5:3 and 2:3:1 in the three growth stages for longer and shorter maturing varieties, respectively.

Evaluation of action thresholds for chronic rice insect pests in the Philippines: II. Whorl maggot and defoliators

Action thresholds as insecticide decision tools were developed and evaluated against chronic vegetative stage insect pests of irrigated transplanted rice in the Philippines: whorl maggot Hydrellia philippina Ferino (Diptera: Ephydridae( and two lepidopterous defoliators, Naranga aenescens Moore and Rivula atimeta (Swinhoe( (Lepidoptera: Noctuidae(. Through an iterative process, new threshold characters and insecticide technologies were evaluated at four sites (categorized as high and low pest density sites( over a 13-year period with the objectives of minimizing insecticide usage and maximizing farmer adoption. Characters were evaluated as to their ability to predict significant pest densities and yield loss. Significant differences occurred between high and low pest density sites among the best characters and monitoring methods for both pests. Earlier-planted fields were used as a forecasting tool, showing best results in the high pest density sites. Overall, most threshold characters performed well but the insecticide response was poor. Insecticide control was better with some threshold characters than others due to better timing. Seedling root soak with isofenphos was more effective than granules or foliar sprays against whorl maggot but required a decision before planting. Foliar sprays were most effective if applied twice (2 and 7 days after transplanting(. The best performing characters for whorl maggot were 1 – 2 eggs/hill for the low pest density sites and 15 – 30% damaged leaves in earlier planted fields in high density sites. The best performing characters for defoliators were 10% damaged leaves monitored in earlier planted fields for high density sites and 10% damaged leaves in low density sites. Carbaryl was the most effective insecticide spray against defoliators that combined performance and relative safety.

Evaluation of action thresholds for chronic rice insect pests in the Philippines. III. Leaffolders

Action thresholds (AT) as insecticide application decision tools were developed and tested against rice leaffolders Cnaphalocrocis medinalis (Guenée) and Marasmia patnalis Bradley (Lepidoptera: Pyralidae) in four sites and 68 crops over a 13-year period in the Philippines. Leaffolder damage levels were generally low with a mean over all sites and crops of 2 – 3% damaged leaves (DL) and 6 – 9% in a given site as a per-crop average based on weekly samplings, with highest incidence per field on a given sampling date of 48%DL. The damage incidence over a typical crop cycle formed a bell-shaped curve with maximum numbers in the late reproductive and early ripening stages. Continuous population buildup over the planting cycle did not occur in any one site over the season, thus a strategy of monitoring earlier planted fields to forewarn against impending economic damage had no basis. ATs were based on different levels of percentage DL, number of larvae per hill (L), and density of flushed moths. Collectively ATs were surpassed in 1, 12, and 4% of fields in each of the three main growth stages. A scoring system was based on benchmark criteria including both leaffolder damage and yield loss. The 15%DL threshold performed best in all growth stages, only equaled by 1L in the vegetative stage, scoring 93 – 99% correct decisions in each of the growth stages. Flushed moths produced the most false positive decisions and the lowest performance scores. The best insecticide response gave only a disappointing 53% control and therefore was a significant weakness in using AT technology. BPMC, endosulfan, and monocrotophos performed the best and azinphos-ethyl and Bt the least. Sites with the highest densities had the most rapid rise in damage levels, thus requiring more frequent monitoring. Low leaffolder damage levels were most likely due to the activity of natural enemies. Given the ability of high tillering varieties to compensate from pest damage, farmers would be better off embracing integrated crop management as a preventative measure to bolster inherent tolerance levels combined with crop monitoring based on historical population levels. In sites with a record of high damage levels, monitoring should start 4 weeks after transplanting (WT) on a weekly basis and more risk averse farmers may increase the interval to twice a week during flag leaf stage. In sites with lower observed levels, monitoring can begin 6 WT on a weekly basis and continue through the flag leaf stage. Significant yield increases were recorded with the best AT characters despite evidence of modern rices to tolerate high damage levels. Reasons for this apparent paradox are discussed.

Parasitoids and Predators of Rice Insect Pests of Jorhat Districts of Assam

Parasitoids and predators of rice ecosystem recorded during 1999-2000 at three locations of Jorhat district of Assam are listed. Altogether 30 species of parasitoids and 26 species of predators were recorded along with their hosts, period of activity and relative abundance.

Translational Fusion Hybrid Bt Genes Confer Resistance against Yellow Stem Borer in Transgenic Elite Vietnamese Rice (Oryza sativa L.) Cultivars

We have shown the efficacies of translationally fused gene (cry1Ab‐1B) under the control of maize ubiquitin promoter and hybrid Bt gene (cry1A/cry1Ac) driven by rice Actin‐1 promoter against the yellow stem borer (Scirpophaga incertulas Walker, YSB) insect in rice (Oryza sativa L.). The integration, expression, and functionality of the transgenes were confirmed by Southern, western, and insect bioassay. The bioassay results correlated with the molecular data. The amount of Bt protein (within the range of 0.8–1.3% of the total soluble protein) in the transgenics was sufficient to cause 100% mortality of the neonate larvae of YSB within 1 wk of infestation. The transgenic plants expressing the foreign Bt protein were normal in phenotype with as good seed setting as the nontransgenic control plants.

Infestation of insect pests in tree-rice agroforestry system

The prevalence of insect pests was studied on rice BR11 (mukta) as understory crop grown in association with 11 years old selected tree species viz, Akashmoni, Jhau and Albida in the field laboratory of the Department of Agroforestry, Bangladesh Agricultural University (BAU), Mymensingh during the period from July to December, 2003. Among the three species Albida and Jhau possessed the largest canopy and there light penetration rate were high. On the other hand, Akashmoni had the lowest canopy but it penetrated low amount of light. Albida-rice association showed the lowest infestation of major rice insects followed by Jhau-rice association, while Akashmoni-rice association showed the highest insect infestation. Light intensity in the control plot (absent of tree species) was maximum and it caused minimum severity of insects infestation as compared to other associations. From the result it appeared that light interception has the relationship with insect population in rice. Therefore, tree species having sparse canopy which allowed easy penetration of sunlight is suitable for tree-rice agroforestry system.

A study on light trap catches of some rice pests in relation to meteorological factors

The effect of meteorological factors on the population build up of green leafhopper Nephotettix virescens Dist (Cicadellidae, Hemiptera), plant hoppers Cofana spectra Dist (Delphacidae, Hemiptera) and C. yasumatsui Young ( Kolla mimica , Hemiptera) and rice gundhi bug Leptocoriza acuta Thunberg (Alydidae, Hemiptera) in rice growing season (July to November) was studied through light trap collection during ten years (1988–1997). Maximum populations of Nephotettix virescens Dist (Cicadellidae, Hemiptera) and C. yasumatsui Young (Kolla mimica, Hemiptera) were recorded in the third week of October during all the years. Cofana spectra Dist had maintained peak activity in respect of population in the last week of September and third week of October. Leptocoriza acuta Thunberg (Alydidae, Hemiptera) had maximum population in second and third weeks of October during the aforesaid period. No meteorological factors have significant effect on the population build up of Nephotettix virescens Dist, Cofana spectra Dist and C. yasumatsui Young in the month of October. In the case of Leptocoriza acuta Thunberg, no other factor but rainfall had positive correlation of order 0.857 with population build up in the fourth week of September. Key words/phrases : Meteorological factors, path analysis, regression analysis, rice insect pests SINET: Ethiopian Journal of Science : Vol. 27 (2) 2004: 165–170