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Kenneth Wilson - One of the best experts on this subject based on the ideXlab platform.
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High levels of genetic diversity in Spodoptera exempta NPV from Tanzania
Journal of invertebrate pathology, 2010Co-Authors: Elizabeth Redman, Kenneth Wilson, David Grzywacz, Jenny S CoryAbstract:The African armyworm, Spodoptera exempta, is a major pest in sub-Saharan Africa. A nucleopolyhedrovirus (NPV) is often recorded in later population outbreaks and can cause very high levels of mortality. Research has been addressing whether this NPV can be developed into a strategic biological control agent. As part of this study, the variation in natural populations of NPV is being studied. An isolate of S. exempta NPV was cloned in vivo and found to contain at least 17 genetically-distinct genotypes. These genotypes varied in size from approximately 115 to 153 kb.
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Evaluation of Spodoptera exempta nucleopolyhedrovirus (SpexNPV) for the field control of African armyworm (Spodoptera exempta) in Tanzania
Crop Protection, 2008Co-Authors: David Grzywacz, Wilfred L. Mushobozi, Mark Parnell, Flavia Jolliffe, Kenneth WilsonAbstract:The African armyworm Spodoptera exempta is a major episodic migratory crop pest over much of Eastern and Southern Africa. Control of this pest has been reliant on the use of synthetic chemical insecticides. However, this approach fails to protect poor farmers and is becoming unacceptable for environmental and cost reasons. A programme of field trials was conducted in Tanzania to evaluate the endemic baculovirus, the S. exempta nucleopolyhedrovirus (SpexNPV), as an alternative control. Field trials demonstrated that both ground and aerial application of SpexNPV to armyworm outbreaks on pasture can initiate outbreaks of NPV disease and population collapses. The SpexNPV was effective when applied at 1×1012 occlusion bodies (OB) per hectare if applied to outbreaks early, when larvae are in I–III instar—mass mortalities appear 3–10 days post treatment. The data from these trials indicate that SpexNPV can have a potential role as a substitute for chemical insecticides in strategic armyworm management programmes.
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New approaches to improve the livelihoods of poor farmers and pastoralists in Tanzania through monitoring and control of African armyworm, Spodoptera exempta.
Aspects of applied biology, 2005Co-Authors: Wilfred L. Mushobozi, David Grzywacz, R. Musebe, M. Kimani, Kenneth WilsonAbstract:Summary A new strategy to control African armyworm in Tanzania, which combines forecasting of armyworm outbreaks with the utilisation of the natural disease of the armyworm, Spodoptera exempta nucleopolyhedrovirus (SpexNPV) has been developed and piloted in Tanzania. Community based armyworm forecasting (CBAF) has shown that village forecasters achieved a high level of forecasting accuracy, with 75% of all positive forecasts having corresponding outbreaks. Results from both ground and aerial applications have shown that SpexNPV is effective in controlling African armyworm if sprayed early in the outbreaks and thus could be used to replace chemical insecticides for armyworm control. Field trials indicate that SpexNPV could be produced by harvesting infected larvae from previously sprayed outbreaks. Thus, when combined with improved forecasting, SpexNPV could provide a new affordable and safe technique for the control of armyworm in Tanzania, and a new mechanism for the strategic control to this important migratory pest.
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baculovirus resistance in the noctuid Spodoptera exempta is phenotypically plastic and responds to population density
Proceedings of The Royal Society B: Biological Sciences, 1998Co-Authors: Kenneth Wilson, Andrew Reeson, Alan Gunn, Rosemary S Hails, Dave GoulsonAbstract:Parasite resistance mechanisms can be costly to maintain. We would therefore predict that organisms should invest in resistance only when it is likely to be required. Insects that show density-dependent phase polyphenism, developing different phenotypes at high and low population densities, have the opportunity to match their levels of investment in resistance with the likelihood of exposure to pathogens. As high population densities often precipitate disease epidemics, the high-density form should be selected to invest relatively more in resistance. We tested this prediction in larvae of the noctuid Spodoptera exempta. Larvae reared at a high density were found to be considerably more resistant to a nuclear polyhedrosis virus than those reared in isolation. A conspicuous feature of the high-density phase of S. exempta and other phase-polyphenic Lepidoptera is cuticular melanization. As melanization is controlled by the phenoloxidase enzyme system, which is also involved in the immune response, this suggests a possible mechanism for increased resistance at high population densities. We demonstrated that melanized S. exempta larvae were more resistant than non-melanized forms, independent of rearing density. We also found that haemolymph phenoloxidase activity was correlated with cuticular melanization, providing further evidence for a link between melanization and immunity. These results suggest that pathogen resistance in S. exempta is phenotypically plastic, and that the melanized cuticles characteristic of the high-density form may be indicative of a more active immune system.
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A Novel Method for Estimating the Pre-Reproductive Period of Female African Armyworm Moths, Spodoptera exempta
International Journal of Tropical Insect Science, 1993Co-Authors: Kenneth WilsonAbstract:In the majority of insects, migration occurs exclusively or predominantly during the pre-reproductive period (PRP) and therefore, the duration of the PRP provides a useful index of migratory potential. The present study describes a novel method for estimating the PRP of Spodoptera exempta (Walker) (Lepidoptera: Noctuidae). It relies on the fact that as the female approaches sexual maturity, there is a substantial change in the shape of her gonopore-patch (an area of black scales at the posterior of the abdomen). Gonopore-patch shape (GPS) is strongly correlated with PRP (as determined by “calling” behaviour) and may prove to be the best method for estimating migratory potential in some circumstances. A number of other species of moths also have gonopore-patches which may aid the study of their migration.
Danny Degheele - One of the best experts on this subject based on the ideXlab platform.
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The Significance of Pharmacokinetics and Metabolism to the Biological Activity of RH-5992 (Tebufenozide) in Spodoptera exempta, Spodoptera exigua, and Leptinotarsa decemlineata
Pesticide Biochemistry and Physiology, 1994Co-Authors: Guy Smagghe, Danny DegheeleAbstract:Abstract Toxicity assays indicated that RH-5992 (tebufenozide), a novel synthetic nonsteroidal ecdysteroid agonist, induces a premature, abnormal, and lethal molt in last instar larvae of the African armyworm, Spodoptera exempta (Walker), and the beet armyworm, Spodoptera exigua (Hubner), by means of an oral application. However, toxicity values differed markedly between the two species. The LC 50 value for S. exempta was 0.034 mg/liter compared to 2.5 mg/liter for S. exigua . On the other hand, RH-5992 had no significant effect on larval growth, development, or adult formation of last instar larvae of the Colorado potato beetle, Leptinotarsa decemlineata (Say), at concentrations up to 50 mg/liter. However, at 100 mg/liter, neurotoxic effects were observed in some cases. To explain the different toxicity to both Spodoptera spp. and L. decemlineata , pharmacokinetics and metabolic detoxification of 14 C-labeled RH-5992 have been determined. In all three insect species excretion of the absorbed compound was high, with a 50% excretion time of 2-3 hr after oral uptake. Data on distribution and metabolism of [ 14 C]RH-5992 suggest that the observed different biological activity in both Spodoptera spp. and L. decemlineata cannot be attributed to pharmacokinetic and metabolic differences.
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Toxicity of benzoylphenylureas to the African armyworm Spodoptera exempta (Walker)
Crop Protection, 1993Co-Authors: Danny Degheele, C BaiAbstract:Abstract Four benzoylphenylureas, assessed under laboratory conditions, have a high level of activity against third-instar larvae of Spodoptera exempta (Lepidoptera: Noctuidae). The LC 50 values were 0.013, 0.035, 0.074 and 0.138 μg ml −1 48 h after exposure; 0.006, 0.007, 0.035 and 0.062 μg ml −1 72 h after exposure and 0.001, 0.004, 0.013 and 0.010 μg ml −1 96 h after exposure for teflubenzuron, hexaflumuron, flufenoxuron and diflubenzuron, respectively. In relation to ovicidal activity, the LC 50 values were 0.186, 0.490, 0.947 and 5.834 μg ml −1 to eggs 0–24 h old and 0.420, 1.085, 5.966 and 18.493 μg ml −1 to eggs 24–48 h old, for hexaflumuron, flufenoxuron, teflubenzuron and diflubenzuron, respectively. The LC 95 value for hexaflumuron was −1 to the eggs. Teflubenzuron, hexaflumuron, flufenoxuron and diflubenzuron are extremely effective pesticides and can be tested against larvae of S. exempta in the field. Hexaflumuron, flufenoxuron and teflubenzuron can also be tested for their ovicidal activity.
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Activity of insecticidal crystal proteins and strains of Bacillus thuringiensis against Spodoptera exempta (Walker)
Journal of Invertebrate Pathology, 1993Co-Authors: C Bai, Danny Degheele, S Jansens, B LambertAbstract:Spodoptera exempta is an important pest in many parts of Africa. Activities of seven purified insecticidal crystal proteins (ICPs) and different strains of Bacillus thuringiensis were determined against larvae of S. exempta . CryIC and CryIE were highly toxic to first-instar larvae; the LC50 values were 0.38 and 0.33 μg/ml, respectively. The LC50 of CryIE was 10-fold higher for third-instar larvae. The other five ICPs all showed an inhibition of the larval growth, but no (CryIA(c)) or a low mortality (CryIA(a), CryIA(b), CryIB, and CryID). Two new strains (B-2 90 and B-1 ke) with a high level of activity and fast action against this pest were found and characterized. The LC50 values of the lyophilized powder of a spore-crystal mixture were 6.7 μg/ml for B-2 90 and 7.8 μg/ml against third-instar larvae 72 hr after exposure. An analysis of the immunotypes of the crystal proteins by ELISA techniques showed that these two strains produced the CryIA(b) and CryIE proteins. Thus a direct correlation exists between the ICP content of a strain and S. exempta activity; strains producing CryIC or CryIE are highly active.
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Metabolism, pharmacokinetics, and toxicity of the first nonsteroidal ecdysteroid agonist RH 5849 to Spodoptera exempta (Walker), Spodoptera exigua (Hübner), and Leptinotarsa decemlineata (Say)
Pesticide Biochemistry and Physiology, 1993Co-Authors: Guy Smagghe, Danny DegheeleAbstract:Abstract RH 5849 is the first nonsteroidal ecdysteroid agonist which induced prematurely an abnormal and subsequently lethal larval moult in larvae of the two lepidopteran species, Spodoptera exempta and Spodoptera exigua . Mortality in larvae of the coleopteran, Leptinotarsa decemlineata , was scored after inhibition of a normal ecdysis or an evolving abnormal and lethal ecdysis. The toxicity of RH 5849 to the two Spodoptera spp. differed markedly. S. exempta was about 50 times more susceptible than S. exigua larvae: LC 50 values in S. exempta larvae of 2nd to 5th and of 6th instar were about 7.5 and 1.8 mg/liter and in S. exigua larvae of 2nd to 4th and of 5th instar 195 and 110 mg/liter. In L. decemlineata , LC 50 values were about 5.5 and 1.8 mg/liter for larvae of 1st to 3rd and of 4th instar. To explain such differences in biological activity of RH 5849 in the three insects, its retention, distribution, and metabolism have been measured. Larvae of S. exempta , S. exigua , and L. decemlineata fed [ 14 C]RH 5849 rapidly absorbed the radiolabel. Excretion of absorbed compound was also high, with a 50% excretion time of approximately 3, 2, and 6 hr after intake in the three respective insects. Following the product in the larval body, a total of 9 and 6%, 8 and 13%, 30 and 26% of the applied dose had penetrated 6 hr after intake into the hemolymph and the cuticle of S. exempta , S. exigua , and L. decemlineata , respectively. In the gut, about 8, 5, and 15% of the applied dose had remained at the same time in the three respective species. After intake, the product also seemed to be metabolically quite stable. Six hours after intake, about 11, 14, and 36% was recovered as parent compound in the larval body of S. exempta , S. exigua , and L. decemlineata , respectively. About 3, 12, and 16% of the applied dose was still present as unchanged RH 5849 in the body of the three respective insects 24 hr after intake. The obtained results suggest that the observed differences in biological activity of RH 5849 to S. exempta , S. exigua , and L. decemlineata cannot be attributed to differences in retention, distribution, and metabolic detoxication in the larval body.
A. G. Gatehouse - One of the best experts on this subject based on the ideXlab platform.
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Seasonal and geographical variation in the migratory potential of outbreak populations of the African armyworm moth, Spodoptera exempta
The Journal of Animal Ecology, 1993Co-Authors: Kenneth Wilson, A. G. GatehouseAbstract:Implicit in a genetic model to explain variation in the migratory potential of outbreak populations of Spodoptera exempta (Lepidoptera: Noctuidae) are predictions regarding the temporal and spatial incidence of migratory phenotypes based on the pattern of rainfall through the season. Migration in female S. exempta moths occurs predominantly in immature adults, therefore migratory potential is assumed to correlate with the duration of the pre-reproductive period (PRP). PRP variation in moths was quantified from 14 outbreak sites in E Africa during the 1989-90 and 1990-91 seasons and correlating this with rainfall prevalences. Extensive intra- and inter-population variation in PRP was observed. Mean PRP was inversely correlated with prevalence of rainfall at the outbreak site during the month that the moths initiating the outbreaks were migrating: longest PRPs were exhibited by moths originating from early season outbreaks in regions of low, variable rainfall, shortest PRPs by moths from areas of high, consistent rainfall. Also as predicted by the model, the mean PRP of moths from outbreaks in Kenya and Tanzania tended to decline through the long rainy season, significantly so for females. Males matured consistently earlier than females. PRP variation cannot be accounted for by any major environmental factor, suggesting that the differences between samples are genetic in origin. -from Authors
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Migration and genetics of pre-reproductive period in the moth, Spodoptera exempta (African armyworm)
Heredity, 1992Co-Authors: Kenneth Wilson, A. G. GatehouseAbstract:Migration in insects occurs predominantly, or exclusively, in sexually immature adults. Therefore, the duration of the pre-reproductive period (PRP) sets an upper limit on an individual's migratory potential and has been measured by a number of authors interested in insect migration. Significant differences in PRP between field populations of the African armyworm moth Spodoptera exempta (Walker) (Lepidoptera: Noctuidae) are suggestive of a genetic basis to PRP regulation. The present study examines the genetics of PRP in more detail using selection and sib-analysis experiments. Both sets of experiments suggest a strong genetic component to PRP regulation in female moths, but little or none in males. Moreover, the sib-analysis experiments indicate that the X-chromosome has a disproportionate influence on PRP in females (the heterogametic sex in Lepidoptera). These results are discussed in relation to the migration biology of this species.
Guy Smagghe - One of the best experts on this subject based on the ideXlab platform.
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The Significance of Pharmacokinetics and Metabolism to the Biological Activity of RH-5992 (Tebufenozide) in Spodoptera exempta, Spodoptera exigua, and Leptinotarsa decemlineata
Pesticide Biochemistry and Physiology, 1994Co-Authors: Guy Smagghe, Danny DegheeleAbstract:Abstract Toxicity assays indicated that RH-5992 (tebufenozide), a novel synthetic nonsteroidal ecdysteroid agonist, induces a premature, abnormal, and lethal molt in last instar larvae of the African armyworm, Spodoptera exempta (Walker), and the beet armyworm, Spodoptera exigua (Hubner), by means of an oral application. However, toxicity values differed markedly between the two species. The LC 50 value for S. exempta was 0.034 mg/liter compared to 2.5 mg/liter for S. exigua . On the other hand, RH-5992 had no significant effect on larval growth, development, or adult formation of last instar larvae of the Colorado potato beetle, Leptinotarsa decemlineata (Say), at concentrations up to 50 mg/liter. However, at 100 mg/liter, neurotoxic effects were observed in some cases. To explain the different toxicity to both Spodoptera spp. and L. decemlineata , pharmacokinetics and metabolic detoxification of 14 C-labeled RH-5992 have been determined. In all three insect species excretion of the absorbed compound was high, with a 50% excretion time of 2-3 hr after oral uptake. Data on distribution and metabolism of [ 14 C]RH-5992 suggest that the observed different biological activity in both Spodoptera spp. and L. decemlineata cannot be attributed to pharmacokinetic and metabolic differences.
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Metabolism, pharmacokinetics, and toxicity of the first nonsteroidal ecdysteroid agonist RH 5849 to Spodoptera exempta (Walker), Spodoptera exigua (Hübner), and Leptinotarsa decemlineata (Say)
Pesticide Biochemistry and Physiology, 1993Co-Authors: Guy Smagghe, Danny DegheeleAbstract:Abstract RH 5849 is the first nonsteroidal ecdysteroid agonist which induced prematurely an abnormal and subsequently lethal larval moult in larvae of the two lepidopteran species, Spodoptera exempta and Spodoptera exigua . Mortality in larvae of the coleopteran, Leptinotarsa decemlineata , was scored after inhibition of a normal ecdysis or an evolving abnormal and lethal ecdysis. The toxicity of RH 5849 to the two Spodoptera spp. differed markedly. S. exempta was about 50 times more susceptible than S. exigua larvae: LC 50 values in S. exempta larvae of 2nd to 5th and of 6th instar were about 7.5 and 1.8 mg/liter and in S. exigua larvae of 2nd to 4th and of 5th instar 195 and 110 mg/liter. In L. decemlineata , LC 50 values were about 5.5 and 1.8 mg/liter for larvae of 1st to 3rd and of 4th instar. To explain such differences in biological activity of RH 5849 in the three insects, its retention, distribution, and metabolism have been measured. Larvae of S. exempta , S. exigua , and L. decemlineata fed [ 14 C]RH 5849 rapidly absorbed the radiolabel. Excretion of absorbed compound was also high, with a 50% excretion time of approximately 3, 2, and 6 hr after intake in the three respective insects. Following the product in the larval body, a total of 9 and 6%, 8 and 13%, 30 and 26% of the applied dose had penetrated 6 hr after intake into the hemolymph and the cuticle of S. exempta , S. exigua , and L. decemlineata , respectively. In the gut, about 8, 5, and 15% of the applied dose had remained at the same time in the three respective species. After intake, the product also seemed to be metabolically quite stable. Six hours after intake, about 11, 14, and 36% was recovered as parent compound in the larval body of S. exempta , S. exigua , and L. decemlineata , respectively. About 3, 12, and 16% of the applied dose was still present as unchanged RH 5849 in the body of the three respective insects 24 hr after intake. The obtained results suggest that the observed differences in biological activity of RH 5849 to S. exempta , S. exigua , and L. decemlineata cannot be attributed to differences in retention, distribution, and metabolic detoxication in the larval body.
B Lambert - One of the best experts on this subject based on the ideXlab platform.
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Activity of insecticidal crystal proteins and strains of Bacillus thuringiensis against Spodoptera exempta (Walker)
Journal of Invertebrate Pathology, 1993Co-Authors: C Bai, Danny Degheele, S Jansens, B LambertAbstract:Spodoptera exempta is an important pest in many parts of Africa. Activities of seven purified insecticidal crystal proteins (ICPs) and different strains of Bacillus thuringiensis were determined against larvae of S. exempta . CryIC and CryIE were highly toxic to first-instar larvae; the LC50 values were 0.38 and 0.33 μg/ml, respectively. The LC50 of CryIE was 10-fold higher for third-instar larvae. The other five ICPs all showed an inhibition of the larval growth, but no (CryIA(c)) or a low mortality (CryIA(a), CryIA(b), CryIB, and CryID). Two new strains (B-2 90 and B-1 ke) with a high level of activity and fast action against this pest were found and characterized. The LC50 values of the lyophilized powder of a spore-crystal mixture were 6.7 μg/ml for B-2 90 and 7.8 μg/ml against third-instar larvae 72 hr after exposure. An analysis of the immunotypes of the crystal proteins by ELISA techniques showed that these two strains produced the CryIA(b) and CryIE proteins. Thus a direct correlation exists between the ICP content of a strain and S. exempta activity; strains producing CryIC or CryIE are highly active.