This study examines the impact of participatory forest management (PFM) on forest-adjacent househ... more This study examines the impact of participatory forest management (PFM) on forest-adjacent household livelihoods in the Arabuko-Sokoke forest in Kenya. It compares the impacts on households near PFM forests (PFM zones) with those near forests with no participatory management (non-PFM zones). The study questions were: does conservation of the Arabuko-Sokoke forest result in net household incomes?; does PFM increase net household benefits?; and are household benefits uniformly distributed within the 5 km PFM intervention zone? The hypotheses tested were: forest conservation benefits exceed forest conservation costs; PFM zones have higher household benefits than non-PFM zones; and benefits and costs reduce with distance from forest edge. In the year 2009, we collected data on household benefits and costs in PFM and non-PFM zones. Data were collected along 10 km transects at 1 km intervals, sampling 600 households up to 5 km away from the forest. The results show varied household dependence on the Arabuko-Sokoke forest. The forest benefits exceed costs in PFM zones but the forest is a cost in non-PFM zones, and costs and benefits reduce with distance from forest edge. The study concludes that, though not cheap, PFM is a tool that can help the Arabuko-Sokoke forest win the support of the adjacent local communities.
Comparing of morphological character variation within taxa continues to play an important role in... more Comparing of morphological character variation within taxa continues to play an important role in improving species inventories. Using morphometrical and non-meristic morphological adult characters, the diversity of the genus Ptychadena in Taita Hills was studied. Comparative material from elsewhere was not used, and therefore species names were only provisionally allocated to the taxa identified. Avail- able names were discussed on the basis of comparisons with morphological data from other regions. The results revealed that female species are larger in size than males. Two species were identified and for each a standardized diagnosis of 32 characters is provided. Comparison of results with morphological data from related studies done elsewhere reveals that certain characters are of critical importance in differentiating the two Ptychadena species. The power of these morphological characters is discussed, especially for the background of rapid and easy identification of Ptychadena ...
Bees provide important pollination services that maintain native plant populations and ecosystem ... more Bees provide important pollination services that maintain native plant populations and ecosystem resilience, which is critical to the conservation of the rich and endemic biodiversity of Kaya forests along the Kenyan Coast. This study examined bee composition and floral resources from the forest core to the surrounding farmlands around Kaya Muhaka forest. In total, 755 individual bees, representing 41 species from three families were recorded: Apidae, Halictidae and Megachilidae. Overall, Apidae were the most abundant with a proportion of 76% of the total bee individuals, Halictidae at 14% and Megachilidae at 10%. Bee composition was similar between forest edge and crop fields as compared to forest core and fallow farmlands. We found a significant decrease in bee diversity with increasing distance from the forest to the surrounding farming area. A high abundance of bees was recorded in fallow farmland, which could be explained by the high abundance of floral resources in the habitat...
Surveys for predators of the tomato red spider mite Tetranychus evansi Baker & Pritchard on solan... more Surveys for predators of the tomato red spider mite Tetranychus evansi Baker & Pritchard on solanaceous plants were carried out in north-eastern and south-eastern Brazil to determine prospective species for the control of the pest in Africa. Surveys were carried out in areas identified as climatically similar to regions in Africa where T. evansi has been reported as a pest and where prospective natural enemies may be introduced. A total of 56,445 mites and insects were found in 330 samples collected from 20 different species of solanaceous plants. Tetranychus evansi was found in only three samples, on Solanum americanum Mill. and Lycopersicon esculentum Mill.. A total of 5,023 specimens of predatory mites, of at least 44 species, and 494 specimens of acarophagous insects, of at least three species were collected. The predominant predatory mites were (in decreasing order): Phytoseius guianensis DeLeon, Pronematus ubiquitus (McGregor), Asca sp., Paraphytoseius orientalis (Narayanan, K...
ABSTRACT The effect of maize-leucaena agroforestry system on the abundance and activity of natura... more ABSTRACT The effect of maize-leucaena agroforestry system on the abundance and activity of natural enemies of maize stem borers was evaluated. The study covered 6 cropping seasons from September 1992 to August 1995 and was conducted at both Mtwapa and Amoyo in coastal and western Kenya, respectively. Treatments included monocropped and intercropped (maize [Zea mays], leucaena [Lencaena leucocephala]) plots, weeded and unweeded, mulched and unmulched plots, and 3 spacing regimes (1.5, 2.25, 3.0 m) for leucaena hedgerows. Maize was interplanted at the onset of each rainy season. Rates of egg parasitism by Trichogramma sp. and Telenomus sp. were not affected by intercropping, but decreased with increased hedgerow spacing. Significantly more egg batches were preyed upon in the maize monoculture plots. Parasitoids recovered included the larval parasitiods Cotesia sesamiae (Cameron), Cotesia flavipes Cameron, Cotesia rufricus (Haliday), Glyptapanteles africanus (Cameron), Goniozus indicus Ashmead, Chelonus curvimaculatus Cameron, unidentified Cotesia sp. and Syzeuctus sp., the pupal parasitoid Pediobius furous Gahan, and the hyperparsitoid Aphanogmus fijiensis (Ferrière). Larval and pupal parasitism at Mtwapa were unaffected by the vegetation structure or cultural treatment. However, at Amoyo, the percentage of stem borer larvae and pupae parasitized were significantly greater in the maize monocrop plot than in the intercropped plots, whereas parasitism also significantly increased with increasing hedgerow spacing. However, at both sites, larval and pupal mortality were unaffected by the vegetation structure. The oviposition preference of the predatory Chrysopa species was not influenced by the cropping system.
The rotation of leguminous shrubs and crops is being tested on farms and recommended as a means o... more The rotation of leguminous shrubs and crops is being tested on farms and recommended as a means of improving soil fertility and increasing crop yield in eastern and southern Africa, including western Kenya. However, this improved fallow practice may also increase the nematode population in the soil. An experiment was conducted to monitor the effects of plant-parasitic nematodes on crops after improved fallow. Soil was collected from a maize (Zea mays L.)/bean (Phaseolus vulgaris L.) field, a natural fallow, a Crotalaria (Crotalaria grahamiana Wight & Arn.) fallow, a Tephrosia (Tephrosia vogelii Hook. f.) fallow and a Crotalaria-Tephrosia mixed fallow and used to fill plastic pots placed in a shade. Three successive crop cycles of 2 months were tested in these pots using maize and beans, the most important staple foods in western Kenya. In the first cycle, beans grew poorly on the Tephrosia and Crotalaria-Tephrosia soil due to the high incidence of root knot nematodes, Meloidogyne spp., while maize did not suffer any loss. Although the populations of root knot nematodes reduced drastically in the second and third cycles, both maize and beans experienced heavy losses on the soil under improved fallow probably due to the spiral nematodes, Scutellonema spp., which became dominant in the nematode communities. Despite the use of fertilisers (N, P, K), both crops became highly sensitive to spiral nematodes in the third cycle because of the degradation of the soil physical properties. The study showed that the benefits of improved fallows in terms of crop production may be limited by the high number of plant-parasitic nematodes they help develop in the process.
Studies were conducted between 2002 and 2004 in experimental plots at two sites in western Kenya ... more Studies were conducted between 2002 and 2004 in experimental plots at two sites in western Kenya and one site in South Africa, to assess the potential role of the 'push-pull' strategy in stemborer resistance management in Bt-maize through its influence on the pests' oviposition and mortality from predation. Experiments in Kenya were conducted with non-Bt-maize while a combination of Bt-maize (expressing Cry1Ab proteins) and its non-Bt-maize isoline was used in South Africa. Treatments comprised of a maize monocrop and an intercrop of maize and desmodium, with Napier grass as a trap crop around the field in each site ('push-pull'). A combination of natural and artificial infestation procedures were employed. Oviposition preference and predation rates of naturally infested stemborer eggs were assessed. Screen house-reared plants (non-Bt-maize) were infested with eggs, early-instar larvae, late-instar larvae and pupae of Busseola fusca and Chilo partellus in natural enemy exclusion studies. Significantly more egg batches were oviposited in the maize monocrop than in the 'pushpull' plots by C. partellus, but not B. fusca. Predation rates of the naturally oviposited C. partellus eggs were significantly higher in the 'push-pull' than in the maize monocrop plots, but not different with B. fusca eggs. Disappearance rates of C. partellus eggs on control plants (those exposed to predators), attributable to predatory activity, was significantly higher in control than exclusion plants and similarly higher in the 'push-pull' than in the maize monocrop plots. There were no differences in disappearance rates of B. fusca eggs between treatments. Recovery of early-instar larvae was generally low for both species, similar between control and exclusion plants, but significantly lower in the 'push-pull' plots in one of the sites. Recovery of late-instar larvae and pupae in control plants was similar between the two cropping systems for both species. The study revealed reduced oviposition by C. partellus and enhanced predatory activity on C. partellus eggs in the 'push-pull' system, pointing to the system becoming a component in Bt resistance management for the pest.
... DOI: 10.1080/09670870701613743 Gashawbeza Ayalew a * , Andrea Sciarretta b , Johan Baumgärtne... more ... DOI: 10.1080/09670870701613743 Gashawbeza Ayalew a * , Andrea Sciarretta b , Johan Baumgärtner c , Callistus Ogol d & Bernhard Löhr e pages 31-38. ... At the field level, the DBM population tended to remain within the cabbage field. ...
Purpose: To determine the potential benefits of nine medicinal plants used by the Samburu communi... more Purpose: To determine the potential benefits of nine medicinal plants used by the Samburu community for the treatment of tuberculosis. Methods: The extract was tested against four strains of Mycobacteria namely; Mycobacterium tuberculosis (Mtb), M. Kansasii (Mk), M. fortuitum (Mf), and M. smegmatis (Ms) using BACTEC MGIT 960 system. The crude extracts were also analyzed for the presence of phytochemical constituents. Results: Both the extracts of Scadoxus multiflorus and Acacia nilotica showed strong antimycobacterial activity against the four tuberculosis-causing strains. Eurphobia scarlatina was the most active against both the slow (Mtb and Mk) and the fast (Mf and Ms) growers with Zero GUs at 0.5mg/ml. Phytochemical screening indicated presence or absence of tannins, saponins and flavonoids, terpenoids, cardiac glycosides and alkaloids in the extracts. Conclusion: The data suggest that some of the methanol extracts could be a rich source of antituberculosis agents. The results further show that there is some merit in the use of some of the plants studied in alternative medical practice. Pharmacological and toxicological studies of the active plants are still under investigation.
The bionomics of Stethorus tridens Gordon fed Tetranychus evansi Baker & Pritchard were studied i... more The bionomics of Stethorus tridens Gordon fed Tetranychus evansi Baker & Pritchard were studied in the laboratory. The number of prey consumed by S. tridens increased with increasing instar levels and the total mean number consumed during immature development was 184.1 ± 18.02 T. evansi nymphs per individual. For adult male and adult female, the daily consumption was 41.3 ± 0.80 and 67.8 ± 1.69 nymphs, respectively. Stethorus tridens successfully developed to adulthood between 20 and 30°C but failed at 10, 15 and 35°C. The lower thermal threshold for egg-to-adult development estimated via linear regression and the modified Logan model was 9.2 and 8.1°C, respectively. The optimum and maximum temperatures for egg-to-adult development were around 29-31 and 32.9°C, respectively. Egg to adult development time was 23.8 ± 0.24, 17.4 ± 0.22, 16.2 ± 0.22 and 12.1 ± 0.16 days at 20, 24, 27 and 30°C, respectively. At 27°C, the sex ratio, expressed as the proportion of females, was 0.54 and the mean preoviposition, oviposition and postoviposition periods were 10.3 ± 0.67, 31.2 ± 4.74 and 30.2 ± 5.24 days, respectively. The oviposition rate was 4.0 ± 0.16 eggs/female/day with a female mean longevity of 71.6 ± 6.19 days and an intrinsic rate of natural increase of 0.104. The potential of S. tridens as a candidate natural enemy of T. evansi is discussed.
The influence of agroforestry practices on the temporal fluctuation of nematodes was studied in w... more The influence of agroforestry practices on the temporal fluctuation of nematodes was studied in western Kenya. The experiment comprised a fallow phase, which had the following treatments: (1) maize/beans intercropping; (2) maize/beans intercropping with rock phosphate; (3) Crotalaria fallow; (4) Crotalaria fallow with rock phosphate; (5) Crotalaria fallow with rock phosphate (+ Calliandra and napier hedges); and a cultivation phase when all plots were planted to maize and beans. There were strong seasonal fluctuations in the abundance of both free-living and plant-parasitic nematodes. The abundance of plant-parasitic nematodes did not vary among cropping systems during the fallow phase, but varied significantly during the cultivation phase of the experiment. Pratylenchus spp. appeared to be stimulated by the application of phosphorus while Scutellonema spp. had higher populations in the maize crops, which were planted after a Crotalaria fallow. In both the fallow and the cultivation phases, the sampling date had a significant impact on nematode abundance. There were more plant-parasitic nematode species during the fallow phase of the study, but the evenness of the different nematode communities was significantly greater in the cultivation phase of the experiment.
We investigated the influence of temperature and infestation sequence on interspecific competitio... more We investigated the influence of temperature and infestation sequence on interspecific competition between two fruit flies: an invasive (Bactrocera invadens Drew, Tsuruta & White, (B) and a native (Ceratitis cosyra Walker, C) (both Diptera: Tephritidae) species. Mango fruits [Mangifera indica L. (Anacardiaceae)] were co-infested with larvae at different constant temperatures (15, 20, 25, and 30°C) and relative humidity of 50 ± 8%, using different infestation sequences at each temperature (BC together; BC ⁄ CB 1, 2, and 3 days apart). There were significant effects of competition in most experimental treatments, resulting in reduced larval survival, pupal mass, and adult emergence for both species. At most of the infestation ⁄ temperature combinations, C. cosyra was clearly the inferior competitor. The only exception was at 20°C when the outcome depended on the sequence of infestation: no C. cosyra survived when the sequence was BC, but more C. cosyra than B. invadens survived when it was CB. At 15°C, all C. cosyra larvae died, while the development of B. invadens was prolonged and adult emergence reduced. We conclude that resource pre-emption and fluctuations in temperature in mango agroecosystems help to explain observed shifts in dominance between B. invadens and C. cosyra on mango in many parts of Africa. The small window of competitive superiority for C. cosyra at 20°C and CB infestation sequence, together with other factors such as fecundity and alternative hosts, may allow for coexistence in some environments.
Natural enemies respond to herbivore-induced plant volatiles (HIPVs), but an often overlooked asp... more Natural enemies respond to herbivore-induced plant volatiles (HIPVs), but an often overlooked aspect is that there may be genotypic variation in these ÔindirectÕ plant defence traits within plant species. We found that egg deposition by stemborer moths (Chilo partellus) on maize landrace varieties caused emission of HIPVs that attract parasitic wasps. Notably, however, the oviposition-induced release of parasitoid attractants was completely absent in commercial hybrid maize varieties. In the landraces, not only were egg parasitoids (Trichogramma bournieri) attracted but also larval parasitoids (Cotesia sesamiae). This implies a sophisticated defence strategy whereby parasitoids are recruited in anticipation of egg hatching. The effect was systemic and caused by an elicitor, which could be extracted from egg materials associated with attachment to leaves. Our findings suggest that indirect plant defence traits may have become lost during crop breeding and could be valuable in new resistance breeding for sustainable agriculture.
We assessed the non-target effects of a habitat management system ('push-pull') on maize stembore... more We assessed the non-target effects of a habitat management system ('push-pull') on maize stemborer specialist natural enemy activity and soil Collembola. Two study sites in western Kenya were sampled. There were two treatments at each site, maize monocrop and 'push-pull'. The latter comprised an intercrop of maize and Desmodium, Desmodium uncinatum Jacq., with Napier grass, Pennisetum purpureum (Schumach), as a trap crop planted around the edge of the plot (spaced 1 m from main crop). Trichogramma spp. were recovered from stemborer eggs while Cotesia sesamiae and Cotesia flavipes were recovered from stemborer larvae, and Dentichasmias busseolae from pupae. Mean number of eggs parasitized was significantly higher in the maize monocrop than in the 'push-pull' plots however proportions parasitized did not differ between the two systems. The number of larvae and pupae parasitized and dead from causes other than parasitism similarly did not differ between cropping systems. Proportions of larvae and pupae parasitized were significantly higher in the 'push-pull' than in the monocrop plots, indicating that the activity of larval and pupal parasitoids was enhanced. C. sesamiae female wasps were attracted to the volatiles from Desmodium flowers but not those from the leaves in a four-arm olfactometer bioassay. A total of 1530 individual Collembola in seven families were recovered from the plots. The 'push-pull' strategy did not have any significant effect on Collembola abundance and dominance. The factors underlying these observations and their implications are discussed.
This study examines the impact of participatory forest management (PFM) on forest-adjacent househ... more This study examines the impact of participatory forest management (PFM) on forest-adjacent household livelihoods in the Arabuko-Sokoke forest in Kenya. It compares the impacts on households near PFM forests (PFM zones) with those near forests with no participatory management (non-PFM zones). The study questions were: does conservation of the Arabuko-Sokoke forest result in net household incomes?; does PFM increase net household benefits?; and are household benefits uniformly distributed within the 5 km PFM intervention zone? The hypotheses tested were: forest conservation benefits exceed forest conservation costs; PFM zones have higher household benefits than non-PFM zones; and benefits and costs reduce with distance from forest edge. In the year 2009, we collected data on household benefits and costs in PFM and non-PFM zones. Data were collected along 10 km transects at 1 km intervals, sampling 600 households up to 5 km away from the forest. The results show varied household dependence on the Arabuko-Sokoke forest. The forest benefits exceed costs in PFM zones but the forest is a cost in non-PFM zones, and costs and benefits reduce with distance from forest edge. The study concludes that, though not cheap, PFM is a tool that can help the Arabuko-Sokoke forest win the support of the adjacent local communities.
Comparing of morphological character variation within taxa continues to play an important role in... more Comparing of morphological character variation within taxa continues to play an important role in improving species inventories. Using morphometrical and non-meristic morphological adult characters, the diversity of the genus Ptychadena in Taita Hills was studied. Comparative material from elsewhere was not used, and therefore species names were only provisionally allocated to the taxa identified. Avail- able names were discussed on the basis of comparisons with morphological data from other regions. The results revealed that female species are larger in size than males. Two species were identified and for each a standardized diagnosis of 32 characters is provided. Comparison of results with morphological data from related studies done elsewhere reveals that certain characters are of critical importance in differentiating the two Ptychadena species. The power of these morphological characters is discussed, especially for the background of rapid and easy identification of Ptychadena ...
Bees provide important pollination services that maintain native plant populations and ecosystem ... more Bees provide important pollination services that maintain native plant populations and ecosystem resilience, which is critical to the conservation of the rich and endemic biodiversity of Kaya forests along the Kenyan Coast. This study examined bee composition and floral resources from the forest core to the surrounding farmlands around Kaya Muhaka forest. In total, 755 individual bees, representing 41 species from three families were recorded: Apidae, Halictidae and Megachilidae. Overall, Apidae were the most abundant with a proportion of 76% of the total bee individuals, Halictidae at 14% and Megachilidae at 10%. Bee composition was similar between forest edge and crop fields as compared to forest core and fallow farmlands. We found a significant decrease in bee diversity with increasing distance from the forest to the surrounding farming area. A high abundance of bees was recorded in fallow farmland, which could be explained by the high abundance of floral resources in the habitat...
Surveys for predators of the tomato red spider mite Tetranychus evansi Baker & Pritchard on solan... more Surveys for predators of the tomato red spider mite Tetranychus evansi Baker & Pritchard on solanaceous plants were carried out in north-eastern and south-eastern Brazil to determine prospective species for the control of the pest in Africa. Surveys were carried out in areas identified as climatically similar to regions in Africa where T. evansi has been reported as a pest and where prospective natural enemies may be introduced. A total of 56,445 mites and insects were found in 330 samples collected from 20 different species of solanaceous plants. Tetranychus evansi was found in only three samples, on Solanum americanum Mill. and Lycopersicon esculentum Mill.. A total of 5,023 specimens of predatory mites, of at least 44 species, and 494 specimens of acarophagous insects, of at least three species were collected. The predominant predatory mites were (in decreasing order): Phytoseius guianensis DeLeon, Pronematus ubiquitus (McGregor), Asca sp., Paraphytoseius orientalis (Narayanan, K...
ABSTRACT The effect of maize-leucaena agroforestry system on the abundance and activity of natura... more ABSTRACT The effect of maize-leucaena agroforestry system on the abundance and activity of natural enemies of maize stem borers was evaluated. The study covered 6 cropping seasons from September 1992 to August 1995 and was conducted at both Mtwapa and Amoyo in coastal and western Kenya, respectively. Treatments included monocropped and intercropped (maize [Zea mays], leucaena [Lencaena leucocephala]) plots, weeded and unweeded, mulched and unmulched plots, and 3 spacing regimes (1.5, 2.25, 3.0 m) for leucaena hedgerows. Maize was interplanted at the onset of each rainy season. Rates of egg parasitism by Trichogramma sp. and Telenomus sp. were not affected by intercropping, but decreased with increased hedgerow spacing. Significantly more egg batches were preyed upon in the maize monoculture plots. Parasitoids recovered included the larval parasitiods Cotesia sesamiae (Cameron), Cotesia flavipes Cameron, Cotesia rufricus (Haliday), Glyptapanteles africanus (Cameron), Goniozus indicus Ashmead, Chelonus curvimaculatus Cameron, unidentified Cotesia sp. and Syzeuctus sp., the pupal parasitoid Pediobius furous Gahan, and the hyperparsitoid Aphanogmus fijiensis (Ferrière). Larval and pupal parasitism at Mtwapa were unaffected by the vegetation structure or cultural treatment. However, at Amoyo, the percentage of stem borer larvae and pupae parasitized were significantly greater in the maize monocrop plot than in the intercropped plots, whereas parasitism also significantly increased with increasing hedgerow spacing. However, at both sites, larval and pupal mortality were unaffected by the vegetation structure. The oviposition preference of the predatory Chrysopa species was not influenced by the cropping system.
The rotation of leguminous shrubs and crops is being tested on farms and recommended as a means o... more The rotation of leguminous shrubs and crops is being tested on farms and recommended as a means of improving soil fertility and increasing crop yield in eastern and southern Africa, including western Kenya. However, this improved fallow practice may also increase the nematode population in the soil. An experiment was conducted to monitor the effects of plant-parasitic nematodes on crops after improved fallow. Soil was collected from a maize (Zea mays L.)/bean (Phaseolus vulgaris L.) field, a natural fallow, a Crotalaria (Crotalaria grahamiana Wight & Arn.) fallow, a Tephrosia (Tephrosia vogelii Hook. f.) fallow and a Crotalaria-Tephrosia mixed fallow and used to fill plastic pots placed in a shade. Three successive crop cycles of 2 months were tested in these pots using maize and beans, the most important staple foods in western Kenya. In the first cycle, beans grew poorly on the Tephrosia and Crotalaria-Tephrosia soil due to the high incidence of root knot nematodes, Meloidogyne spp., while maize did not suffer any loss. Although the populations of root knot nematodes reduced drastically in the second and third cycles, both maize and beans experienced heavy losses on the soil under improved fallow probably due to the spiral nematodes, Scutellonema spp., which became dominant in the nematode communities. Despite the use of fertilisers (N, P, K), both crops became highly sensitive to spiral nematodes in the third cycle because of the degradation of the soil physical properties. The study showed that the benefits of improved fallows in terms of crop production may be limited by the high number of plant-parasitic nematodes they help develop in the process.
Studies were conducted between 2002 and 2004 in experimental plots at two sites in western Kenya ... more Studies were conducted between 2002 and 2004 in experimental plots at two sites in western Kenya and one site in South Africa, to assess the potential role of the 'push-pull' strategy in stemborer resistance management in Bt-maize through its influence on the pests' oviposition and mortality from predation. Experiments in Kenya were conducted with non-Bt-maize while a combination of Bt-maize (expressing Cry1Ab proteins) and its non-Bt-maize isoline was used in South Africa. Treatments comprised of a maize monocrop and an intercrop of maize and desmodium, with Napier grass as a trap crop around the field in each site ('push-pull'). A combination of natural and artificial infestation procedures were employed. Oviposition preference and predation rates of naturally infested stemborer eggs were assessed. Screen house-reared plants (non-Bt-maize) were infested with eggs, early-instar larvae, late-instar larvae and pupae of Busseola fusca and Chilo partellus in natural enemy exclusion studies. Significantly more egg batches were oviposited in the maize monocrop than in the 'pushpull' plots by C. partellus, but not B. fusca. Predation rates of the naturally oviposited C. partellus eggs were significantly higher in the 'push-pull' than in the maize monocrop plots, but not different with B. fusca eggs. Disappearance rates of C. partellus eggs on control plants (those exposed to predators), attributable to predatory activity, was significantly higher in control than exclusion plants and similarly higher in the 'push-pull' than in the maize monocrop plots. There were no differences in disappearance rates of B. fusca eggs between treatments. Recovery of early-instar larvae was generally low for both species, similar between control and exclusion plants, but significantly lower in the 'push-pull' plots in one of the sites. Recovery of late-instar larvae and pupae in control plants was similar between the two cropping systems for both species. The study revealed reduced oviposition by C. partellus and enhanced predatory activity on C. partellus eggs in the 'push-pull' system, pointing to the system becoming a component in Bt resistance management for the pest.
... DOI: 10.1080/09670870701613743 Gashawbeza Ayalew a * , Andrea Sciarretta b , Johan Baumgärtne... more ... DOI: 10.1080/09670870701613743 Gashawbeza Ayalew a * , Andrea Sciarretta b , Johan Baumgärtner c , Callistus Ogol d & Bernhard Löhr e pages 31-38. ... At the field level, the DBM population tended to remain within the cabbage field. ...
Purpose: To determine the potential benefits of nine medicinal plants used by the Samburu communi... more Purpose: To determine the potential benefits of nine medicinal plants used by the Samburu community for the treatment of tuberculosis. Methods: The extract was tested against four strains of Mycobacteria namely; Mycobacterium tuberculosis (Mtb), M. Kansasii (Mk), M. fortuitum (Mf), and M. smegmatis (Ms) using BACTEC MGIT 960 system. The crude extracts were also analyzed for the presence of phytochemical constituents. Results: Both the extracts of Scadoxus multiflorus and Acacia nilotica showed strong antimycobacterial activity against the four tuberculosis-causing strains. Eurphobia scarlatina was the most active against both the slow (Mtb and Mk) and the fast (Mf and Ms) growers with Zero GUs at 0.5mg/ml. Phytochemical screening indicated presence or absence of tannins, saponins and flavonoids, terpenoids, cardiac glycosides and alkaloids in the extracts. Conclusion: The data suggest that some of the methanol extracts could be a rich source of antituberculosis agents. The results further show that there is some merit in the use of some of the plants studied in alternative medical practice. Pharmacological and toxicological studies of the active plants are still under investigation.
The bionomics of Stethorus tridens Gordon fed Tetranychus evansi Baker & Pritchard were studied i... more The bionomics of Stethorus tridens Gordon fed Tetranychus evansi Baker & Pritchard were studied in the laboratory. The number of prey consumed by S. tridens increased with increasing instar levels and the total mean number consumed during immature development was 184.1 ± 18.02 T. evansi nymphs per individual. For adult male and adult female, the daily consumption was 41.3 ± 0.80 and 67.8 ± 1.69 nymphs, respectively. Stethorus tridens successfully developed to adulthood between 20 and 30°C but failed at 10, 15 and 35°C. The lower thermal threshold for egg-to-adult development estimated via linear regression and the modified Logan model was 9.2 and 8.1°C, respectively. The optimum and maximum temperatures for egg-to-adult development were around 29-31 and 32.9°C, respectively. Egg to adult development time was 23.8 ± 0.24, 17.4 ± 0.22, 16.2 ± 0.22 and 12.1 ± 0.16 days at 20, 24, 27 and 30°C, respectively. At 27°C, the sex ratio, expressed as the proportion of females, was 0.54 and the mean preoviposition, oviposition and postoviposition periods were 10.3 ± 0.67, 31.2 ± 4.74 and 30.2 ± 5.24 days, respectively. The oviposition rate was 4.0 ± 0.16 eggs/female/day with a female mean longevity of 71.6 ± 6.19 days and an intrinsic rate of natural increase of 0.104. The potential of S. tridens as a candidate natural enemy of T. evansi is discussed.
The influence of agroforestry practices on the temporal fluctuation of nematodes was studied in w... more The influence of agroforestry practices on the temporal fluctuation of nematodes was studied in western Kenya. The experiment comprised a fallow phase, which had the following treatments: (1) maize/beans intercropping; (2) maize/beans intercropping with rock phosphate; (3) Crotalaria fallow; (4) Crotalaria fallow with rock phosphate; (5) Crotalaria fallow with rock phosphate (+ Calliandra and napier hedges); and a cultivation phase when all plots were planted to maize and beans. There were strong seasonal fluctuations in the abundance of both free-living and plant-parasitic nematodes. The abundance of plant-parasitic nematodes did not vary among cropping systems during the fallow phase, but varied significantly during the cultivation phase of the experiment. Pratylenchus spp. appeared to be stimulated by the application of phosphorus while Scutellonema spp. had higher populations in the maize crops, which were planted after a Crotalaria fallow. In both the fallow and the cultivation phases, the sampling date had a significant impact on nematode abundance. There were more plant-parasitic nematode species during the fallow phase of the study, but the evenness of the different nematode communities was significantly greater in the cultivation phase of the experiment.
We investigated the influence of temperature and infestation sequence on interspecific competitio... more We investigated the influence of temperature and infestation sequence on interspecific competition between two fruit flies: an invasive (Bactrocera invadens Drew, Tsuruta & White, (B) and a native (Ceratitis cosyra Walker, C) (both Diptera: Tephritidae) species. Mango fruits [Mangifera indica L. (Anacardiaceae)] were co-infested with larvae at different constant temperatures (15, 20, 25, and 30°C) and relative humidity of 50 ± 8%, using different infestation sequences at each temperature (BC together; BC ⁄ CB 1, 2, and 3 days apart). There were significant effects of competition in most experimental treatments, resulting in reduced larval survival, pupal mass, and adult emergence for both species. At most of the infestation ⁄ temperature combinations, C. cosyra was clearly the inferior competitor. The only exception was at 20°C when the outcome depended on the sequence of infestation: no C. cosyra survived when the sequence was BC, but more C. cosyra than B. invadens survived when it was CB. At 15°C, all C. cosyra larvae died, while the development of B. invadens was prolonged and adult emergence reduced. We conclude that resource pre-emption and fluctuations in temperature in mango agroecosystems help to explain observed shifts in dominance between B. invadens and C. cosyra on mango in many parts of Africa. The small window of competitive superiority for C. cosyra at 20°C and CB infestation sequence, together with other factors such as fecundity and alternative hosts, may allow for coexistence in some environments.
Natural enemies respond to herbivore-induced plant volatiles (HIPVs), but an often overlooked asp... more Natural enemies respond to herbivore-induced plant volatiles (HIPVs), but an often overlooked aspect is that there may be genotypic variation in these ÔindirectÕ plant defence traits within plant species. We found that egg deposition by stemborer moths (Chilo partellus) on maize landrace varieties caused emission of HIPVs that attract parasitic wasps. Notably, however, the oviposition-induced release of parasitoid attractants was completely absent in commercial hybrid maize varieties. In the landraces, not only were egg parasitoids (Trichogramma bournieri) attracted but also larval parasitoids (Cotesia sesamiae). This implies a sophisticated defence strategy whereby parasitoids are recruited in anticipation of egg hatching. The effect was systemic and caused by an elicitor, which could be extracted from egg materials associated with attachment to leaves. Our findings suggest that indirect plant defence traits may have become lost during crop breeding and could be valuable in new resistance breeding for sustainable agriculture.
We assessed the non-target effects of a habitat management system ('push-pull') on maize stembore... more We assessed the non-target effects of a habitat management system ('push-pull') on maize stemborer specialist natural enemy activity and soil Collembola. Two study sites in western Kenya were sampled. There were two treatments at each site, maize monocrop and 'push-pull'. The latter comprised an intercrop of maize and Desmodium, Desmodium uncinatum Jacq., with Napier grass, Pennisetum purpureum (Schumach), as a trap crop planted around the edge of the plot (spaced 1 m from main crop). Trichogramma spp. were recovered from stemborer eggs while Cotesia sesamiae and Cotesia flavipes were recovered from stemborer larvae, and Dentichasmias busseolae from pupae. Mean number of eggs parasitized was significantly higher in the maize monocrop than in the 'push-pull' plots however proportions parasitized did not differ between the two systems. The number of larvae and pupae parasitized and dead from causes other than parasitism similarly did not differ between cropping systems. Proportions of larvae and pupae parasitized were significantly higher in the 'push-pull' than in the monocrop plots, indicating that the activity of larval and pupal parasitoids was enhanced. C. sesamiae female wasps were attracted to the volatiles from Desmodium flowers but not those from the leaves in a four-arm olfactometer bioassay. A total of 1530 individual Collembola in seven families were recovered from the plots. The 'push-pull' strategy did not have any significant effect on Collembola abundance and dominance. The factors underlying these observations and their implications are discussed.
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