School of Pure and Applied Sciences

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Ecological studies of the Helminth parasites of fish in Lake Naivasha, Kenya
(Karatina University, 1999) Aloo, P. A.
In many parts of the world, wild stocks of fish are dwindling especially in Africa where drought, pollution and over-exploitation are some of the causative factors. The continent is not spared other climatic catastrophies such as global warning with its effects on the flora and fauna (both terrestrial and aquatic). This may lead to the manifestation of diseases caused by parasitic organisms, which have been known to co-exist with their hosts. The work reported here attempted to highlight the importance of studying the ecological relationship between parasites and their hosts in their wild environments i.e. the microhabitats (fish) and the macrohabitat (the lake). This work aimed at determing the distribution of four teleostean fishes Oreochromis leucostictus (Trewavas), Micropterus salmoides (Lacepede). Tilapia zillii (Gervais) and Barbus amphigrama (Boulenger) as hosts of the parasites, to establish the occurrence and prevalence of helminth parasites in each of the four species and to determine and quantify the relationships between the helminth parasites and the teleostean hosts. The distribution of the four fish species as hosts of the helminth parasites was studied for a period of two years. The occurrence of the helminth parasites, intensity of infection in each species, prevalence of each parasite on each host, differential establishment, seasonal variation in prevalence and intensity of infection and the effects of these parasites on their hosts were determined. The effect of water chemistry on the intensity of infection was established by comparing the main Lake Naivasha which is fresh and the more saline Oloidien Bay. Statistical tests used to establish the relationship between the parasites and their hosts were the chi-square, analysis of variance, split-plot technique and regression analysis. The results showed a significant variation in the monthly distribution of the fish species within the lake (F11,32=4.07, P<0.001). Fish abundance also varied within the sampling sites with Oreochromis leucostictus being the most abundant. Depth was found to be the only single factor influencing the distribution of fish in the lake with fish numbers decreasing with depth (b=3.04; t11=4.15, P<0.01). It was established that there are four helminth parasites whose larval stages infect Lake Naivasha fishes viz: a nematode, Contracaecum sp.; an acanthocephalan Polyacanthorhynchus kenyensis, a trematode Clinostomum sp and a dilepidid cestode of the genus Amirthalingamia. A differential establishment of these parasites on the hosts was observed. (F5,2860 =14.044; P<0.001). No significant variation was observed in the monthly occurrence of the parasites (F11,132=1, P>0.05). Host specificity was also revealed among the parasites with two parasites Clinostomum and Amirthalingamia being very specific on O. leucostictus and T. zillii respectively (F15,2860=21.63; P<0.001). A strong relationship between the intensity of infection and the sex of the fish was also revealed (X2(1)=64.43; P<0.001). Although the relationship between the age of the fish and the intensity of infection with Contracaecum sp. was not significant (t4=0.425;P>0.05), the intensity of infection of O. leucostictus with P. kenyensis increased with age (t4=7.061; P>0.01). These parasites showed no harmful effects no harmful effects on their host from the observation of the relationship between intensity with Contracaecum and the condition factor of the fish (F3,33=0.02; P>0.05). In conclusion, Lake Naivasha fish species do not harbour any ectoparasites but they are infected by larval stages of four endoparasites
Functional response of Orius albidipennis (Hemiptera: Anthocoridae) to Megalurothrips sjostedti (Thysanoptera: Thripidae)
(Karatina University, 2002-05-02) Gitonga (a), Linus M.; Löhrb (b), B.; Magambo (a), J. K.; Mueke (c), J. M.
A locally available anthocorid predator, Orius albidipennis Reuter, was evaluated as a candidate biocontrol agent for Megalurothrips sjostedti Trybom, a major pest of French beans, Phaseolus vulgaris (L), in Kenya. The functional response of adult O. albidipennis to larval and adult M. sjostedti was studied at 15, 25, and 28 °C and densities of 5, 10, 20, and 30 larval and adult M. sjostedti per cage, over 24 h. More larvae and adult M. sjostedti were killed at the higher densities and with an increase in temperature. The data provided good fit to both type I and II functional response models. Attack rates increased with temperature for both the second instar larva and adult M. sjostedti. Handling times for the larvae decreased with an increase in temperature while those for the adults increased with increase in temperature. The implications of these results are discussed.
Functional response of Orius albidipennis (Hemiptera: Anthocoridae) to Megalurothrips sjostedti (Thysanoptera: Thripidae)
(Karatina University, 2002-05-02) Gitonga, Linus M.; overhalt, W.A.; Löhr, B.; Magambo, J. K.; Mueke, J. M.
A locally available anthocorid predator, Orius albidipennis Reuter, was evaluated as a candidate biocontrol agent for Megalurothrips sjostedti Trybom, a major pest of French beans, Phaseolus vulgaris (L), in Kenya. The functional response of adult O. albidipennis to larval and adult M. sjostedti was studied at 15, 25, and 28 °C and densities of 5, 10, 20, and 30 larval and adult M. sjostedti per cage, over 24 h. More larvae and adult M. sjostedti were killed at the higher densities and with an increase in temperature. The data provided good fit to both type I and II functional response models. Attack rates increased with temperature for both the second instar larva and adult M. sjostedti. Handling times for the larvae decreased with an increase in temperature while those for the adults increased with increase in temperature. The implications of these results are discussed.
Temperature-dependent development of Megalurothripssjostedti and Frankliniellaoccidentalis (Thysanoptera: Thripidae)
(2002-09) Gitonga, Linus; Lohr, B.; Overholt, Bill; Magambo, J. K.
Megalurothrips sjostedti (Trybom) and Frankliniella occidentalis (Pergande) (Thysanciptera: Thripidae) are among the most serious pests of French beans, Phaseolus vulgaris var. Monel in Kenya and occur in all major growing areas. The former seems to be prevalent during cold and rainy periods while the latter is mainly a problem during hot and dry conditions. The development of the two species was studied at temperatures ranging from 15 degreesC to 30 degreesC. The average developmental times of each stage are given. For both species, the developmental times decreased with an increase in temperature. The degree-days required to complete development from egg to adult were 212 and 256 above the estimated threshold temperatures of 9.6 degreesC and 9.0 degreesC for M. sjostedti and F.occidoitalis, respectively. Between 19 and 23 generations of M. sjostedti and between 17 and 20 generations of F. occidentalis; could possibly develop under Kenyan field conditions in one year. Overall mortality was lowest at 25 degreesC. Mortality rates for both species decreased from larval instars to adult and were higher for M. sjostedti than for F. occidentalis. Since the developmental times were not different, the differential pest status of M. sjostedti and F. occidentalis must be a result of other factors.
Biological diversity of the Yala Swamp lakes, with special emphasis on fish species composition, in relation to changes in the Lake Victoria Basin (Kenya): threats and conservation measures
(2003-05) Aloo, P.A.
During the second half of the last century, the Lake Victoria ecosystem has undergone drastic ecological changes. Most notable has been the decline in the populations of many endemic cichlid fishes. The lake has lost nearly 200 haplochromines and one tilapiine, Oreochromis esculentus. The above changes have been attributed to effects of species stocking and, in particular, from predation pressure by the introduced Nile perch, Lates niloticus. Other factors that have led to the decline of the endemic species include intensive non-selective fishing, extreme changes in the drainage basin, increased eutrophication, and the invasion of the lake by the water hyacinth, Eichhornia crassipes. However, the remnants of some species that had disappeared from Lake Victoria occur abundantly in the Yala Swamp lakes (Kanyaboli, Sare and Namboyo). This paper discusses the biodiversity of the swamp and the three lakes and gives suggestions for their conservation
Antimicrobial acitivity of extracts from Tephrosiavogelii Hook F.
(Jomo Kenyatta University of Agriculture & Technology (JKUAT), Kenya, 2006) Wanga, B. N.; Akenga, T.; Imbuga, M.; Gitonga, L.; Olubayo, F.; Namungu, P.
The dichloromethane extracts of the root and leaf of Tephrosia vogelii Hook F. (Family: Papilionaceae) grown in Kenya, were subjected to antimicrobial assays against Staphylococcus aureus, Escherichia coli and Fusarium phoseolida. The minimum inhibition concentrations (MIC) ranged between 0.25 to 6.4 μg/ml for all the microorganisms tested. The crude root and leaf extracts were also toxic to the brine shrimps, organisms used as indicators of toxicity (LC50: 0.960; 0.958μg/ml,respectively). Chromatographic separation led to the identification of (6aß, 12aß, 5'ß)-6a, 12a, 4',5'-tetra hydro-2,3-dimethoxy 5'-ß- isopropenyl–furano (3',2': 8,9)-6H-rotoxen-12-one, (rotenone) in 9.75% yield, (roots), and 11.75% (leaves). Characterisation was achieved by use of spectroscopic techniques and comparison with rotenone standard and literature data. Novel HPLC conditions for purification of rotenoids were established. The MIC of rotenone against the tested microbes was found to be 5.2 and 1.0 μg/ml for Staphylococcus aureus and Escherichia coli respectively, while the LC50 against the brine shrimps was found to be 3.20 μg/ml. The findings indicate that the extracts of T. vogelii contain metabolites that have antimicrobial activity comparable to other medicinal plants.
Biological impact of the exotic parasitoid, Diadegma semiclausum (Hellen), of diamondback moth, Plutella xylostella L., in Kenya
(Karatina University, 2006-08) Momanyi, Caleb; Loehr, Bernhard; Gitonga, Linus
Diadegma semiclausum (Hellen) was introduced to Kenya from Taiwan for the control of diamondback moth (DBM), Plutella xylostella L., and released for the first time in July 2002. Seven and twelve months after release, field mortality studies using the cage exclusion method were conducted at two release sites (Werugha/Taita Hills and Tharuni/Central Kenya). Four treatments were applied: fully closed and partially open cages, both with and without glue applied to the base of the plants for the exclusion of crawling predators. During this time interval, parasitism of exposed larvae rose from 15 to 60% at Werugha and from 8 to 18% at Tharuni, with a concomitant decrease of parasitism by indigenous parasitoids. Crawling predators did not seem to have an effect on mortality. Unexplained mortality increased by half between the first and second experiment at both sites, indicating additional mortality due to the parasitoid. A subsequent field simulation with different parasitoid populations showed that in the presence of parasitoids more larvae died because of abandoning the plant than due to parasitism. Dissections of larvae on the ground showed most were parasitized. Thus, it appears that mortality due to D. semiclausum is more than twice the measured rate of parasitism. Additional information on parasitism was collected from concurrently executed DBM yield loss trials. Parasitism by D. semiclausum was in the same range as in the cage exclusion method. Seven months after release, local parasitoids were present at Werugha and dominant at Tharuni, after one year, they were almost completely displaced at both locations.
Lake Baringo: Addressing threatened biodiversity and livelihoods
(2006-12-08) Odada, Eric O.; Onyando, Japheth O.; Obudho, Peninah A.
Lake Baringo is a shallow, internal drainage, freshwater lake located in the Kenyan Rift Valley. The lake is an important source of water for humans and livestock, as well as a significant income source for local communities through activities such as tourism, biodiversity conservation, and fish sold in local markets. The lake has been subject to overfishing, as well as to greatly enhanced sedimentation as a result of land use changes in the drainage basin. This paper provides an analysis of the conditions prevailing at Lake Baringo, and examines in detail the management response to the problems facing the lake. The roles of the many and varied institutions in the lake basin's management are discussed, and an analysis of internationally funded projects designed to ameliorate the situation is provided
The risk of pathogenic intestinal parasite infections in Kisii Municipality, Kenya
(Karatina University, 2008-07-14) Nyarango, Robert M; Aloo, Peninah A; Kabiru, Ephantus W; Nyanchongi, Benson O
Background: Intestinal parasitic infections are among the most common infections worldwide. Various epidemiological studies indicate that the prevalence of intestinal parasites is high especially in developing countries, although in many of these, the environmental risk factors have not been clearly elucidated. The objective of this study was to determine the risk of pathogenic intestinal parasites infections in Kisii Municipality. Methods: Random sampling was used in the selection of the study samples. Stool parasitological profiles of food handlers were done by direct smear and formalin-ethyl acetate sedimentation method. Both vegetable and meat samples were examined for the presence of intestinal parasites. The storage and meat handling practices of the various butcheries were observed. Results: Types of samples examined for occurrence of intestinal parasites includes, a total of 84 vegetable, 440 meat and 168 stool samples. Fifty five (65.5%) vegetable, 334 (75.9%) meat and 69 (41.1%) of the stool samples were found positive for intestinal parasites indicating a high overall risk (66.18%) for intestinal parasite infections. Of the parasites detected, the most common parasites infesting the foodstuffs and infecting the food handlers were Ascaris lumbricoides and Entamoeba histolytica. Parasites were significantly less likely to be present on meat that was refrigerated during display than meat that was displayed at ambient temperature. Conclusion: There is a high risk of infection with intestinal parasites in the sampled Municipal markets. About half of the food handlers surveyed (41.1 %) at the Municipal Hospital had one or more parasitic infections. Furthermore, meat (65.5%) and vegetables (75.9%) sold at the Municipal market were found to be contaminated with parasites hence the inhabitants requires a need for education on food safety, good distribution practices and improvement on sanitary conditions.
The Impact Of Policy Changes In The Education Sector On The Development Of The Book Publishing Industry In Kenya
(Unisa Press, 2009) Mbengei, Bernard; Francis, Galloway
This article explores the impact of policy changes in the education sector on the de-velopment of the book publishing sector in Kenya. The article begins by detailing the current status of the book publishing sector in Kenya. Then the interdependence between the education and book publishing sectors is highlighted. The government policies that have shaped the education system in Kenya are analysed with a view to establishing how they have affected the book publishing sector. An overview of the new school textbook policy that was introduced in 1998 is presented in order to show how it has influenced the textbook production and procurement. Then the introduction of the Free-Primary Education (FPE) is discussed because it is the most recent development in the education sector that has provided tremendous impetus to the development of the book publishing industry in the country. The challenges encountered by the Government of Kenya in implementing the FPE and those faced by the book publishers in producing books for the school market are analysed. Finally, a way forward is proposed in the form of recommendations that can contribute to positive growth and mainstreaming of the school textbook publishing sub-sector in Kenya. A literature review approach isused in which sources that include newspapers, government and institutional websites, journals, books and dissertations have been consulted.
Relationship between virulence and repellency of entomopathogenic isolates of Metarhizium anisopliae and Beauveria bassiana to the termite Macrotermes michaelseni
(Journal of Insect Physiology, 2009) Mburu, D.M.; Ochola, L.; Maniania, N.K; Njagi, P.G.N.; Gitonga, L.M.; Ndung'u, M.W.; Wanjoya, A.K.; Hassanali, A.
Termites encounter a diverse array of potentially useful and harmful fungi in their subterranean habitats. These vary from symbiotic to harmful species with varying levels of virulence. How these hemiedaphic insects survive in habitats with infective fungi is not well understood. Possible mediation of olfactory signals in avoiding contact with entomopathogenic fungi has been explored by a number of workers. In the present study, we initially found that Macrotermes michaelseni detected a virulent isolate of Metarhizium anisopliae from some distance and avoided direct physical contact. We hypothesized that there may be a relationship between virulence and repellency of different isolates of M. anisopliae and Beauveria bassiana to the termite. We compared these for selected isolates of the two fungi. Positive correlations between the two parameters for both sets of isolates of the fungi were obtained. The results show an interesting co-evolutionary phenomenon in which the termite’s response to either M. anisopliae or B. bassiana is directly related to potential harm these fungi can inflict on the insect and that the virulent strains are more likely to be recognized from some distance and avoided.
Open relationships in the castles of clay: high diversity and low host specificity of Termitomyces fungi associated with fungus-growing termites in Africa
(International Union for the Study of Social Insects (IUSSI), 2010-08) Lagat, Zipporah Osiemo; Marten, Andreas; Kaib, M.; Gitonga, L. M.; Boga, H. I.; Brandl, R.
In the African and Asian tropics, termites of the subfamily Macrotermitinae play a major role in the decomposition of dead plant material. Their ecological success lies in the obligate mutualism of the termites with fungi of the genus Termitomyces. Before the advent of molecular studies, the interaction with these fungi was poorly understood. Here, we combined available ITS sequence data from West, Central, and South Africa with data of 39 new samples from East Africa to achieve the most comprehensive view of the diversity and host specificity of Termitomyces symbionts across Africa to date. A high amount of sequence divergence in the ITS sequences was found; 11 different Termitomyces lineages in East Africa and >30 lineages across Africa were identified, and the expected diversity is estimated to be about 41 lineages. The fungal lineages belong to four major clades, each almost exclusively associated with one termite host genus. Analysis of molecular variance revealed that 40% of the ITS sequence variation occurred between host genera, indicating close co-evolution at this level. However, within host genera, fungal lineages and haplotypes were frequently shared among host species and sampling localities, except for fungal symbionts of Odontotermes. Horizontal transmission of fungal symbionts may facilitate the transfer of haplotypes and species among hosts. However, at present, we have little understanding of the maintenance of specificity at the genus level. Possible explanations range from substrate specificity of fungi to an active selection of fungi by termites.
Host plant resistance among tomato accessions to the spider mite Tetranychusevansi in Kenya
(Springer, 2011-04-11) Onyambus, G. K.; Maranga, R. O.; Gitonga, L. M.; Knapp, M.
The spider mite Tetranychus evansi has a broad range of host plants. Control of T. evansi has been a big challenge to tomato farmers due to its fast rate of reproduction, development of resistance to chemical pesticides and its ability to use weeds as alternative hosts when the tomato plants are not available. The aim of the current study was to determine the host plant acceptance and the relative contributions of trichomes in the control of the red spider mite by comparing the survival, development and oviposition rates of the red spider mite on eight tomato accessions. Leaflets from eight tomato varieties were assayed with the spider mites to determine the egg laying capacity and developmental time of the spider mites on the tomato accessions as well as the trichome densities. Densities of trichome types I, IV, V and VI varied among the tomato accessions. Variation in types I, IV and VI accounted for most of the variation in mite responses. The varieties with high densities of types IV and VI had the highest fecundity and mite development did not go beyond the larval stage. The developmental time varied significantly among the tomato accessions. The results indicated that the higher the density of trichome type I the lower the adult survival. The findings indicated possible resistance of some of the tested tomato accessions against T. evansi which is partially associated with trichomes types and density.
Radiometric assessment of natural radioactivity levels around Mrima Hill, Kenya
(International Journal of the Physical Sciences, 2011-07) Kebwaro, Jeremiah Monari; Rathore, I.V.S.; Hashim, N.O.; Mustapha, A.O.
Mrima Hill, located in the South coast of Kenya is known for high natural background radiation, due to the presence of radiogenic heavy minerals such as monazites and carbonatites. The activity concentration of 238U, 232Th and 40K in soil samples from the hill have been determined by gamma ray spectrometry using NaI(Tl) detector and decomposition of measured gamma-spectra. As a measure of radiation hazard to the public, gamma radiation dose rates were also estimated. The average activity concentrations of 238U, 232Th and 40K were 207.0±11.3, 500.7±20.0 and 805.4±20.0 Bqkg-1, respectively. The mean absorbed dose rate in air is 440.7±16.8 nGyh-1 while the estimated annual average effective dose rate is 1.11±0.01 mSvy-1. The absorbed dose rate due to gamma radiation from naturally occurring radioactive materials is above the global average value of 60 nGyh-1 (UNSCEAR, 2000)
Performance of a semiochemical-baited autoinoculation device treated with Metarhizium anisopliae for control of Frankliniella occidentalis on French bean in field cages
(Karatina University, 2011-12-16) Niassy, S.; Maniania, N. K.; Subramanian, S.; Gitonga, L. M.; Ekesi, S.
The performance of an autoinoculation device was evaluated in field cage experiments for control of Western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), in French bean, Phaseolus vulgaris L. var. Samantha (Fabaceae). Treatments consisted of a fungus-treated device with and without semiochemical (Lurem-TR), and a fungusfree device as control; the fungus used was Metarhizium anisopliae (Metchnikoff) Sorokin (Hypocreales: Clavicipitaceae). The overall mean number of conidia acquired by a single insect was higher in the fungus-treated semiochemical-baited device than in the device without 10 × 0.6 ± semiochemical: 5.04 10 × 0.4 ± vs. 2.24 conidia per insect. The overall thrips mortality was also higher in the semiochemical-baited device than in the device without the 3.5%. Conidial viability was not ± 3.9 vs. 41.7 ± semiochemical: 59.3 affected in the M. anisopliae-treated device without days after treatment, whereas it was considerably semiochemicals, 7 days post-inoculation 1.1%, 2 and 7 ± 1.3 to 6.5 ± decreased – from 81.0 – in the M. anisopliae-treated semiochemical-baited device. Thrips mortality was positively correlated with M. anisopliae conidial viability, and conidial viability was negatively correlated with conidial acquisition. This suggests that the semiochemical volatiles reduced the conidial viability, which in turn resulted in significant reduction in thrips mortality, despite the highest conidial acquisition in the semiochemical-baited fungus-treated device. Thrips density per plant was significantly reduced in both fungus-treated 1.7 adults per plant; without ± treatments (with semiochemical: 8.7 1.4 adults per plant) compared with the fungus-free ± semiochemical: 6.6 2.6 adults per plant). These results demonstrate the ± control (19.8 potential for an autoinoculation device strategy for the control of thrips, particularly in screenhouses.
The Challenges of Using Lesson Plan Formats for Effective Teaching of Chemistry in Kisii District, Kenya
(Journal of Emerging Trends in Engineering and Applied Sciences (JETEAS), 2012) Olunga, Maureen Stella
The study sought to review the state of the use of lesson plans by teachers in teaching Chemistry in six secondary school s of Mosocho Division of Kisii District, namely Cardinal Otunga, Mosocho Academy, Raganga, Kioge, Nyatieko and Nyabururu. The research tool used was the questionnaire. The respondents included the headteachers, the heads of the Science departments and Chemistry teachers and, therefore, three types of questionnaires were administered. The Chemistry teachers’ questionnaire sought information regarding the problems that teachers faced in preparing and using the lesson plans. The heads of science department’s questionnaire solicited for information regarding problems they faced in trying to see that teachers prepared and used the lesson plan, if Chemistry teachers in one school used more than one lesson plan format and the format that was found easier to use. The head teachers’ questionnaire was used to collect information on how they carried out their duty of seeing that teachers prepared and used the lesson plan in teaching chemistry. The head teachers also made comments concerning the use of the lesson plan in teaching chemistry. From the findings of the study, it was noted that most teachers used the columnar format and understood the importance of the lesson plan. However, some were completely unable to use the lesson plan. This shows that there is need to employ qualified teachers. The study contributes useful knowledge to scholars and other education stakeholders that may help in improving teachers’ effectiveness in their teaching of Chemistry among other science subjects.
Selection of promising fungal biological control agent of the western flower thrips Frankliniella occidentalis (Pergande)
(Karatina University, 2012) Niassy, S.; Maniania, NK; Gitonga, LM; Mburu, DM; Masiga, D.; Ekesi, S.
Aims: Larval stages of Frankliniella occidentalis are known to be refractory to fungal infection compared with the adult stage. The objective of this study was to identify promising fungal isolate(s) for the control of larval stages of F. occidentalis. Methods and results: Ten isolates of Metarhizium anisopliae and eight of Beauveria bassiana were screened for virulence against second-instar larvae of F. occidentalis. Conidial production and genetic polymorphism were also investigated. Metarhizium anisopliae isolates ICIPE 7, ICIPE 20, ICIPE 69 and ICIPE 665 had the shortest LT(50) values of 8.0-8.9 days. ICIPE 69, ICIPE 7 and ICIPE 20 had the lowest LC(50) values of 1.1 × 10(7), 2.0 × 10(7) and 3.0 × 10(7) conidia ml(-1), respectively. Metarhizium anisopliae isolate ICIPE 69 produced significantly more conidia than M. anisopliae isolates ICIPE 7 and ICIPE 20. Internally transcribed spacers sequences alignment showed differences in nucleotides composition, which can partly explain differences in virulence. Conclusion: These results coupled with the previous ones on virulence and field efficacy against other species of thrips make M. anisopliae isolate ICIPE 69 a good candidate. Significance and impact of the study: Metarhizium anisopliae isolate ICIPE 69 can be suggested for development as fungus-based biopesticide for thrips management.
Selection of promising fungal biological control agent of the western flower thrips Frankliniella occidentalis (Pergande)
(Letters of Applied Microbiology, 2012-02) Niassy, S.; Maniania, N.K; Subramanian, S.; Gitonga, L.M.; Mburu, D.M.; Masiga, D.; Ekesi, S.
Aims: Larval stages of Frankliniella occidentalis are known to be refractory to fungal infection compared with the adult stage. The objective of this study was to identify promising fungal isolate(s) for the control of larval stages of F. occidentalis. Methods and Results: Ten isolates of Metarhizium anisopliae and eight of Beauveria bassiana were screened for virulence against second-instar larvae of F. occidentalis. Conidial production and genetic polymorphism were also investigated. Metarhizium anisopliae isolates ICIPE 7, ICIPE 20, ICIPE 69 and ICIPE 665 had the shortest LT50 values of 8Æ0–8Æ9 days. ICIPE 69, ICIPE 7 and ICIPE 20 had the lowest LC50 values of 1Æ1 · 107 , 2Æ0 · 107 and 3Æ0 · 107 conidia ml)1 , respectively. Metarhizium anisopliae isolate ICIPE 69 produced significantly more conidia than M. anisopliae isolates ICIPE 7 and ICIPE 20. Internally transcribed spacers sequences alignment showed differences in nucleotides composition, which can partly explain differences in virulence. Conclusion: These results coupled with the previous ones on virulence and field efficacy against other species of thrips make M. anisopliae isolate ICIPE 69 a good candidate. Significance and Impact of the Study: Metarhizium anisopliae isolate ICIPE 69 can be suggested for development as fungus-based biopesticide for thrips management.
Compatibility of Metarhizium anisopliae isolate ICIPE 69 with agrochemicals used in French bean production
(Journal of Pest Management, 2012-04) Niassy, S.; Maniania, N.K; Subramanian, S.; Gitonga, L.M.; Maranga, R.; Obonyo, A.B.; Ekesi, S.
The compatibility of the Metarhizium anisopliae (Metschnikoff) Sorokin isolate ICIPE 69, which is being developed as a biopesticide for the control of Frankliniella occidentalis Pergande, was assessed under laboratory conditions with 12 agrochemicals including 5 insecticides (thiamethoxam, L-cyhalothrin, imidacloprid, chlorpyrifos, diazinon), 1 botanical insecticide (azadirachtin), 2 acaricides (abamectin, spiromesifen), and 3 fungicides (carbendazim, copper hydroxide, probineb) used in French bean production. The insecticides abamectin and imidacloprid were highly compatible with M. anisopliae; thiamethoxam was compatible, whereas azadirachtin and L-cyahalothrin were toxic to the fungus, adversely affecting vegetative growth and sporulation. The acaricide spiromesifen was moderately toxic, while the fungicides carbendazim, probineb, and copper-hydroxide were very toxic to the fungus. The combination of the M. anisopliae isolate ICIPE 69 with imidacloprid or thiamethoxam did not result in any synergistic or antagonistic effects to larvae of F. occidentalis. However, the combination of lower concentrations of the fungus with thiamethoxam resulted in a shorter lethal time (LT50) compared with individual treatments. Our results suggest that application of the fungus with agrochemicals has to be assessed carefully prior to any field intervention.
Bioecology of thrips in French bean growing ecosystem in Kenya
(2012-10-31) Gitonga, Linus Muthuri
Studies on the bioecology ofthrips on French beans were carried out at Machakos, Kaguru and JKUAT. The general objectives of this study were twofold, namely to study the biology and population dynamics of thrips on French beans and to identify and evaluate indigenous natural enemies of the thrips. Two thrips species, M sjostedti and F occidentalis were found throughout the year on French bean crops in all localities of the study. Their population peaks occurred at different times in the course of the year. Populations of M sjostedti peaked after the rains while those of F occidentalis occurred during the hot and dry months of the year at all the localities. Studies on the movements of thrips, into and out of the French bean crops showed that colonization by both species begins soon after germination and that both species preferred the flowers to other plant parts. F occidentalis was found to thrive equally well on the leaves, unlike M sjostedti which only inhabited flower buds and flowers. During the pre-flowering phase ofthe crop, M sjostedti were found on the terminal buds from where they moved to the flowers immediately after the onset of flowering. Most first instar larvae emerged from the pods and flowers. Petioles, leaves, flower buds, flowers and pods were used as oviposition substrates by the thrips.to varying extents. Analysis of the spatial distribution showed both species to be significantly aggregated in the respective plant parts. Laboratory studies indicated that developmental period decreased with an increase in temperature for all the stages of M sjostedti and F. occidentalis. Developmental threshold temperatures were calculated as 9.6 and 9.0 for M sjostedti and F. occidentalis respectively. Development from egg to adult required 212.0 and 256.8 Degree Days for M sjostedti and F. occidentalis respectively. However, at 15?C and 300C, mortality rates for all the developmental stages were higher for M sjostedti than F. occidentalis. The highest mortalities were recorded for the first instar larvae for both species, ranging from 15% to 42% and 11 % to 30% for M sjostedti and F. occidentalis respectively. Pre-pupae and pupae had the lowest mortality rates. An indigenous anthocorid bug, Orius albidipennis was found throughout the year in all the three field sites. Studies on the functional responses of 0. albidipennis to M sjostedti showed that more second instar larvae than adult M sjostedti were killed at all the temperature profiles and densities. With increase in temperature, more second instar larvae and adult M sjostedti were killed. High f2 values shows that both Types I and IT functional responses provided good fit for the data at 15?C, 25?C and 28?C. Attack rates also increased with an increase in temperature. Mortality rates of the 0. albidipennis nymphal instars decreased from the first to the 5th instar at all the temperatures. The mortality rates at 25?C were lower than at 20?C and 30?C for all the nymphal instars except the first instar. Temperatures had a significant effect on the pre-oviposition period, which decreased with an increase in temperature. The eggs took long to hatch at 20?C. Developmental periods of each of the nymphal instars decreased with an increase in temperature. An indigenous larval endoparasitoid of thrips, Ceranisus menes, was found throughout the year in the three localities and its population peaks occurred in the late and early months of the year, from October to April. A closer correlation was found between C. menes and F. occidentalis than with M sjostedti. At JKUAT, percentage parasitism, over the entire crop cycle, ranged from 3.5% to 19.5% and peaked in the months of Marchi April. The lowest percentage parasitism coincided with the period of the highest M sjostedti infestation on French beans. Linear regression analysis showed a density dependence relationship between parasitism and larval density. Laboratory experiments showed that C. menes successfully parasitized and completed development in both M sjostedti and F. occidentalis. Developmental times of C. menes in M sjostedti and F. occidentalis were not significantly different.