Farmers in Kenya continue to raise concerns of difficulty in managing <em>Tetranychus evansi</em>, the most widespread pest species of tomato applying the most commonly used acaricides. This invasive pest species is not only found in Kenya, but in Eastern and Southern Africa, as well as parts of Europe and Asia. In the current study, populations of <em>T. evansi</em> were collected from farms in the four major tomato-growing areas of Kenya (Loitoktok, Kibwezi, Athi-River and Subukia) and their susceptibility compared to a laboratory culture (ICIPE) that had been maintained for three years without exposure to acaricides. Susceptibility of <em>T. evansi</em> eggs and adults (contact and residual) to Brigade (bifenthrin), Dimethoate (dimethoate), Karate (lambdacyhalothrin), Kelthane (dicofol), Omite (propargite) and Polytrin (profenofos+ cypermethrin) was tested in the laboratory using respective manufacturer’s recommended concentrations. Dimethoate resulted in variable ovicidal mortality while Kelthane, Brigade, Karate, Omite and Polytrin had high mortality across all populations. Similarly, adult contact and residual mortality was lower than that of the other chemicals when exposed to Dimethoate regardless of the location. Furthermore, it also had no residual effect on the mites from ICIPE and Kibwezi. On the other hand, Kelthane was most lethal against the mites from all locations followed by Brigade and Polytrin in that order. Omite caused significantly lower mortality on mites from Subukia while Karate produced variable effects on mites from Kibwezi, Loitoktok and Subukia. The implications of these findings are further discussed.
Thrips are major pest of snap bean that cause losses as high as 60% but the use of synthetic pesticides is restricted due to strict market regulations on maximum residue levels (MRLs). This study aimed at reducing the use of synthetic pesticides by integrating biological and botanical pesticides in the management of thrips in snap bean. On farm experiments were carried out over two cropping cycles to evaluate the efficacy of spray regimes consisting of different combinations of the following: Thunder® (Imidacloprid 100g/L + Betacyfluthrin 45g/L), biological (Metarhizium anisopliae ICIPE 69), botanical (Azadirachtin 0.15%), and Decis (Deltamethrin). Data on thrips population and pod yield were collected and benefit-cost ratio of each spray regime calculated. Integrating synthetic chemical with biological Metarrhizium anisopliae was the most cost effective causing more than 69% thrips reduction, and 50% increase in yields, while integrating Azadirachtin with Metarrhizium anisopliae was the least effective causing less than 20% thrips reduction, and 30% increase in yields compared to control. Integrating synthetic pesticide with Metarrhizium anisopliae had the highest benefit-cost ratio. The results indicated that integrating synthetic pesticides with neem-based and Metarrhizium anisopliae effectively reduces thrips infestation and increase yields, while reducing overall costs and chemical residues in the produce.
This paper reports 18 tetranychid mite species (Acari: Tetranychidae) from various plant hosts in Kenya. Four species of these belong to the subfamily Bryobiinae and the other 14 belong to the subfamily Tetranychinae. Eight of the mite species identified belong to the genera Bryobia, Petrobia, Peltanobia, Paraplonobia, Duplanychus, Eutetranychus and Mixonychus and are being reported for the first time in Kenya while the other ten had already been reported before. The paper provides a list of these species and their brief descriptions as well as a redescription of Peltanobia erasmusi Meyer (Acari: Tetranychidae) to include male characters that were not included in the original description.
Aflatoxin contamination impinges on grain quality worldwide. The causative agent, Aspergillus spp. colonizes grain in the field down to postharvest stages in storage where they may produce toxins. Kenya has experienced recurring cases of aflatoxicosis in Eastern region especially during periods of maize grain deficit. The risk of chronic exposure has not been widely studied. Therefore, seasonal variation in abundance and species composition of toxigenic Aspergillus in maize and soils of Eastern Kenya was investigated. Samples were obtained from farmers, two months after the first (May) and second (December) harvest seasons. Aspergillus spp. were isolated from maize and soil samples by direct and dilution plate techniques respectively on Czapek Dox Agar (CZ) and thereafter sub-cultured on potato dextrose agar (PDA). Positive identification was done using culture-morphological and microscopic characteristics in PDA media. The ammonium vapour test was used to screen for the putative toxigenic strains. A total of 229 Aspergillus spp. cultures were obtained (55% -maize, 45% -soil). Eleven Aspergillus sp. were identified: Aspergillus niger, Aspergillus flavus, Aspergillus clavatus, Aspergillus awamori, Aspergillus parasiticus, Aspergillus ochraceus, Aspergillus candidus, Aspergillus ustus, Aspergillus niveus, Aspergillus terreus and Aspergillus wentii. Of these 41 (18 %) were potentially toxigenic while the rest were putatively atoxigenic. Out of the 41 toxigenic isolates, 22 were from maize. The first season had 15 (68.2%) toxigenic maize isolates while 7 (31.8%) were from the second season. Generally, there were more fungal isolates in the first season (54.1%) than the second one (45.9%) while Aspergillus niger was the most abundant in both seasons. Such variation in fungal abundance supports the hypothesis that aflatoxin contamination of grain may vary seasonally but that remains to be unravelled and herein, a contrary opinion was presented.
Background: Aflatoxins (AFs) are poisonous compounds produced by species of fungi belonging to the genus Aspergillus mainly A. flavus and A. parasiticus. However, there are some members of these species that do not produce toxins and have since become of interest for use in Biological Control programs. The species that produce AFs are believed to have clusters of aflatoxin-associated genes that confer aflatoxigenicity. However, recent findings suggest that the presence of aflatoxin genes may not imply aflatoxin production capability. We therefore examined the extent to which the presence or absence of aflatoxin-associated genes (genetic) infers aflatoxigenicity using the Dichlorvos-Ammonia (chemical) method as reference.Results: We report a dissonance between the genetic and chemical methods of ascertaining aflatoxigenicity. Fungi (n = 314) that were morphologically identified as A. flavus and A. parasiticus were isolated from maize kernels and soil from Eastern Kenya. The fungi were further characterized to confirm their identities using a PCR-sequence analysis of the internal transcribed spacer (ITS) region of rDNA which confirmed them to be Aspergillus species. We selected and induced 16 isolates in YES media amended with Dichlorvos to produce AFs. Seven of the sixteen isolates were DM-AM positive (aflatoxigenic) but lacked at least one of the key aflatoxin-associated genes. Even more confounding, A. flavus isolate (1EM2606) had all aflatoxin-associated genes but was non-aflatoxigenic (DV-AM negative) while A. flavus (1EM1901) having all genes was aflatoxigenic (DV-AM positive). The genetic abundance of the AF-asscociated genes among the isolates was as follows: aflQ (100%), aflD (62.5%) followed by aflR (37.5%) and aflP (25%). Conclusion: We report that either method alone is limited in ascertaining aflatoxigenicity among Aspergillus section Flavi. The discordance between presence of aflatoxin-associated genes and aflatoxigenicity may be due to epigenetic factors that affect secondary metabolism, or even other signaling processes that alter toxin production that still remain poorly understood.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.