J. H Nderitu

Evaluation of companion crops for thrips (Thysanoptera: Thripidae) management on French bean Phaseolus vulgaris (Fabaceae)

Six companion crops, i.e. Tagetes erecta, Daucus carota L., Coriandrum sativum L., Brassica oleraceae L. var. acephala, Capsicum annuum L. and Zea mays L., were evaluated for their efficacy in suppressing field populations of Frankliniella occidentalis (Pergande) and Megalurothrips sjostedti Trybom on French bean Phaseolus vulgaris L. Each companion crop was interplanted with French beans in a 3 × 10 m plot and replicated three times in a completely randomized block design. Fhe thrips populations on French bean flowers in experimental plots were compared with those on beans treated with two insecticides: l-cyhalothrin (Karate 1.75% EC) and methiocarb (Mesurol 500 SC) or untreated (control). Coriandrum sativum, Z. mays and T. erecta are recommended as companion crops for intercropping with French beans to reduce populations of thrips and hence minimize the use of chemical insecticides on this crop.RésuméSix plantes associées, i.e. Tagetes erecta, Daucus carota L., Coriandrum sativum L., Brassica oleraceae L. var. acephala, Capsicum annuum L. et Zea mays L., ont été évaluées pour leur capacité à contrôler les populations naturelles de Frankliniella occidentalis (Pergande) et Megalurothrips sjostedti Trybom sur le haricots vert Phaseolus vugaris L. Chaque plante a été plantée en alternance avec des haricots verts dans des parcelles de 3 × 10 m, á raison de trois répétitions par plante dans un bloc complétement aléatoire. Les populations de trips présentes sur les fleurs de haricots verts dans les différentes parcelles expérimentales ont été comparées a celles de haricots verts traités avec deux insecticides L-cyhalothrin (Karate 1,75% EC) et methiocarb (Mesurol 500 SC) et, un témoin. Les résultats montrent que C. Sativum, Z. mays et T. erecta sont les meilleures plantes associées pour réduire l’utilisation des insecticides.

Susceptibility of eight potato cultivars to Myzus persicae Sulzer in the greenhouse

Eight potato cultlvars namely Anett, Desiree, Feldeslohn, Kerr’s Pink, Kenya Baraka, Roslin Eburu, Roslin Gucha and Roslin Tana were tested in the greenhouse to compare their susceptibility to Myzus persicae Sulzer. Differences in the susceptibility of the potato cultivars to aphids were reflected in the number of the apterae aphids that developed on them. Anett, Kerr’s Pink and Feldeslohn supported the highest, and Roslin Tana the lowest population of M. persicae. Roslin Tana was found to be resistant. The bottom leaves of most potato cultivars maintained the highest aphid population while the upper leaves maintained the lowest. There were no significant correlations between leaf area and yield of potatoes with the number of apterae aphids on the eight potato cultivars.RésuméHuit varietés de pomme de terre, Anette, Désirée, Feldeslohn, Rose de Kerr, Kenya Baraka, Roslin Eburu, Roslin Gucha, et Roslin Tana ont été testées dans une serre afin de comparer leur sensibilité aux aphidés, ont été observées en tenant compte de nombre d’ aphidés Myzus persicae Sulzer. Des diferences dans la sensibilité de variétés de pomme de terre aux aphidés ont été observées en tenant compte de nombre d’ aphidés aptéres qui ont dévelopé sur elles. La population la plus élevée de M. persicae a été observée sur Anett, Rose de Kerr et Feldeslohn; tandis que Roslin Tana a donné la plus faible population d’aphidés. Cette derniére variété de pomme de terre a été ainsi trouvée résistante á cette espéce d’ aphidés. La plus part de variétés de pomme de terre ont presenté des febilles ayant un nombre élevé d’aphidés á leur partie inférieure alors que la population d’aphidés la moinsélevée était localisée sur la partie supérieure de feuilles. Il n’y avait pas de correlat’ions significant entre la surface de la fenille, la quantité de pomme de terre ré coltée avec le nombre d’aphidés aptéres.

Diversity and abundance of native bees foraging on hedgerow plants in the Kakamega farmlands, western Kenya

Summary We determined the diversity and abundance of native bees foraging on hedgerow flowers, and documented the plant species composition of those hedgerows, from October 2008 to March 2009 at Kakamega, western Kenya. We made observations on hedgerow sectors located in five different land use types: Kakamega forest; roads; sugarcane plantations; maize/bean fields; and grazing land. Our findings show that a high diversity of bees is supported by the hedgerows, and that bee diversity and abundance significantly (P < 0.05) differed across the five land use types. A total of 82 bee species belonging to three families (Apidae, Megachilidae and Halictidae) were recorded, with Apidae having the highest species richness and abundance. The suitability of hedgerow plants as bee forage sources differed greatly, except for Megachilid bees. Most important bee plants belonged to the families Acanthaceae, Asteraceae and Fabaceae. We conclude that hedgerow plants play an important role in providing bee food resources and can be used for managing bees in Kakamega farmed areas. We also suggest the inclusion of hedgerows in community based management of bees in areas where hedgerows are present or have viability to succeed, as they can support bee life and hence the pollination of crops in agricultural ecosystems.

Diurnal population trends of Megalurothrips sjostedti and Frankliniella occidentalis (Thysanoptera: Thripidae) and their natural enemies on French bean Phaseolus vulgaris (Fabaceae)

A field experiment was conducted to track the daily population trends and occurrence of the flower thrips Megalurothrips sjostedti Trybom and Frankliniella occidentalis (Pergande), and their indigenous natural enemies Orius spp. and Ceranisus menes (Walker), infesting French beans. French beans in monocrop or interplanted with six companion crops (Zea mays L., Coriandrum sativum L., Tagetes erecta L., Brassica oleracea var. acephala L., Daucus carota L. and Capsicum annuum L.), and two chemical insecticides, methiocarb (Mesurol 500SC) and L-cyhalothrin (Karate 1.75% EC), were evaluated for their effects on the abundance of flower thrips, throughout the day, at 1-h intervals. The average population peak of thrips was found to occur at around 1300 h, but each species had different peak periods. Adult F. occidentalis populations peaked at midday and adult M. sjostedti populations at 1500 h, while the larvae of the two thrips species peaked at around 1300 h. Orius spp. were the most abundant natural enemies and their populations peaked at around 1400 h. Ceranisus menes population also peaked at around 1400 h.RésuméUne expérimentation de terrain a été conduite afin de déterminer la dynamique des populations des trips de fleurs Megalurothrips sjostedti Trybom et Frankliniella occidentalis (Pergande), et de leurs ennemis naturels indigènes Orius spp. et Ceranisus menes (Walker) sur haricot vert au cours de la journée. L’abondance des trips a été évaluée sur des haricots verts cultivés en monoculture ou en culture associée avec six autres plantes (Zea mays L., Coriandrum sativum L., Tagetes erecta L., Brassica oleracea var. acephala L., Daucus carota L. et Capsicum annuum L.) et avec deux insecicides methiocarb (Mesurol 500SC) et L-cyhalothrin (Karate 1.75% EC), pendant toute la journée, à 1 heure d’intervalle. Le pic d’infestation des trips a été observé vers 1300 h, avec toutefois une période différente pour chaque espèce. Le pic de population des adultes de F. occidentalis est observé à la mie journée et celui de M. sjostedti à 1500 h, alors que le pic de populations des larves des deux espèces est observé à 1300 h. Les espèces du genre Orius sont les ennemis naturels les plus abondants avec un pic de population vers 1400 h. La population de Ceranisus menes est maximum vers 1400 h.

Effect of date of sowing on beanfly infestation of the bean crop

The effect of planting dates on beanfly infestation was investigated in successively planted bean plants during cropping seasons. The population tended to build up in the course of the season following the initial invasion by egg-laying females. Ophiomyia spencerella (Greathead) and Ophiomyia phaseoli (Tryon) were the species of beanflies infesting the bean plants in all seasons. The number of beanfly leaf punctures, eggs, larvae and puparia were more in late planted than early planted bean crop. The bean crop planted late in the season was severely damaged due to the generally higher population levels which had been building up in the course of the season.RésuméL’effet des jours de plantations des haricots sur l’infestation des haricots par Ophiomyia spencerella (Greathead) et O. phaseoli (Tryon) a èté analysé. Les populations des insectes ont tendance à se former pendant la saison de cultures aprés l’invasion initiale par les femelles prêtes à pondre des ouefs. Le nombre des perforations sur les feuilles par les insectes, celui des oeufs, des larves et chrysallides furent tres elevés sur les haricots plantés tard par rapport a ceux plantés très tôt. Les haricots plantes tard ont étè severement endommagé par les populations des insectes qui sont entrain de se former pendant la saison.

Beanfly infestation on common beans (Phaseolus vulgaris L.) in Kenya

The population patterns of eggs, larvae and puparia in the bean plants and leaf punctures made by adults were investigated during cropping (March-July and October-January) and noncropping (July-October) seasons at two sites in Kenya. The beans planted in noncropping seasons had more leaf punctures, eggs, larvae and puparia than beans planted in cropping seasons. Beans planted in noncropping season attracted unusually high population from surrounding weeds as well as previous crop which cause severe damage. Under field conditions Ophiomyia spencerella Greathead and Ophiomyia phaseoli Tryon were the species of bean flies infesting the bean plants in all seasons. Both O. spencerella and O. phaseoli normally oviposited in punctures on the leaves but O. spencerella also oviposited in the stems of bean seedlings.RésuméLes echantillons des oeufs, larves et chrysallides sur les haricots et les perforations faites sur les feuilles par les adultes ont èté analysé pendant les deux saisons Mars-Juillet et Octobre-Janvier ainsi que pendant les mois de Juillet à Octobre dans deux locations au Kenya. Les haricots plantés entre Juillet et Octobre avaient plus des feuille perforées, beaucoup d’ouefs, larves et chrysallides par rapport aux haricots plantés pendant les autres saisons. Les haricots plantés entre Juillet et Octobre ont attiré beaucoup des mauvaises herbes et d’autres cultures qui peu vent causées des pertes enormes. Sur les champs Ophiomyia spencerella Greathead et O. phaseoli Tryon etaient les espèces d’insectes attacquant les haricots pendant toutes les saisons. Toutes les deux espèces pondaient normalement sur les feuilles perforées bien que O. spencerella puissent pondre sur les tiges des haricots en germination.

Effect of grain moisture content and storage time on efficacy of inert and botanical dusts for the control of Sitophilus zeamais in stored maize

The effect of grain moisture content and time of storage on the efficacy of inert and botanical dusts, conventional and bacterial metabolite insectcides were evaluated in the laboratory. Maize grains at 10, 12, 14 and 16% moisture content were admixed with inert powder (diatomaceous earth Kensil Superfine®), maize cob and bean trash ashes, and botanical (neem seed cake powder) at a dose rate of 0.9% w/w. Actellic Super® and Spintor® dusts applied at the recommended rate of 50 g/90 kg grain and diatomaceous earth Dryacide® at 0.9% w/w were included as positive controls. Untreated maize grain served as the negative control. Thirty (30) unsexed two ‐week-old Sitophilus zeamais Motsch. adults were introduced in the treated maize. The treatments were replicated four times and held undisturbed for 14 days at ambient conditions (26 ± 2°C and 67 ± 3% r.h.), after which mortality was assessed. Results showed that grain moisture content significantly (p<0.05) affected efficacy of grain protectants and superior control was achieved when it did not exceed 12% for inert dusts and 14% for pesticides. For the evaluation of the effect of time of storage, 4 kg maize grain were admixed with each treatment except for Spintor® dust, maize cob ash, neem seed cake powder as described earlier and put into the 5 kg capacity hessian baglets, replicated four times. Untreated grain acted as the control. Adult S. zeamais (population of 1500) were put in the plastic Petri dish and left to infest the baglets naturally. The potency of the protectants began to wane significantly (p<0.05) after 6 months. Dryacide ® followed by Kensil Superfine® dusts performed better than Actellic Super® with the grain weight loss of 2 and 4%, respectively, over a period of 9 months. The study demonstrates that Superfine ® dust has the potential but should be further evaluated on ‐ farm, for the control of storage insect pests and serve as another stored products protectant option.

Insects associated with the potato crop in Kenya

Abstract Seventy species of insects were found on potato; 52 of them were pests and 17 were predators of those pests. Their importance as pests and predators is discussed.

Field evaluation of foliar and soil insecticides for the control of Aphis gossypii glover (Homoptera: Aphididae) on potatoes in Kenya

Abstract—Field evaluation showed oxydemeton methyl 25% E.C. at 0.6 2kg a.i./ha and dimethoate 40% E.C. at 0.74 kg a.i./ha to be more effective than Cypermethrin 40% E.C. at 0.25 kg a.i./ha, decamethrin 2.5% E.C. at 0.03kg a.i./ha, endosulphan 35% E.C. at 0.8kg a.i./ha and profenofos 50% E.C. at 0.74 a.i./ha in the control of apterae on potatoes. Disulfoton 10G at 1.6 kg a.i./ha and carbofuran 10G at 5.2 kg a.i./ha were superior to oxamyl 10G at 5.2 kg a.i./ha and terbufos 5G at 2.6 kg a.i./ha applied in the furrow at planting for the control of aphids. Although these insecticides gave good control of apterae, the alate population in the treated plots varied from significant reduction to no reduction. All the insecticides tested did not significantly increase potato yield, although mean yields were increased.Résumé—Les expériences entreprises sur le terrain ont montré que l’‘oxydemeton methyl 25% E.C. á 0.6 kg m.a./ha’ et le ‘dimethoate 40% E.C. á 0.74 kg m.a./ha’ sont plus efficaces que le ‘Cypermethrin 40% E.C. á 0.25kg m.a./ha’, ‘decamethrin 2.5% E.C. á 0.03 kg m.a./ha’, ‘endosulphan 35% E.C. á 0.8kg m.a./ha’ et ‘profenofos 50% E.C. á 0.74kg m.a./ha’ pour la suppression des ‘apterae’ sur les pommes de terre. Le ‘disulfoton 10G á 1.6kg m.a./ha’ et le ‘carbofuran 10G á 5.2kg m.a./ha’ étaient meilleurs que l’‘oxamyl 10G á 5.2kg m.a./ha’ et le ‘terbufos 5G á kg m.a./ha’ dans le sillon au lemps desemence pour la suppression des aphis. Mênce si ces insecticides ont fait une bonne suppression des ‘apterae’, la population ‘alate’ dans les ceins traites a varié d’une réduction significative á une réduction nulle. Aucun de ces insecticides á accru significativement la production des pommes de terre.

Assessment of Yield Loss Caused by the African White Rice Stem Borer (Maliarpha separatella Rag (Lepidoptera: Pyralidae) at Mwea Irrigation Scheme, Kirinyaga County, Kenya

Information on losses caused by the African white rice stem borer, Maliarpha separatella rag, which is an important rice pest in Kenya is scanty. The development and implementation of effective pest management strategies relies on accurately defined Economic Injury Levels (ElL) for that pest. Investigations were, therefore, conducted to determine yield losses caused by M. separatella and economic injury level of the pest. The experiment was conducted in an insect proof screen house at Kenya Agricultural and Livestock Research Organization, Mwea station. The experiment was arranged as a (2×6) factorial design and each treatment replicated three times. First factor was time of infestation at two levels, early and late which was 3 and 6 weeks after transplant date, respectively. Second factor was infestation rate at six levels (0, 1, 2 4, 6 and 8 egg masses). Results indicated that infestation levels of 1, 2, 4, 6 and 8 M. separatella egg masses at early infestation resulted in grain yield losses of 59.8, 83.2, 84.8 90.2 and 90.9%, while losses of same infestation levels at late infestation was 34.3, 52.1, 63.4, 81.8 and 80.8%. There was a strong positive relationship between yield loss and M. separatella population levels (y = -214.29x+ 1693.4, r2 = 0.8416). On the basis of cost benefit ratio, the economic injury level was 6 and 8 egg masses per square meter in the early and late infestation, respectively. The action threshold for early infestation was 4 egg masses and 6 egg masses for late infestation.