G. Nyamasyo

Products derived from the leaves of Ocimum kilimandscharicum (Labiatae) as post-harvest grain protectants against the infestation of three major stored product insect pests.

The bioactivity of materials from the leaves of Ocimum kilimandscharicum was tested against Sitophilus zeamais Mots chulsky (Coleoptera: Curculionidae), Rhyzopertha dominica (Fabricius) (Coleoptera: Bostrichidae) and Sitotroga cerealella (Olivier) (Lepidoptera: Gelechiidae) in maize and sorghum grains in the laboratory. Exposure of adults of the three insect species to dried ground leaves and essential oil extract of O. kilimandscharicum induced 100% mortality after 48 h. Fresh and dried whole leaves were not toxic to Sitophilus zeamais or R. dominica. Grains treated with dried ground leaves and essential oil extract caused significant reductions in the number of progeny and survival rate of all three pest species tested. There was no adult survival or progeny production in grains treated separately with each of the two materials at doses of 25.0 g (dried ground leaves) and 0.3 g (essential oil) per 250 g of grain, respectively. Unlike R. dominica and Sitotroga cerealella, grains treated with fresh leaves enhanced the feeding activity of Sitophilus zeamais. Ground leaves and the essential oil, however, protected the grains against feeding by all three species, resulting in lower weight loss and number of damaged seeds compared with untreated grains. All the plant materials were repellent to S. zeamais with the essential oil extract applied at 0.3 g/250 g of grain evoking the highest repellent action. There was, however, considerable variation in the repellency of the materials against R. dominica and Sitotroga cerealella. The results are discussed in terms of the efficacy of O. kilimandscharicum for protection against loss due to insects in traditional grain storage in developing countries.

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.

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.