Samuel Kyamanywa

Effect of endophytic Beauveria bassiana on populations of the banana weevil, Cosmopolites sordidus, and their damage in tissue-cultured banana plants

The entomopathogen Beauveria bassiana (Balsamo) Vuillemin (Ascomycota: Hypocreales) survives as an endophyte in a wide range of plants, offering substantial protection against tunneling insect pests. Although current research indicates that the fungus can live as an endophyte in tissue‐cultured banana plants, there is no information on the efficacy of endophytic B. bassiana against the banana weevil, Cosmopolites sordidus (Germar) (Coleoptera: Curculionidae). Our study aimed at determining the effects of endophytic B. bassiana on oviposition rate and populations of the banana weevil, and their plant damage. Screenhouse studies were undertaken in which 8‐week‐old B. bassiana‐inoculated tissue‐cultured banana plants [cultivar Kibuzi, Musa spec. (Musaceae), genome group AAA‐EA] were infested with female banana weevils. Five days after plant infestation with the banana weevil, there was no effect of B. bassiana on oviposition rate and egg hatchability. However, after 15 weeks, the presence of B. bassiana as an endophyte in banana tissues greatly reduced banana weevil populations and their damage to plants. Between 53.4 and 57.7% of the banana weevil adults died because of B. bassiana infection, resulting in a reduction of plant damage by 29.1–62.7% depending on plant part. Beauveria bassiana was re‐isolated from different plant parts, but to a greater extent from the roots and rhizomes than from pseudostem bases. Artificial inoculation of B. bassiana in banana plants caused no negative impact on banana growth. Our study demonstrated for the first time that endophytic B. bassiana reduced populations of C. sordidus and the plant damage they cause, and can thus be an alternative method for effective delivery of this fungus to banana plants for the management of C. sordidus.

Life-table analysis of mortality factors affecting populations of Bemisia tabaci on cassava in Uganda

A study was set up to determine the sources and rates of mortality of Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae) on field‐grown cassava in Uganda. Using a cohort‐based approach, daily direct observations were used to construct partial life tables for 12 generations of egg and nymph populations which were studied over a 1‐year period. Mortality was categorized as dislodgement, predation, parasitism (for nymphs only), unknown death, and inviability (for eggs only). The highest mean rate of marginal mortality across all stages was attributed to parasitism, with dislodgement and predation following, respectively. Across all factors, the highest mean rate of marginal mortality was observed in the fourth instar followed by the eggs, first‐, second‐, and third‐instars, respectively. Key factor analysis revealed that dislodgement was the major mortality factor contributing to generational mortality in eggs while for nymphs, parasitism in the fourth instar was the main driving force behind the observed generational mortality. Highest irreplaceable mortality in both the egg and nymph stages was attributed to dislodgement followed by parasitism and predation, and least was due to unknown death. Across stages, highest irreplaceable mortality rates were observed in the eggs and the fourth‐instar nymphs. The other stages had relatively low rates of irreplaceable mortality. Rain‐protection experiments revealed no significant differences in marginal mortality rates when compared to the open field situation.

Population dynamics of Bemisia tabaci (Homoptera: Aleyrodidae) parasitoids on cassava mosaic disease–resistant and susceptible varieties

Abstract Three field trials were conducted at Namulonge Agricultural and Animal Production Research Institute to investigate the population dynamics of Bemisia tabaci Gennadius and its associated aphelinid parasitoids in Uganda. Results showed that more whitefly occurred on the cassava mosaic disease-resistant variety, (Nase 4) compared to the susceptible variety, (Ebwanatereka). Two species of aphelinid parasitoids, Eretmocerus mundus Mercet and Encarsia sophia Girault and Dodd, were identified during the study. Overall percent parasitism did not differ significantly (P>0.05) between varieties in all the trials, but significant differences occurred at 13, 15 and 21 weeks after planting during late season (2000), 18 weeks after planting during early season (2001), and 8 weeks after planting during late season (2001). The trends in the build up in numbers of both parasitoids species and apparent parasitism were similar, differed significantly on certain dates. It was, however, noted that percent parasitism decreased with nymph number. The significance of this phenomenon on the potential use of these aphelinid parasitoids as biocontrol agents of the cassava whitefly is discussed.

Cereal stemborer species complex and establishment of Cotesia flavipes Cameron in Eastern Uganda.

Studies were conducted in two districts of eastern Uganda from 1997 to 1999 to introduce and monitor the establishment of an exotic parasitoid, Cotesia flavipes Cameron (Hymenoptera: Braconidae), for the control of the stemborer Chilo Partellus (Swinhoe) (Lepidoptera: Pyralidae), and also to determine the stemborer species complex in maize and sorghum. The study confirmed the presence of four important stemborers, two pyralids Ch. partellus and Eldana saccharina Walker and two noctuids, Busseola fusca Fuller and Sesamia calamistis Hampson. Chilo Partellus was dominant, constituting 53-88% of stemborers fourd followed by B. fusca at 8–37 %. The most abundant local parasitoid was the larval parasitoid Cotesia sesamiae (Cameron) (Hymenoptera: Braconidae). The pupal parasitoids Pediobius furvus Gahan (Hymenoptera: Eulophidae) and Dentichasmias busseolae Heinrich (Hymenoptera: Ichneumonidae) were also recorded. Parasitism of Co. sesamiae on Ch. partellus ranged between 0 and 13.1 %. The introduced Co. flavipes was recovered from all sites in four consecutive seasons (between 1998 and 1999) causing parasitism of between 4 and 32.9 % on Ch. partellus. Cotesia flavipes was also recovered from the indigenous stemborers B. fusca and S. calamistis. This study indicates that Co. flavipes has established in eastern Uganda.RésuméDes études ont été menées dans deux départements en Ouganda entre 1997 et 1999 infin d’introduire et de suivre l’aclimatation d’un parasitoïde exotique, Cotesia flavipes Cameron (Hymenoptera: Braconidae), dans le cadre de la lutte contre le foreur, Chilo Partellus (Swinhoe) (Lepidoptera: Pyralidae), et de determiner le complexe d’espèces de foreurs sur maïs et sorgho dans cette région. Cette étude a confirmé la présence de 4 espèces importantes de foreurs; deux pyrales, Ch. partellus et Eldana saccharina Walker et deux noctuidés Busseola fusca Fuller et Sesamia calamistis Hampson. Chilo Partellus était l’espèce dominante formant près de 53-88% des borers collectés, suivit par B. fusca à 8–37 %. Le parasitoïde local le plus abundant a été le parasitoïde larvaire Cotesia sesamiae (Cameron) (Hymenoptera: Braconidae). Les parasitoïdes des pupes Pediobins furvus Gahan (Hymenoptera: Eulophidae) et Dentichasmias busseolae Heinrich (Hymenoptera: Ichneumonidae) ont aussi été trouvés. Le parasitisme par Co. sesamiae sur Ch. partellus a varié entre 0 et 13.1%. Le parasitoïde introduit Co. flavipes a été collecté sur tous les sites pendant quatres saisons consécutives (entre 1998 et 1999) avec un taux de parasitisme entre 4 et 32.9 % sur Ch. partellus. Cotesia flavipes a aussi été collecté sur des foreurs locaux, B. fusca et S. calamistis. Cette étude a montré que Co. flavipes s’est acclimaté dans l’est de l’Ouganda.

Evaluation of Serangium n. sp. (Col., Coccinellidae), a predator of Bemisia tabaci (Hom., Aleyrodidae) on cassava

Abstract  The potential of a new, previously unidentified Serangium species (Col., Coccinellidae) to control the high Bemisia tabaci (Gennadius) (Hom., Aleyrodidae) populations on cassava was evaluated. Field and laboratory studies were carried out to determine the abundance and feeding capacity of this Serangium species feeding on B. tabaci on cassava. Serangium nymphs and adults were most abundant in cassava fields late in the season, rising sharply from 5 months after planting (MAP) to a peak at 7–8 MAP. Pre‐imaginal development averaged 21.2 days and was longest in eggs and shortest in the L1 instar. Mean total prey consumption of immature Serangium increased with the stage of development with the lowest consumption in the L1 instar and highest in the L4 instar. Mean daily consumption was lowest on the first day after hatching in the L1 instar and rose to a peak on the 13th day after hatching in the L4 instar. Each Serangium larva consumed a mean of over 1000 nymphs during its entire development. These results have demonstrated the potential of this Serangium species to control B. tabaci populations on cassava.

Effect of maize plants on colonisation of cowpea plants by bean flower thrips, Megalurothrips sjostedti.

The effect of non‐host maize plants on colonisation of cowpea by Megalurothrips sjostedti (Trybom) (Thysanoptera; Thripidae) was investigated.

Prevalence of viruses infecting cowpea in Uganda and their molecular detection

This item can be retrieved directly from the publishers site at http://dx.doi.org/10.5897/AJB11.398

Effect of Mixed Cropping Beans, Cowpeas and Maize on Population Densities of Bean Flower Thrips, Megalurothrips sjostedti (Trybom) (Thripidae)

The effect of growing cowpeas mixed with either beans or maize on population densities of Megalurothrips sjostedti (Trybom) was investigated. Also investigated was the effect of varying the cropping densities of the host plants on the pest populations.There was a significantly lower population of M. sjostedti in cowpea/maize, bean/maize, and cowpea/bean/maize mixed stands as compared with that in either cowpea/bean stands or monoculture stands of cowpeas and beans. Increasing the cropping densities of the host crops increased the abundance of the pest in non-maize based mixed stands, but this effect was not observed in the maize-based mixed stands.The results indicate that with regard to infestation by M. sjostedti, the practice of mixed cropping beans with cowpeas confers no advantage to either crop with respect to attack by M. sjostedti. On the contrary, combining the two crops attracted infestation levels similar to those attracted by either crop grown in monoculture. But the inclusion of a non-host plant (maize) in the mixture, significantly reduces infestation.RésuméNos recherches ont porté sur l’effet que la culture mixte des petits pois, melés soit aux haricots, soit au maïs peut avoir sur la densité de la population de Megalurothrips sjostedti (Trybom). Egalément, nous avons examiné l’effet de la variation de la quantité des plantes hôtes sur la population des parasites.Il y a eu une réduction significative des populations des M. sjostedti dans les emplacements mixtes des petits pois/maïs, haricots/maïs, et petits pois/haricots/maïs en comparaison avec la quantité quise constituait les mélanges des petits pois/haricots ou d’une seule culture individuelle. L’augmentation des densités des cultures des plantes hôtes a mené à l’accroissement des parasites dans les mélanges qui n’avaient pas de maïs, maïs cet effet n’a pas été constaté dans les mélanges avec le maïs.Les résultats ont indiqué qu’en ce qui concerne l’infection M. sjostedti, la pratique de la culture mixte des haricot et des petits pois n’apporte pas d’avantages à aucune de ces deux plantes, cela a plutôt pour effet d’augmenter la densité des plantes hôtes ce qui, par conséquent, conduit les deux plantes à s’exposer à une étrangère dans le mélange réduit, à un degré significatif le danger d’infection.

Oviposition preference and offspring performance of Crocidolomia pavonana (Lepidoptera: Pyralidae) on different host plants

The cabbage head caterpillar Crocidolomia pavonana (Fabricius) (Lepidoptera: Pyralidae) is an increasingly devastating pest on white cabbage (Brassica oleracea var. capitata) in Uganda. Screen house and field trials were used to assess oviposition preference and offspring performance of C. pavonana on six hosts in the genus Brassica: kale (B. oleracea var. acephala), cauliflower (B. oleracea var. botrytis), broccoli (B. oleracea var. italica), Chinese cabbage (B. campestris spp. pekinensis), Indian mustard (B. juncea (L.) Czern.) and white cabbage (B. oleracea var. capitata). To assess oviposition preference, the hosts were offered to C. pavonana in multiple‐choice (all six); two‐choice (cabbage with each of the other hosts) or cabbage‐only situations. After specified oviposition periods, egg numbers on individual plants were recorded. To determine C. pavonana offspring performance on the six hosts, whole plants were placed in individual cages, where larvae were monitored for development time, pupal weight and foliage consumption. Results of the choice tests indicated that C. pavonana preferred Chinese cabbage and broccoli for oviposition. In two‐choice arrangements, all the tested host plants were able to greatly reduce oviposition on white cabbage (69–100%) when compared with the monocrop. Chinese cabbage was the most suitable host with regard to C. pavonana offspring performance as demonstrated by the shortest development time and highest pupal weight. Chinese cabbage and broccoli can be used as traps for the pest but the resulting larvae should be destroyed regularly to prevent accumulation in the system.

Parasitism of Bemisia tabaci (Homoptera: Aleyrodidae) by Eretmocerus mundus (Hymenoptera: Aphelinidae) on cassava

Parasitism rates of Bemisia tabaci (Gennadius) and searching and oviposition behaviours of its parasitoid Eretmocerus mundus Mercet were compared on two cassava varieties: a glabrous variety, Nase 4 and a hirsute variety, MM97/0245 with c. 88 leaf hairs/cm2. Parasitism was assessed after potted plants of both varieties were exposed in open fields to natural infestation by B. tabaci and its natural enemy. For the behavioural studies, naive, less than 24-h-old females were individually observed on infested cassava leaflets under a microscope for a maximum of 1 h each. The different foraging behaviours were recorded using the computer software ‘The Observer 5.0’ (Noldus Ltd, Wageningen, The Netherlands). Total per cent parasitism and parasitism by E. mundus did not differ significantly between varieties. Upon encounter with leaf hairs, the parasitoids stopped and groomed before resuming the host search. The frequency of repeat probing, host feeding and antennation after probing and host feeding were higher on the glabrous than on the hirsute variety, while the converse was observed when feeding on liquids on the leaf. The duration of host assessment, initial probing, grooming and resting on the leaf was higher on the glabrous than on the hirsute variety. Leaf hairiness at the density investigated caused some changes in the behaviour of the parasitoids, but did not have an overall effect on field parasitism. Since cassava is generally considered to have glabrous leaves and the variety MM97/0245 is one of the most hirsute varieties, we discount leaf hairiness as a factor in determining levels of parasitoid activity.