Paul N. Ndegwa

Comparative performance of the Mbita trap, CDC light trap and the human landing catch in the sampling of Anopheles arabiensis, An. funestus and culicine species in a rice irrigation in western Kenya

BackgroundMosquitoes sampling is an important component in malaria control. However, most of the methods used have several shortcomings and hence there is a need to develop and calibrate new methods. The Mbita trap for capturing host-seeking mosquitoes was recently developed and successfully tested in Kenya. However, the Mbita trap is less effective at catching outdoor-biting Anopheles funestus and Anopheles arabiensis in Madagascar and, thus, there is need to further evaluate this trap in diverse epidemiological settings. This study reports a field evaluation of the Mbita trap in a rice irrigation scheme in KenyaMethodsThe mosquito sampling efficiency of the Mbita trap was compared to that of the CDC light trap and the human landing catch in western Kenya. Data was analysed by Bayesian regression of linear and non-linear models.ResultsThe Mbita trap caught about 17%, 60%, and 20% of the number of An. arabiensis, An. funestus, and culicine species caught in the human landing collections respectively. There was consistency in sampling proportionality between the Mbita trap and the human landing catch for both An. arabiensis and the culicine species. For An. funestus, the Mbita trap portrayed some density-dependent sampling efficiency that suggested lowered sampling efficiency of human landing catch at low densities. The CDC light trap caught about 60%, 120%, and 552% of the number of An. arabiensis, An. funestus, and culicine species caught in the human landing collections respectively. There was consistency in the sampling proportionality between the CDC light trap and the human landing catch for both An. arabiensis and An. funestus, whereas for the culicines, there was no simple relationship between the two methods.ConclusionsThe Mbita trap is less sensitive than either the human landing catch or the CDC light trap. However, for a given investment of time and money, it is likely to catch more mosquitoes over a longer (and hence more representative) period. This trap can therefore be recommended for use by community members for passive mosquito surveillance. Nonetheless, there is still a need to develop new sampling methods for some epidemiological settings. The human landing catch should be maintained as the standard reference method for use in calibrating new methods for sampling the human biting population of mosquitoes.

Development of an exposure-free bednet trap for sampling Afrotropical malaria vectors

Abstract An exposure‐free bednet trap (the ‘Mbita trap’) for sampling of Afrotropical malaria vectors was developed during preliminary studies of mosquito behaviour around human‐occupied bednets. Its mosquito sampling efficiency was compared to the CDC miniature light‐trap and human landing catches under semi‐field conditions in a screen‐walled greenhouse using laboratory‐reared Anopheles gambiae Giles sensu stricto (Diptera: Culicidae). When compared in a competitive manner (side by side), the Mbita trap caught 4.1 ± 0.5 times as many mosquitoes as the CDC light‐trap, hung beside an occupied bednet (P < 0.0001) and 43.2 ± 10% the number caught by human landing catches (P < 0.0001). The ratio of Mbita trap catches to those of the CDC light trap increased with decreasing mosquito density. Mosquito density did not affect the ratio of Mbita trap to human‐landing catches. In a non‐competitive comparison (each method independent of the other), the Mbita trap caught 89.7 ± 10% the number of mosquitoes caught by human landing catches (P < 0.0001) and 1.2 ± 0.1 times more mosquitoes than the CDC light trap (P = 0.0008). Differences in Mbita trap performance relative to the human landing catch under non‐competitive vs. competitive conditions were explained by the rate at which each method captured mosquitoes. Such bednet traps do not expose people to potentially infectious mosquito bites and operate passively all night without the need for skilled personnel. This trap is specifically designed to catch host‐seeking mosquitoes only and may be an effective, sensitive, user‐friendly and economic alternative to existing methods for mosquito surveillance in Africa.

Tsetse and other biting fly responses to Nzi traps baited with octenol, phenols and acetone

Abstract Octenol (1‐octen‐3‐ol), acetone, 4‐methylphenol, 3‐n‐propylphenol, and other potential attractants (human urine, stable fly faeces), as well as guiacol, creosol (potential repellents), were tested as baits for biting flies in North America using standard phthalogen blue IF3GM cotton Nzi traps, or similar commercial polyester traps. Baits were tested during the summers of 2001–04 at a residence in Canada and during January–August 2001 at a dairy in the U.S.A. Behaviour in the presence of octenol was also studied by intercepting flies approaching a trap through the use of transparent adhesive film. Analogous bait and/or trap comparisons were conducted in natural settings in June 1996 in Kenya and in September–December 1997 in Ethiopia. In Canada, catches of five of six common tabanids (Tabanus similis Macquart, Tabanus quinquevittatus Wiedemann, Hybomitra lasiophthalma [Macquart], Chrysops univittatus Macquart, Chrysops aberrans Philip) and the stable fly Stomoxys calcitrans L. were increased significantly by 1.2–2.1 times with octenol (1.5 mg/h). Catches of T. quinquevittatus and S. calcitrans were 3.5–3.6 times higher on a sticky enclosure surrounding a trap baited with octenol. No other baits or bait combinations had an effect on trap catches in North America. In Ethiopia, standard Nzi traps baited with a combination of acetone, octenol and cattle urine caught 1.8–9.9 times as many Stomoxys as similarly baited epsilon, pyramidal, NG2G, S3, biconical and canopy traps, in order of decreasing catch. When baits were compared, catches in Nzi traps of six stable fly species, including S. calcitrans, were not affected by octenol (released at approximately 1 mg/h), or cattle urine (140 mg/h), used alone or in combination with acetone (890 mg/h). Acetone alone, however, significantly increased the catches of common Stomoxys such as Stomoxys niger niger Macquart, Stomoxys taeniatus Bigot, and S. calcitrans by 2.4, 1.6 and 1.9 times, respectively. Catches of Glossina pallidipes Austen were increased significantly in traps baited with acetone, urine or octenol, or any combination, relative to those in unbaited traps (1.4–3.6x). Catches of Glossina morsitans submorsitans Newstead were increased significantly by 1.5–1.7 times, but only when baits were used individually. Unlike other studies with East African tsetse, catches of both tsetse species with the complete bait combination (acetone, urine and octenol) did not differ from those in unbaited traps. Experiments with an incomplete ring of electric nets surrounding a Nzi trap, and a new approach using a sticky enclosure made from transparent adhesive film, revealed diverse responses to artificial objects and baits among biting flies. In Kenya, daily trap efficiency estimates for traps baited with either carbon dioxide (6 L/min) or a combination of acetone, cattle urine and octenol were 21–27% for G. pallidipes, 7–36% for Glossina longipennis Corti, 27–33% for S. n. niger, and 19–33% for Stomoxys niger bilineatus Grünberg, assuming 100% electrocution efficiency. Actual trap efficiencies may have been lower, given observed outside : inside electric net catch ratios of 0.6 : 1.6. Observed ratios averaged 54% of expected values, with 10 of 15 possible ratios less than the minimum possible value of 1.0.

Effect of puparia incubation temperature: increased infection rates of Trypanosoma congolense in Glossina morsitans centralis, G. fuscipes fuscipes and G. brevipalpis

Abstract. Puparia of Glossina morsitans centralis (Machado), G.fuscipes fuscipes (Newstead) and G.brevipalpis (Newstead) were incubated at 25 ± 1°C, 28±1:25±1°C, day:night or 29±1°C throughout the puparial period, and maintained at 70–80% relative humidity. Puparial mortality was higher at 29 than at 25°C (optimum temperature) in all three species, particularly in G.f.fuscipes and G.brevipalpis. Adults of G’.m.centralis from puparia incubated at 29°C, and those of this subspecies, G.f.fuscipes and G.brevipalpis from puparia incubated at 28:25°C, day:night or 25°C throughout, were infected as tenerals (27 h old) by feeding them at the same time on goats infected with Trypanosoma congolense (Broden) IL 1180 after the parasites were detected in the wet blood film. Infection rates on day 25 post‐infected feed were higher in G.m. centralis from puparia incubated at 29°C and in adults of the three different tsetse species from puparia incubated at 28:25°C, day:night, than in those from puparia incubated at 25°C. However, in G.f.fuscipes the labral and hypo‐pharyngeal infection rates were not significantly different from those of the tsetse produced by puparia kept at 25°C.

Life history of Oplostomus haroldi (Coleoptera: Scarabaeidae) under laboratory conditions and a description of its third instar larva

The life history of Oplostomus haroldi (Witte), a recently reported pest of honeybee colonies in East Africa, was studied for the first time under laboratory conditions. Adult O. haroldi collected from beehives in the coastal part of Kenya were reared on a mixture of moist sterilized soil and cow dung. At 25 ± 2 °C, 50 ± 5% relative humidity and a 10h light-14h dark photoperiod, the laid eggs took 11.9 ±1.3 days to hatch into a curved pear-shaped scarabaeiform larva with a well-developed head and thoracic legs. The first, second and third larval instars lasted 14.6 ± 2.6, 17.5 ± 2.4 and 34.6 ± 2.4 days, respectively. The pupal stage, which was marked by formation of a mud cocoon, lasted 31.1 ± 6.7 days with the adults surviving for 2–6 months under laboratory conditions, suggesting that the beetle is multivoltine. A detailed taxonomic description of the external morphology of the third instar larva is provided.

The Biology and Control of the Greater Wax Moth, Galleria mellonella

The greater wax moth, Galleria mellonella Linnaeus, is a ubiquitous pest of the honeybee, Apis mellifera Linnaeus, and Apis cerana Fabricius. The greater wax moth larvae burrow into the edge of unsealed cells with pollen, bee brood, and honey through to the midrib of honeybee comb. Burrowing larvae leave behind masses of webs which causes galleriasis and later absconding of colonies. The damage caused by G. mellonella larvae is severe in tropical and sub-tropical regions, and is believed to be one of the contributing factors to the decline in both feral and wild honeybee populations. Previously, the pest was considered a nuisance in honeybee colonies, therefore, most studies have focused on the pest as a model for in vivo studies of toxicology and pathogenicity. It is currently widespread, especially in Africa, and the potential of transmitting honeybee viruses has raised legitimate concern, thus, there is need for more studies to find sustainable integrated management strategies. However, our knowledge of this pest is limited. This review provides an overview of the current knowledge on the biology, distribution, economic damage, and management options. In addition, we provide prospects that need consideration for better understanding and management of the pest.

Male Annihilation Technique Using Methyl Eugenol for Field Suppression of Bactrocera dorsalis (Hendel) (Diptera: Tephritidae) on Mango in Kenya

The Oriental fruit fly, Bactrocera dorsalis (Hendel), is one of the most devastating tephritid fruit flies of horticulture worldwide. Field trials were carried out for two seasons on mango (Mangifera indica L.) to evaluate the use of male annihilation technique (MAT) using methyl eugenol laced with deltamethrin instead of the commonly used malathion for the suppression of the pest on mango in coastal Kenya. Prior to application of the MAT, mean total numbers of B. dorsalis flies per trap per day (FTD) in pre-suppression monitoring data were comparable in orchards assigned to MAT treatment (FTD = 3.5) and those assigned to the control (FTD = 3.5) in season 1 and 12.4 and 10.5 FTD, respectively, in season 2. Following the application of MAT systems, total FTD were significantly lower in MAT-treated orchards (0.1 and 2.7 FTD, for seasons 1 and 2, respectively) compared to that in the control (18.6 and 21.5 FTD, for seasons 1 and 2, respectively) at 49 days after deployment of the control measures. This represented a reduction in the B. dorsalis population of 99.5%in both seasons, resulting in a significant reduction of fruit infestation in the MAT-treated orchards compared to the control. The percentage of infested fruit was 25 and 18 times lower in MAT-treated orchards compared to the control for the first and second season, respectively. The number of puparia/kg ofmangofruit was 17 and 24 fold lower in MAT-treated orchards compared to the control for the two consecutive seasons. These findings demonstrate the suppression of B. dorsalis using the MAT, and subsequent reduction in fruit damage by the pest. It is therefore recommended that MAT be adopted within a holistic Integrated Pest Management (IPM) approach in the mango agro-system, preferably covering large areas.

Pathogenicity and performance of two candidate isolates of Metarhizium anisopliae and Beauveria bassiana (Hypocreales: Clavicipitaceae) in four liquid culture media for the management of the legume pod borer Maruca vitrata (Lepidoptera: Crambidae)

The aim of this study was to identify and develop entomopathogenic fungi as biopesticides for management of Maruca vitrata (Fabricius). Fourteen isolates of Metarhizium anisopliae (Metchnikoff) Sorokin and six of Beauveria bassiana (Bals.-Criv.) Vuill. were screened against first instar larvae of M. vitrata. The two most virulent isolates were selected and further tested for production in four liquid media. Different formulations of one isolate were evaluated against different developmental stages. Metarhizium anisopliae ICIPE 18 and ICIPE 69 caused highest larval mortality of 91 and 81%, with lethal time to 50% mortality (LT50) values of 1.8 and 1.7 days and LC50 of 1.07 dx 107 and 3.01 dx 106 conidia/ml, respectively. ICIPE 69 yielded more biomass and propagules in two liquid media than ICIPE 18. All developmental stages and adult moths were susceptible to fungal infection and horizontal transmission caused a significant reduction in fecundity. Isolate ICIPE 69 was identified as the most potent isolate for managing M. vitrata based on demonstrated efficacy against different developmental stages and amenability to production in liquid media and could be utilized as an alternative to pesticides in cowpea IPM.

Habitat preferences and activity patterns of glossina swynnertoni Austen (diptera: glossinidae) in Aitong, Masai Mara, Kenya

The habitat preferences and activity patterns of Glossina swynnertoni Austen were studied using Siamese traps, electrified screens and vehicle patrols in Aitong, southwestern Kenya in three habitats: large thicket, wooded grassland and an Acacia community. Except in the Acacia community, G. swynnertoni occurred in association with Glossina pallidipes Austen. Apparent density varied significantly among the three habitats, being highest in the Acacia community, intermediate in wooded grassland and lowest in large thickets. Density also varied seasonally, with higher densities occurring in the rainy season than in the dry season in all three areas. Vehicle patrol was a more effective and rapid method for sampling G. swynnertoni than either Siamese traps or electrified screens. However, vehicle patrol catches were strongly biased in favour of males (4:1). Diurnal activity in the Acacia community was unimodal for both sexes, with peaks of activity occurring at 1100–1200 h for males and at 1400–1500 h for females. Both sexes remained active in the afternoon but activity declined rapidly towards dusk (1700–1800 h).RésuméLes préférences d’habitat et les rythmes d’activité de Glossina swynnertoni Austen ont été étudiés à l’aide de pièges de Siamese, d’écrans electrifies et de récoltes (patrouilles) en voiture, à Aitong, dans le Sud-ouest du Kenya dans trois habitats des grands bosquets, de la savane arborée et une forêt d’acacias. A l’exception de la forêt d’acacias, G. swynnertoni est rencontrée en association avec G. pallidipes Austen. La densité apparente varie significativement entre les trois habitats; elles est la plus forte dans la forêt d’acacias, intermédiaire en savane arborée et plus faible dans les grands bosquets. La densité varie également avec la saison, avec de plus fortes densités observées en saison des pluies par rapport à la saison sèche dans les trois habitats. Les captures réalisées lors des patrouilles en voiture sont plus efficaces et rapides pour l’échantillonnage de G. swynnertoni que les pièges de Siamese, et que les écrans électrifiés; ces captures sont cependant fortement biaisées en faveur des mâles (4:1). L’activité diurne dans la forêt d’acacias est unimodale pour les deux sexes, avec des pics d’activité entre 1100–1200 h pour les mâles et 1400–1500 pour les femelles. Les deux sexes restent actifs dans l’après-midi mais l’activité décline rapidement vers le crépuscule (1700–1800 h).

Temperature-dependent phenology of Plutella xylostella (Lepidoptera: Plutellidae): Simulation and visualization of current and future distributions along the Eastern Afromontane.

There is a scarcity of laboratory and field-based results showing the movement of the diamondback moth (DBM) Plutella xylostella (L.) across a spatial scale. We studied the population growth of the diamondback moth (DBM) Plutella xylostella (L.) under six constant temperatures, to understand and predict population changes along altitudinal gradients and under climate change scenarios. Non-linear functions were fitted to continuously model DBM development, mortality, longevity and oviposition. We compiled the best-fitted functions for each life stage to yield a phenology model, which we stochastically simulated to estimate the life table parameters. Three temperature-dependent indices (establishment, generation and activity) were derived from a logistic population growth model and then coupled to collected current (2013) and downscaled temperature data from AFRICLIM (2055) for geospatial mapping. To measure and predict the impacts of temperature change on the pest’s biology, we mapped the indices along the altitudinal gradients of Mt. Kilimanjaro (Tanzania) and Taita Hills (Kenya) and assessed the differences between 2013 and 2055 climate scenarios. The optimal temperatures for development of DBM were 32.5, 33.5 and 33°C for eggs, larvae and pupae, respectively. Mortality rates increased due to extreme temperatures to 53.3, 70.0 and 52.4% for egg, larvae and pupae, respectively. The net reproduction rate reached a peak of 87.4 female offspring/female/generation at 20°C. Spatial simulations indicated that survival and establishment of DBM increased with a decrease in temperature, from low to high altitude. However, we observed a higher number of DBM generations at low altitude. The model predicted DBM population growth reduction in the low and medium altitudes by 2055. At higher altitude, it predicted an increase in the level of suitability for establishment with a decrease in the number of generations per year. If climate change occurs as per the selected scenario, DBM infestation may reduce in the selected region. The study highlights the need to validate these predictions with other interacting factors such as cropping practices, host plants and natural enemies.