Urbanus N. Mutwiwa

Effects of UV-Absorbing Plastic Films on Greenhouse Whitefly (Homoptera: Aleyrodidae)

Abstract Studies were conducted to investigate the effects of ultraviolet (UV)-absorbing plastic films on the orientation and distribution behavior of the greenhouse whitefly, Trialeurodes vaporariorum (Westwood). In field experiments, small tunnels were constructed and covered with either an UV-transmitting (Thermilux) or UV-absorbing (K-Rose) plastic film. Results show that significantly more whiteflies were recorded in the tunnels with high compared with those with low UV intensities. Moreover, whitefly penetration and dispersion were less inside the UV-deficient tunnels. These results suggest that the type of plastic film used for greenhouse covers may have a significant influence on both the initial immigration and distribution of T. vaporariorum into greenhouses. The possibilities of using UV-absorbing plastic films for whitefly integrated pest management in greenhouses are discussed.

A Spanner in the Works: Human–Elephant Conflict Complicates the Food–Water–Energy Nexus in Drylands of Africa

The two major conservation issues for drylands of Africa are habitat loss or degradation and habitat fragmentation, largely from agriculture, charcoal production, and infrastructural development. A key question for management is how these landscapes can retain their critical ecological functions and services, while simultaneously supporting resilient livelihoods. It is a clear nexus question involving food (agriculture), water and energy (fuelwood), which is complicated by human-wildlife conflicts. While these could appear disparate issues, they are closely connected in dryland forest landscapes of Africa where elephants occur close to areas of human habitation. For instance, crop failure, whether due to weather or wildlife damage, is a key driver for rural farmers seeking alternative livelihoods and incomes, one of the commonest being charcoal production. Similarly, heavy reliance on wood-based energy often leads to degradation of wildlife habitat, which heightens competition with wildlife for food and water, increasing the possibility of crop-raiding. So, for multifunctional landscapes where elephants occur in close proximity with humans, any food-water-energy nexus activities towards achieving sustainability and resilience should consider human-elephant conflicts. Here, we broach these food-water-energy nexus issues with a focus on dryland areas of Africa and human-elephant conflicts. We highlight an ongoing study attempting to address this nexus holistically by employing a climate-smart agriculture and agro-forestry based design, augmented by an elephant deterrent study and an eco-charcoal production venture.

Assessment of Sedimentation Status of Ruiru Reservoir, Central Kenya

Reservoir sedimentation can adversely affect the storage capacity of water bodies; reduce flood attenuation, change water quality, damage valves and conduits amongst others. This study investigated sedimentation rate in Ruiru reservoir as a measure for monitoring water resource management using capacity survey method. Water depth was measured using a transducer fitted on the side of the boat which also recorded corresponding geographic positions with an inbuilt GPS receiver. About 5000 points covering approximately 36 hectare of the water surface were surveyed. A total of eleven sediment sampling points were identified in the reservoir in which five were strategically selected at location near entry from respective streams. The depth of sediments, which relate to the quantity of sediment deposition from the streams ranged between 600 mm and 2100 mm. Ruiru stream demonstrated the highest level of sediment influx into the dam while Ngeteti stream had the least. The reservoir volume was calculated to be 2,632,347m3 and estimate volume of the sediments 389,245 m3, which is a 13.1% storage capacity loss. A related recent study noted storage capacity loss of 11%, which shows that the reservoir has lost about 11-14% of its storage capacity in 65 years. Results further showed that the Area Specific Sediment Yield (ASY) was 38.84 Mg ha-1 y-1, which is higher than the tolerable soil loss of 2 to 18 Mg ha-1 y-1 for the tropics, but is within the range of 10 - 200 Mg ha-1 y-1 typical of savanna ecosystems. These findings are useful to water resource managers because they can help in computing the useful life of a reservoir.