Field margin vegetation in tropical African bean systems harbours diverse natural enemies for biological pest control in adjacent crops

Non-crop vegetation around farmland can be valuable habitats for enhancing ecosystem services but little is known of the importance of field margins in supporting natural enemies of insect pests in tropical agriculture. This study was conducted in smallholder bean fields in three elevation zones to assess the importance of field margin vegetation to natural enemy populations and movement to the bean crop for biological pest control. The pests and natural enemies were assessed using different coloured water pan traps (to ensure the capture of insects with different colour preferences) and the interactions of the two arthropod groups with the margin vegetation and their movement to the bean crop were monitored using fluorescent dye. Sentinel plants were used to assess predation and parasitism levels. A total of 5003 natural enemies were captured, more in the field margin than within the bean field for low and mid elevation zones, while in the high elevation zone, they were more abundant within the bean field. Pests were more abundant in the crop than margins for all the elevation zones. The use of a dye applied to margin vegetation demonstrated that common natural enemy taxa moved to the crop during the days after dye application. The proportion of dye-marked natural enemies (showing their origin to be margin vegetation) sampled from the crop suggest high levels of spatial flux in the arthropod assemblage. Aphid mortality rates (measured by prey removal and parasitism levels on sentinel plants) did not differ between the field edges and field centre in any of the three elevation zones, suggesting that for this pest taxon, the centre of the fields still receive comparable pest control service as in the field edges. This study found that field margins around smallholder bean fields are useful habitats to large numbers of natural enemy taxa that move to adjacent crops providing biological pest control service

Characterization of hymenopteran parasitoids of aphis fabae in an African smallholder bean farming system through sequencing of COI 'mini-barcodes'

Parasitoids are among the most frequently reported natural enemies of insect pests, particularly aphids. The efficacy of parasitoids as biocontrol agents is influenced by biotic and abiotic factors. For example, hyperparasitoids can reduce the abundance of the primary parasitoids as well as modify their behavior. A field study was conducted at three contrasting elevations on Mount Kilimanjaro, Tanzania, to identify the parasitoids of aphids in smallholder bean farming agroecosystems. Sentinel aphids (Aphis fabae) on potted bean plants (Phaseolus vulgaris) were exposed in 15 bean fields at three elevations for 2 days. The sentinel aphids were then kept in cages in a greenhouse until emergence of the parasitoids, which were collected and preserved in 98% ethanol for identification. Of the 214 parasitoids that emerged from sentinel aphids, the greatest abundance (44.86%) were from those placed at intermediate elevations (1000–1500 m a.s.l), compared to 42.52% from the lowest elevations and only 12.62% from the highest elevation farms. Morphological identification of the parasitoids that emerged from parasitized aphids showed that 90% were Aphidius species (Hymenoptera: Braconidae: Aphidiinae). Further characterization by sequencing DNA ‘mini-barcodes’ identified parasitoids with ≥99% sequence similarity to Aphidius colemani, 94–95% sequence similarity to Pachyneuron aphidis and 90% similarity to a Charipinae sp. in the National Center for Biotechnology Information (NCBI) database. These results confidently identified A. colemani as the dominant primary aphid parasitoid of A. fabae in the study area. A Pachyneuron sp., which was most closely related to P. aphidis, and a Charipinae sp. occurred as hyperparasitoids. Thus, interventions to improve landscapes and farming practice should monitor specifically how to augment populations of A. colemani, to ensure any changes enhance the delivery of natural pest regulation. Further studies are needed for continuous monitoring of the hyperparasitism levels and the dynamics of aphids, primary parasitoids, and secondary parasitoids in different cropping seasons and their implications in aphid control

Addressing pest and disease challenges in the national forest plantations: lessons learned from the national forest health forum

Proceedings of the 1st TAFORI Scientific Conference on Forestry Research for Sustainable Industrial Economy in Tanzania (2018), pg. 99-106This paper presents the results of the work carried out by the National Forest Health Forum (NFHF), which covered five National Forest Plantations: Mbizi (Sumbawanga), Meru/Usa (Kilimanjaro), Meru (Arusha), Shume (Tanga) and Sao Hill (Iringa) for the period of five years (May, 2012 - July, 2017). The problems addressed are diseases caused by pathogens and those caused by inadequacies of various requirements from the soils. Many of the diseases have been soil-borne which gave rise to foliar symptoms, with Armillaria root rot being in the lead. Occasionally, the ravage by insect pests was encountered at Sao Hill and Meru Forest Plantations. These problems threaten the productivity of the plantations against the objective for the plantations of supporting the much needed industrialization process. To a large extent, these problems which were recorded in the visited plantations were noted to be accelerated by two phenomena namely; climate change and taungya. Therefore, this paper describes the problems addressed in the plantations; the steps adopted in addressing them, key findings and recommendations for achieving better plantations

Addressing pest and disease challenges in the national forest plantations: lessons learned from the national forest health forum

Proceedings of the 1st TAFORI Scientific Conference on Forestry Research for Sustainable Industrial Economy in Tanzania (2018), pg. 99-106This paper presents the results of the work carried out by the National Forest Health Forum (NFHF), which covered five National Forest Plantations: Mbizi (Sumbawanga), Meru/Usa (Kilimanjaro), Meru (Arusha), Shume (Tanga) and Sao Hill (Iringa) for the period of five years (May, 2012 - July, 2017). The problems addressed are diseases caused by pathogens and those caused by inadequacies of various requirements from the soils. Many of the diseases have been soil-borne which gave rise to foliar symptoms, with Armillaria root rot being in the lead. Occasionally, the ravage by insect pests was encountered at Sao Hill and Meru Forest Plantations. These problems threaten the productivity of the plantations against the objective for the plantations of supporting the much needed industrialization process. To a large extent, these problems which were recorded in the visited plantations were noted to be accelerated by two phenomena namely; climate change and taungya. Therefore, this paper describes the problems addressed in the plantations; the steps adopted in addressing them, key findings and recommendations for achieving better plantations