Effectiveness of biological control and socioeconomic impacts of the invasive parthenium hysterophorus in Arusha, Tanzania

A Dissertation Submitted in Partial Fulfilment of the Requirements for the Degree of Master’s in Life Sciences of the Nelson Mandela African Institution of Science and TechnologyThis study assessed the methods which are likely to be biologically and socio-economically effective to control the invasive species P. hysterophorus in Arusha Tanzania. A variety of methods have been found ineffective in long-term control of P. hysterophorus. Thus, an effective integrated approach needs to be identified. In addition, perception and socioeconomic consequences about P. hysterophorus by farmers and pastoralists are still poorly understood. The study assessed the effect of a newly implemented bio-control agent, Zygogramma bicolorata, in 4 m 2 field plots. Further a novel approach of controlling P. hysterophorus was tested by using herbicidal extracts of the naturalized plants Dovyalis caffra and Cassia auriculata and compared it with 2,4-D. Finally, 123 farmers and 128 pastoralists in Mbuguni, Olasiti, Murieti and Sepeko wards were interviewed. It resulted that Z. bicolorata, particularly at highest population densities, is capable of reducing height of P. hysterophorus by 87% and biomass by 91%. There was a significant reduction (50%) in the measured parameters after application of low concentration of extracts of C. auriculata leaves and bark and D. caffra leaves and fruits (DcL and DcF). Invasion of farm fields by P. hysterophorus leads to yield reduction by half according to 21% of farmers, and 46% of farmers claimed that their income was negatively affected. Therefore, this study suggests the use of environmentally friendly bio-herbicides since it can foster P. hysterophorus control and emphasize that this method should be integrated with Z. bicolorata in the infestation areas for long-term suppression of P. hysterophorus

Effectiveness of Zygogramma bicolorata as a biocontrol agent against Parthenium hysterophorus in Arusha, Tanzania

This research article published by Taylor & Francis Online, 2020Parthenium hysterophorus is an invasive weed that poses significant threats to crop production, biodiversity, human and animal health. Few experiments have been carried out to test the effectiveness of biological control agents such as the beetle Zygogramma bicolorata against this invasive. We released Z. bicolorata beetles as bio-agent to control P. hysterophorus at the Tropical Pesticides Research Institute in Arusha, Tanzania, across two seasons, from February – July 2019 (wet) and August 2019 – January 2020 (dry). Feeding by Z. bicolorata reduced P. hysterophorus leaves, flowers, height as well as biomass, both in the dry and wet season. During the wet season, 100% of all P. hysterophorus leaves were eaten already 28 days after the onset of the experiment, particularly under the highest beetle population treatment (30 individuals). Parthenium hysterophorus flower numbers were greatly reduced under high beetle populations (30 individuals) compared to the control treatment (0 individuals) during both the wet and dry season. Parthenium hysterophorus height was reduced by 87% and 90% during the wet and dry season, respectively when 30 beetles were released. Similarly, biomass was reduced by 90% and 87% during the wet and dry season, respectively. Parthenium hysterophorus responses to beetle treatments did not differ significantly across seasons but the development of both the invasive and its control, Z. bicolorata, was slightly delayed in the dry season. We conclude that Z. bicolorata can be used as bio-agent to manage P. hysterophorus in Tanzania, particularly when released in large numbers