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

ABSTRACT

Parthenium 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.

KEYWORDS:

• Biological control
• beetles
• famine weed
• biomass
• Eastern Africa

Acknowledgments

The authors would like to thank Rufford Small Grant for nature conservation, grant number 27383–1 and the Centre for Research, Agricultural advancement, Teaching Excellence and Sustainability (CREATES, supported by the World Bank) for supporting this study. Thanks go to D. Samwely and M. Macha for help in collecting P. hysterophorus seeds, transplanting of seedlings, and data collection in the experimental site. The authors also thank the Tropical Pesticides Research Institute (TPRI) for granting permission to conduct these experiments.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by Rufford small grant for nature conservation: [Grant Number 27383-1]; Center for Research, Agricultural advancement, Teaching Excellence and Sustainability (CREATES, supported by the World Bank): [Grant Number M530/T17].