Author
Khethani V. Mawela
mawelak@arc.agric.za
Agricultural Research Council– Plant Health and Protection,
Pretoria
Coauthors
Naweji Katembo, Agricultural Research Council– Plant Health and Protection, Pretoria , South Africa
David O Simelane, Agricultural Research Council– Plant Health and Protection, Pretoria , South Africa
Abstract
A biological control programme against the Mexican sunflower, Tithonia diversifolia (Hemsl.) A. Gray (Asteraceae) was initiated in South Africa in 2007. After a decade of surveys and risk assessment of potential agents, a defoliating tortoise beetle Physonota maculiventris Stål (Coleoptera: Chrysomelidae) was approved for release in 2018: as the first biocontrol agent for T. diversifolia. Over 50 000 P. maculiventris have been released at 55 sites, with population sizes ranging from 200-1000 adults per site throughout the distribution range of T. diversifolia in KwaZulu-Natal, Limpopo, and Mpumalanga provinces in South Africa. Release sites were monitored to assess establishment, insect population density, impact, and spread of the tortoise beetle since 2019. Initial establishment of the beetle was confirmed in 2020, with over 60% of the release sites fully established in all three provinces to date. The size of the population released did not influence the establishment of the beetles. Populations of P. maculiventris are increasing at study sites, from an average of five beetles per plant in 2020 to 40 beetles per plant in 2024. The highest population density of the beetle was recorded in Limpopo while the lowest in Mpumalanga province. Field observations show demonstrable signs of severe defoliation and noticeable reduction of reproductive output of T. diversifolia due to significant feeding damage; population increase and spread of the beetle across all three provinces.
keywords
Defoliation
Population density
Reproductive output
Release
Spread
Highlights
Establishment of Physonota maculiventris was confirmed in 2020
The population density of the tortoise beetle is increasing
Severe defoliation by the tortoise beetle reduced reproductive output of T. diversifolia