mesquite
Evippe sp. #1 leaf-ties. Photograph: F. Heystek ARC-PHP.

The leaf feeding moth, Evippe sp. #1 was released into South Africa (SA) for the control of invasive Prosopis (mesquite) species on 24 February 2021 at the MeerKAT reserve at the Square Kilometre Array (SKA) Radio Telescope in the Northern Cape. A second release was made in North West near Bloemhof on 3 March 2021. More releases will commence in spring once the insect comes out of diapause.

Mesquite degrade arid regions

Mesquite is particularly well adapted to arid conditions and have an expansive root system, reaching over 50m to tap into groundwater. It was widely planted in the arid regions of SA from the late 1800s, mainly for shade and firewood and to use its pods as fodder. Having no natural enemies in Africa, these species and hybrids have proliferated and subsequently became invasive.

Adult Evippe sp. #1 under microscope stacked. Photograph: R. Lyle, ARC-PHP.

They have been demonstrated to have increasingly adverse effects compared to the benefits. They reduced plant species density and diversity, increased native tree mortality, reduced the cover of native grass and herbaceous plants. Furthermore, bare soil was directly correlated to the density of Prosopis invasions, and this loss of ground cover under mesquite facilitates soil erosion.

Impacts measured during studies on the bird and insect community composition in SA showed a loss of diversity associated with mesquite invasion. Ecosystem services such as soil quality, grazing and water supply are impacted by Prosopis invasions. This leads to a range of consequences for local human communities. These impacts occur across all biomes invaded by mesquite in SA but is more pronounced at high densities. These impacts are also set to increase as mesquite continues to expand its range and densifies.

Funding for research solutions

To obstruct its rapid expansion, seed-feeding bruchid species were the first natural enemies of mesquite introduced from their countries of origin. This followed research conducted at the Agricultural Research Council’s Plant Health and Protection (ARC-PHP) department in SA. Since 2014, the ARC, with generous funding provided by the Department of Environmental Affairs’ Natural Management Resource Programmes (DEA: NRMP), among others, focussed on studying the safety of a potential introduction of Evippe sp. #1 into Africa.

Prosopis stand with seedling recruitment. Photograph: F. Heystek ARC-PHP

This new biocontrol candidate, a species of gelechiid moth belonging to the genus Evippe, originally from Argentina, was found safe for release in Australia and introduced there in 1998. It proved to be their most successful biocontrol agent of mesquite. Our studies confirmed that Evippe sp. #1 was only able to develop to adulthood on the invasive alien Prosopis species and their hybrids, and not on related African species. Therefore, the Department of Agriculture, Land Reform and Rural Development granted permission for the introduction of Evippe sp. #1 as biocontrol agent of mesquite in SA on 21 December 2020.

What to expect from Evippe sp. #1

The feeding of the developing immature stages of the moth causes damage to the mesquite. A female moth lays about 75 eggs on the trees throughout her two- to three-week lifespan. The first instar larva of Evippe sp. #1 mines in a pinna of a mesquite leaf, while larger larvae feed externally in a shelter created by tying a few pinnae of a leaf together with silk threads. Entire stands of mesquite may be repeatedly defoliated, which reduces its fitness and may kill stressed trees. The moth’s entire lifecycle can be completed in less than 45 days.

Evippe sp. #1 is anticipated to establish widely in Africa, and could disperse well unaided, based on experience in Australia. These insects, and biological control in general, co-exist in their countries of origin on the trees that are maintained at much lower densities than in SA, where the trees have become invasive. A reduction in plant densities is thus a likely scenario, rather than eradication of mesquite. Lower densities add value to the plants in the field as it limits the impact caused by high plant densities, while simultaneously, greater value is derived from sparser trees. – Press release, ARC Marketing and Communications