Written by Almero Bosch, Timbavati Ecologist.

The Timbavati Private Nature Reserve (TPNR) has an active Alien Plant Control Program (APCP), which was established in 2010.

Over the years, the TPNR had used the initial approach of applying registered herbicides to combat invasive alien plants however, due to the massive increase in the price of these registered herbicides, other alternatives were looked at to eradicate these plants.

The two main problematic invasive alien plant species found on the TPNR are Opuntia stricta and O.humifusa. Both these species can successfully be controlled with the use of a biological agent, the Cochineal insect. The TPNR is actively spreading these Cochineal insects over the entire reserve on identified infected areas which were spotted and marked during annual surveys.

What is Biocontrol?

Biological control according to the Department of Forestry, Fisheries and the Environment is the attempt to introduce the problem species' natural enemies to its new habitat, with the assumption that these natural enemies will remove the problem species' competitive advantage until its vigour is reduced to a level comparable to that of the natural vegetation.

Natural enemies that are used for biological control are called biocontrol agents.

In the control of invasive plants, the biocontrol agents used most frequently are insects, mites and pathogens (disease-causing organisms such as fungi). Biocontrol agents target specific plant organs, such as the vegetative parts of the plant (its leaves, stems or roots) or the reproductive parts (flowers, fruits or seeds).

Co-creation of Cochineal

Cochineal insects are placed on so-called “breeding host plants” within a certain area with high densities of alien plants, doing so creating a breeding population which actively grows and self-propagates. These Cochineal insects will then become climatised within these areas of the reserve, this will increase the immediate success after infecting plants in the specific area.

After the initial placement on the breeding host plants, the insects will be harvested by cutting entire cladodes (leaf) from the host plant with the Cochineal intact and placing these cladodes on plants that need to be controlled, the insects feed and reproduce on these plants and eventually kill the plant.

A breeding host plant.  Note the white fluff on the plant, these are Cochineal established on the plant.  In time these insects will feed and kill the entire plant.

A close-up of the Cochineal.  White fluff all over the plant is the only visual indication that Cochineal is on the plant.

Plants infected by Cochineal will die after a couple of months.  The size of individual plants will determine the time it will take to die. Remembering that Cochineal are insects and that external environmental factors such as temperature and rainfall will affect them too.  But ultimately the plant will die with very limited human interference.

The harvesting of cladodes infected by Cochineal.  These cladodes will be placed on new plants to be eradicated, only one infected cladode is enough to kill a plant 50 times the infected cladode’s size.

Harvested cladodes with Cochineal ready to be transported and placed on other plants.

The Combat Bug

Two (2) of the Cochineal insects (crawlers) on a cladode. The white 'fluff' can only be produced by females, meaning at least one must be a female. The white fluff that is produced is made into a loose cocoon-like structure to protect the female and her eggs against predators and parasites.

A female that created a white fluff nest/cocoon wherein she will lay eggs. Other insects (crawlers) are present.

Video: This is a Cochineal insect (Crawler) busy either feeding or getting itself ready to settle on the cladode, to follow will be the production of the white fluff and then the laying of eggs in the white fluff cocoon structure.

Should you want to learn more about the other reserve activities follow the link here