Chris Thorpe has very kindly being assisting with a new project on Mansimvula and Ingwelala using biological control to eradicate Opuntia spp (prickly pear).
Thank you to Chris for taking the time to record and share his latest update which is extremely interesting.
"We have conducted five releases/inoculations since we started the project in November 2022.
- 24th November: The training session and launch and demonstration release of Mealie Bugs (Hypogeococcus festerianus) on Queen of the Night (Cereus jamacaru) on both Mansimvula and Argyle, Ingwelala. (Sourced from DFFE, White River, Daleen Strydom).
- Second week of December 2022: Release of these mealie bugs on Mansimvula. (Sourced from DFFE Tzaneen, Victor Thelemi).
- 12th Feb 2023: Release of both Cochineal (Dactylopius opuntia) on Stricta Prickly Pears (Opuntia stricta) and Creeping Prickly Pears (Opuntia humifusa) on Mansimvula only. A follow up release of Mealie Bugs on Queen of the Night on both Mansimvula and on Argyle, Ingwelala. (Both the cochineal and mealie bugs were sourced from Ruth Scholtz, Rhodes University).
- During March, I have on occasions, done random releases of Mealie Bugs on Mansimvula.
- April 17, 2023; Release of the remainder of the Mealie Bugs on Mansimvula.
Releases were hampered by the heavy rains right at the time that we received the samples from Rhodes University. The flooding not only affected impassability to areas on the reserves, but especially Ingwelala, but it is not ideal to inoculate/release during heavy rains.
Lack of transport at Mansimvula and staff availability, hinder the ability of staff to carry out releases, and monitoring and reporting on their own.
Spraying of Prickly pear/Opuntia colonies on Ingwelala with MSMA is mutually exclusive to using biocontrol agents.
Results: Prickly Pears (Opuntia)
The picture below on the left shows Creeping Prickly Pears (Opuntia humifusa) in River Camp which was treated with cochineal in February. The impact and spread of the cochineal beetles on that colony is extensive.
The picture on below right shows Stricta Prickly Pear (Opuntia stricta) in full fruit that was also treated in February next to the Sibon cutline at River Camp. The cochineal is attacking the fruit, visible as the white fluffy waxy coatings covering the cochineal beetles.
These results are really encouraging to the extent that we may in future be able to harvest our own cochineal without relying on insects to be sent by the DFFE.
Challenges on Prickly Pears Project:
There are no biocontrol agents for Bunny Ears or Teddy Bear cactus (Opuntia microdasys). The work we did mid 2022 in digging up and bagging the Bunny Ears or Teddy Bear cactus colony below River Camp in an attempt to dehydrate or dry out the plants in sunlight failed dismally. In fact, our actions actually caused the colony to spread. See picture below. We are therefore left with only two options: either mechanical removal and burying, or chemical spraying with MSMA.
Results: Queen of the Night (Cereus jamacaru)
The pictures above are from the large Queen of the Night colony near the River Camp borehole and show the growth of the mealie bugs with their white waxy coatings attacking the growth tips of the cactus. The effect of this is that new growth is hindered.
On the mature cactus the mealie bugs find it difficult to penetrate the thick skin of the Queen of the Night, so concentrate round the base of the spines. These are less obvious but can be seen in the picture below.
Conclusion:
There have been varying degrees of success of the inoculations on Queen of the Night and further inoculations/releases will be required.
I have not carried out a recent inspection of the impact of the inoculations on Ingwelala, but we already have sufficient evidence on Mansimvula that the project is working; albeit slowly on Queen of the Night.
We are already self-sufficient on the bio agents for the two predominant species of prickly pear being Creeping Prickly Pears and Stricta Prickly Pear that we do not need to source more from the DFFE.
I believe we will need to source more mealybugs (Hypogeococcus festerianus) from the DFFE to continue inoculating/ releasing until these colonies are sufficiently well established that we can harvest and release locally on Queen of the Night.
This project is long term. We have not been sending monthly monitoring results through to the DFFE yet and really should do so. Ingwelala does not have the requisite software loaded and Mansimvula staff will need additional coaching.
Updated as at 7th May 2023.
I carried out an inspection yesterday (Saturday 6th May) on Mansimvula and am delighted to report that the mealybugs (Hypogeococcus festerianus) released onto Queen of the Night (Cereus jamacaru) have reproduced and spread vigorously in the three weeks since this report was written in mid-April. This is on all the plants, except one. See picture below.
If this rate of reproduction continues there will be no need for additional stocks of bugs to be obtained from DFFE and Mansimvula will shortly be able to provide both cochineal and mealy bugs for use on Ingwelala, ensuring self-sufficiency going forward”.
by Chris Thorpe