The biological control insect numbers on the hyacinth on Hartbeespoort Dam have increased dramatically and because plants are dying off, the insects have started moving off the plants.

Residents are currently complaining about swarms of insects invading homes and some have even reported biting.

According to Prof. Julie Coetzee of the Rhodes University’s Centre for Biological Control, because the nutritional quality of the water hyacinth plants is in decline as a result of the bugs, the insects have been seen swarming during the evenings.

“The hyacinth cover on the dam is slowly declining, and the plants are turning brown. These insects are dispersing away from the damaged plants to find new water hyacinth that is more nutritious. However, they are attracted to lights that interfere with their navigation ability. The insects are host specific and cannot complete their life cycles on plants other than water hyacinth. They will not damage garden ornamentals or vegetables. However, they may attempt to feed on other plants to get moisture before they fly. This behaviour is purely investigative, and the insects will not survive on other plants. Furthermore, the insects are herbivores and cannot bite. They do not have biting mouthparts. Any reports of bites are from other insects like mosquitoes or biting flies that breed opportunistically in the water hyacinth mats,” she said.

There are currently three biocontrol agents on the hyacinth, namely Eccritotarsus catarinensis, Megamelus scutellaris, and Neochetina eichhorniae.

“While the inconvenience residents feel is regrettable, this is a short term problem. Furthermore, the swarming insects is a positive sign for managing the water hyacinth this summer. Please be patient as the benefits to the Hartbeespoort community from a decline in water hyacinth are tremendous. It is recommended that windows and doors are closed for a few hours in the early evening, and large outdoor lights are turned off to prevent the insects from coming into your homes”