Recently there have been reports about the hyacinth biological control agents, or hyacinth bugs as they are known, leaving the water hyacinth on the dam overnight and congregating at lights and windows of residents and homeowners. But residents need not worry, the Centre for Biological Control at Rhodes University says it is a good thing and it won’t eat other plants!

“We have received a number of reports to this effect, but here is no need for concern. While this may be troubling, please be advised that this is a good sign, as the plant quality has deteriorated to such an extent that the insects have been forced to move off the plants to seek healthier water hyacinth on which to feed. This situation has only been recorded twice previously, once in Lake Victoria in the 1990s and another time in south Florida in the USA in the 1980s where the insects were noted to have become “crunchy underfoot”. In both of these occasions, the movement of the insects was closely linked to a significant decrease in water hyacinth biomass as a result of biological control,” Benjamin Miller of the BCBC said.

Around the dam, both the weevils (Neochetina bruchi and Neochetina eichhorniae) and the planthopper Megamelus scutellaris have been recorded moving off the water. “Please note, these insects are host specific, and cannot complete their lifecycles on other plant species except water hyacinth, and any feeding that may occur on other plants is either exploratory or to gain moisture for them to continue moving to find more water hyacinth. The most likely cause for this scenario is that these insects have recently emerged from juvenile life-stages, expecting the large healthy plants they had earlier in the season to find plants that have deteriorated drastically, thus prompting them to disperse,” Miller said.

Although a nuisance, the insects pose no health threat to humans. Much like the brown rose beetles, the insects are attracted to lights at night, and therefore reducing the amount of light around windows and outside areas may help to reduce the extent to which the insects congregate around these areas when they move. This is only temporary and the insects will soon move off to other areas.

The Centre for Biological Control at Rhodes University will be sending a team of researchers to the dam to take some samples and survey the plant quality at the Hartbeespoort Dam.