Some areas are seeing this orchard-floor dweller moving up and damaging fruit. By Carin Smith.
Cenaeus carnifex, commonly known as the red bug due to its colour, is indigenous to South Africa and ubiquitous in orchards, usually on the orchard floor.
Until recently, red bugs were not known to cause problems for producers, but there are now reports of these insects changing their usual harmless behaviour.
Red bugs are principally seed feeders, but observations from the Langkloof indicate that they have started moving up into trees to feed on fruit. Similar behaviour has been seen in other major production areas, such as the EGVV and Ceres.
Apples, pears, and some stone fruit have been affected. In the Langkloof, some pear orchards suffered extensive damage estimated to have affected up to 50% of the fruit. The increased damage is not due to an outbreak of red bugs but probably represents a host shift of this common orchard insect.
What is Cenaeus carnifex?
Cenaeus carnifex is an oval red bug with prominent black legs and markings. They are sucking insects that use piercing mouthparts to suck sap, primarily from seeds but also from other plant parts, including fruit and stems.
The species has short- and long-winged forms. The short-winged form, which is flightless, seems to be the culprit damaging fruit in the Langkloof.
Dr Minette Karsten, entomology researcher at Hortgro, says red bugs are often seen paired up, with the male and female attached to each other. The female lays her eggs —about 1 mm in size — on the orchard floor.
Red bugs usually feed on plants in the mallow family, for example Malva parviflora, better known as kiesieblaar, a common orchard weed.
“They have certainly managed to shift to direct feeding on deciduous fruit,” says Dr Steffan Hansen, a postdoctoral fellow in the Department of Conservation Ecology and Entomology at Stellenbosch University.
Matthew Addison, Crop Protection Programme Manager at Hortgro Science, says it is unclear why red bugs in the Langkloof started feeding directly on the fruit. “It is all still speculative,” he notes.
There are various theories. Their feeding habits could have been impacted by drought, reducing the supply of their favourite kiesieblaar, or there could have been changes in weed management practices.
When sucking insects feed on fruit, they pierce the skin and probe the flesh. This causes indentations and browning of the fruit flesh. Exposure of the underlying tissue can also lead to secondary infections by decay-causing organisms.
It is not known if red bugs feed only on mature fruit. “We are not sure when in the phenology of the tree feeding takes place,” says Karsten. “We know they feed on the fruit, but some of the typical damage we see on fruit — indents and misformed fruit — may have been caused by early feeding during blossoming.”
If the damage occurs close to harvest, it might not show immediately. Damaged fruit could be packed and shipped only for the damage to be discovered and the fruit rejected by the receiver.
New red-bug research planned
Karsten says very little is known about red bugs because they have never been reported to cause financial losses in deciduous fruit. That is why she will lead a two-year Hortgro-funded research project based at Stellenbosch University.
The project has three main objectives: a comprehensive survey of sucking insects in orchards in three production areas and the characterisation of fruit damage; an evaluation of monitoring methods and biological control agents; and an evaluation of attractants for sucking insects.
“One can only manage what you can measure,” explains Karsten. “Once one can determine population numbers or measure the damage caused and has data, potential management and control measures can be implemented.”
As a first step, the researchers hope to develop a simple and practical monitoring method to determine if red bugs are present in an orchard. It is important to specify what red-bug damage looks like because other insects can cause similar damage. The survey will also indicate when during fruit development, damage occurs.
“Apart from monitoring, you need primary research on the biology and habits of the insect before you can manage it effectively,” explains Hansen.
The researchers plan to place net bags over blossoms and fruit bunches at different times during the season. In some treatments, called exclusion experiments, the net bags will keep out all insects. In others, called inclusion experiments, insects will be placed in the bags at different times. This will allow the researchers to study the association between the bugs and damage.
The project will also investigate plant volatiles that can potentially be used to attract bugs for monitoring and control. In addition, biological control agents, specifically entomopathogenic fungi, will be assessed.
Initial observations suggest that weevil stem bands might protect the fruit from being damaged by the flightless red bugs. Weevil bands create barriers which prevent insects from crawling up tree trunks.
“We need a sustainable approach or a physical control method such as a stem barrier,” says Addison, “coupled with the use of a biological control agent, as well as the management of weeds in orchards.”