Cotton seed bugs in stone fruit

A sporadic pest identified as Oxycarenus annulipes is the focus of a new Hortgro-funded project. By Jenny Underhill.

In the 2022–23 harvest season, two farms observed infestations of Lygaied bugs belonging to the genus Oxycarenus. The farms, located near Paarl and Greyton in the Western Cape, described extensive fruit damage caused by adult insects aggregating and feeding in stone-fruit orchards.

“These bugs were initially reported by experimental farms, and it seemed likely that the usual pest management protocols in commercial orchards were effective at keeping sporadic outbreaks under control,” says Dr Shelley Johnson, Hortgro Market Access Specialist and Research Associate in Phytosanitary Entomology.

“However, we are committed to a proactive approach to pest management, and these infestations prompted further investigation,” she adds. “It has become evident that the bugs can also be problematic in commercial orchards.”

Johnson is leading a Hortgro-funded project to study the new pest. The MSc student on the project is Melissa Calitz, currently registered at Stellenbosch University and supervised by Johnson and Dr Marelize de Villiers, Hortgro Entomology Market Access Specialist. Calitz plans to submit her MSc thesis at the end of 2026.

The project aims to identify these bugs, investigate their biology, assess their threat to the stone-fruit industry, and test postharvest mitigation measures, in case these are needed in the future.

What is Oxycarenus annulipes?

Oxycarenus annulipes, the cotton seed bug, only occurs in the southern parts of Africa and is a documented pest on cotton. The bugs are sap suckers. Although they only cause superficial black pinpricks on maturing fruit (figure 1), the damaged fruit are susceptible to secondary infection.

Michael Stiller, entomologist in the Biosystematics Division, ARC Plant Health and Protection, assisted with the initial identification, based on morphology.

DNA sequencing has not previously been done on O. annulipes. Consequently, when specimens were sent for DNA analysis, they were matched to closely related Oxycarenus species not found in South Africa.

“The taxonomic relationships within this genus were last revised in 1969, and are complex and poorly known,” says Calitz. “One of my project goals is to sequence several specimens of O. annulipes. This will help with future species identification and with updating the taxonomy.”

Interestingly, O. annulipes was reported in 1978 as a sporadic pest in fruit orchards in the Western Cape, but it has not been mentioned since. However, it may have been misidentified in the past because it can easily be confused with the grain chinch bug, Macchiademus diplopterus, a different Lygaeid bug that is morphologically similar (figure 2).

“Grain chinch bug is a known phytosanitary pest that does not feed on maturing fruit, but may potentially contaminate export fruit,” explains Johnson. “Its host plants are wild grasses, cultivated wheat, and other grains. After crops are harvested, it may opportunistically, and quite incidentally, seek shelter in fruit orchards.”

Remove mallows to manage bugs

In late 2024, Calitz began monitoring and scouting for O. annulipes to track its seasonal cycle and biology. Her study sites include one of the experimental farms where the infestations were first recorded and a grain research farm in Malmesbury.

The Malmesbury site was included because O. annulipes and M. diplopterus have consistently been reported in the wheat, canola, and oats fields used in crop rotation studies. This provides an opportunity to compare the behaviour of the two species as part of the project.

“I inspected the wheat and canola plants, the fruit orchards and every weed that was growing at these sites,” says Calitz. “The only plant that contained O. annulipes was the mallow plant, Malva parviflora. The presence of eggs, nymphs and mating behaviour suggested that this was their preferred host plant.”

Mallows are annual weeds that germinate in late autumn and set seed by October.

“Oxycarenus annulipes goes through its breeding cycle on the mallows,” says Johnson. “When the mallows die off or are disturbed — such as when grain fields are harvested in late spring to early summer — the bugs look for feeding sites and shelter elsewhere. If they enter nearby orchards and are still feeding, they may damage fruit.”

While M. diplopterus is already in summer dormancy when it seeks shelter in orchards, O. annulipes continues to feed until it enters a facultative diapause. This is also a period during which development is suspended due to suboptimal environmental conditions.

These findings are significant because they suggest that O. annulipes is not a primary pest of stone fruit. Since infestations by M. diplopterus and O. annulipes in orchards may occur close to harvest, chemical control is not usually feasible. Crucially, because its life cycle is host-dependent, pest control may be possible solely through weed management.

“If the host plant is well established in or near an orchard, then there may be an infestation. But if you remove the mallows, it is likely O. annulipes will go too,” says Calitz. She will continue monitoring the field sites until the end of the 2025–26 season.

Have you seen this bug?

To date, Calitz has carried out 221 morphological identifications of O. annulipes collected during her field monitoring and surveys. Most of the specimens were found at the Malmesbury site. In contrast to the 2022–23 season, O. annulipes was not observed in high numbers in the two subsequent seasons, confirming the sporadic nature of outbreaks.

The next step will be to assess the risk of O. annulipes to the industry by interviewing growers. Calitz hopes to determine if they are aware of this pest and whether it has previously caused any damage to their stone-fruit orchards.

“Even if we don’t get feedback from growers about problems with this species, it is important for this information to be communicated to a wider audience so that growers can distinguish between M. diplopterus and O. annulipes,” says Johnson.

If anyone has seen this insect or would like more information about the project, they are encouraged to contact Melissa Calitz at mcalitz@sun.ac.za.