Are surging populations of antestia bugs in pome- and stone-fruit orchards responsible for fruit defects? By Rae Oelofse.
Damage, including puncture wounds, sunken areas, brown spots, and distortion, is rising in pome and stone fruit. The defects are not visible during the early growth stages but manifest later in the growing season. Affected fruit is juiced instead of achieving high export prices.
Alongside fruit deformities, antestia bug numbers appear to be increasing, leading experts to speculate about their role in fruit defects.
What are antestia bugs?
Antestia bugs are insects in the genus Antestiopsis. Several Antestiopsis species have been documented in East Africa, but only A. thunbergii has been reported from South African deciduous-fruit orchards. More research on the distribution and seasonal variation of antestia in deciduous fruit in the Western Cape is required.
The bugs measure around 10 mm and emit a strong odour when disturbed. They undergo incomplete metamorphosis, progressing through egg, nymph, and adult stages — there is no pupal stage.
Detecting these elusive bugs is challenging, as they tend to emerge early in the season, primarily in boundary rows of orchards. It may be that nearby windbreak trees, such as pines and alders, act as alternative host plants. However, further research is needed to confirm this and identify other potential hosts.
Immature and adult bugs feed on vegetative and fruiting plant parts. They damage coffee, macadamias, and deciduous fruit during summer. The extent of the damage varies depending on the crop type and phenological stage.
According to Matthew Addison, Crop Protection Programme Manager at Hortgro, the sudden increase in antestia populations in pome- and stone-fruit orchards cannot be solely attributed to the gradual effects of climate change. He believes restricting chemical pesticide use may also be a contributing factor.
Scientists study sucking insects
Growing concerns about sucking insects have motivated various stakeholders in the pome- and stone-fruit industries, members from other sectors also affected by sucking insects, and several institutions to form a workgroup to gather information, share research findings, and prioritise research projects.
Hortgro is also funding a new project, led by Dr Minette Karsten, Hortgro entomology researcher, that will aim to develop an integrated pest-management system, including monitoring guidelines for sucking insects such as antestia in deciduous-fruit orchards.
The research team, based at Stellenbosch University, is refining monitoring strategies to determine the distribution and infestation levels of antestia bugs. This will help explain why high infestation levels occur in certain orchards. As part of this project, the team is also exploring alternative host plants.
“Despite the lack of information regarding the species or subspecies that are prevalent in orchards, our primary focus is to monitor antestia populations to understand their infestation patterns,” explains Karsten. “While identifying the species is beneficial, our primary focus is pest management to mitigate financial losses.”
One challenge when assessing sucking insects is that their damage can look similar to that from other causes. An earlier Hortgro-funded investigation into pear stony pit concluded that sucking insects and apple stem pitting virus can produce similar fruit deformities, so the characterisation of fruit damage will form part of the antestia project.
The research team hopes to develop a comprehensive catalogue of sucking insects, including images and species names. They will sample insects from production regions and identify them using morphological and molecular analyses.
The search for control strategies
One aspect of the new project is studying the effect of semiochemicals extracted from coffee berries. Insects or plants release semiochemicals to attract or repel insects. For example, when plants are attacked, they release volatiles to attract insect predators.
Semiochemicals can potentially be used in lures for monitoring or trapping antestia bugs.
With a focus on integrated pest-management strategies, the research team is exploring whether antestia populations can be managed using entomopathogenic fungi. These naturally occurring fungi are highly effective at killing insects without harming humans, beneficial animals, or the environment.
Addison emphasises that strict regulations help minimise the risks associated with introducing non-indigenous biocontrol agents to ecosystems. Rather than introducing exotic organisms, the team tries to identify and multiply native entomopathogenic fungi.
The idea would be to spray the fungi on the bugs. “Damage occurs when the bugs are in the orchard,” says Addison. “Therefore, as a starting point, we will target the stage actively causing harm.”
Antestia eggs are usually sheltered, whereas nymphs and adults are more exposed, adds Dr Steffan Hansen, postdoctoral researcher at Stellenbosch University. “Our goal is to control the adult insects before they lay eggs in the orchard.”
Hansen, who is keenly interested in South African sucking insects, strongly advocates for an integrated approach. “We explore different options, beginning with entomopathogenic fungi, until we find a solution,” he says. “Even if we discover an effective management method, long-term control requires multiple approaches.”
“Although our understanding of the antestia bug is incomplete, insights gained from research on similar insects and various crops are valuable to refine our strategies,” concludes Karsten. “Additionally, continuous monitoring, industry feedback, and integrated pest management will be pivotal in addressing the antestia bug challenge.”