Integrated mealy bug management

Growers must adopt a strategic approach to overcome this ancient pest. By Anna Mouton.

Mealy bugs co-evolved with vascular plants over millions of years, and modern mealy bugs comprise more than 2 000 species exploiting a vast range of hosts. Despite their soft bodies and sedentary habits, mealy bugs are successful agricultural pests, resisting growers’ attempts to eliminate them.

In South Africa, mealy bugs are problematic on apples and pears and sporadically infest stone fruit. The obscure mealy bug (Pseudococcus viburni) infests pome and stone fruit and is the most common species on apples (figure 1). Pseudococcus viburni is called obscure because it is easily mistaken for other mealy bug species.

The long-tailed mealy bug (P. longispinus) also attacks pome and stone fruit (figure 2), while the citrophilus mealy bug (P. calceolariae) is occasionally found on pome fruit.

Mealy bugs could be confused with woolly apple aphids on apple trees, as both form white, furry colonies. If in doubt, squash the bugs. Mealy bugs have clear or yellowish bodily fluids, and woolly apple aphids have red or brownish bodily fluids.

The rise of the obscure mealy bug

It’s not only the identity of P. viburni that’s obscure — its origins are also unknown, but it’s believed to have spread from either Australia or South America. Obscure mealy bugs have been recorded from nearly 300 host plants across almost 100 families and in over 60 countries.

Pseudococcus viburni was already an established pest of South African vineyards by the 1930s, but only became a problem in apple orchards in 1961. Researchers believe that chemical control of codling moths (Cydia pomonella) facilitated the rise of obscure mealy bugs by exterminating their natural enemies.

Mealy bugs seldom impact the health of deciduous fruit trees. However, they can cause significant financial losses, as illustrated by events in 2002, reported in publications by Dr Waktola Wakgari and Prof. Jan Giliomee, when 30% of apples and 9% of pears intended for export to the United States were rejected due to mealy bug eggs and juveniles.

Even though the eggs and immatures were likely those of obscure mealy bugs, which occur in the United States, officials were unable to identify them and unwilling to take any phytosanitary risks. Mealy bugs species are difficult to tell apart, especially when immature, and identification may require molecular tools.

Besides raising phytosanitary concerns, mealy bug-infested fruit is unacceptable to consumers. The sugary honeydew excreted by the insects is a substrate for sooty mould, and the bugs themselves often hide in the stem and calyx ends of fruit, even finding their way into fruit cores.

Three surveys of pome orchards

The rejections of 2002 prompted the Deciduous Fruit Producers Trust (the predecessor of Hortgro) to fund a survey of mealy bugs and their parasitoids in Western Cape pome-fruit orchards in 2003. The project was led by Giliomee, who has since retired from Stellenbosch University.

A follow-up survey was conducted in 2007–2009 as part of Dr Pride Mudavanhu’s MSc research on integrated pest management of mealy bugs. This study was led by Prof. Pia Addison of the Department of Conservation Ecology and Entomology at Stellenbosch University and was also funded by the Deciduous Fruit Producers Trust.

The most recent survey was conducted in 2024–2025 as part of an ongoing Hortgro-funded project on integrated pest management of mealy bugs led by Dr Minette Karsten, Crop Protection Programme Manager at Hortgro Science. The doctoral student, Liana de Araujo, is expected to graduate in 2026.

In the two earlier surveys, obscure mealy bugs were the most common species in apple orchards, with long-tailed and citrophilus mealy bugs seldom encountered. De Araujo surveyed two apple orchards, finding obscure mealy bugs dominating in one and long-tailed mealy bugs in the other.

In pear orchards, obscure and long-tailed mealy bugs were equally common, and citrophilus mealy bugs were again rare. Long-tailed mealy bugs caused severe infestations in some orchards.

Mealy bugs on the move

Mealy bugs overwinter in crevices and under bark on the tree. They breed year-round, but reproduction during cold weather is slow. Females produce eggs that hatch into mobile crawlers. Rising temperatures in spring trigger waves of crawlers that scale the tree with the intent of colonising young shoots.

Crawlers are the first instar. Female mealy bugs have three instars, and males four. Males pupate to become winged adults. Adult male mealy bugs live only a few days and don’t feed. Their only goal is to seek and mate with females.

During his surveys, Mudavanhu observed crawler migration from December to June, with fruit infestations starting in January, when apples and pears were large enough to accommodate the pests in the calyx, stem end, and core. Mealy bug populations declined from late June until November.

Obscure mealy bugs develop at temperatures of 16–28 °C. Females can take up to four months to complete their life cycle when it’s cold, but only 6–7 weeks at optimal temperatures of 25 °C. They can produce up to 200 eggs.

Mealy bugs frequently partner with ants, which transport and guard the bugs in exchange for honeydew. When present, the ants defend mealy bug against predators and parasitoids. However, De Araujo reports finding no ants in the canopies of mealy bug-infested trees in her survey, suggesting that this association may be less significant in pome fruit.

Know when to strike

Female mealy bugs are hard to kill because they lurk in inaccessible places, and they’re protected from spray applications by a waxy layer. Crawlers are more vulnerable because they’re exposed while moving, and they haven’t yet secreted a thick water-repellent coating. Successful control hinges on detecting and eliminating crawlers before they reach new growth or fruit.

Monitoring for mealy bugs rests on three pillars: orchard history, seasonal scouting, and damage assessments. Orchard history informs choices about dormant applications and the control strategy for the coming season.

The patchy distribution of mealy bugs within an orchard complicates scouting. Therefore, it’s crucial to monitor a representative sample of evenly distributed trees weekly from mid-September. Scouts should inspect 25 pome trees per two hectares, checking five fruit clusters, five shoots, and two leaves per tree.

Scouting should include potential overwintering sites (females also hide here during summer), such as under bark and in crotches. Corrugated cardboard bands placed around branches and trunks may aid detection, as females like to congregate underneath.

Recording the locations of mealy bug hotspots within orchards is useful for follow-up scouting and assessing the effectiveness of control.

Fruit damage assessments should be done twice, once before thinning (late November to early December) and once before harvest (between February and early April). These can be combined with weekly scouting. In addition to visual inspection of five fruit clusters, one fruit from each cluster must be cut through the core.

Pheromone traps could be an additional monitoring tool in the future, with registrations for species-specific lures for obscure and long-tailed mealy bugs currently pending in South Africa. Traps catch only males because female mealy bugs are flightless.

Mudavanhu tested pheromone traps at three traps per hectare and estimated that 2.5 males per trap per two weeks was weakly correlated with the economic threshold of 2% fruit infestation.

De Araujo collaborated with Insect Science to test the company’s obscure and long-tailed mealy bug lures and found both to be effective for detecting males. In table grapes, the advent of male catches in spring signals that the first crawler waves are imminent, and that scouting should intensify, and the same is likely true in pome fruit.

Chemical control

Dr Gideon van Zyl of ProCrop discussed chemical control of mealy bugs in detail in a presentation at the 2024 Hortgro Technical Symposium. Watch his full presentation on the Hortgro YouTube channel or read a summary in Fresh Quarterly issue 26.

Van Zyl explained that dormant applications of organophosphates and growing-season applications of systemic pesticides form the basis of mealy bug control. He outlined the appropriate positioning and timing for different active ingredients in low- and high-pressure scenarios.

An important take-home from his presentation is that crawlers must be stopped before they reach the fruit calyx. Once inside the fruit, they are protected from chemicals. This highlights why regular and thorough monitoring is indispensable for preventing fruit rejections.

Biological control

The biological control of mealy bugs in certain crops relies on parasitoids and predators, but their contribution in pome fruit is still under investigation. The three industry-funded surveys mentioned above all found several wasp species parasitising mealy bugs, including Pseudaphycus maculipennis.

Pseudaphycus maculipennis was first described from the Canary Islands and has proven valuable for controlling obscure mealy bugs in several countries, including Australia and New Zealand. It’s not commercially available in South Africa.

Parasitoids and predators, whether commercially bred or naturally occurring, can significantly augment mealy bug control, but only when intentionally integrated into a holistic control programme. De Araujo’s ongoing research includes investigating how cover crops and crop protectants interact with natural enemies.

Hortgro has also funded projects on entomopathogenic fungi and nematodes for mealy bug control, including work by Drs Antoinette Malan and Noma Stokwe of the Department of Conservation Ecology and Entomology at Stellenbosch University, and Dr Letodi Mathulwe, currently at the KwaZulu-Natal Department of Agriculture. The most recent results are summarised in a SAFJ article.

Two entomopathogenic fungi (Beauveria bassiana and Metarhizium anisopliae) are available as registered products and could be incorporated into a spray programme when targeting crawlers.

Biological control is still in its infancy, without a solid evidence base and many unanswered questions. Still, it will undoubtedly assume a greater role as conventional pesticides come under increasing pressure. Growers are encouraged to consult their crop-protection advisers on how best to integrate biocontrol into their mealy bug management.