Hercinothrips dimidiatus Hood is a tiny thrips of South African origin that has emerged in the last decade as a serious and spreading pest of cultivated aloes across southern Europe. First detected in Portugal in 2012 on Aloe arborescens, it has since been recorded in Italy (Sicily, 2021), France (Corsica, 2018), the Netherlands (in a commercial greenhouse, 2015), Gibraltar, Mallorca and Germany. Unlike the better-known aloe mite (Aceria aloinis), which is an eriophyid mite that causes galls, Hercinothrips dimidiatus is an insect — a true thrips that feeds by rasping the leaf surface, producing characteristic silvery scarring that darkens to necrotic black patches and can progressively kill the plant. Because it is still poorly known — its life cycle has not been fully described and no formal control protocols exist — this article gathers all currently available information from the scientific literature and European plant health authorities.
Classification and naming
Hercinothrips dimidiatus was described by J.D. Hood in 1937 from specimens collected in Bloemfontein, in the Free State province of South Africa, on an unidentified liliaceous plant. It belongs to the order Thysanoptera (thrips), family Thripidae, subfamily Panchaetothripinae — a group of thrips characterised by their relatively large size (for thrips) and their association with broadleaved plants in tropical and subtropical regions.
The genus Hercinothrips contains several species of economic importance. The most widespread is Hercinothrips femoralis (the banded greenhouse thrips), a polyphagous pest of ornamental plants in greenhouses worldwide. Hercinothrips dimidiatus was much more obscure until its emergence in Europe in the 2010s.
A key to the species of Hercinothrips, including a new species, was published by Goldarazena and Vierbergen in 2022 (Zootaxa 5169: 322–330).
Distribution
Native range
South Africa. The species was originally described from the Free State and appears to be native to the drier interior regions of southern Africa. In its native range, it presumably exists in ecological balance with natural predators — a balance that does not exist in the invaded European range.
Invaded range
Portugal (2012/2014): the first European and Palaearctic record. Hercinothrips dimidiatus was detected on Aloe arborescens in the municipalities of Lisbon, Oeiras and Cascais (Mateus et al. 2015, Phytoparasitica 43: 689–692). Plants in public gardens, private gardens and along roadsides were severely infested. EPPO reports that the first damage was actually observed in January 2012 in the gardens of a laboratory in Lisbon, though the thrips was not formally identified until 2014. It is suspected that the pest was introduced through the activities of the Lisbon international maritime port or airport.
Netherlands (2015): found in a commercial greenhouse on a batch of imported Aloe vera.
France (2018): first record from Corsica on Aloe arborescens, reported in the BSV JEVI FLASH n°5 of 28 September 2018 (plant health bulletin of the French plant protection services).
Italy (2021): first Italian record, on Aloe arborescens in a private collection in Sicily (Schifani & Mazza 2021, Zootaxa 5039: 440–442).
Other records: Gibraltar, Mallorca. Thrips-ID also reports records from Germany on imported Aloe vera and other succulents (Ulitzka, unpublished).
California, USA (1940/1941): historically, Hercinothrips dimidiatus was intercepted in the United States on Haworthia altilinea plants imported from South Africa. This early record (USDA 1942) predates the European invasion by seven decades. Whether the species established a permanent population in California is unclear.
Trajectory
The pattern is unmistakable: Hercinothrips dimidiatus is expanding its range through the Mediterranean basin, following the distribution of cultivated Aloe arborescens and Aloe vera. Every Mediterranean country with significant outdoor aloe cultivation is at risk.
Host plants
Hercinothrips dimidiatus feeds primarily on species of Aloe (Asphodelaceae). The most commonly infested species in Europe is Aloe arborescens, which is widely planted as an ornamental and semi-wild landscape plant throughout Mediterranean coastal areas. Aloe vera has also been recorded as a host.
Thrips-ID notes that the species is “occasionally found in association with Hercinothrips aethiopiae” and has been recorded on Haworthia (specifically Haworthia altilinea in the original US interception). Other related genera in the subfamily Asphodeloideae — Gasteria, Haworthiopsis, Aloidendron — should be considered potentially susceptible, though no formal records exist.
Damage symptoms
Visual progression
EPPO and the original Portuguese study (Mateus et al. 2015) describe the damage progression in detail:
Stage 1 — early feeding damage: mature (older) leaves develop silvery areas on the upper surface, caused by the thrips rasping open the epidermal cells and feeding on the released cell contents. Small, discoloured scarification marks are visible. Dark-coloured excrement droplets (frass) are deposited on the leaf surface, appearing as tiny black specks.
Stage 2 — expanding necrosis: the silvery feeding areas enlarge and darken, developing into larger black necrotic patches. The leaf surface becomes progressively disfigured.
Stage 3 — leaf death: heavily attacked leaves turn dark brown to almost black over their entire surface and die. The damage typically begins on the oldest (outermost) leaves and progresses inward toward the younger foliage.
Stage 4 — plant death: in severe, untreated infestations, the progressive loss of leaves weakens the plant until it collapses and dies. The Italian succulent association Festa del Cactus describes “progressive and irreversible decay of Aloes until they die.”
Distinction from other aloe pests
The damage pattern of Hercinothrips dimidiatus is distinct from that of the aloe mite (Aceria aloinis) and from common spider mite damage:
Aloe mite: produces fleshy, warty galls (tumorous growths) — not silvering or blackening. The galls are three-dimensional protuberances, not flat surface damage.
Spider mites (Tetranychus spp.): produce fine webbing on the underside of leaves and a generalised stippled, bronzed discolouration — not discrete silvery patches with black frass.
Aloe thrips (Hercinothrips dimidiatus): produces silvery scarring on the upper leaf surface with black frass droplets, progressing to large black necrotic areas. No galls, no webbing.
Possible viral vectoring
Festa del Cactus raises an alarming possibility: Hercinothrips dimidiatus “would be the vector of a disease whose etiological agent is unknown, which causes progressive and irreversible decay of Aloes.” Several thrips species in other systems are known vectors of tospoviruses (e.g., Frankliniella occidentalis transmits Tomato spotted wilt virus, TSWV), but no specific virus has been identified in association with Hercinothrips dimidiatus to date. If a viral component is confirmed, this would make the pest considerably more dangerous than the feeding damage alone suggests, because even plants that survive thrips feeding could carry a persistent, transmissible virus. Research is ongoing.
Biology
What is known
Very little. The life cycle of Hercinothrips dimidiatus has not been formally described. In general, thrips in the subfamily Panchaetothripinae complete their life cycle on the host plant, with eggs laid into plant tissue (endophytic oviposition), two active larval stages that feed on the leaf surface, and two non-feeding pupal stages (prepupa and pupa) that may occur on the plant or in the soil.
Parthenogenesis: all thrips specimens collected in Portugal and in other European populations have been female. This indicates that Hercinothrips dimidiatus reproduces by thelytokous parthenogenesis (production of females without mating) in the invaded range — a common strategy for thrips colonising new environments, where a single female can found an entire population. In South Africa, both sexes are present.
Pupation site unknown: EPPO notes that “it is not excluded that it implements some stages (prepupa and pupa) in the soil, a possibility that would complicate the control of its presence and spread.” If pupae are in the soil, topical foliar sprays alone may not break the reproductive cycle.
All stages on the host: Mateus et al. (2015) observed thrips at all developmental stages on the infested plants, confirming that the entire life cycle can be completed on the aloe host.
What is not known
The generation time (egg to adult), the number of generations per year, fecundity (eggs per female), the role of abiotic factors (temperature, humidity) in population dynamics, the overwintering strategy, and the predator community in the invaded range are all undocumented.
Control
The challenge
Because the biology of Hercinothrips dimidiatus is so poorly studied, no evidence-based integrated pest management (IPM) protocol exists. All current recommendations are extrapolated from control measures for related thrips species or based on limited field observations.
Chemical control
Abamectin (trade name Vertimec) is the most commonly recommended active ingredient. The Dutch and Italian plant health authorities suggest preventive treatments with abamectin on Aloe crops in areas where the pest has been reported. Abamectin is a macrocyclic lactone with translaminar activity — it penetrates the leaf tissue and can reach thrips feeding on the surface and within leaf folds.
However, abamectin alone may not be sufficient if pupal stages occur in the soil (beyond the reach of foliar applications). In that case, soil drenches with systemic insecticides may be needed to target emerging adults.
Spinosad is another option commonly used against thrips in horticultural settings. It is derived from naturally occurring soil bacteria (Saccharopolyspora spinosa) and is effective against thrips larvae on contact and by ingestion.
Important: always test any chemical treatment on a small area of the plant first before extensive application, as some aloe species may show phytotoxicity (leaf burn) from certain formulations.
Physical and cultural control
Inspection of new acquisitions: as with all invasive pests, the most effective measure is preventing introduction. Inspect all newly purchased aloes — especially Aloe arborescens and Aloe vera — for silvery leaf scarring, black frass, or tiny elongated insects in the leaf axils.
Removal and destruction of heavily infested leaves: removing the most severely damaged (usually the oldest) leaves reduces the thrips population and removes breeding sites. Seal infested material in plastic bags and dispose in household waste.
Isolation: quarantine infested plants well away from the rest of the collection. Thrips are weak flyers but can be carried short distances by wind.
Biological control
No specific biological control agents have been studied for Hercinothrips dimidiatus. In its native South African range, natural predators presumably keep populations in check — but these predators are absent in Europe. General predators of thrips include minute pirate bugs (Orius spp.), predatory mites (Amblyseius cucumeris, Amblyseius swirskii), and lacewing larvae. Whether these generalist predators can effectively suppress Hercinothrips dimidiatus in Mediterranean outdoor conditions is unknown.
Regulatory status
Hercinothrips dimidiatus is not currently listed as a regulated quarantine pest by EPPO. However, it is monitored through the EPPO reporting service, and multiple EPPO alerts have been issued (2015, 2016). The speed of its spread through Mediterranean Europe — Portugal (2012), Netherlands (2015), France (2018), Italy (2021) — suggests that regulatory attention may increase if the pest continues to expand and cause economic damage to the aloe nursery industry.
In southern Europe, Aloe arborescens is not only an ornamental plant but also an increasingly important crop for the cosmetic and health industries (aloe gel production). The arrival of a specialist pest capable of killing mature plants is a significant phytosanitary concern.
What to watch for: advice for aloe growers
If you grow aloes outdoors in a Mediterranean climate — particularly Aloe arborescens and Aloe vera — monitor your plants regularly for the following early warning signs:
Silvery or pale grey patches on the upper surface of older leaves, especially toward the leaf tips.
Tiny black specks (frass) on or near the silvery areas.
Small, elongated, dark-bodied insects (approximately 1.5 mm long) in leaf axils or on the underside of leaves. A hand lens (10x) helps significantly.
Progressive blackening and death of outer leaves, moving inward over weeks or months.
If you suspect Hercinothrips dimidiatus, isolate the plant immediately, remove and bag the worst-affected leaves, and consider contacting your regional plant health authority to report the occurrence — particularly if you are in a country where the species has not yet been formally recorded.
References
Hood, J.D. (1937). New genera and species of Thysanoptera from South Africa. Annals and Magazine of Natural History (10) 19: 97–113.
Mateus, C., Franco, J.C., Caetano, M.F., Borges da Silva, E., Ramos, A.P., Figueiredo, E. & Mound, L.A. (2015). Hercinothrips dimidiatus Hood (Thysanoptera: Thripidae), a new pest of Aloe arborescens Miller in Europe. Phytoparasitica 43: 689–692. DOI: 10.1007/s12600-015-0492-z
Schifani, E. & Mazza, G. (2021). Hercinothrips dimidiatus (Thysanoptera, Thripidae), an emerging pest of Aloe arborescens [Asphodelaceae] newly recorded from Italy. Zootaxa 5039(3): 440–442.
Goldarazena, A. & Vierbergen, G.B. (2022). A key to species of Hercinothrips, with one new species, and a neotype designation for H. trilineatus (Priesner). Zootaxa 5169(4): 322–330.
BSV JEVI FLASH n°5 (2018). Hercinothrips dimidiatus Hood sur Aloe arborescens, premier signalement en France. Bulletin de Santé du Végétal Corse, 28 septembre 2018.
EPPO (2015). First report of Hercinothrips dimidiatus in Portugal. EPPO Reporting Service 2015/043.
EPPO (2016). Details on the situation of Hercinothrips dimidiatus in Portugal. EPPO Reporting Service 2016/045.
USDA (1942). List of intercepted plant pests. United States Department of Agriculture, Bureau of Entomology and Plant Quarantine.
Simmonds, M.S.J. (2004). Pests of aloes. In: Reynolds, T. (ed.), Aloes: the genus Aloe, pp. 367–380. CRC Press.
Mound, L.A. (1965). The genus Hercinothrips (Thysanoptera) with one new species. Annals and Magazine of Natural History 13(8): 243–247.