Biological alert

After the report received from the renowned succulent plant production company AG of San Remo and the control of samples performed by the Regional Institute for Floriculture of San Remo, the presence of the thrips Hercinothrips dimidiatus (Hood, 1937) in Liguria on some old specimens of Aloe arborescens naturalized in the city green areas of San Remo is definitely confirmed.

Reported in Italy for the first time in 2021 in Sicily on Aloe arborescens (Schifani Mazza, 2021), its presence in Liguria poses a real risk of contamination of commercial productions of Aloe spp. and Haworthia spp. implemented in the numerous succulent plant production plants in the area.

Readers are invited to report any cases of infestation to info@festadelcactus.it, specifying the location and attaching some pictures of the affected plants. This information will be published as an update to this article. The person’s name and email address will be omitted out of respect for privacy.

Aside effect of globalization is the potential risk of the spread of exotic pests through the importation of host-plants, a forced migration flow that brings insects, fungi and other pests that in their country of origin live in balance with their predators, to new environments where they can eventually grow and spread undisturbed, causing substantial damage. After the death of palms caused by the red weevil, to the damage to fruit production caused by the Asian fruit bug, it is now the turn of our beloved succulent plants with a pest that threatens the survival of Aloes, a category of primary importance in Italian ornamental and industrial nursery production.

Description

Hercinothrips dimidiatus would be the vector of a disease whose etiological agent is unknown (some thrips species are responsible for tospovirosis such as Tomato spotted wilt virus – TSWV, but no other virosis is reported for this subfamily), which causes progressive and irreversible decay of Aloes until they die.
The following is some important information about this pest, published by theNational Plant Protection Organization, Netherland Food and Consumer Product Safety Authority – Ministry of Economic Affairs. Hercinothrips dimidiatus [Thysanoptera (thrips): Thripidae: Panchaetothripinae], of South African origin, was first reported in Europe in 2012 in Portugal (EPPO, 2015; Mateus et al., 2015), while in 2015 its presence was noticed in a Dutch commercial greenhouse on a batch of Aloe vera.
It was previously reported in the USA on Haworthia altilinea (Aloaceae; USDA, 1941).
In Italy, the first report is related to infestations present on some Aloe arborescens plants in a private collection in Sicily (Schifani & Mazza, 2021).
From the first description of damage observed on Aloe arborescens (Mateus et al. 2015) we know that “the older leaves of the damaged plants were dark brown or almost black.
Mature leaves showed silver areas on the upper surface, associated with small discolored scarifications and covered with dark-colored droplets of droppings, indicating the presence of thrips.
Some of those mature leaves showed dark red areas associated with small black necrosis.
A diffuse silvery discoloration was observed in the most necrotic branches.
Apparently discolored spots from pest attack at a later stage originate larger blackish necrosis surrounded by dark red areas.
These areas may expand to the entire surface of the leaf, including the underside.
Often, the leaves turn black and die.”

Spread of the parasite

Hercinothrips dimidiatus is a winged insect that spreads mainly by air. Air currents can spread it over considerable distances. Its global spread is through import-export of infested plants.

More information

All thrips specimens observed in Portugal were of the female gender, so it is assumed that in the colonization phase of new environments this insect implements telithotic parthenogenesis (generation of only female individuals without breeding), whereas in its country of origin both sexes are present. The life cycle of Hercinothrips dimidiatus is not known, so 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.

Remedies

In areas devoted to the production of Aloe spp., in case of reports of the presence of the pest, preventive chemical treatments based on Abamectin (e.g., Vertimec) are suggested on Aloaceae crops, taking care to test the product on plants before its extensive use. Thrips are present on host plants at all stages of their biological cycle (Mateus et al., 2015).

Bibliography

• EPPO (2015) First report of Hercinothrips dimidiatus in Portugal. EPPO Reporting Service 2015/025. https://gd.eppo.int/reporting/article-4451 [last access 23-10-2015]
• Hood JD (1937) New genera and species of Thysanoptera from South Africa. Annals and Magazine of Natural History (10) 19: 97-113.
• Mateus C, Franco JC, Caetano MF, Silva, EB da, Ramos AP, Figueiredo E Mound LA (2015) Hercinothrips dimidiatus Hood (Thysanoptera: Thripidae), a new pest of Aloe arborescens Miller in Europe. Phytoparasitica 10/2015; DOI: 10.1007/s12600-015-0492- z. http://link.springer.com/content/pdf/10.1007%252Fs12600-015-0492-z.pdf [last access 23-10-2015]
• 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.
• USDA (1942) List of intercepted plant pests (List of Pests Recorded During the Period July 1, 1940, to June 30, 1941, Inclusive, as Intercepted in, on, or with Plants and Plant Products Entering United States Territory.). United States Department of Agriculture, Bureau of Entomology and Plant Quarantine, Service and Regulatory, Washington, USA.https://archive.org/stream/inte41unit/inte41unit_djvu.txt [last access 23-10-2015]

September 1, 2024 Reported a case of infestation on a large specimen of Aloe arborescens of considerable age present in a private garden. The specimen shows several apices with different stages of infestation and dead.