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Pests in Gardens and Landscapes

Myoporum Thrips Published 11/13 In this Guideline:

Adult myoporum thrips.

Myoporum thrips eggs in curled leaf.

Life stages from right: first instar larva, second instar larva, prepupa, pupa, adult female, adult male.

Galling of leaves and shoots caused by myoporum thrips.

Two black adult thrips and an orange prepupa within twisted leaves.

The myoporum thrips, Klambothrips myopori (Thysanoptera: Phlaeothripidae), is an invasive species that has been causing great damage to Myoporum plants in landscapes and nurseries along the California coast from San Diego to San Francisco. Native to New Zealand, this thrips has a limited host range and is primarily found on Myoporum trees, shrubs and groundcovers.

In California, myoporum thrips has only been observed on two species of Myoporum: M. laetum, which is a shrub or small tree, and M. pacificum, a creeping form grown as a ground cover. Live thrips and damage have not yet been observed on M. parvifolium, a common prostrate form of Myoporum typically used for erosion control in California landscapes.

In Hawaii, it has also been found attacking Naio, Myoporum sandwicense. The Naio tree is a dominant, native tree species that is both culturally and ecologically important to Hawaii.

A decline in the aesthetic quality of susceptible Myoporum plantings and tree death is now a common occurrence in California, where these plants have been widely planted because of their visual appeal, minimal management needs, low water requirement, and lack of pests prior to the introduction of the myoporum thrips.

Little is known about myoporum thrips, and it was only recently described in the scientific literature from samples collected in California and sent to Australia's Commonwealth Scientific and Industrial Research Organization. It is a new genus, Klambothrips, and the new species name is Klambothrips myopori.

IDENTIFICATION

Myoporum thrips adults are slender insects, 2-2.5 mm long. They are dark brown to black with fringed wings. Males are slightly smaller and similar in appearance to females. Their oblong white eggs are relatively large compared to the adult female and are deposited on leaf surfaces where they are enclosed within distorted plant tissue. In California, myoporum thrips adults may be confused with the greenhouse thrips, Heliothrips haemorrhoidalis, or the Cuban laurel thrips, Gynaikothrips ficorum, which has an almost identical life history and appearance and produces similar symptoms on Ficus species.

LIFE CYCLE

The life cycle of myoporum thrips includes the egg, two actively feeding larval stages, two non-feeding pupal stages, and the adult. The length of the life cycle from egg to adult depends on temperature, and there are multiple generations per year. The following are the average lengths of each life stage for myoporum thrips reared at 86°F (30°C): egg, 14 days; two larval stages, 14 days total; pre-pupa, 5.3 days; and pupa, 5.0 days. Adults live an average of 9.2 days. A generation from egg to an egg-producing adult is about 38 days. These times compare closely with the Cuban laurel thrips, a closely related thrips species. In warm areas, myoporum thrips can reproduce throughout the year and have many generations.

DAMAGE

Myoporum plants damaged by this thrips are characterized by gall-like distortion of new leaves. Terminal growth can be severely stunted, and leaf curling or folding is frequently found, with colonies of thrips within the folds. These thrips populations are difficult to reach with pesticides, making control difficult. When damage is persistent on terminal growth, death of well-established plants can occur.

Research has shown that it requires only 4 hours for a single female thrips placed on terminal growth to cause significant growth distortion. Therefore, when considering control measures for sensitive and expensive plantings of Myoporum, preventive measures are most effective.

MANAGEMENT

Monitoring

To monitor for myoporum thrips, examine plant terminal growth. It is especially important to perform an early-season search for females infesting the expanding leaf tissue, which can allow you to identify and treat infested plants before thrips become protected within leaf folds. A useful technique involves tapping the terminal shoots of the plant on white paper to see whether the insect falls out. Another monitoring technique is to collect terminal growth, place it into a jar with 70% alcohol (ethanol), and shake vigorously. This will dislodge the thrips. The solution can then be filtered through filter paper, and the thrips can easily be seen and counted.

Cultural and Physical Controls

The best way to prevent problems with myoporum thrips is to avoid planting susceptible species of Myoporum. The only two species that have been affected in California to date are Myoporum laetum and M. pacificum. Consider planting resistant Myoporum species or other landscape plants that do not have serious pest problems.

On affected plants, infested terminal shoots may be pruned, bagged, and disposed of. Dying or dead plants should be disposed of in the same manner to prevent spread of the pest to other plants. Be aware that excessive pruning can stress, or even kill, both large and small Myoporum trees and shrubs.

Biological control

Minute pirate bugs (Orius spp.), green lacewings (Chrysopa and Chrysoperla spp.), and several species of predatory mites naturally help to control myoporum thrips. However, damage can still be severe even when beneficials are present.

Chemical control

Where infestations are severe on susceptible species, insecticide applications will be required to manage myoporum thrips. Because this thrips mostly lives protected within twisted terminal growth, it cannot be successfully managed with the reduced-risk and organic contact insecticides such as oils, soaps, and spinosad that control other species of thrips. Gardeners who do not want to use insecticides should replace affected myoporum plants with resistant plant species.

The most effective products for myoporum thrips control are systemic insecticides that move throughout the plant, killing thrips within leaf galls and folds and preventing infestation of new growth. Effective systemic insecticides include the neonicotinoids thiamethoxam (for professional use only), dinotefuran, imidacloprid, and combination products that include one of these systemics plus bifenthrin, a pyrethroid insecticide with contact and residual activity.

Any of the systemic materials listed above, or bifenthrin used alone, may also be effective as a preventive treatment if applied early in the season when new terminal growth is expanding. However, using bifenthrin or other pyrethroids will also kill beneficial organisms that may be assisting in control of this pest. Pyrethroid insecticides are very persistent in the environment; a lengthy period of time may be required before beneficials will reintroduce themselves into the system after an application. Systemics applied as drench or soil injections may be safer for natural enemies, but can have negative impacts on bees and other pollinators that visit treated plants. Always follow label instructions carefully. Systemics should never be used during the flowering period or when bees are present.

Research has shown that applying dinotefuran to Myoporum tree trunks is very effective against this pest. However, products labeled for this use are only available to licensed pesticide applicators. This application method uses a small amount of pesticide solution that is applied in a narrow band around the tree trunk. The active ingredient penetrates the bark, and systemically moves throughout the tree, eventually reaching the new terminal growth. This method avoids soil drenching, spray drift, and contact with numerous beneficial predators and parasites. However, basal trunk applications may still impact pollinators if applied before or during bloom, as mentioned above.

WARNING ON THE USE OF PESTICIDES

REFERENCES

Bethke, J. A. and D. A. Shaw. 2008. Myoporum Thrips Control. CAPCA Advisor. February 2008 Vol. XI (1): 28-31.

Hoddle, M. Updated 2009. Myoporum Thrips. Center for Invasive Species Research, U.C. Berkeley.

Mound, L.A. and D.C. Morris. 2007. A new thrips pest of Myoporum cultivars in California, in a new genus of leaf-galling Australian Phlaeothripidae (Thysanoptera). Zootaxa. 1495: 35-45.

PUBLICATION INFORMATION

Pest Notes: Myoporum Thrips

UC ANR Publication 74165        

Authors: J. A. Bethke and L. Bates, UCCE San Diego

Produced by University of California Statewide IPM Program

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