Thrips

CISR: Myoporum Thrips

Anonymous — Mon, 20 Jan 2020 21:10:05 +0000

CISR: Myoporum Thrips Anonymous (not verified) Mon, 01/20/2020 - 13:10 More Blog Posts CISR Team October 20, 2009

The Situation: In southern California, Klambothrips myoporiMyoporum, a plant genus native to Australia and New Zealand. This thrips causes considerable leaf deformation through the feeding activity of larvae and adults. This pest is likely native to Australia or New Zealand where it is probably a specialist on members of Myoporum.

Damage: The plant species on which thrips galling damage to leaves has been noted is primarily Myoporum laetum, a plant native to New Zealand. However, new varieties of Myoporum developed by the horticultural trade, include a susceptible prostrate form, “Myoporum Pacificum”. Additional Australian species are sold in California, including M. debile and M. parvifolium, and M. insulare. It is likely all species of Myoporum in California will be attacked by K. myopori.

Economic Impact: Species of Myoporum are planted along 1000’s of kms of residential and freeway road margins in California. Consequently, continued planting and traffic movement can be expected to facilitate the continued widespread distribution of this thrips. The drought hardiness of Myoporum, and the fact that the plants are generally so pest free, has made members of this genus desirable for ornamental planting. The broad environmental tolerances of Myoporum is now leading to Myoporum to be considered an invasive weed in some areas of California. Seed dispersal by birds is thought to be a primary mechanism causing the spread of this weed in wilderness areas. Paradoxically, if the weed status of Myoporum increases in California, then this new pest thrips my actually come to be regarded as beneficial because it has value as a biological control agent, especially if it manages to either reduce the competitiveness of invasive Myoporum or kill it outright.

Distribution: Myoporum thrips has been reported from at least ten California counties; Los Angeles, Marin, Orange, Riverside, Santa Barbara, Santa Clara, Santa Cruz, San Diego, San Mateo, San Luis Obispo, and Ventura. It is expected that the horticultural trade will help to rapidly spread this thrips into new areas as plants are shipped from infested to non-infested areas. Consequently, this thrips potentially poses a huge threat to naio, Myoporum sandwicense, a keystone native species in Hawaii. Myoporum thrips was unofficially detected on the island of Hawaii in March 2009. It is imperative that border control officials in countries with native myoporum collectively watch for imports of Myoporaceae and remove Myoporaceae plants from around ports of entry to reduce the likelihood of invaders establishing readily.

Research: There is currently no concerted research effort against this pest investigating control strategies (i.e., the potential for biological control), climate preferences, or basic life history studies. Limited trials have been conducted to evaluate the efficacy of pesticides for controlling Myoporum thrips in residential areas in San Diego County.

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CISR: Avocado Thrips

Anonymous — Mon, 20 Jan 2020 21:07:21 +0000

CISR: Avocado Thrips Anonymous (not verified) Mon, 01/20/2020 - 13:07 More Blog Posts CISR Team October 21, 2009

The Situation: Avocados are subtropical perennial fruit trees 6-10 meters in height. California produces 95% of the nation’s crop, and 85% of this harvest is from one cultivar, the black fruit Hass avocado. Annually, 6,000 growers in California produce 260 million pounds of fruit on 65,000 acres, and the harvest in 2007 was worth $245 million. Avocado thrips were first noticed in California in June of 1996 when they were discovered damaging foliage in a Saticoy avocado orchard in Ventura County. Since this initial discovery, the thrips population has increased rapidly causing significant damage to foliage and fruit in Ventura. In little under a year, the thrips spread southward and was found in San Diego County in May of 1997. By July of 1997, significant damage attributable to avocado thrips was noticed in several orchards in San Diego County. Foreign exploration for the avocado thrips and its natural enemies indicates that this pest is commonly found on avocados grown between Mexico City and Guatemala City. Genetic analyses suggest that the source of California’s thrip population was Coatepec-Harinas in Mexico. Avocado thrips have not been recorded in any other host plant in California, indicating it may have a limited host plant range and close evolutionary history with avocados. Avocados evolved in the southern Mexico to northern Guatemala area.

Damage: Thrips numbers build to very high levels (i.e., 100-400 larvae per leaf) over winter and spring causing damage to leaves and, more importantly, scarring on young fruit. In some orchards up to 80-100% of the fruit has been scarred, often with 100% of the surface scarred, resulting in brown mummified fruit. The quantity of first-grade fruit produced has been reduced, on average, by 27% (± 6%) in orchards with avocado thrips.

Distribution: Avocado thrips infests 80% of the commercial avocado acreage in California. To date, this pest has been unable to establish in inland valley areas not within the influence of marine breezes that moderate summer temperatures. Laboratory work has confirmed that this pest is intolerant of moderately high temperatures (30oC [86oF]) and population growth is greatest when temperatures are low (20oC [67oF]). Consequently, populations can decline rapidly over summer.

Research: University of California researchers at Riverside have studied the phenology of avocado thrips in orchards, its preferences for fruit of different ages, and temperature requirements for development. Evaluations assessing the efficacy of various pesticides for control of this pest are ongoing. Work been conducted on the biology and efficacy of commercially available natural enemies for releases into orchards for control of avocado thrips. Field evaluations have shown that augmentative biological control is ineffective for avocado thrips. Extensive foreign exploration efforts in Mexico and Guatemala have been undertaken and no promising natural enemy species were found for possible importation and establishment in California.

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CISR: Western Flower Thrips

Anonymous — Mon, 20 Jan 2020 20:28:03 +0000

CISR: Western Flower Thrips Anonymous (not verified) Mon, 01/20/2020 - 12:28 More Blog Posts CISR Team October 22, 2009

The Situation: In southern California, the native western flower thrips (WFT) Frankliniella occidentalis is the most common vector responsible for transmission of an exotic plant virus, Tomato Spotted Wilt Virus (TSWV). The pathogen was discovered on tomatoes in 1915 in Australia, and has been spreading around the world ever since. TSWV is a tospovirus (Bunyaviridae) of which there are at least 12 known plant pathogenic species that are spread by around 10 species of thrips. TSWV became problematic in California when a new highly pathogenic isolate established. This virus has become a major problem for pepper and tomato growers from Orange County to the Mexican border in San Diego County.

Damage: Once the plant is infected it can not be cured and different symptoms may be expressed depending on the strain of the virus. Typical symptoms include stunting, distortion, mottling, general necrosis, and ring spots. Virulent forms of the virus can kill plants resulting in major economic losses. When feeding thrips larvae acquire TSWV they are permanently infected (the virus replicates in the thrips and stays with them as they mature.) An infected adult that lands on a susceptible plant and starts feeding can transmit the pathogen in as little as 5 minutes. Large numbers of these pests migrating from other crops and weeds cause high levels of virus transmission and disease outbreaks. TSWV is highly mutable and can rapidly develop strains that overcome resistant host crop varieties.

Economic Impact: Economic losses to California tomato producers can be dramatic, For example, in 1998 fresh market tomato growers in Southern California lost 50% of their tomato plants to TSWV transmitted by the western flower thrips. Other important crops affected by the WFT and TSWV include lettuce, peppers, eggplant, beans, cabbage, celery, artichokes, potatoes and a variety of ornamentals such as chrysanthemums, petunia, impatiens, gladiolus and Ranunculus. Because California produces 55% of the fresh vegetables grown in the United States, the economic losses that may occur can be immense.

Distribution: WFT and TSWV are found worldwide. Highly virulent strains of the virus are known from Orange and San Diego counties. Consequently, these highly pathogenic strains of virus can cause substantial economic losses in other counties with major domestic and export markets.

Research: Currently, there are few good techniques available for controlling this pathogen and its vector. The University of California is examining the population dynamics and movement of western flower thrips populations and the acquisition and spread of TSWV. Integrated pest management strategies including resistance host plant varieties, selective pesticides to kill thrips, screening of greenhouses to exclude thrips, alteration of planting dates, manipulation of row spacings, and use of virus free planting material are being developed to reduce the impact of this pathogen on vegetable and ornamental crops.

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