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Project description

Determining the area of origin of avocado thrips using molecular techniques. (02XA010)
Program Exotic Pests and Diseases Research Program
R. Stouthamer, Entomology, UC Riverside
M.S. Hoddle, Entomology, UC Riverside
Host/habitat Avocados; Tree Crops
Pest Avocado Thrips Scirtothrips perseae
Discipline Entomology
Agricultural Systems
Start year (duration)  2002 (Two Years)
Objectives Determine if the S. perseae is a single species or consists of several cryptic species.

Determine the area of origin in Latin America for the avocado thrips population in California using molecular techniques.

Determine if the invasion in California originates from a single invasion event or several, and additionally estimate the number of thrips that were involved in the original colonization of California.

Collect and preserve avocado thrips pests and natural enemies from the natural distribution of avocado in Central America, to be used for future identification and determination of origin of anticipated thrips pest invasions of avocados.

The avocado thrips invaded California in or before 1996. Initially two foci existed of this invasion but the thrips spread rapidly over all avocado-growing areas in California. This proposal aims at collecting thrips from avocado in its natural distribution in Central America. This collection of thrips will be used to determine taxonomic status of what is now known as Scirtothrips persea, the origin of the California population, if the California population originated from a single invasion, and establish a specimen bank to be used for the study of future avocado pest invasions.
Final report We have accomplished the following: 1) Using DNA techniques we determined with high accuracy the area of origin of the avocado thrips that invaded California in 1996 and, subsequently, spread through most (95%) of the avocado growing regions in California. Our results show that the most likely source of the single invading population is the area of Coatepec-Harinas, Mexico, or immediate surroundings. Coatepec-Harinas is a remote rural town and the only reason for visiting is because it is the major avocado breeding center in Mexico. 2) To determine the area of origin for avocado thrips, we made large collections of thrips and other insects from avocados in Mexico and Central America. These collections have been placed in a specimen bank at the University of California in Riverside and have been screened, and in this process we have discovered 40 species of thrips in 15 genera that use avocado as a host plant and may in the near future also invade California. We have already discovered a new invasion in San Diego County by one thrips species identified from this survey work. This new invasive thrips is Neohydatothrips burungae. 3) Additionally, we have used collected material to construct an identification key to easily and rapidly recognize avocado thrips from other closely related thrips species that may invade California in the future. This molecular key will speed up the identification of these potential future thrips pests and may allow eradication of incipient populations of new pest thrips before large distance spread occurs.

During this funding period the work on this project began in earnest. We have amplified and sequenced three genes (CO1, ITS1 & ITS2) that will be used to determine if avocado thrips is a single species or in fact several cryptic species. The development of more specific molecular markers that will be used for the characterization of the avocado thrips populations is in progress. So far, we have identified two good markers, but require two or three more to increase the robustness of the study. These markers will be used to determine the Latin American origin of the avocado thrips population now present in California. In addition, the first of two planned collecting trips (funded by the Californian Avocado Commission) took place in November 2003. The collectors (Mark Hoddle [UCR] and Phil Phillips [UCCE Ventura]) on this trip worked north from San Cristobal de las Casa (state of Chiapas) to Mazatlan (state of Sinaloa) in Mexico, collecting thrips and associated natural enemies from wild and commercially grown avocados. The material from this trip has been sorted to genus and all collected Scirtothrips spp. will be analyzed as part of the molecular work outlined in objectives 1-3. Non-Scirtothrips material will be incorporated into a "specimen bank" which will greatly speed-up the identification, determination of origin, and search for natural enemies of future thrips pest introductions on avocado.

During this funding period only a beginning was made in this project, roughly one months of work was done. We have begun developing the markers that we will use for the characterization of the avocado thrips populations. These markers will later be used to try to determine the origin of the Avocado thrips population that is now present in California. In addition, we will collect thrips in the Mexico and Central America to collect all thrips species associated with Avocado and their natural enemies. We will be doing the collecting of the thrips later in the year - around October-November to complete that study. The California Avocado Commission has provided funds for two researchers to travel from Central Mexico through to Costa Rica collecting thrips and associated natural enemies on commercially grown and wild avocados.

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