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Project description

Invasive citrus peelminer populations in California: Home grown or invasion from Mexico? (04XA011)
Program Exotic Pests and Diseases Research Program
R. Stouthamer, Entomology, UC Riverside
D. Vickerman, Entomology, UC Riverside
Host/habitat Citrus; Avocados; Pomegranates; Olives; Stone Fruits; Melons; Cotton; Grapes; Vegetable Crops
Pest Citrus Peelminer
Discipline Entomology
Agricultural Systems
Start year (duration)  2004 (One Year)
Objectives Determine if the citrus peelminer, Marmara gulosa, in California is a single species by comparing mitochondrial and ribosomal DNA sequences of M. gulosa populations on different hosts from different locations in California and Mexico.

Determine if there was an invasion event of citrus peelminer into California and whether Mexico was the area of origin by developing microsatellite markers to differentiate the populations.

The citrus peelminer, a minor pest on citrus prior to 1998, has recently become an economically important pest with a dramatic increase in hosts used and degree of infestation in the San Joaquin Valley of California. Circumstantial evidence suggests that a more invasive biotype/species was introduced from Mexico. We propose to determine if the peelminer in California is a single species/biotype, or consists of several distinct populations by comparing Californian (pestiferous and nonpestiferous) and Mexican populations using molecular techniques. Knowledge of the origin of the peelminer strain is important for the development of management tactics (pheromone trap development, biocontrol agents).

Final report Circumstantial evidence suggests that an introduction of the citrus peelminer (CPM) occurred in the San Joaquin Valley in winter 1998 to 1999 when a freeze resulted in the need to import citrus from northern Mexico. Our project used DNA fingerprinting techniques to determine if the San Joaquin population was indeed closely related to the CPM originating from northern Mexico.

Using several different gene regions we show that: 1. The citrus peelminer populations collected in the San Joaquin Valley on different crops (bell pepper, citrus, cotton, and oleander) cannot be distinguished from each other. Based on our data, there is no evidence for the existence of peelminer biotypes that specialize on particular host plants. And, consequently, the CPM may be cycling between different crops during the course of a growing season. 2. Using the >COI gene region we show that the more aggressive and polyphagous San Joaquin Valley population and the Mexican population are similar to each other, but very different from the Coachella Valley population.

However samples that we received from cotton around Phoenix, Ariz. were also similar to those from northern Mexico and the San Joaquin Valley. These results show that it is possible that the native range of the San Joaquin "type" of citrus peelminer stretches from northern Mexico through Arizona to the San Joaquin Valley. Consequently, we cannot exclude the possibility that the problem caused by the citrus peelminer in the San Joaquin Valley is simply a home-grown problem and that the importation of the CPM-infested fruit in 1999 had nothing to do with the subsequent outbreaks of CPM in the San Joaquin Valley.

We have collected citrus peelminer (CPM) from multiple host plants in the San Joaquin Valley, the Coachella Valley, and from Hermosillo, Mexico. We have amplified and sequenced three gene regions (ITS1, ITS2, COI) from these Californian (pestiferous and nonpestiferous) and Mexican populations. We were able to use sequences of the ITS1 gene region to distinguish CPM from other species of lepidopteran miners to exclude them from analysis.

We found two other species of miner in the San Joaquin Valley, one on lemon and the other on Himalayan blackberry (mines on stem). We have also identified a restriction enzyme (Afl II) that can be used on the ITS1 gene region to differentiate these species without the time commitment and high cost of cloning and sequencing. This technique can be used to determine if CPM is the pest responsible for crop damage. The COI gene region provides evidence that the more aggressive and polyphagous San Joaquin Valley population and the Mexican population are similar to each other, but very different from the Coachella Valley population. This suggests that the pestiferous San Joaquin Valley strain could have originated from Mexico.

We have also developed four species-specific microsatellite markers, two of which demonstrate sufficient variation to use for further population analyses. The results of this research will provide essential information to pest control managers on where to search for natural enemies that could help control citrus peelminer in the future.

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