Research Library

Goal of the work was to improve obtain natural enemies for the Polyphagous and Kuroshio shot hole borers in California.

Goal of the work was to improve our ability to trap the beetles for detection of the invasive shot-hole borers.

Invasive ambrosia beetles (Euwallacea spp.) commonly called shot hole borers (SHB) have been posing a threat to avocado groves as well as urban landscape and wildlands in California. Previous studies show that SHB tend to colonize primary, secondary and tertiary branches including branch collars of avocado. Therefore, effective management strategies for commercial avocado groves are limited to removal of infested branches to reduce beetle populations. However, some beetle galleries still remain around the branch collar which support future beetle reproduction and spread This investigation into pesticides for use in avocado against California invasive pest E. whitfordiodendrus commonly known as the polyphagous shot hole borer (PSHB) and FD indicate pesticide candidates have significant effectiveness against PSHB and their fungal symbionts in vitro and in field trials.

Molecular analyses of field-collected persea mite (Oligonychus perseae) specimens established that (1) ITS-2 provides reliable Oligonchyus species identification and (2) COI analyses were able to discern that California’s persea mite population originated from central Mexico. A comparison of predatory mite species (Phytoseiidae) from Mexico and California as originally intended was limited by challenges in amplifying COI/ITS-2 DNA from individual specimens but significant progress was made in optimizing non-destructive DNA extraction protocols for this taxonomic group. 

Several isothermal amplification techniques recently have been developed that are tolerant of inhibitors present in many plant extracts, which can reduce the need for obtaining purified DNA for running diagnostic assays. One such commercially available technique that has similarities with real-time polymerase chain reaction (PCR) for designing primers and a labeled probe is recombinase polymerase amplification (RPA).

We have further refined methods for evaluating field populations of avocado thrips and persea mite for resistance to abamectin, spinetoram, and fenprothrin. It appears to us that abamectin resistance is evolving with both avocado thrips and persea mite but it has not proceeded far enough such that field failures are common – instead, one sees a shortening of field efficacy (for example, spring avocado thrips treatments used to control persea mite through the summer and fall in the Ventura region; most years it no longer does and a second treatment with a miticide is needed).

The polyphagous shot hole borer (Euwallacea fornicatus) is an invasive species in California that has been present at least since 2003. Using DNA finger prints Dr. R. Stouthamer’s lab at UCR determined that the PSHB invading California shared a DNA finger print with the invasion that was taking place in Israel where this beetle/fungus combination caused severe damage to avocado. It was not until we received a large sample from Viet Nam that we found beetles having DNA fingerprints identical to ours, in addition to beetles with slight variants of the DNA finger print were found in Viet Nam was well, indicating that Viet Nam most likely belong to the native area of this beetle.

Armored scales present on California avocados are under excellent biological control and rarely build to economic levels. This study is the first to determine which species of parasitoids attack these scales and the results are somewhat different than what we expected. The dominant parasitoids in California are 5 species of unidentified and poorly studied Signiphora wasps.

The current CAC project over the 5-year period 2007-2012 focused on continuing to monitor for avocado thrips and persea mite resistance to abamectin and on developing pesticides in other classes of chemistry that could be used in rotation with abamectin; efficacy data were generated to support registration and working with pest control advisors (PCAs), we began to evaluate the strengths and weaknesses of each of these new products.

The objective of this project is to educate and inform California avocado growers on laurel wilt disease symptoms and the risks of introduction to California.