Arizona Biological Control Working Group

Minutes of the Fall Meeting, Sept. 16, 1999


In attendance: Peter Ellsworth, James Hagler, Darcy Reed, Cesar Rodriguez, Glen Thaxton, Bill Roltsch, Rick Santangelo, Molly Hunter, Suzanne Kelly, Steve Naranjo, Juli Gould, Paul Mertin

Meeting started: 10 am

Items of Business:

1) Steve Naranjo mentioned that the Mid West Biological Control Newsletter was going to become web-based and was interested in expanding its scope and source of contributions. Contributions from the AZBCWG were solicited. This newsletter has had a history of being very well read and distributed, especially among biological control extension agents.

2) The AZBCWG web page is in need of updating, with a new membership list, recent minutes of meetings, etc. Peter Ellsworth suggested that the computer person at the U of A's Maricopa Agricultural Station, Jenny Jones might be willing to take it on a short term basis. New bios were solicited for the web site, to be posted in December. (Editor's note: The revised website is now up and running at

Research Briefs:

Rick Santangelo, U of A, reported the end of the mass-rearing effort of sweetpotato whitefly (Bemisia tabaci) parasitoids. In the past year, the Beneficial Insect Rearing Facility reared 21 million of the Ethiopian Eretmocerus sp. and shipped them to Juli Gould (USDA- APHIS) and James Hagler (USDA- ARS) for research use. The APHIS rearing effort at Brawley, CA is also in its last year, then will be shutting down. He also reported Karin Hallborg has now moved on to work for Koppert in Romulus Michigan.

Molly Hunter, U of A, reported on ongoing experiments to characterize the effects of competition between native and exotic sweetpotato whitefly parasitoids on coexistence and pest suppression. Encarsia pergandiella, a small-egged species was predicted to lose in within-host contests with the larger-egged Encarsia formosa yet the reverse was true. In another contest between the closely related Encarsia luteola and E. formosa, the impact of competition by the second species was symmetric, and the second female on the patch appeared to have a competitive advantage. The studies of the ecology of two species of pecan aphids continue. Results suggest that plant quality influences the outcome of competition between these aphids and that feeding damage by one influences the reproductive success of the other.

Bill Roltsch, Cal. Dept. of Food and Agriculture, reported on new projects he has started in response to recent pest invasions. The pink hibiscus mealybug (probably of Australian origin?) has arrived in Imperial Valley and has established near the Imperial, Mexicali Valley borders. The mealybug has been found in high numbers on mulberry trees, but also on natal plum, hibiscus, silk oak, pomegranate, and other plants. Because of Dale Meyerdirk's (USDA-APHIS) proactive biological control program for this pest, started when the pest reached the Carribean, there were parasitoids known that had been released in the Carribean and were effective there, that were imported and released in the Imperial Valley. Two parasitoids, in the encyrtid genera Anagyrus and Gyranusoidea have been released in ten locations in Imperial and Mexicali, with about 200 individuals being released per site. It is too soon to say whether these parasitoids have established, but some reproduction had been observed. Another project involved another new pest, the glassy-winged sharpshooter.

Juli Gould, USDA - APHIS reported on several of her current projects on sweetpotato whitefly. 1) Different release methods for augmentative control of whiteflies using Eretmocerus sp.were evaluated in cotton. The center point release of 10,000 parasitoid pupae in a cup has the drawback that the Eretmocerus sp. does not disperse sufficiently to cover the plot. Other methods included mixing pupae and vermiculite and spreading it on foliage ( this didn't work well, recovery was very low) and putting large numbers of pupae in a gelatin capsule with a hole (4 per 1/4 acre) in the canopy (this worked well). Releasing parasitoid adults was also not very effective. 2) Methods of censusing parasitism are also being evaluated. 3) Ongoing regional surveys are being made to look at recovery of exotic species released. 4) A multivariate analysis of recovery data from the Imperial Valley is being performed to determine whether the impact of parasitism on whitefly numbers can be quantified. In the biological control of the weed salt cedar, cage releases of the salt cedar leaf beetle had finally been made in Wyoming California, Nevada, Utah and Texas. Observers were seeing defoliation in some of these cage trials, but many years of defoliation is probably required before the tree will be killed. Lastly, Juli reported on the recent invasion of the water fern, giant salvinia. This is a weed that has been under bc in other parts of the world, and a weevil that has been used in Australia has been released in Texas. However, host specificity tests have not been done for this weevil in this country, and until the tests are complete, the weevil will not be released in AZ (perhaps in summer of 2000?)

Glen Thaxton, AZ Dept. of Agriculture, also reported on giant Salvina. It is now in the Lower Colorado, prevalent near banks and in eddies. It is also in the Palo Verde Irrigation drainage system and in Martinez lake ADA has been trying to eradicate it. "Diquat" has been recommended but there are some concerns about water quality issues. He said that there was some concern that the weevil would only work in large monocultures. He also reported on efforts to prevent the red imported fire ant from entering AZ, as it is now in CA and NM, and has been reported in Utah and Nevada. The infestation in a school in Yuma seems to be on the way to being successfully eradicated - from 8,000 nest sites in the beginning of the year to 70 nests now.

Cesar Rodriguez is a new postdoc at USDA - ARS Western Cotton, and is working to try and explain plant interactions with the foraging behavior of natural enemies. He is interested in the two major plant induction pathways - the jasmonic acid and salicylic acid pathways, and is trying to determine how they interact in their effects on resistance to herbivores and attraction to natural enemies.

Darcy Reed continues her work on the egg-larval parasitoid Chelonus curvimaculatus. A field study designed to investigate parasitism and longevity of this wasp involved setting out egg cards with pink bollworm eggs in large field cages and releasing parasitoids. The study was complicated by very high rates of predation on the eggs (by Orius, Geochoris and Zelus) but of the eggs that remained, there were high rates of parasitism, and parasitoids were found to live up to a month. In another project to try and preserve diapause in the moth to enable the stockpiling of (diapausing) parasitoid larvae, pink bollworm moths were collected in Blythe last year. Early on they accepted diapausing conditions, but within 7 generations on diet were refractory to diapausing conditions.

James Hagler, USDA-ARS, Western Cotton, continues to study generalist predator foraging behavior (Orius, Geochoris, Hippodamia, Collops, and Drapetis, a predatory fly). He's found most of these predators prefer to feed on whitefly adults to nymphs. He has been setting up experiments to look at the circadian rhythm of predator activity. Most observations so far suggest they are diurnal. In another project, work continues on the immuno-labeling marking technique - a project to mark the pests for later predator gut analyses found that when pink bollworm first instars feed on the antigen, they retain the mark until the pupal stage, while Lygus retain the mark until at least the 4th instar. Experiments demonstrated that the technical grade antigens were not effective for field use, so reagent grade antigens used again. Dispersal studies using immuno-labelled Eretmocerus are also continuing.

Peter Ellsworth reported on his ongoing collaboration with Steve Naranjo on estimating mortality factors in whiteflies using the life table approach. They are now expanding their study to include the overwintering generation and have a PhD studentship available. In addition, Peter is conducting a large scale study evaluating the arthropod fauna in cotton with a second Bt gene, including the non-target impacts.

Steve Naranjo reported that 14 whitefly life tables have been completed in untreated cotton and 6 comparative life tables have been completed contrasting whitefly mortality in untreated cotton and cotton treated with IGRs or conventional insecticides. In another project, his study of intraguild predation in whiteflies continues. He finds that many predators appear to prefer to feed on parasitized whiteflies. In Geocoris and Orius, this can be explained by the fact that the parasitized whiteflies used were thicker than early 4th instar (unparasitized) whiteflies and more visually apparent - the difference in feeding rate disappeared when the unparasitized whiteflies used were late 4th instars. For Hippodamia, the difference in preference persisted even when late 4th instar unparasitized whiteflies were used, suggesting that visual discrimination could not explain the preference for parasitized hosts.

Bill Roltsch gave a mini-seminar regarding releases and evaluation of exotic Eretmocerus and Encarsia for control of sweetpotato whiteflies. Releases and evaluations took place in many habitats - in home gardens, in annual plant refuges consisting mostly of okra and basil (summer), cantaloupe and cotton (spring) and collards and sunflowers (winter), and in perennial plant refuges using a variety of desert-adapted perennials (including Tacoma stans, chuparosa, rue, and an exotic blue hibiscus from Australia). It appears that of many Eretmocerus and Encarsia released, a population of Encarsia transvena from Pakistan is established, as well as an Ethiopian population of Eretmocerus and Er. mundus.

Meeting finished at approximately 12:30, after which many of the attending members reconvened at a local restaurant.

S. Naranjo & M. Hunter

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