Arizona Biological Control Working Group
Minutes of the 20 July 1998 Meeting
The summer meeting of the Arizona Biological Control Working Group convened at 10:00 AM, July 20, 1998 at the Western Cotton Research Laboratory, Phoenix, AZ. Present at the meeting were D. Akey (USDA-ARS), L. Elhoff (USDA-ARS), P. Ellsworth (UA), J. Gould (USDA-APHIS), J. Hagler (USDA-ARS), K. Hoelmer (USDA-ARS), M. Hunter (UA), S. Kelly (UA), S. Naranjo (USDA-ARS), D. Reed (USDA-ARS), B. Roltsch (CDFA), R. Santangelo (UA), D. Seagloff (UA), B. Staten (USDA-APHIS), F. Tezcan (visiting Turkish Scientist), G. Thaxton (ADA),
1. Research Briefs 1998:
Hoelmer: Has recently accepted a position with the USDA-ARS, European Biological Control Lab in France. Initially his responsibilities will include exploration for exotic agents of Lygus hesperus and L. lineolaris. In the Imperial Valley of CA he has been studying parasitism of Bemisia in citrus by Eretmocerus. Preliminary results indicated that mortality of WF in citrus is high from causes other than parasitism. Continued studies to examine the relationship between percentage parasitism and capture of adult parasitoids on sticky cards.
Roltsch: Continues to evaluate and monitor the establishment of exotic Eretmocerus and Encarsia for control of Bemisia. The United Arab Emirates strain of Eretmocerus appears to be well established in the Imperial Valley, CA. Field cage and host-specificity testing is being conducted for various Encarsia transvena cultures. Work continues on evaluation of perennial refuge crops for WF parasitoids. Some promising hosts are Tacoma stans, Justicia sp. and Lavatera sp..
Tezcan: Is a regional leader for IPM of cotton in western Turkey. Projects include sampling, biological control and insecticide resistance. Bemisia affects melons and watermelon throughout Turkey and is a key pest of cotton in the Mediteranean production area.
Santangelo: Continues mass-rearing of Bemisia parasitoids in Tucson. This year over 26 million Eretmocerus emiratus (UAE strain) were produced (17 million to Phoenix, the remainder to Imperial Valley, CA and Mission, TX). The facility will begin rearing the Spain and Pakistan strains of E. mundus in the fall.
Gould: Disseminating Tucson-reared E. emiratus in the Phoenix area. Initiated a study to release WF parasitoids in commercial melon fields in Aguila. Will be releasing the new species reared in Tucson in the future. Continues the homeowner parasitoid release program in Phoenix. Initiated studies with Naranjo to evaluate and compare several different methods for estimating parasitism and parasitoid impact on WF populations in cotton. The salt-cedar biocontrol program is still in a holding pattern pending approval by Fish and Wildlife to release a leaf beetle and a mealybug in AZ, NM and TX.
Thaxton: Arizona is considering regulating the plowdown of melons to minimize sources of WF for cotton. Melon growers are resistant and cotton growers are supportive. The wholly whitefly has become a problem in citrus in Yuma the past few years and a quarantine will likely be imposed to control movement of the pest into Maricopa county. Concern is growing over the potential for citrus tristeza virus in Yuma and Maricopa county when and if its vector the brown aphid arrives.
Naranjo: Continues field studies to examine and compare the effects of IGR and conventional insecticides on population dynamics of WF parasitoids and predators including field life table studies with Ellsworth to quantify and partition mortality of WF in IGR, conventional insecticide and untreated plots. Studies also continued on evaluating the effect of a new imidicloprid-like insecticide on predators and parasitoids in the field. Initiated studies to evaluate probability of predation of parasitized WF.
Reed: Interested in physiology of host-parasitoid interactions with emphasis on arrested development and sterility of the host. Now rearing the Chelonus nr. curvimaculatus colony.
Staten: Reports that biocontrol dollars within APHIS are being largely taken from the Bemisia pot. APHIS is planning to refill at least one of the positions in Brawley to replace Holemer and Simmons.
Akey: Continues efficacy testing of commercial formulations of entomopathogenic fungi for control of Bemisia in cotton. Also testing other biorational materials (neem, etc.) and evaluating their effects on natural enemy populations.
Hagler: Continues work with gut assays of predators using monoclonal antibodies for Bemisia. Results show that Orius, Collops and Drapetis are promising biocontrol agents in cotton. Continues evaluation of a protein-based marking technique. Continuing studies to examine WF parasitoid dispersal between melons and cotton. Also conducting studies to examine predation of marked parasitoids. Initiating biological control project on Lygus hesperus using predators and the egg parasitoid Anaphes iole.
Ellsworth: Continues evaluation and demonstration of IGR for whitefly management including life table analysis of WF with Naranjo. Conducting surveys of natural enemies in Lygus insecticide trial plots to help identify those compounds more compatible with biological control. Initiating studies with WF on soybean, a developing new crop for Arizona. .
Kelly: Initiating a project to study Wolbachia in Encarsia formosa
Hunter: Continues studies of the interactions between Eretmocerus eremicus and Encarsia transvena. Results indicate that male Encarsia production is better on Eretmocerus hosts compared with conspecific hosts and Encarsia is a superior competitor for hosts. Field experiment are being continued in Tucson to examine WF and parasitoid dynamics under 4 treatments (no parasitoids, Eretmocerus only, Encarsia only, and combination of the two parasitoids). Continues a pecan aphid project with Petersen. Surveys for native natural enemies are underway. Lacewings look promising and preference studies are being conducted.
Naranjo presented a mini-seminar entitled "Measuring Percentage Parasitism of Bemisia –What does it Mean? He briefly discussed recent results from partial life table analysis of Bemisia populations in cotton. Predation is a major source of mortality of both eggs and nymphs of WF in untreated plots and in plots treated with the insect growth regulators buprofezin and pyriproxyfen. Results from these studies revealed very low rates of parasitism by native WF parasitoids in all study plots. These parasitism rates differed considerably from those estimated using standard leaf samples taken from the 7th mainstem node. He discussed some of the causes of this discrepancy including overlapping generations, detecting early stages of parasitism, sampling error and accounting for immature mortality prior to parasitoid oviposition. The first three were further discussed by examining the distribution of hosts and immature parasitoids on cotton plants and considering differing rates of host and parasitoid development. Several alternatives were suggested to more accurately estimate stage-specific parasitism within the same generation including 1) using host exuviae as a measure of host density rather than 4th instar WF or 2) estimating host density on the 5th mainstem node leaf and parasitoid density on the 7th node leaf. The problem of immature WF mortality prior to parasitoid oviposition (which can be very large and variable) is more complex and makes estimation of the generational impact of parasitism problematic. The potential impact of even small amounts of parasitism when high rates of morality are imposed by predators and other causes was demonstrated with a simulation model.
Naranjo announced that the research summary document for the working group was completed and distributed to all members, to members of W-185, to county agents in Arizona and to members of the Arizona Cotton Growers Association. He has so far received no feedback or requests for additional copies.
The Fall meeting will be held in November or December of 1998.
M. Hunter & S. Naranjo
12 August 1998
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