Arizona Biological Control Working Group
Minutes of the 4 June 1999 Meeting
The spring meeting of the Arizona Biological Control Working Group convened at 10:00 AM, June 4, 1999 at the University of Arizona Karsten Turf Grass Center, Tucson, AZ. Present at the meeting were E. Andress (USDA-APHIS), T. Collier (UA), G. DeGrandi-Hoffman (USDA-ARS), D. Donnell (UA), Karin Hallborg (UA), M. Hunter (UA), S. Kelly (UA), M. McElween (UA), S. Naranjo (USDA-ARS), C. Otiodobiga (visiting scientist from Burkina Faso), A. Owen (UA), D. Reed (USDA-ARS), B. Roltsch (CDFA), R. Santangelo (UA), G. Thaxton (ADA).
1. Research Briefs 1999:
Reed: Research focuses on physiological interactions in lepidopteran host-parasitoid systems. The current systems involves the egg-larval parasitoid Chelonus nr. curvimaculatus on pink bollworm and cabbage looper. Effects of host diet and host immune responses are being studied. Attempting to develop a diapausing pink bollworm culture to examine parasitoid diapause as a component of mass-rearing.
Naranjo: Continues field life table studies to examine and compare the effects of IGR, conventional insecticides, and no insecticide use on the sources and rates of whitefly mortality factors. Further studies are planned for summer 1999. Examining the probability of predation of parasitized WF in laboratory bioassays with Geocoris, Orius and Hippodamia. Results indicate preference by all species for parasitized WF that may be related to visual cues. Initiated toxicological studies on Geocoris with Applaud and Knack, two insect growth regulators. Early results indicate that Applaud has little to no effect at field rates, but Knack may disrupt molting of terminal stage immatures at field rates. Studies this summer will compare the natural enemies faunas of transgenic Bt and non-Bt cotton.
Otiodobiga: Scientist/Ph.D. student from Burkina Faso, West Africa visiting the Western Cotton Research Lab. Bemisia was first found affecting vegetables in Burkina in 1994; it has since spread to cotton and reached outbreak proportions in 1998. Is hypothesized that problem resulted from heavy insecticide use to control Heliothis. Interested in cultural, biological and insecticidal control strategies for cotton and tomato production.
Roltsch: Continues to evaluate and monitor the establishment of exotic Eretmocerus for control of Bemisia in Imperial Valley. It appears that inoculations in refuge plots from 1995-97 has resulted in a high percentage of exotic Eretmocerus (Ethiopian strain, E. mundus, E. emiratus) in parasitoid collections from various host plants in 1998. Surveys of Encarsia transvena in urban landscapes indicate a high percentage of females, but sex ratios are highly variable. Work continues on screening and selection of host plant species for perennial refuge plantings. Distributed a photo series depicting development of Encarsia and Eretmocerus parasitoids.
DeGrandi-Hoffman: Involved in development of a model for biological control of whitefly in greenhouse poinsettias in the northeast US. Within house movement of parasitoids and WF will be a focus of the modeling effort. Working on host-parasite model for varroa mites attacking honey bees with emphasis on timing of control tactics. General discussion of the mite problem in the bee industry and potential problems with sole reliance on the most commonly used insecticide.
Andress: Just starting new job for USDA-APHIS in Brawley, CA to continue past efforts by Hoelmer and Simmons. Involved in mass-rearing and augmentative releases of exotic Eretmocerus (Ethiopian strain, E. mundus) in spring melons. Interested in release rate evaluations and parasitoid dispersal.
Thaxton: The woolly whitefly is a problem in citrus in Yuma but the pest does not appear to be spreading due in part to enforcement activities. Citrus growers are seeking Section 18 approval of Applaud and Knack and plan to coordinate use with cotton and vegetable growers. The imported fire ant (Solenopsis invicta) has become established in California and strict quarantine activities are helping to prevent establishment in AZ. A major source of infestation is soil on bee hives moving between CA and AZ. Discussed the sticky cotton problem in the 1998 AZ crop.
Kelly: Working on interspecific competition among Bemisia parasitoids.
Donnell Working on gene expression of vitellogenins in Encarsia and the role of parasitoid host-feeding on yolk protein formation.
Owen: Studying ovicide (intentional killing of competitor eggs in WF hosts) in Encarsia. Looking at competition between E. formosa females by using antibiotics as a marker - most females produce only females, but when treated with antibiotics to cure Wolbachia males are produced.
McElween: Confirmed ovicide in Encarsia luteola. Working with Bt resistance in pink bollworm using defined artificial diets.
Santangelo: Continues mass-rearing of Bemisia parasitoids in Tucson. Rearing Ethiopian strain of Eretmocerus. Lead tour of mass-rearing facility (see below).
Collier: Studying interference competition between Eretmocerus eremicus and Encarsia transvena via multiple oviposition in hosts, host-feeding on parasitized hosts. Results from laboratory assays in which parasitoids are introduced sequentially suggest that Eret. suppresses reproduction in Enc by ovipositing in parasitized host and that Enc. suppresses reproduction in Eret by host feeding. In general, the second parasitoid introduced suppresses the first regardless of which is introduced first. Further studies are planned to explain this paradoxical result.
Hunter: Continues studies of the competitive interactions among whitefly parasitoids. Results indicate that Encarsia transvena has a large detrimental effect on Eretmocerus eremicus reproduction in both the laboratory and the field; however, this interaction did not affect overall biological control of the host in a field cage study. Laboratory studies are in progress to look at mechanisms of interactions between different Encarsia species by examining several species with different biological characteristics, such as egg size. Ongoing studies are examining aphids on pecans at two sites in southern AZ, including surveys for native natural enemies, and estimation of the impact of predators on aphids using exclusion methods.
2. Whitefly Parasitoid Mass-Rearing Facility
Rick Santangelo lead a tour of the parasitoid mass-rearing facility at the UA, Campbell Avenue Farm. Rick is assisted by Karin Hallborg. The Eretmocerus strain from Ethiopia is currently the only species being reared, but there are plans to rear Eretmocerus mundus (Spain) in the future. The "clean" greenhouse is used to rear whitefly host plants. Tobacco is grown to maintain the whitefly culture, and eggplant is grown to rear whiteflies that will eventually be used to produce parasitoids. The parasitoids prefer whiteflies on eggplant and so this helps to keep the whitefly culture on tobacco free of parasitoids. New tobacco plants are periodically introduced into a second greenhouse that maintains the whitefly culture. New eggplants are also introduced into this greenhouse for a short period of time for whitefly oviposition. After adult whiteflies are blown from these eggplant with a shop-vac they are moved into a third greenhouse and held until the whiteflies reach the 2nd-3rd instar. These plants are then moved to a fourth greenhouse where they are exposed to parasitoids. Once parasitoids on the eggplant reach the pupal stage they are harvested from the leaves with a special washing procedure and provided to end-users in Tucson and Phoenix. The rearing facility is also currently producing cotton "banker" plants for use in experimental parasitoid release studies in Phoenix.
The Fall meeting will be held in November of 1999.
S. Naranjo & M. Hunter
10 June 1999
Meeting Minutes page