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Annual Reports

1995UC IPM Competitive Grants Program

Biological Controls

Biological control is narrowly defined here as the use of predators, parasites, pathogens, competitors, or antagonists to control a pest. Efforts of the UC IPM Project should address those problems that have a reasonable chance of implementation within three years. An area of special interest for IPM funding is work to establish effective biological control in field situations. The project would support studies of indigenous or introduced biological control agents to determine their efficacy, how they can be manipulated by cultural or other management practices to improve their efficacy, and how they are affected by pesticides. The Project would support development of methods for growers and PCAs to use in evaluating potential effectiveness of existing biological control agents in relation to pest populations and potential crop damage.

Proposals must include a description of how proposed practices could fit into the current production or management systems. If current management practices must be altered to ensure the successful adoption of the research, these changes should be outlined. Proposals must be designed to produce practical guidelines, tools, and/ or methods by the end of the project. Investigators should detail mechanisms for transferring methods or tools to field use.


New Projects Funded for 1995-96
Continuing Projects Funded for 1995-96
Projects that Ended in 1994-95
Final Reports for Projects that Ended in 1994

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New Projects Funded for 1995-96

Improving Parasite Application Methods

Improving the technology of Trichogramma augmentation against codling moth in walnuts in California. (Year 1 of 1; $23,709)

Principal Investigator: N. J. Mills, Environmental Science, Policy and Management, Berkeley

Objectives:
Develop a ground delivery system to broadcast an even dispersion of Trichogramma platneri through the canopy of a commercial walnut orchard.
Evaluate the survival and performance of T. platneri through each step of the delivery system.
Determine the pattern of distribution of parasitized eggs within the tree canopy and the parasitoid emergence rate after broadcast application from the ground.
Evaluate the effectiveness of T. platneri augmentation against codling moth in replicated field trials, comparing broadcast and point source release.
Demonstrate season-long control of codling moth using the most effective strategy for augmentative releases of T. platneri in several commercial walnut orchards.

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Continuing Projects Funded for 1995-96

Reducing Codling Moths in Apples

The potential of early season releases of Trichogramma platneri and sanitation practices to reduce codling moth in mating-disrupted apple orchards. (Year 3 of 3; $26,763)

Principal Investigator: N. J. Mills, Environmental Science, Policy and Management, Berkeley

Objectives:
Evaluate early season releases of Trichogramma platneri for the suppression of codling moth during its first generation in apple orchards under mating disruption.
Compare the effectiveness of Trichogramma platneri in the two major climatic regions for apple growing, the north coastal region and the Central Valley.
Evaluate the potential and timing for sanitation practices in reducing codling moth populations in apple orchards.

Summary of Progress: In this project we set out to clarify whether the early-season release of Trichogramma egg parasitoids can supplement the control of codling moth in two mating disrupted apple orchards in the central valley. In addition, we monitored the occurrence of codling moth in ground fruit throughout the season in the same two orchards to address the potential effectiveness of within-season sanitation practices.

Damage at harvest in a high pressure orchard (>500 moths in a high 10 mg trap over the season) declined from 50% in the no release plots to 16% in release plots in which either 100,000, 400,000 or 800,000 Trichogramma had been released per week through the first generation of the codling moth. In a low pressure orchard (<100 moths in a high 10 mg trap over the season) there was very little difference between the no release plots at 0.03% damage and release plots of 100,000, 200,000 or 400,000 Trichogramma where damage ranged from 0.03-0.43%. Continued releases, at a rate of 100,000 per week throughout the season, provided some improvement in damage reduction. However, a four-fold increase in release rate with no change in the number of release points in a plot did not provide a notable improvement in damage control, suggesting that a more even distribution of released parasitoids may be more important than the number released.

From monitoring of ground fruit, Granny Smiths dropped less than 5 apples per tree throughout the season, whereas Golden Delicious dropped approximately 100 apples per tree each week. Fruit dropping early in the season had a low level of codling moth infestation but by the middle of the first generation of the codling moth 90% of the ground fruit were infested. The probability that ground fruit still contained codling moth larvae was low throughout the season, suggesting that sanitation of within-season ground fruit would have little impact on levels of codling moth damage.


New Microbials for Caterpillars

Field evaluation and implementation of selective microbial biopesticides in IPM programs. (Year 2 of 2; $15,464)

Principal Investigator: B. A. Federici, Entomology, Riverside

Objectives:
Develop a series of pathogens specific for key lepidopterous pests as alternatives to synthetic chemical insecticides for use within a few years in IPM systems for a variety of crops.
Evaluate a new nuclear polyhedrosis virus of the celery looper, Anagrapha falcifera, as a microbial pesticide for use in IPM programs against noctuid larvae.
Evaluate a new isolate of Bacillus thuringiensis subsp. kenyae as a microbial pesticide for use in IPM programs against the beet armyworm, Spodoptera exigua.

Summary of Progress: In the first year of our project, we focused on the evaluation of a new virulent insecticidal virus, originally isolated from the celery looper, as a control agent for major caterpillar pests in fresh market tomatoes. In our initial trials, we applied the virus at a moderately low rate, equivalent to a cost of production, i. e., the cost to commercially produce a viral insecticide, of about $1.00 per acre treatment. The virus was produced and formulated in the laboratory at Riverside, and then applied after first fruiting weekly on Petroseed VFN variety tomatoes at the UC South Coast Field Station at Irvine, California. Treatments were made from July 21 through September 8, after which tomatoes were harvested and evaluated for internal and external damage. Controls used in the trials included a standard chemical insecticide (Lannate), new chemical insecticides (such as American Cyanamid's pyroles), commercial formulations of the beet armyworm virus, the alfalfa looper virus, several bacterial insecticides (Bt's) on the market or under development, and untreated plants.

In these initial trials, the celery looper virus did moderately well, proving more effective than the alfalfa looper virus, equivalent to the beet armyworm virus, slightly less effective than existing Bt products, and not as effective as existing and new chemical insecticides. More specifically, total damage due to caterpillar pests in the untreated plots averaged 23%, whereas in the plots treated with the celery looper virus damage was 12%, and in plots treated with the alfalfa looper virus, 14%. Damage in most Bt treated plots was about 8%, and in the plots treated with the standard and new chemical insecticides, damage ranged from 2-4%. Neither the viruses nor the Bt products resulted in resurgence of leafminer populations, nor did they cause significant mortality to leafminer parasites. Considering that the celery looper virus contained no UV protectants, spreaders or stickers, all of which are included in commercial formulations, our initial results are quite promising.


Whitefly Biocontrol

Enhancement of biological control of the silverleaf whitefly. (Year 2 of 3; $10,000)

Principal Investigators: T. M. Perring, Entomology, Riverside; T. S. Bellows, Entomology, Riverside

Objectives:
Increase the diversity of natural enemies through importation, mass rearing, release, and establishment of exotic parasites of the silverleaf whitefly.
Summary of Progress: In the first year of this 3-year study, we introduced a new parasite species, Amitus bennetti, into the Imperial Valley. This parasite is native to the Caribbean and we have observed aggressive parasitism of silverleaf whitefly by this species in the laboratory. Parasites in the genus Amitus are especially effective when whitefly numbers are high, much like the situation on melon, cotton, and cole crops in the desert valleys.

Funding received from the UC IPM Project was combined with resources from the Imperial Valley Whitefly Management Committee, the California Cotton Pest Control Board, the California Melon Research Advisory Board, and the University of California Center for Pest Management. While approval from the UC IPM Project was not received until July, we began our releases in April under approval of the other funding agencies. Our releases of A. bennetti will continue through March, 1995. At the writing of this report, we have released just over 200,000 parasites distributed over 17 locations in urban and agricultural settings near Brawley and El Centro. With the onset of cooler fall weather, we have recovered A. bennetti from 2 urban sites, suggesting some establishment. Continued releases over the winter may result in more recoveries.


Integrating Predator Release and Acaricides

Timing of predatory mite releases in strawberries and the effect of acaricides on the survival and establishment of Phytoseiulus persimilis Anthias-Henriot. (Year 2 of 2; $16,902)

Principal Investigators: P. A. Phillips, UC IPM Project, Ventura County; J. P. Newman, UC Cooperative Extension, Ventura County

Objectives:
Determine the benefit of early season predatory mite releases related to later season releases. Examine the effect of four miticides (abamectin, fatty-acid soap, propargite and fenbutatin oxide) on the survival and establishment of introduced predatory mites in strawberry fields.
Examine residual effects and feeding toxicity of these miticides in laboratory bioassays using field sprayed foliage and spider mites.

Summary of Progress: At the time of reporting, investigators had established plots but no results were available.


Application of Predaceous Mites

Mechanical distribution and physical damage to predators during field releases. (Year 2 of 2; $19,830)

Principal Investigators: D. K. Giles, Biological and Agricultural Engineering, Davis; H. E. Studer, Biological and Agricultural Engineering, Davis

Objectives:
Evaluate the field reliability of a prototype mechanical system for controlled distribution of predaceous mites (within a granular carrier) onto strawberry beds.
Determine the effects and interactions of compression, shear, and vibration forces and carrier material on physical damage of selected predaceous organisms.
Summary of Progress: A mechanical system for field distribution of commercial formulations of vermiculite carrier and Phytoseiulus persimilis predaceous mites was developed and field tested. The handling system consisted of an insulated storage reservoir, a rotating metering plate and air-cleared ejection port. Release rate of the mites was controlled through rotational speed of the metering plate and the size of cells on the plate. The release rate could be calibrated much like a conventional pesticide sprayer. Field testing found the system to uniformly release mobile mites with an average accuracy of 98% of the desired release rates from 32,000 to 92,000 predators/ha. Proper chilling of a gently-prepared mite-vermiculite mixture was essential for predictable performance of the distributor. Agitation of mite-vermiculite mixture can result in significant physical damage to mites. Moisture content of carrier materials can affect the performance of mechanical distributors. Particularly, excess moisture can cause plugging of small passageways and bridging of reservoirs when agitation is not used. Moisture content of commercial formulations varied considerably. On-site preparation of a predator-carrier mix, using locally prepared carrier was successfully demonstrated for use in the distributor.

In field comparisons between hand release and mechanical release, a single mechanical distributor required 1 driver and 43 minutes to cover 0.37 ha for a resulting productivity of 1.94 worker-hours/ha. Hand release required 6 workers and 15 minutes to cover 0.42 ha for a resulting productivity of 3.61 worker-hours/ha. Machine distribution was approximately twice as labor efficient as hand release. Use of a 4-row system would be approximately 8 times more efficient.

The mite distributor has been adapted for distribution of green lacewing, Chrysoperla, eggs in vermiculite mixture. Preliminary results indicate that the distributor can uniformly release viable eggs. Vibration of the distributor, at frequencies and accelerations measured on agricultural vehicles, does not significantly reduce viability, as measured by hatch rates, of eggs.

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Projects that Ended in 1994-95

Biological Control of the Eucalyptus Longhorned Borer

Introduction and establishment of natural enemies of the eucalyptus longhorned borer (Phoracantha semipunctata).

Principal Investigators: J. G. Millar, Entomology, Riverside; T. D. Paine, Entomology, Riverside; L. M. Hanks, Entomology, Riverside

Objectives:
Introduce and establish natural enemies of the eucalyptus longhorned borer, P. semipunctata, (ELB) into California.
Optimize propagation conditions for ELB natural enemies, to increase natural enemies available for field releases.
Evaluate efficiency of introduced natural enemies as ELB control agents.
Conduct field releases and monitor establishment of ELB natural enemies.
Summary of Progress: During 1993 and 1994, multiple releases of three species of parasitoids of the eucalyptus longhorned borer (ELB) were carried out at 13 sites in California, including more than 118,000 egg parasitoids (Avetianella longoi), 10,000 of the larval parasitoid Syngaster lepidus, and 2,500 of the larval parasitoid Jarra phoracantha (formerly identified in the genus Doryctes). The egg parasitoid has apparently established at eight of these sites, and populations survived the winter of 1993-1994. At these sites, the egg parasitoid has dispersed widely, being recovered at distances up to 10 miles from the release points within a few month's time, and by 1994 was ubiquitous in release areas. Moreover, this species appears to be a very efficient parasitoid; of 94 ELB egg masses collected from the field, the parasitoid had discovered and parasitized eggs in 94.7%, resulting in an overall parasitism rate of 88.5%. By killing the ELB eggs, A. longoi reduces the number of borer larvae that are colonizing the bark, improving the chances that a eucalyptus tree will survive the attack.

The larval parasitoid S. lepidus was recovered away from the release point at the Santa Barbara site, with more than 400 adults emerging from a wind-thrown tree that was infested with ELB larvae. At UC Riverside, this wasp has been observed ovipositing on infested eucalyptus trees, and adults of both sexes have been seen in the area of the campus. The benefit of this wasp is that it will kill beetle larvae that are feeding in living trees.


Biocontrol of Russian Wheat Aphid

Evaluation of parasites of Russian wheat aphid.

Principal Investigator: D. Gonzalez, Entomology, Riverside

Objectives:
Release three Russian wheat aphid parasites in one climate zone.
Evaluate temperature thresholds, longevity, fertility, and other demographic and biological characteristics of the three parasites in order to help characterize their potential effectiveness against RWA under a wide range of conditions.
Assess the control potential of each parasite species separately and together, and compare with an untreated area and an insecticide treatment, using an experimental field evaluation involving four fields (replicates).
Summary of Progress: Two parasites of Russian wheat aphid (RWA) were mass reared in the insectary at the University of California, Riverside, and released in cereal crops in 5 fields in northern California. Impact on RWA from these wasps was compared on plants where wasps were released versus plants on which no wasps were released.

Both species were recovered. However, one of these, Aphelinus albipodus which forms a characteristic black, cigar-shaped mummy was clearly the most effective of all parasites recovered from RWA. These wasps were recovered from all areas where they were released and from more than half of the adjacent areas where they were not released. They persist in finding and attacking only RWA of all aphids feeding on cereal plants. They are especially effective in finding and killing RWA in low numbers inside tightly curled leaves. We also recovered this parasite from RWA at low densities in Gazelle and McArthur in northern California in the spring and summer of 1994 before initiating parasite releases. It is clearly established in northern California.

Naturally-occurring (excluding new introductions) biological control species are becoming increasingly effective against RWA. Lady beetles, and to a lesser extent syrphid flies, account for more than 60% of this "native" biological control. However, these generalist feeders do not attack the invading low numbers of RWA found only in tightly curled leaves.

Impact from RWA on crop yield in both quantity and quality remains unresolved because many unpredictable and related variables are involved. Healthy plants growing under optimal conditions of water, nutrients, and soil, combined with naturally-occurring biological control, will in most cases recover from RWA attack. Plants stressed especially by lack of water, with poor nutrients and grown in poor soils, are most susceptible to severe damage from RWA. Unfortunately, these are the conditions under which many "dry-land" cereals are grown, and "dry-land" cereals represent a substantial amount of the total cereal plantings. Other factors as plant species and variety, age of plant at infestations, and duration and intensity of RWA attack will also greatly influence yields. For all of these reasons, a single application of an insecticide does not usually result in yield increase. Furthermore, under most conditions, multiple insecticide applications are economically unjustified.


Manure Removal and Biocontrol of Flies

Impact of staggered manure removal schedules on pest flies and associated natural enemies in caged-layer poultry housing.

Principal Investigators: B. A. Mullens, Entomology, Riverside; N. C. Hinkle, Entomology, Riverside

Objectives:
Determine whether staggered manure removal results in significantly reduced fly numbers when compared with the usual simultaneous removal in caged-layer poultry housing.
Determine whether staggered manure removal enhances recolonization by fly natural enemies when compared with simultaneous removal.
Summary of Progress: We are in the 17th month of a 2-year project to determine whether alternate removal of accumulated manure helps preserve natural fly predators and thus improves fly control. Four caged layer poultry ranches were selected for study, with a total of 20 houses in the test. Data analysis is still very incomplete, but certain trends have emerged. First, cleanout of the manure during warm weather often leads to a substantial increase in house flies during the next 1-2 months, even if a pad of dry manure is left. The little house fly rebound in cooler weather is less obvious, but also tends to occur. Past research has shown that flies are less abundant when a pad is left. The mechanism has been unclear, but was assumed to reflect carryover of beneficials and better drying of the newly deposited manure. The pad actually appears to harbor very few residual predators immediately after cleanout; essentially all of the fly larvae and predaceous mites, and 70% of the predaceous beetles, are removed. The dry pad is rather sterile. The cleanout disturbance, however, appears to cause a lot of movement of mobile predators (beetles), which may enhance recolonization. Experiments to determine the drying role of the pad indicate that, surprisingly, absorption of moisture (blotter effect) from the fresh droppings is minimal. Likewise, the 3-dimensional nature of the dry manure pad is no significant advantage to drying when compared with a smooth surface (e.g. concrete or dirt floor). The mechanism is simply height, and the better air flow that results. In summer, manure on the floor is almost twice as wet after a week when compared with manure elevated even by 6 inches. Preliminary analysis thus far suggests that seasonal timing of manure removal may be more important than whether one cleans out all or only part of the manure mass. However, we will need to analyze the entire data set to determine whether the alternate row removal scheme is more of an advantage in certain seasons or with different types of housing.
Searching for an Effective Whitefly Parasite

Efficacy, behavior & reproductive demography of parasitoids of Bemisia tabaci Type B.

Principal Investigators: T. S. Bellows, Entomology, Riverside; T. M. Perring, Entomology, Riverside

Objectives:
Quantify the reproductive biology and searching behavior of Eretmocerus sp. nr. californicus, attacking Bemisia tabaci Type B on four host plant species.
Quantify the efficacy of the natural enemy on each host plant in a glasshouse environment, and assess the suitability of the reproductive and search parameters to discriminate among the efficacy of the natural enemy in glasshouse trials.

Summary of Progress: The general theme of this project is twofold: first, to identify and quantify possible reasons why parasitism by a very common natural enemy of silverleaf whitefly is high on some plants but very low on others, and secondly to determine if these reasons can be related to laboratory and greenhouse tests on the natural enemy, thus paving the way for developing evaluation procedures for natural enemies during the process of introducing them into the pest management system.

In the first year of this two-year project, we have successfully quantified and described all aspects of the search behavior of the parasite we are studying on five host plant species. We have also raised the parasites on a host plant which has selected quantifiable differences to evaluate the role of the natal host plant on parasite searching ability, host plant species selection, and other short-term behavioral adaptations. We have uncovered major differences in some aspects of these behaviors, most significantly in the willingness of adult parasites to remain on the different species of plant and search for whitefly nymphs. Additional differences were found in the time budget of behavioral activities on the different plants. Durations of some behavioral activities, such as assessment of the host for oviposition and host feeding of the whitefly by the parasites, were strikingly different among the plant species.

These findings indicate important biological distinctions among the host plants in the mixed agricultural systems attacked by silverleaf whitefly, and indicate specific traits which can be sought in additional species of natural enemies when they are introduced into the system.


Microbials for Turf Pests

Biological control of the scarab, Cyclocephala hirta, in turf with the bacterium, Bacillus popilliae.

Principal Investigator: H. K. Kaya, Nematology, Davis

Objectives:
Control the white grub, Cyclocephala hirta (Coleoptera: Scarabaeidae), in turfgrass with the milky disease bacterium, Bacillus popilliae(BP)
Compare the pathogenicity and virulence of the Cyclocephala and the Japanese beetle strain of BP against C. hirta and the Japanese beetle, Popillia japonica,
Determine whether the pathogenicity and virulence of the Japanese beetle strain of BP to C. hirta will be increased by passage through C. hirta,
Determine the feasibility of using a commercial preparation of Japanese beetle BP to control C. hirta in the field.
Assess whether milky-diseased C. hirta are more susceptible to entomopathogenic nematode infection under field conditions.

Summary of Progress: We conducted three trials which indicated that there were problems with the spores of the milky disease bacterium, Bacillus popilliae (BP), or with the insect Cyclocephala hirta, that limited disease development. The problems that we encountered were (1) the inability of the Cyclocephala hirta (designated as Oakmont) BP spores to infect C. hirta, and (2) the low infectivity of the Japanese beetle BP spores to infect C. hirta. The C. hirta BP spores which were produced in 1991 and stored at room temperature were not as infectious as they once were. The reason for this is not clear, but we hypothesize that the C. hirta BP spore and the parasporal body are enclosed very loosely within a sporangium making them less stable during storage. We believe that fresh spores should be highly infectious. However, we cannot rule out the possibility that the physiological state of the grub makes them less susceptible to the C. hirta BP spores. We doubt that the grubs are more resistant to the BP spores. The low infectivity of Japanese beetle BP spores to C. hirta grubs suggests that this might be the normal situation as has been observed by others. The higher rate that we observed previously may have been because the grubs were stressed and therefore more susceptible to infection to the Japanese beetle BP spores. Attempts to infect C. pasadenae grubs with the high concentration of BP spores were not successful. There was a natural BP infection in these grubs. We believe that BP is a viable control agent for white grubs in California. However, we must determine the factor(s) that adversely affected the infectivity of the BP from C. hirta.

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Final Reports for Projects that Ended in 1994

Biological Control for Blue Gum Psyllid

Biological control implementation for the blue gum psyllid, Ctenarytaina eucalypti (Maskell), a new pest for the California foliage industry.

Principal Investigators: D. L. Dahlsten, Entomology, Berkeley; R. L. Tassen, D. L. Rowney, W .A. Copper, and J. C. Herr, Laboratory of Biological Control, Berkeley; W. E. Chaney, UC Cooperative Extension, Monterey County

Summary of Accomplishments: The blue gum psyllid is native to Australia where it feeds on blue gum and other Eucalyptus species that have waxy-blue juvenile foliage. Since the original find in Monterey County in 1991 the psyllid has spread in a very short time throughout the California coastal area. One Eucalyptus species, E. pulverulenta, a suitable host for the blue gum psyllid, has been planted in plantations along the coastal counties of California. Foliage from this Eucalyptus is used by the floral industry in flower arrangements. Large amounts of pesticides were used to control the psyllid in these plantations, but spraying has been reduced or eliminated in most areas in the past 18 months.

Two sampling methods were evaluated for the psyllid: foliage sampling for all stages and sticky traps for adults. Sampling and monitoring sites have been established in northern, central and southern California. The numbers of psyllids of all stages and parasites on foliage can be predicted from sticky trap counts of adults from up to three weeks previous to the foliage count. The sticky trap method may be used by growers to monitor psyllid and parasite populations.

A search for natural enemies of the blue gum psyllid was made in Australia and New Zealand in late 1991 - early 1992; one species of primary parasitoid was found, shipped to our quarantine facility, and reared; over 6000 parasites were released in 1993 at eight sites in California. By the end of 1993 the parasite was established at all release sites; at several sites parasitization rates of 50% or more were recorded. In 1994 at all release sites the parasites were abundant and psyllid levels were down from 10 to 500 times below the peak levels of 1993. Psyllid levels were low enough in previously sprayed plots that no spraying was needed in these plots in 1994. Parasites are spreading rapidly to counties adjacent to the release sites. Based on the 1994 results, the biological control program has successfully controlled psyllid numbers to below economic thresholds in all areas where releases were made the previous year. One more year of monitoring in 1995 should confirm the success of this program.


Biological Control of Lygus

Parasitism rates and survivorship of Anaphes iole in California strawberry.

Principal Investigator: S. C. Welter, Environmental Science, Policy, and Management, Berkeley

Summary of Accomplishments: Previous work on biological control with Anaphes iole has determined that releases of this parasitoid may significantly reduce the development of damaging lygus bug populations. The focus of this research project is to estimate the effects of three potential factors that may limit the efficiency of this parasitoid under the conditions of commercial strawberry management. These factors are the effect of residues of seven commonly used pesticides on Anaphes survivorship, the effect of lygus population density on parasitoid efficiency, and the effect of the age of lygus eggs on parasitism rates by Anaphes.

Of the compounds tested, the insecticide residues exhibited the greatest effect on parasitoid mortality, with all insecticides killing 100% of the parasitoids one- and two- days after application of the compound. Insecticides commonly used for lygus management (malathion and Dibrom) resulted in heavy mortality of Anaphes for up to 22 days, thus limiting the potential effectiveness of a combined chemical/ biological control strategy for this pest using these compounds. Mortality rates for the acaricides and fungicides are lower and more variable than those for the insecticides. With the exception of the acaricide Omite, mortality rates decline to less than 20% after the residues have aged for four days. These results indicate that biological control of lygus with Anaphes may be compatible with some pesticide treatments for other strawberry pests.

Following field releases of Anaphes, densities of lygus nymphs are significantly reduced. We did not detect any effect of lygus densities on either percent parasitism of sentinel eggs, or on the proportional level of lygus reduction obtained. There is a linear decline in parasitism of lygus eggs by Anaphes in response to egg age. Young (less than one-day old) eggs exposed to Anaphes are parasitized at a rate of 82%, and this declines to 50% after eggs have aged 6 days. Most of this decline in parasitism is explained by an increase in egg mortality, indicating that Anaphes may be ovipositing in older eggs, yet parasitoid survivorship is reduced.


An Application System for Predatory Mites

Mechanical distribution of predaceous mites.

Principal Investigators: K. Giles, Biological and Agricultural Engineering, Davis; H. Studer, Biological and Agricultural Engineering, Davis

Summary of Accomplishments: A prototype mechanical system for field distribution of predaceous mites was developed and evaluated. The system uses common formulations of vermiculite carrier and Phytoseiulus persimilis as provided by commercial insectaries. The distributor consists of an insulated storage reservoir, a rotating metering plate and air-cleared ejection port. The system can be mounted on a standard tractor tool bar and is powered by 12 Vdc supplied by the tractor electrical system. The rotating plate is driven by a small electric motor. The system is operated by loading the reservoir with a well-mixed, chilled mixture of mites and vermiculite. As the rotating plate turns, small portions of the mixture fill the plate cells. As the filled cells pass an opening on a stationary bottom plate, the cell contents fall downward. A small, brief pulse of air ensures that each cell is cleared. Release rate of the mites can be controlled by adjusting the ground speed of the tractor, the rotational speed of the cell plate, the size of cells on the plate or a combination these variables. Voltage adjustment on the motor allows rotational speed to be easily adjusted. Growers can calibrate the mite release operation in a similar manner to that of calibrating a pesticide sprayer.

Laboratory testing found the mites to be easily damaged by excessive handling of the mite-vermiculite mixture. Agitation of the mixture resulted in physical injury to the mites and subsequent mortality. Since mites become more mobile with increasing temperature and will migrate to the upper surface of any storage container, the distributor was designed to keep the mite mixture well chilled until release from the chamber. This avoided the need for mechanical agitation. Laboratory studies have shown the distributor to release uniform rates of mites for up to 1 hour periods. No significant mortality of mites released from the current prototype has been observed.

Field trials have demonstrated the feasibility of accurate, mechanical release of predaceous mites. Accuracy of release, as measured by comparing desired or target release rates to the actual release rates over 0.5 to 1.1 acre plots averaged 97%. No significant mortality of mites due to mechanical handling was noted during field release. Mechanical reliability and ruggedness appeared high since no components have failed during field testing.

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