Augmentative Release Research Articles

Release, establishment, and movement of the predator Typhlodromus pyri (Acari: Phytoseiidae) on apple

AbstractIn Ontario apple [Malus × domestica Mill. (Rosaceae)] orchards, the application of certain pesticides kills phytoseiid predatory mites and causes outbreaks of phytophagous mites. We released a strain of the predatory mite Typhlodromus pyri Scheuten (Acari: Phytoseiidae), obtained from Nova Scotia and with organophosphate- and pyrethroid-resistant traits, into adjacent ’McIntosh’ and ’Red Delicious’ apple orchards and followed its progress over four seasons. The T. pyri strain established in the orchards, became the dominant predator, and was associated with low densities of the phytophagous mites Panonychus ulmi Koch and Tetranychus urticae Koch (Acari: Tetranychidae) and Aculus schlechtendali (Nalepa) (Acari: Eriophyidae). It moved slowly through the orchards and took 4 years to reach the 28th tree (84 m) from the release point in both orchards. The predominant wind direction did not appear to influence T. pyri movement. It was present in high numbers on release trees, or trees near these release trees, each summer after release, unlike other predatory species including Typhlodromus caudiglans (Schuster) (Acari: Phytoseiidae), Amblyseius fallacis (Garman) (Acari: Phytoseiidae), and Zetzellia mali (Ewing) (Acari: Stigmaeidae). This species appears particularly useful for biological control of phytophagous mites in Ontario and is worthy of further testing for conservation and augmentative release.

Evaluation of Green Lacewings for Suppressing Azalea Lace Bug Populations in Nurseries

Abstract Greenhouse and nursery studies were conducted to determine an optimal release rate and efficacy of green lacewing (glw) larvae, Chrysoperla carnea (Stephens), for suppression of azalea lace bug (alb), Stephanitis pyrioides (Scott). In a greenhouse study, different densities of lace bugs (40 or 80 per plant) did not influence the percent mortality caused by green lacewings. However, greater numbers of green lacewing larvae released resulted in higher lace bug mortality (5 and 20 glw per plant resulted in an average lace bug mortality of 79% and 97%, respectively). Lacewing larvae released in a production nursery, at rates of 5/plant and 10/plant, and acephate (Orthene) significantly reduced lace bug populations, with green lacewings at 10/plant and acephate reducing lace bug densities more than green lacewings at 5/plant. In a second nursery trial, lacewing larvae released into production blocks of azaleas resulted in a 97% reduction in lace bugs. These studies suggest that augmentative release of green lacewing larvae may provide an alternative control tactic that can be integrated into lace bug pest management programs.

Use of Entomopathogenic Nematodes for Control of Grape Phylloxera (Homoptera: Phylloxeridae): A Laboratory Evaluation

The effectiveness of 2 species of entomopathogenic nematodes was examined in the laboratory against the root-form of grape phylloxera Daktulosphaira vitifolia (Fitch). Our basic unit of measurement was survival of grape phylloxera established on root pieces of the cultivated grape Vitis vinifera L. variety ‘Cabernet Sauvignon’ in the presence or absence of nematodes. In petri dish trials, the Oswego strain of Heterorhabditis bacteriophora Poinar reduced survival of attached grape phylloxera by up to 80% relative to the control treatment, whereas Steinernema glaseri Steiner (isolate 326) had no measurable impact and was not used in further experiments. Hb Oswego significantly reduced survival of grape phylloxera on root pieces placed in small cups filled with soil, but only when soil moisture was high (>13% water content wt:wt) and when high densities of infective nematodes were used (>15,000/g soil). Grape phylloxera exposed to Hb Oswego often turned a brick-red color, indicating successful infection. However, we did not detect any evidence that Hb Oswego could successfully reproduce within the bodies of grape phylloxera hosts. Therefore, although Hb Oswego can exert significant mortality in the laboratory, their use in the field in an augmentative release program may be constrained by the need to use high densities, their dependence on moist soils, and their inability to propagate themselves within grape phylloxera hosts.

Augmentative Release Trials with Metaphycus spp. (Hymenoptera: Encyrtidae) Against Citricola Scale (Homoptera: Coccidae) in California's San Joaquin Valley

In recent years, citricola scale, Coccus pseudomagnoliarum (Kuwana) (Homoptera: Coccidae), has re-emerged as an important pest of citrus in California's San Joaquin Valley. We seek a biological control solution to citricola scale's pest status as part of an evolving, ecologically based integrated pest management (IPM) program for citrus. We report on augmentative release trials against citricola scale involving 4 species of Metaphycus (Hymenoptera: Encyrtidae)— M. flavus (Howard), M. helvolus (Compere), M. luteolus (Timberlake), and M. stanleyi Compere. We released these parasitoids against sleeve-caged citricola scales in a San Joaquin Valley citrus grove. Releases were made on 3 dates (hereinafter “early,” “intermediate,” and “late” release dates), each date representing scales of different size, all between 1 and 1.5 mm in length. Two to 4 of the parasitoid species were released on any of the dates. Relative to a control (no parasitoid release), the M. flavus treatments (2 densities were released) provided the greatest degree of reduction in scale numbers in the early release (from >3,600 to 2,000 to <6 per cage), followed by M. luteolus, whereas M. stanleyi did not differ from the control. In the late release, all parasitoid treatments ( M. flavus, M. helvolus, M. luteolus, and M. stanleyi ) provided similar degrees of reduction in scale numbers (from ≈1,150 to ≈6 per cage) relative to the control. We discuss the relevance of citricola scale's size at the time of parasitoid release to the results obtained with each of the parasitoid treatments on each of the release dates. In addition, we discuss the perceived impact of hyperparasitism by a facultative autoparasitoid, Coccophagus lycimnia (Walker), on our results. We conclude that citricola scale's size at the time of release is particularly important for deciding which parasitoid(s) to release, and that M. flavus and M. luteolus are the most promising parasitoids, among those currently available to us, for further research toward developing augmentative biological control tactics against citricola scale.

Effects of augmentative releases of eggs and larvae of the ladybird beetle, Adalia bipunctata, on the abundance of the rosy apple aphid, Dysaphis plantaginea, in organic apple orchards

AbstractThe impact of augmentative releases of larvae and eggs of the indigenous ladybird beetle Adalia bipunctata (L.) (Coleoptera: Coccinellidae) against the rosy apple aphid Dysaphis plantaginea Pass. (Homoptera: Aphididae), a major pest insect on apple trees, was assessed in field experiments in Switzerland, during 1997. In a first experiment, eggs and larvae were released on 3‐year old apple trees infested with five aphids at four different predator‐prey ratios (0:5, 1:5, 1:1, 5:1). In a second experiment, eggs and larvae were released at a predator‐prey ratio of 5:1 on branches of apple trees naturally infested with aphids. In both experiments, the interaction with ants was taken into account and the releases were done at two different times in spring. The results showed that an augmentative release of larvae significantly prevented the build‐up of colonies of D. plantaginea. Significant reductions in aphid numbers were recorded at the two highest predator‐prey ratios, 1:1 and 5:1. Larvae were efficient just before flowering of apple trees at a time when growers normally have to spray their trees. On trees where ants were present the larvae of A. bipunctata were significantly less efficient. Effects of eggs of A. bipunctata, however, were less reliable. At the first date of release (5 April), they did not hatch, probably as a consequence of bad weather conditions.

Oviposition Response of Cotesia plutellae (Hymenoptera: Braconidae) to Sterile and Normal Diamondback Moth (Lepidoptera: Plutellidae) Larvae

Augmentative release of the endoparasitoid Cotesia plutellae (Kurdjumov) to control diamondback moth, Plutella xylostella (L.), in cabbage. Brassica oleracea variety capitata (L.), would be expensive for growers if done continually during a growing season. A method for establishing released parasitoids would be very beneficial in the control of this pest. One method under consideration is to use sterile diamondback moth larvae deposited on 'nursery' collard plants as hosts for C. plutellae to allow the parasitoid to build up in numbers and spread into adjacent cabbage fields. Therefore, the ability of C plutellac to accept and develop successfully in normal and sterile diamomlback larvae was evaluated, C. plutellae does not discriminate between normal larvae and larvae from parents sterilized by gamma radiation, and both sets of larvae served as suitable hosts for the parasitoid. Parasitism, foliage consumption, and survivorship were similar for the 2 types of larvae. Adult female F 1 parasitoids developed from sterile diamondback larvae were as fit as those from normal larvae. In laboratory bioassays, sterile and normal diamondback larvae traversed similar distances before pupation. Field cage assays showed less distance traversed by both types of larvae compared with the laboratory studies. Survivorship for both types of larvae was very low under field conditions. Results indicate that sterile diamondback moth larvae are acceptable hosts for C. plutellae and suggest that the nursery approach toward establishment and build up of numbers would be a viable approach to in-field production of the parasitoid with little chance for harm to nearby cabbage because of spread of sterile larvae from the nursery plants. This approach could be a cost effective way to augment naturally occurring parasitoids and predators in diamondback moth management programs.

Areawide management of the cotton boll weevil: use of a spatio–temporal model in augmentative biological control

Recent advances in computer technology have facilitated the development of spatio–temporal models for simulation of ecological systems. The explicit modeling of space allows scientists to investigate the effects of spatial arrangements and heterogeneities, as well as temporal changes, in model systems. We describe an example of a host–parasitoid spatio–temporal model, consisting of integrodifference equations, which model both biological processes and population dispersal. Our model ecosystem consists of the host, boll weevil, ( Anthonomus grandis Boheman) (Coleoptera: Curculionidae), and its exotic parasitoid, Catolaccus grandis (Burks) (Hymenoptera: Pteromalidae). We use the model to explore different strategies in the augmentative biological control of the host by simulating different release methods (single or multiple sites, aerial release), and the effects of wind and heterogeneities in host density on efficacy of the parasitoid. Our preliminary simulations indicate greater host suppression when the parasitoid is released over multiple sites, or aerially, despite identical release rates. The methods used to simulate wind effects resulted in plausible dispersal and parasitization patterns, but the inclusion of heterogeneities in host densities resulted in perhaps non-intuitive parasitization patterns, likely due to boundary effects. Data are being collected currently for calibration and validation of this model. With further development, this spatial model should be useful in designing optimal strategies for the augmentative release of C. grandis against the boll weevil as part of an areawide integrated pest management program.

Interactions Between Augmentatively Released Diachasmimorpha longicaudata (Hymenoptera: Braconidae) and a Complex of Opiine Parasitoids in a Commercial Guava Orchard

A study was conducted to determine the eVect of augmentatively releasing mass-reared Diachasmimorpha longicaudata (Ashmead) on a complex of four co-existing parasitoid species which attack the oriental fruit fly, Bactrocera dorsalis (Hendel). The species belonging to this complex are the egg-pupal parasitoid, Biosteres arisanus (Sonan) and the larval-pupal parasitoids, Biosteres vandenboschi (Fullaway), D. longicaudata and Psyttalia incisi (Silvestri). The study site was a 160-ha commercial orchard of common guava, Psidium guajava L. (cv. Beaumont) located on Kauai island. One year before the release of D. longicaudata, B. arisanus was the dominant parasitoid, accounting for 91.1% of the parasitoids recovered. Despite releases of large numbers of D. longicaudata (600000-800 000 parasitized puparia/ week), B. arisanus continued to account for 90% of all parasitoids recovered from the oriental fruit fly. The larval parasitoid P. incisi may have been reduced as a result of D. longicaudata releases. D. longicaudata was significantly more abundant in over-ripe and rotting fruits compared with freshly fallen fruits. However, no increase in the overall percentage parasitism was observed in any fruit ripeness category. B. arisanus was eY cient at colonizing hosts when fruit fly densities and fruit abundance were relatively low in the orchard. The implications for future augmentative release programmes with D. longicaudata are discussed.

Contribution of Biological Control to Integrated Pest Management of Tephritid Fruit Flies in the Tropics and Subtropics

The biological control of pest tephritid flies using parasitoids has been successful in relatively few subtropical and tropical regions. The best documented successes were in Hawaii and Florida, USA, Fiji and southern Europe. There were relatively limited successes in Australia, Costa Rica and Mexico. With the accidental establishment of new pest tephritids, such as Bactrocera latifrons (Hendel) in Hawaii or Bactrocera papayae Drew and Hancock in Australia, foreign exploration for new parasitoids is essential. A renewal of interest in classical biological control has recently occurred, although not at the same level as in the 1940s and 1950s. New parasitoid species are currently being obtained for several tephritids, such as Ceratitis capitata (Weidemann), B. latifrons and Anastrepha suspensa (Loew). The advances in mass rearing and quality control technology for parasitoids has enabled researchers to perform large-scale field testing of these parasitoids to determine the potential of augmentative releases. Numerous studies on the augmentative release of parasitoids have been done. Historically, the larval—pupal parasitoid Diachasmimorpha longicaudata (Ashmead) has been the most frequently studied parasitoid, due to the ease of rearing this species. However, recent successes in rearing other species with different biologies, e.g. the egg—pupal parasitoid Biosteres arisanus (Sonan), the gregarious eulophid, Tetrastichus giffardianus (Silvestri) and the pupal parasitoid, Coptera sp., will enable researchers to broaden the repertoire of parasitoid species for the future. Both successes and failures in augmentative releases have occurred. Without knowledge of the behavioural ecology of parasitoids, the reasons for success or failure can only be surmised. Recent research on the dispersal and host habitat finding of tephritid parasitoids will provide insights into improving augmentation and conservation strategies. The integrated pest management (IPM) of tephritid flies in the tropics has been less well-developed than research and programmes for tephritids in temperate zones. Significant emphasis is now being placed on the development of quarantine treatment methods that are environmentally sound; thus IPM will take a larger role. Several existing pest management strategies are reviewed which show the potential for compatibility with the activities of tephritid parasitoids. These include trap cropping, insecticides with selective toxicity to the target pests, mass trapping with parapheromones, the sterile insect technique and field sanitation.

Characterization of a microsatellite locus in the parasitoid waspAphelinus abdominalis(Hymenoptera: Aphelinidae)

AbstractPrimers for DNA amplification using the polymerase chain reaction (PCR) were synthesized for a microsatellite locus isolated from a partial genomic library of the aphid parasitoidAphelinus abdominalis(Dalman). Screening for genetic polymorphism at this locus in two laboratory strains of this wasp revealed the presence of two alleles different in the number of (GT) and (GGC) repeats. The relative frequencies of the two alleles were not significantly different between the two strains or between diploid females and haploid males. Heterozygosity at this microsatellite locus was estimated to be 0.40 which is within the range in other hymenopterous species. Given thatA. abdominalisis a good candidate for augmentative release programmes in greenhouses against aphids, we suggest that microsatellite markers may have application in discriminating among aphelinid sibling species and strains. The markers provide a means for studying the performance and impact of selected parasitoid lines on pest dynamics in field release experiments.

Ground Cover Influence on Microclimate and Trichogramma (Hymenoptera: Trichogrammatidae) Augmentation in Seed Corn Production

As pest management practices include more biological control implementation, the effect of different cropping systems on microclimate and efficacy of natural enemies should be considered. In a 1993 experiment, physical and microolimatic differences between hybrid field corn, Zea mays L., and inbred seed corn were assessed. Seed corn fields had 4.2-fold less leaf surface area and higher maximum temperature at the soil surface than field corn fields. Emergence of Trichogramma brassicae Bezdenko from cardboard capsules was significantly lower in seed corn when capsules were placed at the soil surface, but was not significantly different when capsules were at canopy level. In 1994, a rye grass Lolium multiflorum Lambert intercrop planted with seed corn significantly reduced maximum soil surface temperature compared with seed corn plots in which soil was bare or was covered (62%) with corn residue. Soil surface temperature was significantly higher in corn residue plots than in bare soil plots. Minimum temperatures were not significantly affected by ground cover. The mean number of hours per day that temperatures were 35°C or higher (lethal to T. brassicae) was significantly higher in residue and bare soil microhabitats than in rye grass plots or the corn canopy. When T. brassicae inside cardboard capsules were put into plots in the same manner as an augmentative release (i.e., 2 developmentally staggered cohorts), emergence from both cohorts was not significantly different in rye grass than in the corn canopy, but was significantly reduced in bare soil and corn residue plots.

Increased parasitization of California red scale in the field after exposing its parasitoid, Aphytis melinus, to a synthetic kairomone

AbstractThe introduced parasitoid, Aphytis melinus DeBach (Hymenoptera: Aphelinidae), utilizes a kairomone, O‐caffeoyltyrosine, to recognize California red scale, Aonidiella aurantii (Maskell) (Homoptera: Diaspididae). Wasps used in augmentative release programs for California red scale on California citrus are reared on oleander scale, Aspidiotus nerii Bouché (Homoptera: Diaspididae), themselves reared on squash. Previous laboratory studies demonstrated that wasps reared on oleander scale but exposed to O‐caffeoyltyrosine before bioassay more readily accepted California red scale covers for probing than wasps reared similarly but not exposed to O‐caffeoyltyrosine. The goal of this study was to determine if wasps reared on oleander scale but exposed to O‐caffeoyltyrosine actually parasitized a greater number of field‐reared California red scale than unconditioned wasps. In order to distinguish between progeny of conditioned and unconditioned wasps in the field, we utilized two A. melinus strains that carried different electrophoretically distinguishable alleles. In half of the releases, Strain ‘A’ was conditioned to O‐caffeoyltyrosine and Strain ‘B’ served as the control, while this pattern of conditioning was reversed for the remaining releases. Although there were differences in the rates of population growth of the two strains, whichever strain was the conditioned strain left a greater than expected number of progeny compared to the control strain in all comparisons. Exposure of A. melinus reared in commercial insectaries to O‐caffeoyltyrosine prior to release may be a means to improve the effectiveness of such wasps in augmentative release programs to control California red scale.

Ripeness effects of three vegetable crops on abundance of augmentatively released psyttalia fletcheri (Hym.: Hraconidae): Improved sampling and release methods

Studies were done to determine the effect of 4 fruit ripeness levels on the abundance of Psyttalia fletcheri (Silvestri),a parasitoid of Bactrocera cucurbitae (Coquillett). In addition,an improved trapping method was developed for monitoring massreleased adult parasitoids in the field. A total of 420,000 adult P. fletcheri were released over a period of 15 weeks,in a 0.16 ha experimental field plot containing cucumber,zucchini and tomato in Kauai,HI. We recovered significantly more P. fletcheri from rotting fruits of all fruit types than from immature,commercial grade or oversized fruits. In addition,there was a positive correlation between the number of P. fletcheri and B. cucurbitae recovered from rotting fruits. Average parasitism in rotting tomato,zucchini and cucumber was 5,19 and 36% respectively. Yellow pan traps were as effective as sticky sphere traps for monitoring P. fletcheri,indicating that parasitoids were foraging close to the ground where rotting fruits occurred. The pan traps were much easier to use,less expensive and required less set up time. Recovery of parasitoids from both fruit collections and pan traps indicated that P. fletcheri was least abundant in tomato. Both male and female parasitoids exhibited a weakly aggregated distribution in each crop. We discuss modified sampling and release methods for population estimation and augmentative release studies of P. fletcheri.

Priming Aphytis: behavioral modification of host selection by exposure to a synthetic contact kairomone

AbstractThe introduced parasitoid, Aphytis melinus DeBach (Hymenoptera: Aphelinidae), utilizes a kairomone, O‐caffeoyltyrosine, to recognize California red scale, Aonidiella aurantii (Maskell) (Homoptera: Diaspididae). Wasps used in augmentative release programs for California red scale on California citrus are reared on oleander scale, Aspidiotus nerii Bouché (Homoptera: Diaspididae), themselves reared on squash. The goals of this study were: 1) to determine if long‐term rearing on oleander scale had caused A. melinus to develop a preference for oleander scale, and 2) to determine if the preference of oleander‐reared A. melinus for California red scale might be enhanced by exposing them to synthetic O‐caffeoyltyrosine prior to release. Wasps that were removed from their hosts as pupae and allowed to emerge as adults isolated from their hosts retained a strong preference for California red scale regardless of rearing host. This preference was reduced if wasps were allowed to emerge from oleander scale, thus acquiring early adult experience with oleander scale. The preference for California red scale was restored, however, by exposing wasps reared on oleander scale to synthetic O‐caffeoyltyrosine prior to bioassay. Exposure of A. melinus reared in commercial insectaries to O‐caffeoyltyrosine prior to release may be a means to improve the effectiveness of such wasps in augmentative release programs to control California red scale.

Report of an Intracellular Bacterial Symbiont in Noctuidonema guyanense, an Ectoparasitic Nematode of Spodoptera frugiperda

The Banks grass mite, Oligonychus pratensis (Banks) (Acari: Tetranychidae), is a serious pest in dates (Phoenix dactylifera L.) in the New World. Currently O. pratensis is managed using the miticide, Savey, and alternative strategies are necessary to remove pressure from a single control method due to the risk of resistance evolution. For this purpose, studies are underway to develop biological control strategies using the predatory mite, Galendromus flumenis (Chant) (Acari: Phytoseiidae). The current study determined the consumption rate of G. flumenis at constant densities of O. pratensis eggs, larvae, protonymphs and deutonymphs, and defined the functional response of predator females. The predator consumed significantly more eggs than other prey stages, and displayed a type II functional response on all prey stages. The highest attack rate and shortest handling time were obtained for predators feeding on prey larvae and eggs, respectively. The proportions of prey consumed by G. flumenis were higher at lower densities for all stages of Banks grass mite, implying that G. flumenis should be more effective at suppressing Banks grass mite populations at lower densities. Therefore, in an augmentative release program, G. flumenis would need to be released early in the infestation.

Improvements in the Production System for Green Lacewings: An Adult Feeding and Oviposition Unit and Hot Wire Egg Harvesting System

Abstract Green lacewings ( Chrysoperla spp.) are used in augmentative release programs against a variety of arthropod pests. As part of an ongoing research program to improve the mass production technology for green lacewings, an Adult Feeding and Oviposition Unit (AFOU) and a hot wire egg harvesting system were developed. The AFOU is a cylindrical unit, which can be unrolled to facilitate egg harvest with a hot wire system. The hot wire egg harvesting system consists of two devices, one of which uses a pneumatic cylinder to pull the cylinder portion of the AFOU past the hot wire and the other which is used to harvest eggs from the top of the AFOU. These improvements make adult handling and egg harvesting easier. The improved system requires less manual labor than the conventional paper cartons and manual egg harvesting system commonly used in the United States. Egg recovery was higher when a hot wire egg harvesting system was used than when the traditional loose ball of nylon netting was used. There was no difference in the percentage hatch of eggs recovered with either of these systems or with a sodium hypochlorite based egg harvesting system. This equipment may provide the basis for an automated adult handling and egg harvesting system for the mass production of green lacewings.

Effect of seasonal placement ofCotesia melanoscela (Hym.: Braconidae) on its potential for effective augmentative release againstLymantria dispar (Lep.: Lymantriidae)

Cohorts ofCotesia melanoscela (Ratzeburg) (Hymenoptera: Braconidae) cocoons were exposed in the field at three Maryland locations to attack by natural enemies for two week periods, then were held in an outdoor insectary untilC. melanoscela adult or hyperparasitoid emergence. The timing of placement of theC. melanoscela cocoons in the field had a profound effect on the number ofC. melanoscela that survived and emerged as adults in synchrony with the field occurence of susceptible early-instarLymantria dispar (L.) larvae. The proportion of emerged adults available during susceptible host stages ranged from 1–92%, depending on dates of release. November or December placements ofC. melanoscela cocoons were most effective with 74–92 % emergence of adults during peak periods of susceptible host stages. Spring placements were least effective. The causes of ineffective placement, which varied with location and with date, were program (handling) loss, non-emergence, attack by hyperparasitoids, predation, andC. melanoscela adult emergence at times when appropriateL. dispar life stages would not be present. We concluded that November/December releases avoided natural enemies and promoted appropriate diapause and post-diapause development that enhanced survival and synchrony of adult emergence with host stage susceptibility.

Influence of Guava Ripening on Parasitism of the Oriental Fruit-Fly, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae), by Diachasmimorpha longicaudata (Ashmead) (Hymenoptera: Braconidae) and Other Parasitoids

Abstract The effects of guava ripening on abundance and parasitism rates of parasitoids of oriental fruit fly, Bactrocera dorsalis (Hendel), were determined in three guava ( Psidium guajava L.) orchards. Diachasmimorpha longicaudata (Ashmead) was released in Kilauea, Kauai, and Waiakea, Hawaii. Natural densities of this parasitoid were measured in a third orchard in Panaewa, Hawaii. Fruits ripening on the tree and the ground after abscission of fruit were classified into four categories, ranging from to mature-green to rotten fruit. The egg parasitoid, Biosteres arisanus (Sonan) was the dominant parasitoid emerging from tree-harvested guavas at all sites and composed 90-98% of all parasitoids recovered but decreased in abundance as guava fruit aged on the ground. In all three orchards, D. longicaudata increased in abundance and parasitism rates were highest in guavas that remained on the ground for 6-10 days. Consequently, the impact of this parasitoid is usually underestimated by sampling commercially ripe guava fruit from the tree or freshly fallen fruit on the ground. The eulophid parasitoid, Tetrastichus giffardianus (Silvestri), was more abundant in 4- to 9-day-old ground fruit. We discuss modified sampling methods for population estimation and augmentative release studies of parasitoids of oriental fruit fly.

Field-Cage Evaluation of Augmentative Biological Control of Bemisia argentifolii (Homoptera: Aleyrodidae) in Southern California Cotton with the Parasitoid Eretmocerus nr. californicus (Hymenoptera: Aphelinidae)

A field cage evaluation of the parasitoid Eretmocerus nr. californicus as a biological control agent of Bemisia argentifolii Bellows & Perring was conducted in Southern California cotton during June through August of 1992. Percentage of parasitism was highest in early August at 61% in the high parasitoid release treatment and was significantly higher than both the low parasitoid release and control treatments. The density of B. argentifolii pupae on leaves in the high parasitoid release treatment was approximately one-fifth of the other treatments. Seed cotton yield was significantly higher in the high parasitoid release cage in comparison with those of the low parasitoid release and control cages. We conclude that E. nr. californicus may be a useful control agent in an augmentative release strategy against whitefly on cotton and is deserving of large-scale, open field studies.

Behavioral time budget and periodicity exhibited byMicroplitis croceipes in field cages withHeliothis virescens on spring host plants

Microplitis croceipes (Cresson) females were observed between 06:00 and 20:00 hours in cages containing spring host plants infested withHeliothis virescens (F.), tobacco budworm, larvae, Cages containedGeranium dissectum L. andTrifolium incarnatum L. in plantings of equal area, each infested with 50H. virescens larvae. A time budget for the various behaviors exhibited by the wasps was obtained. In order of decreasing time spent,M. croceipes females were observed to exhibit standing still, searching on plant surface, preening, oriented flight, general flight, and walking. The proportion of time spent preening increased over the day. Oriented flight, general flight, searching, and walking peaked in the morning between 09:00 and 12:00 hours. Oriented flight, general flight, and walking showed minor increases in the afternoon.Microplitis croceipes females spent significantly more time preening, orienting to, and walking and searching on clover than on geranium. However, there was no difference in time spent standing still on geranium or clover. Significance of these findings for development of effective augmentative release strategies is discussed.