Augmentative Releases Research Articles

Influence of Anastrepha host fruit size over parasitism by Diachasmimorpha longicaudata in open-field augmentative releases

ABSTRACT Fruit size can act as a physical barrier providing refuge for larvae of pest Anastrepha species against parasitoid attack. Therefore, the aim of this study was to evaluate the influence of fruit size in six fruit species infested by Anastrepha larvae on the parasitism of Diachasmimorpha longicaudata after its augmentative release. About 1500 parasitoids were weekly released in disturbed wild vegetation patches. Fruit sampling was performed at the Coastal Lowlands of the Soconusco Region, southeastern Mexico, between June 2021 and October 2022. Overall, 310 ripe fruits belonging to grapefruit, creole mamey (large-size fruits), sweet orange, creole mango, wild guava (medium-size fruits), and wild hog plum (small-size fruit) were collected. The length, frontal width, lateral width and pulp thickness of all sampled fruits were measured. Such physical characteristics are indicators of the fruit size. Fruit collection was performed 48 h after release. Results indicated an inverse correlation between fruit size and parasitism, with a significant r 2 value higher than 75%. Host larvae in all fruits were parasitised only by D. longicaudata. The highest mean parasitism, which exceeded 90%, was recorded on hog plum and the lowest, below 20%, on Citrus spp. and mamey. Results corroborated the influence of host fruit size on parasitism levels by D. longicaudata regardless of its large-scale, open-field releases. Augmentative releases of D. longicaudata can be focused on wilderness areas with prevalence of medium-size to small-size Anastrepha host fruits. This would encourage long-term sustainable conservation of released parasitoid populations.

Natural-Enemy-Based Biocontrol of Tobacco Arthropod Pests in China

The devastating impact of chemical pesticides has prompted a shift towards sustainable agricultural pest management, such as biological control with natural enemies. In recent years, commercialization advancements have enabled the suppression of pest populations through augmentative releases of biological control agents, with natural enemies being a major tactic. China has successfully implemented natural-enemy-based biocontrol strategies, particularly for controlling aphids and lepidopterans. This article provides a comprehensive overview of the state-of-the-art natural-enemy-based biocontrol against arthropod pests in tobacco in China, including practical achievements in mass-rearing methods, augmentative release strategies, and the wide-scale use of natural enemies. Current and potential future challenges for natural-enemy-based biocontrol in China are also discussed.

Medfly Population Suppression through Augmentative Release of an Introduced Parasitoid in an Irrigated Multi-Fruit Orchard of Central–Western Argentina

Biological control through the augmentative release of parasitoids is an important complementary tool that may be incorporated into other strategies for the eradication/eco-friendly control of pest fruit flies. However, not much information is available on the effectiveness of fruit fly parasitoids as biocontrol agents in semi-arid and temperate fruit-growing regions. Therefore, this study evaluated the effect of augmentative releases of the larval parasitoid Diachasmimorpha longicaudata (Ashmead) on Ceratitis capitata (Wiedemann) (medfly) populations over two fruit seasons (2013 and 2014) on a 10 ha irrigated fruit farm in San Juan province, central-western Argentina. The parasitoids were mass reared on irradiated medfly larvae of the Vienna-8 temperature-sensitive lethal genetic sexing strain. About 1692 (±108) parasitoids/ha were released per each of the 13 periods throughout each fruit season. Another similar farm was chosen as a control of non-parasitoid release. The numbers of captured adult flies in food-baited traps and of recovered fly puparia from sentinel fruits were considered the main variables to analyze the effect of parasitoid release on fly population suppression using a generalized least squares model. The results showed a significant decrease (p < 0.05) in the medfly population on the parasitoid release farm when compared to the Control farm, demonstrating the effectiveness of augmentative biological control using this exotic parasitoid. Thus, D. longicaudata could be used in combination with other medfly suppression strategies in the fruit production valleys of San Juan.

Annual and Seasonal Changes in Parasitism Rates by Hadronotus Pennsylvanicus (Hymenoptera: Scelionidae) on the Squash Bug Anasa Tristis (Hemiptera: Coreidae) in Squash Fields: Implications for Augmentative Releases.

This study evaluated parasitism rates by Hadronotus pennsylvanicus (Ashmead) (Hymenoptera: Scelionidae) on the squash bug Anasa tristis DeGeer (Hemiptera: Coreidae) over a six-year period in squash fields in Maryland. From 2016-2021, 2226 wild squash bug egg masses were collected, 2180 (98.0%) A. tristis egg masses and 46 (2.0%) A. armigera egg masses. The mean (±SE) parasitism rate was 10.9 ± 0.16%. Yearly parasitism rates were significantly different with rates in 2017 and 2018 that were significantly lower than in 2019, 2020, and 2021. The significant difference in parasitism rates based on planting date was primarily due to the high parasitism rate observed in 2021. These results suggest that the use of augmentative releases early in the season could result in effective control by increasing parasitism earlier in the season and by causing the parasitism rate in the field to peak at a higher number late in the season.

Trissolcus kozlovi in North Italy: Host Specificity and Augmentative Releases against Halyomorpha halys in Hazelnut Orchards

Simple SummaryThe Asian brown marmorated stink bug, Halyomorpha halys, is an invasive crop pest introduced into Europe in the 2000s. Due to its high harmfulness, and the increased chemical use for its control in the invaded areas, research has focused on biological control. In North Italy, the native parasitoid Trissolcus kozlovi emerged from field-collected H. halys eggs and proved to successfully parasitize H. halys eggs in the laboratory. Therefore, since little is known on T. kozlovi, this study aimed at assessing its physiological host range on 12 bug species in the laboratory, as well as its potential as a biological control agent of H. halys in the field by releases in two hazelnut orchards. In the laboratory, among the tested bug species, only Nezara viridula was an unsuitable host. On all others, T. kozlovi was able to develop, even if at different levels, suggesting that it is as oligophagous as Trissolcus japonicus, with which it shares many similarities. In the field, T. kozlovi was found to parasitize H. halys eggs, but only immediately after field releases. Therefore, further field surveys are required to assess its favorably environmental conditions and its possible interaction with T. japonicus, currently present in Italy.Trissolcus kozlovi (Hymenoptera: Scelionidae) emerged from field-laid eggs of Halyomorpha halys (Hemiptera: Pentatomidae) in North Italy, and it emerged in significantly higher numbers from fresh H. halys eggs compared to other native scelionids. Since few data on T. kozlovi are available, its host-specificity and some biological traits were investigated in laboratory tests, and its impact after augmentative releases was evaluated in two hazelnut orchards. Among the 12 tested bug species (Hemiptera: Pentatomidae, Scutelleridae), only Nezara viridula was an unsuitable host, while the highest offspring proportions were obtained from Arma custos, Pentatoma rufipes, and Peribalus strictus, followed by Acrosternum heegeri and Palomena prasina. Furthermore, when reared on P. strictus, T. kozlovi showed a high longevity as well as a high adaptation to H. halys eggs. In both hazelnut orchards, T. kozlovi emerged from H. halys eggs after field releases, but it was not found in the next two years. The physiological host range of T. kozlovi was quite similar to that of T. japonicus, and probably T. kozlovi has just begun to attack H. halys as a new host. This aspect needs to be further investigated, as well as its favorable environmental conditions, its distribution and also its possible interaction with T. japonicus, currently present in Italy.

Bioefficacy of Rhynocoris longifrons (St\xe5l) (Heteroptera: Reduviidae) against multiple cotton pests under screen house and field conditions

Rhynocoris longifrons (Hemiptera: Reduviidae) is a generalist predator of many cotton insect pests. The hiding behaviour of this predator, which is one of the key factors of predation success, was investigated under screen house conditions. Moreover, we evaluated its biocontrol potential against Aphis gossypii (Hemiptera: Aphididae), Dysdercus cingulatus (Hemiptera: Pyrrhocoridae), Phenacoccus solenopsis (Hemiptera: Pseudococcidae), and Helicoverpa armigera Hübner (Lepidoptera: Noctuidae) under screen house and field conditions. Results showed that R. longifrons life stages preferred to hide under small pebbles in the screen house tests. All the R. longifrons life stages showed a biocontrol potential against the four insect pests under screen house conditions. However, their biocontrol potential had not varied in relation to day and night hours. Augmentative releases of R. longifrons were carried out for two seasons such as South-west monsoon, 2011 and post-monsoon, 2012. The augmentative release of R. longifrons reduced significantly insect pests on cotton. In fact, the release of this predator in cotton fields was capable to reduce the population of H. armigera (50%), P. solenopsis (28%), D. cingulatus (18.8%), and A. gossypii (11.8%) during the rain fed condition (south-west monsoon season). During irrigated condition (post-monsoon season), populations of D. cingulatus were reduced by 26%, than P. solenopsis (20.6%), and A. gossypii (16.8%). Except ants, no negative impact was reported on other natural enemies present in the cotton field. Significantly higher crop yield and cost benefit ratio was observed in the predator release plots indicating that R. longifrons can be used in an integrated pest management program for multiple cotton pests.

Efficacy of augmentative release of the parasitoid wasp Bracon hebetor against the pearl millet headminer

The yield losses in pearl millet, estimated to be about 85%, are mainly due to millet headminer, Heliocheilus albipunctella . This study is aimed at determining the status of this serious insect pest in the pearl millet production system within the groundnut basin of Senegal and to assess the efficacy of augmentative releases of its parasitoid wasp, Bracon hebetor , to control it. The study area was divided into three homogenous blocks (Northern, Southern and Eastern parts) where a set of three villages was selected for release of the parasitoid and another three as control villages where no releases were made. The results revealed that in all the villages where the parasitoid was released, an increase in larval mortality due to parasitism ranging between 9% and 26% was recorded in comparison with the control villages. Consequently, damages recorded were significantly lower in the villages with parasitoid releases.

Optimizing cold storage of the ectoparasitic mite Pyemotes zhonghuajia (Acari: Pyemotidae), an efficient biological control agent of stem borers.

Pyemotes zhonghuajia Yu, Zhang and He is a newly discovered native ectoparasitic mite that efficiently controls stem borers in China. To provide a steady and sufficient supply, extend adult lifespan and synchronize field augmentative releases of P. zhonghuajia, we determined the optimal cold storage temperature and duration by storing 1-day-old mated females at 8, 10 and 12°C for 10-90days with a 10-day interval in the laboratory. We then recorded mite survival during storage and monitored the post-storage reproductive performance of mites at a control temperature of 25°C. We found that all mites survived at 10 and 12°C for different durations, but mortality occurred when mites were stored at 8°C for ≥ 30days with more than 70% of mites dead when the storage duration prolonged up to 50days. The proportion of reproductive females was higher at 10°C but decreased with the prolonged storage duration at all test temperatures. Storage temperature had no significant effect on the pre-reproductive period and offspring sex ratio, whereas prolonged storage induced longer pre-reproductive period and lower proportion of female offspring. The reproductive period increased with increasing storage temperature and with prolonged storage up to 50 and 60days; however, the longer reproductive period did not directly translate into greater reproductive output. We found that compared with the control, mites stored at 10°C for up to 30days did not significantly reduce their survival, proportion of reproductive success and number and sex ratio of offspring, suggesting that 10°C and ≤ 30days were the optimal cold storage temperature and duration, respectively, for post-mass production storage before the field augmentative release of P. zhonghuajia.

Augmentative releases of Trichopria drosophilae for the suppression of early season Drosophila suzukii populations

Biological control agents may play an important role in regulating Drosophila suzukii Matsumura (Diptera: Drosophilidae), particularly after the winter population bottleneck. Here we test the ability of the cosmopolitan pupal parasitoid, Trichopria drosophilae (Perkins) (Hymenoptera: Diapriidae), to reduce early season D. suzukii populations. We performed augmentative releases of the parasitoid during late March–April and carried out extensive monitoring activity on both parasitoid and fly populations. Results clearly showed a mitigation of the D. suzukii population in the treated areas, associated with a higher T. drosophilae parasitism. A 34% reduction in fruit infestation was observed in the unmanaged vegetation surrounding orchards. Accordingly, pest eclosion was significantly lower in the treated area compared to the untreated one. Our results suggest that augmentative release of T. drosophilae can improve pest control of D. suzukii in the unmanaged areas surrounding the crops, thus lowering the severity of pest outbreaks in the orchards.

Field persistence of Habrobracon hebetor (Say) (Hymenoptera: Braconidae) following augmentative releases against the millet head miner, Heliocheilus albipunctella (de Joannis) (Lepidoptera: Noctuidae), in the Sahel

Biological control by augmentative releases of the parasitoid wasp Habrobracon hebetor Say (Hymenoptera: Braconidae) is a promising strategy for controlling the millet head miner (MHM), Heliocheilus albipunctella (de Joannis) (Lepidoptera: Noctuidae). A current biological control program in the Sahel region involves inoculative releases of the parasitoid each growing season, but this is prohibitively expensive. The present study aimed to quantify residual parasitism of MHM in years after augmentative release. We also investigated the impact of two successive annual releases of H. hebetor on MHM parasitism. Two successive releases did not increase parasitism, but slightly reduced MHM damage in terms of number of mines and their length. Parasitism levels decreased in subsequent years if no additional parasitoids were released. Nevertheless, in the first year after release, parasitism levels in release villages remained significantly higher than in control villages. These findings suggest that augmentative releases could be carried out biennially instead of annually. Possible means of enhancing parasitoid survival between seasons are discussed.

An analysis of heterosis and outbreeding depression among lab-reared populations of the parasitoid Diachasmimorpha tryoni (Cameron) (Hymenoptera: Braconidae); potential implications for augmentative releases

Augmentative biological control is a process in which a biocontrol agent is mass-reared and released to either augment the existing population present in the field or inundate the target pest population. Although research into the utility of augmentative biocontrol has been conducted for ∼50years, little is known about the effect of inundative releases on the progeny of the released population and the wild population. We used the arrhenotokous haplo-diploid tephritid parasitoid Diachasmimorpha tryoni (Cameron) (Hymenoptera: Braconidae) to model a theoretical augmentative release interaction. By employing a combination of molecular techniques and a fitness proxy, our results were capable of documenting the hybridization of a “released” and “wild” population (as modeled in vitro). These analyses revealed significant hybridization interactions between two moderately differentiated populations (Fst/Rhost=0.1352/0.0641), as would be the case during an augmentative release. Our analysis also revealed an outcrossing asymmetry of hybrid progeny relating to parental population origin. This interaction has the potential to either hinder or facilitate augmentative control and may prove useful to future augmentative releases.

Parasitoid fauna of Queensland fruit fly, Bactrocera tryoni Froggatt (Diptera: Tephritidae) in inland New South Wales, Australia and their potential for use in augmentative biological control

Augmentative releases of parasitic wasps may improve management of the Queensland fruit fly, Bactrocera tryoni Froggatt, in inland New South Wales (NSW). A survey was conducted from October 2008 to April 2009 to detect the presence of parasitoids of fruit fly. Fruit fly-infested fruits were collected in Wagga Wagga, Cootamundra, Ganmain, Gundagai, Lockhart and Lake Cargelligo on the south-west slopes and plains of NSW and Albury-Wodonga on the NSW-Victorian border. Two species of opiine parasitoids were detected: Diachasmimorpha kraussii (Fullaway) and D. tryoni (Cameron); both species from fruits that also yielded B. tryoni and island fruit fly, Dirioxa pornia (Walker). Nine per cent of fruit samples yielded parasitoids. There were statistically significant differences between fruit type, fruit species, sampling events and towns. Fruit fly parasitoids were most commonly detected in fig (27.2% of samples), followed by stone fruit (11.5%), pome fruit (6.1%), loquat (4.3%) and citrus (2.1%). Parasitoid incidence varied throughout the fruit fly season, peaking in February–March 2009 (17.4%). Of the towns surveyed, Cootamundra had the highest incidence of parasitoids (28.8%), followed by Wagga Wagga (9.5%), Gundagai (10.2%) and Lockhart (1.2%), with no parasitoids detected in Albury-Wodonga, Ganmain or Lake Cargelligo. Diachasmimorpha tryoni was detected in all surveys except January–February 2009, during a heatwave. Diachasmimorpha tryoni was most prevalent in November–December 2008 (5.2%). Diachasmimorpha kraussii was most prevalent in February–March 2009 (14.5%), but was not detected in October 2008 or April 2009. Diachasmimorpha tryoni was detected in Wagga Wagga (6.1%) and Cootamundra (1.9%), with D. kraussii detected in Wagga Wagga (9.5%), Cootamundra (26.9%), Gundagai (10.2%) and Lockhart (1.2%). The presence of these parasitoid species in the region suggests they may be suitable for augmentative release in the control of B. tryoni in inland NSW.

Evaluation of augmentative release of Zygogramma bicolorata Pallister (Coleoptera: Chrysomelidae) for biological control of Parthenium hysterophorus L.

Augmentative release of biocontrol agents has been largely successful for the management of insect pests but it has not been a common approach for weed management. Augmentation methods need to be developed for weed management, especially for pernicious weeds like Parthenium hysterophorus L., commonly known as pathenium or carrot weed. The leaf beetle Zygogramma bicolorata is a potential biocontrol agent of P. hysterophorus. Initial release of biocontrol agents is subject to uncertainties as to whether timely population built-up will take place in sufficient numbers. Several augmentative releases may be required to ensure early establishment of the biocontrol agents, for successful biological control of noxious weeds including pathenium. We made augmentative releases of larvae or adults of Z. bicolorata each to three sites, severely infested with pathenium at Jabalpur, India consecutively for a period of three years. Initially 10 larvae or adults per sq m were released in each plot, followed by a second, third and fourth release of 3, 1.5 and 1.5 larvae or adults per sq m at an intervals of 3, 7 and 14 days after the first augmentation. The pathenium at augmented sites were completely defoliated in 45 and 60 days by larvae and adults respectively. There was also a reduction in the pathenium density and plant height in the augmented sites as compared to the non-augmented sites. Over a period of 3 years augmentation resulted in a noteworthy negative effect on the weed.

Evaluation of Aphytis melinus De Bach (Hymenoptera: Chalcidoidea: Aphelinidae) in Citrus Orchards as a Biocontrol Agent of Black Scale, Parlatoria ziziphi (Lucas) (Hemiptera: Coccoidea: Diaspididae) in Egypt

The black parlatoria scale, Parlatoria ziziphi (Lucas) (Coccoidea: Diaspididae), is one of the most important pests attacking citrus trees in different parts of the world including Egypt. This work deals with rearing, release and evaluation of the parasitoid, Aphytis melinus De Bach (Hymenoptera: Aphelinidae) to control P. ziziphi biologically. In all, 250000 adult parasitoid individuals were released monthly on citrus at five locations in Cairo, Giza and Qalyubiya governorates during 2006 and 2007. At Heliopolis (Cairo), where A. melinus was present prior to the augmentative release, the per cent parasitism in the control block was 15 and 75% while it was 73 and 87% in the treatment block during the two years under consideration. At Dokki (Giza) also, A. melinus was present prior to the augmentative releases and the peak of parasitism reached 18 and 82% in the control block, compared to 86 and 91% in the treatment block. At El-Qanater El-Khriya and Tukh in Qalyubiya, A. melinus was present prior to the augmentative releases. In El-Qanater El-Khriya, the peak of parasitism reached 41 and 67% in the treatment block, compared to 8 and 46% in the control block. In Tukh, the peak of parasitism reached 31 and 65% in the treatment block, compared to 4 and 35% in the check block. At Qalub, where the parasitoid was not present prior to the augmentative releases, the peak of parasitism reached 22 and 36% in the treatment block, compared to 0 and 22% in the control block during the two years, respectively.

Evaluation of Aphytis melinus De Bach (Hymenoptera: Chalcidoidea: Aphelinidae) in Citrus Orchards as a Biocontrol Agent of Black Scale, Parlatoria ziziphi (Lucas) (Hemiptera: Coccoidea: Diaspididae) in Egypt

The black parlatoria scale, Parlatoria ziziphi (Lucas) (Coccoidea: Diaspididae), is one of the most important pests attacking citrus trees in different parts of the world including Egypt. This work deals with rearing, release and evaluation of the parasitoid, Aphytis melinus De Bach (Hymenoptera: Aphelinidae) to control P. ziziphi biologically. In all, 250000 adult parasitoid individuals were released monthly on citrus at five locations in Cairo, Giza and Qalyubiya governorates during 2006 and 2007. At Heliopolis (Cairo), where A. melinus was present prior to the augmentative release, the per cent parasitism in the control block was 15 and 75% while it was 73 and 87% in the treatment block during the two years under consideration. At Dokki (Giza) also, A. melinus was present prior to the augmentative releases and the peak of parasitism reached 18 and 82% in the control block, compared to 86 and 91% in the treatment block. At El-Qanater El-Khriya and Tukh in Qalyubiya, A. melinus was present prior to the augmentative releases. In El-Qanater El-Khriya, the peak of parasitism reached 41 and 67% in the treatment block, compared to 8 and 46% in the control block. In Tukh, the peak of parasitism reached 31 and 65% in the treatment block, compared to 4 and 35% in the check block. At Qalub, where the parasitoid was not present prior to the augmentative releases, the peak of parasitism reached 22 and 36% in the treatment block, compared to 0 and 22% in the control block during the two years, respectively.

Augmentative releases of Metaphycus sp. nr flavus against citricola scale on oranges in the San Joaquin Valley of California: are early releases better than late ones?

We conducted an augmentative release trial with the encyrtid parasitoid Metaphycus sp. nr flavus (Howard) against citricola scale, Coccus pseudomagniolarum (Kuwana), in three citrus orchards in the San Joaquin Valley of California. Three parasitoid release timings (14 October-13 November, 4 January-5 February, and 26 February-16 March; hereinafter "early," "intermediate," and "late") were compared with a no-release check. Approximately 2,400 female parasitoids were released per central release tree. Late releases were associated with reduced scale survival on the release trees but no evidence of scale suppression was found on adjacent trees. Early and intermediate releases resulted in less pronounced scale suppression than late releases. Intermediate and late, but not early, releases were associated with an increase in the numbers of recovered female M. sp. nr flavus. Early releases, however, increased the numbers of recovered male Metaphycus spp. Thus, at the time of early releases, the scales may have been too small for the production of female parasitoids. A multiple regression model relating the degree of scale mortality in one orchard to the levels of recovered female Metaphycus helvolus (Compere), M. sp. nr flavus, or M. luteolus (Timberlake) (these latter two species are morphologically indistinguishable), and Coccophagus spp., suggested that the number of Coccophagus spp. females followed by M. helvolus females, were most strongly associated with scale mortality.

Toxicity of field-weathered insecticide residues to Anaphes iole (Hymenoptera: Mymaridae), an egg parasitoid of Lygus lineolaris (Heteroptera: Miridae), and implications for inundative biological control in cotton

Anaphes iole Girault is an egg parasitoid that has potential as an inundative biological control agent for the tarnished plant bug Lygus lineolaris (Palisot de Beauvois) in cotton in the midsouth USA. Our research addressed survival of A. iole wasps exposed to field-weathered residues of insecticides important to cotton production in the region. Our objectives were to identify insecticides with decay profiles that might be compatible with augmentative releases of A. iole in cotton. Survival of female wasps exposed to field-weathered residues on cotton leaves was determined at 0, 2, 4, 8, 16, 23, and 30 days after treatment with field rates of nine compounds. Immediately after treatment, residues of most insecticides (acephate, cyfluthrin, λ-cyhalothrin, imidacloprid, thiamethoxam, spinosad, fipronil, and oxamyl) resulted in <3% survival. Indoxacarb was the exception with about 30% survival at this time. Survival of wasps exposed to oxamyl, imidacloprid, indoxacarb, and acephate increased considerably during the first week after treatment. Upper limits of 95% CI values for ST 50 estimates (days for 50% survival) were ⩽5 days for these insecticides. Survivorship of wasps exposed to λ-cyhalothrin and thiamethoxam was intermediate (95% CI values between 5 and 11 days). Of the insecticides tested, residues of cyfluthrin, fipronil, and spinosad were most deleterious to A. iole (95% CI values > 11 days). Precipitation and wind speed during the study period were less than 30-year averages; thus, under typical weather conditions insecticides might decay more rapidly than observed in this study. Our results suggest that while most insecticides tested exhibited high acute toxicity to A. iole wasps, residues of several compounds decayed rapidly enough to show promise in an augmentative release program.

Augmentative releases of a parasitoid (Metaphycus sp. nr. flavus) against citricola scale (Coccus pseudomagnoliarum) on oranges in the San Joaquin Valley of California

Abstract Augmentative release trials with Metaphycus sp. nr. flavus (Howard), an encyrtid parasitoid of citricola scale, Coccus pseudomagnoliarum (Kuwana), were conducted in two orange groves in the southern San Joaquin Valley of California. Between mid-February and early May 1998, over 4000 female parasitoids were released per experimental tree. Control trees, where no parasitoids were released, were at least eight trees (45 m) distant from release trees. Samples taken between 18 April and 20 May indicated that levels of live citricola scales on release trees were significantly reduced on twigs, greater numbers of female M . sp. nr. flavus were recovered from scales, and the fraction of scales parasitized by Metaphycus spp. was significantly higher. These data support the hypothesis that parasitism by the released wasps suppressed the scale population. By mid-May, more M. helvolus (Compere) were recovered from control than from release trees, suggesting that released M . sp. nr. flavus had depleted the scales available to M. helvolus . Additionally, in May, more male Coccophagus lycimnia (Walker) were recovered from release trees. C. lycimnia produces male offspring by heterospecifically or conspecifically hyperparasitizing parasitoids of citricola scale. The implications of these results for developing augmentative parasitoid release strategies against citricola scale in California citrus are discussed.

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.

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.