Introduction Of Parasitoids Research Articles

Incidence of the introduced parasitoids Cotesia kazak and Microplitis croceipes (Hymenoptera: Braconidae) from Helicoverpa armigera (Lepidoptera: Noctuidae) in tomatoes, sweet corn, and lucerne in New Zealand

Abstract Two parasitoids, Cotesia kazak (Telenga) and Microplitis croceipes (Cresson) have been successfully introduced into New Zealand to improve control of Helicoverpa armigera (Hubner), tomato fruitworm. C. kazak has spread throughout the North Island, but M. croceipes is restricted largely to its release areas in crops in the Gisborne and Hawke’s Bay regions in the East Coast of the North Island and in pine plantations in the central North Island. Rates of mortality of H. armigera from parasitism were studied in processing tomato crops where these parasitoids are a key component of an integrated pest management programme, and in sweet corn, lucerne and soybeans. C. kazak was the dominant parasitoid in tomatoes and soybeans. It emerged from small H. armigera larvae and usually killed the host before it caused major damage to fruit. M. croceipes emerged from larger host larvae than C. kazak . Death rates from parasitism of H. armigera larvae in tomatoes increased from less than 1% caused by native parasitoids prior to parasitoid introductions, to 25–45% in 1988 and 70–80% in 1996 following the establishment of both introduced parasitoids. M. croceipes was the most common parasitoid in lucerne and total mortality from all parasitoids was similar to that in tomatoes. Low rates of parasitism by C. kazak in sweet corn were attributed to the reduced penetration of the adult parasitoid into sweet corn fields and to the protection afforded by sweet corn when H. armigera larvae burrowed into corn cobs. The implementation of an IPM programme based partly on the effectiveness of these parasitoids has contributed to a decrease in insecticide applications to processing tomatoes.

Competition between Gonatocerus ashmeadi and G. triguttatus for glassy winged sharpshooter (Homalodisca coagulata) egg masses

The introduction of a biological control agent can have significant effects on natural enemies that use the same host. Interspecific competition between natural enemies can impact the efficacy of control and, consequently, is the subject of increasing research scrutiny. Three experimental approaches were used to evaluate competitive outcomes between Gonatocerus ashmeadi and G. triguttatus parasitizing Homalodisca coagulata egg masses in the laboratory. (1) When both species were introduced to high densities of host eggs 1, 3 and 5 days of age, mean percentage offspring was significantly higher for G. ashmeadi offspring (23.2% greater than G. triguttatus). (2) When a female parasitoid of each species was offered a single egg mass, offspring production was statistically similar for the two species. Gonatocerus triguttatus showed aggressive behavior, although this only accounted for 0.8% of the female's total foraging time and did not lead to proportionately higher offspring production. (3) Regardless of order, more G. triguttatus offspring (up to 96%) emerged than G. ashmeadi offspring when one female was introduced sequentially to one egg mass. The relative success in offspring production was affected primarily by the sequence in which the parasitoids were introduced, and to a lesser extent by the interval between successive parasitoid introductions, and the age of the egg mass. These results illustrate the importance of experimental design in the assessment of competitive superiority between two species of parasitoids. Improper experimental design can lead to contradictory outcomes in laboratory-based competition studies due to the interplay of extrinsic and intrinsic competitive behavior. Biological control practitioners need to be aware of the complexity of competitive behavior when designing pre-introduction laboratory tests to determine a priori which natural enemy from several candidate species is likely to be the most effective agent at controlling the target.

Insect parasitoids : a Canadian perspective on their use for biological control of forest insect pests

An overview of biological control programs against forest insect pests is presented with emphasis on Canadian case histories. The work is examined in the context of conservation, introduction, and augmentation (environmental manipulation and inoculative and inundative release) of insect natural enemies, specifically parasitoids. Historically, studies have concentrated on introductions of exotic parasitoids for control of introduced pests where a number of successes have been recorded. More recent work has entailed inoculative and inundative releases of parasitoids against native pests in an attempt to establish new host-parasitoid relationships to reduce pest populations. These have had limited success and are still being explored by Canadian researchers. Current strategies for using natural enemies are inundative release of native species against native pests and conservation of native parasitoids through selective insecticide timing and forest manipulation. Future directions in biological control programs will include these approaches with increased emphasis on biotechnology and the genetic selection or manipulation of 'desired strains' for release. Continued ecological studies will be essential to ensure a more complete understanding of the interaction between these 'selected parasitoids' and the forest/tree parameters which will influence their success (tri-trophic interactions). These parameters, such as tree vigour (pest resistance), spatial distribution and diversity, will also be targeted for selection to improve the effect of insect natural enemies in the forest environment.

Diaeretiella rapae Limits Myzus persicae Populations After Applications of Deltamethrin in Oilseed Rape

In fall, Myzus persicae (Sulzer) (Homoptera: Aphididae) may exhibit population resurgence in winter oilseed rape in France. This resurgence may arise from pyrethroid treatments against Coleoptera (Psylliodes chrysocephala L.) that either kill parasitoids present during treatment or prevent recolonization by off-crop parasitoids. We studied the impact of Diaeretiella rapae (M'Intosh) (Hymenoptera: Braconidae) on populations of M. persicae when parasitoids were introduced on deltamethrin-treated plants at increasing intervals after treatment. Parasitoids were introduced 1, 2, 7, or 14 d posttreatment on individually caged plants infested with established populations of M. persicae. Aphids were counted 7, 14 and 21 d after parasitoid introduction. First, we observed that both the pesticide and the parasitoid reduced aphid population growth and that their effects were additive. Second, there was no mortality of parasitoids exposed to treated leaves in a device with a refuge area, and only 20% of mortality without the refuge area. Furthermore, deltamethrin residues had no effect on the reproduction of D. rapae females. Compared with the known toxicity of deltamethrin to D. rapae on glass, this low mortality may have been due to both the high liposolubility of deltamethrin (leading to a rapid diffusion of residues in the oilseed rape leaf cuticle) and to the existence of a refuge area. This work suggests that D. rapae could limit populations of M. persicae in the fall, even after pyrethroid treatment, because the presence of deltamethrin residues had little impact on the parasitoid.

ハウス栽培コマツナにおけるアブラムシの生物的防除の可能性 ＩＩＩ．ダイコンアブラバチの大量生産法

We developed the mass production procedure of Diaeretiella rapae, a biological control agent against pest aphids. Twenty female adults of D. rapae were introduced into a cage containing Lipaphis erysimi on two plants of komatsuna Brassica rapa nothovar. kept at 20°C and a 15L–9D light cycle. Five treatments were used (i.e., 50-A, 100-A, 50-B, 75-B, 100-B); differing in the number of viviparous female adults provided (50, 75, 100) and interval between introduction of aphids and parasitoids (A: 0 day, B: 3 days). The newly mummified aphids (mummies) were counted and removed on days 7–9, 13–15 and 18–20 after aphid release, and the emergence rate and sex ratio of the parasitoids were assessed by rearing the mummies under the same conditions. From these results, the number of female parasitoids produced was calculated to be largest in 50-B (768), followed by 75-B (719), 100-A (584), 50-A (446) and 100-B (400). A simulation model for producing mummies developed from the life history traits of D. rapae and L. erysimi was used to analyze the present results.

Coconut hispine beetle Brontispa longissima (Gestro) (Coleoptera: Chrysomelidae)

Coconut hispine beetle, Brontispa longissima (Gestro) was originally described from the Aru Islands (Maluku Province). It is native to Indonesia (Aru Islands, Maluku Province and possibly to Papua Province formerly known as Irian Jaya), and also to Papua New Guinea, including the Bismarck Archipelago, where it seldom causes serious problems. It has now spread widely in Asia, Australasia and Pacific Islands attacking not only coconut palm but also several other cultivated and wild palms. In recent times it has spread to Singapore, Vietnam, Nauru, Thailand, Maldives and Hainan Island (China). In the absence of natural antagonists it has become a very serious and devastating pest in new areas of its spread. It is feared that B. longissima will find its way from Maldives to Sri Lanka and southern parts of India to derail the economy of these important coconut-growing regions of the world. Thus emergency operations are necessary to try to decimate it down in the Maldives. A number of natural enemies such as Hispidophila (Haeckeliania) brontispae Ferriere, Ooncyrtus podontiae Gahan, Trichogrammatoidea nana Zehntner, Tetrastichus brontispae Ferriere, Asecodes hispinarum Boucek, Chrysonotomyia sp., Metarhizium anisopliae (Metchnikoff) Sorokin, Chelisoches morio Fabricius, Oecophylla smaragdina (Fabricious), mites on adults (Anoplocelaeno sp. and Celaenopsis sp.), geckoes, skinks, tree frog and unidentified bacterial pathogen have been recorded. Biological control by introduction and enhancement of parasitoids- A. hispinarum and T. brontispae has proved very effective. Similarly spray of improved strains of entomopathogenic fungus, M. anisopliae has proved effective. Exploratory surveys for parasitoids in the original home of B. longissima are suggested.

Is spatial density‐dependent parasitism necessary for successful biological control? Testing a stable host–parasitoid system

AbstractOne of the most famous examples of successful, classical biological control in Japan is the introduction of the parasitoids Coccobius fulvus and Aphytis yanonensis against the citrus pest arrowhead scale Unaspis yanonensis. Together, they comprise a host‐parasitoid system that has been demonstrated to be stable. To test the conventional theory that successful biological control of pests occurs through the establishment of a low stable equilibrium, brought about by the density‐dependent responses of natural enemies to the pest species, sampling was carried out at five sites in the field during 2000 and 2001 to examine the relationship between the rate of parasitism by C. fulvus and the density of its host. The data were analysed using three statistical techniques at nine spatial scales.Contrary to conventional theoretical predictions, each method of analysis detected very little density‐dependence at any spatial level in this study. Parasitoid aggregations independent of host density were not sufficient to stabilise host–parasitoid interactions. Our results suggest that neither spatial density‐dependent nor density‐independent parasitism is necessary for successful biological control, or for the stability of the host–parasitoid system. We propose an alternative mechanism: a spatial refuge induced by parasitoid introduction may stabilise a system.

Establishment of Citrostichus phyllocnistoides (Hymenoptera: Eulophidae) as a biological control agent for the citrus leafminer Phyllocnistis citrella (Lepidoptera: Gracillariidae) in Spain

A program of introduction of exotic parasitoids for the biological control of the citrus leafminer Phyllocnistis citrella Stainton (Lepidoptera: Gracillariidae) was carried out in València (Spain) between 1996 and 1999. Eleven species of parasitoids were imported through a total of 37 shipments coming from nine countries. Six species were released in the field, the encyrtid Ageniaspis citricola (Logvinosvskaya), and the eulophids Quadrastichus sp., Semielacher petiolatus (Girault), Galeopsomyia fausta LaSalle, Cirrospilus ingenuus (Gahan), and Citrostichus phyllocnistoides (Narayanan). A. citricola was recovered in summer in many release points, reaching nearly 50% of parasitism and dispersing more than 300 m, but it was not able to overwinter. Quadrastichus sp. and S. petiolatus established temporarily in some sites, but produced little differences in parasitism or density of host population. In 1999, a substantial expansion of C. phyllocnistoides of more than 30 km in all directions was observed from one release point. In 2000 and 2001 this parasitoid expanded to all citrus grown in continental Spain and the Balear Islands, becoming the most abundant parasitoid in all the orchards, and displacing native and other introduced parasitoids. As a consequence, parasitism on second instars increased from less than 16% to 65% and on third instars from 35–38% to 59%. Overall, the mean percentage of parasitism increased from 20–25% to near 60%. Apparently, C. phyllocnistoides reduced by 34% the number of eggs and early instars of the host, and by 72% the number of adults. Damage to citrus foliage decreased by 56%.

Introduction and establishment of parasitoids for the biological control of the apple ermine moth, Yponomeuta malinellus (Lepidoptera: Yponomeutidae), in the Pacific Northwest

Four parasitoids were imported from five countries in Eurasia and released in northwestern Washington, US, to control the apple ermine moth (AEM), Yponomeuta malinellus Zeller, which colonized the Northwest around 1981. From 1988 to 1991, 95,474 individuals of Ageniaspis fuscicollis (Dalman) from France, China, Korea, and Russia were released in Washington. Parasitism of AEM increased 4- to 5-fold over that produced by preexisting natural enemies between 1989 and 1994 at 22 monitored sites. Subsequently, the wasp dispersed up to 20 km from release sites. A. fuscicollis also parasitized the cherry ermine moth, Yponomeuta padellus (L.), which was discovered in the Pacific Northwest in 1993. A total of 1813 individuals of Herpestomus brunnicornis (Gravenhorst) from France, Korea, and Japan were released in 1989–1991, and 26 wasps were recovered in 1994–1995. From 1989 to 1991, 2647 Diadegma armillata (Gravenhorst) individuals from France were released. D. armillata was recovered at one site in 1991 two months following release, but no other recoveries have been made. A total of 8274 Eurystheae scutellaris (RobineauDesvoidy) individuals were released in 1989 to 1991. However, this tachinid has not been recovered. A consistent decline of AEM populations occurred in 1989–1995, including at sites where A. fuscicollis was not recovered, suggesting other factors also contributed to this pests decline. Now well established in western Washington, A. fuscicollis may help suppress future outbreaks of Y. malinellus and its congener, Y. padellus. Published by Elsevier Science (USA).

Rapid change in the settling behavior of the arrowhead scaleUnaspis yanonensisas an avoidance mechanism against introduced parasitoids,Aphytis yanonensis and Coccobius fulvus

AbstractParasitoids are thought to exert immense selection pressures that shape the traits of herbivores. We examined whether two species of parasitoid wasps,Aphytis yanonensisDeBach et Rosen andCoccobius fulvusCompere et Annecke (Hymenoptera: Aphelinidae), affect the settling behavior of the arrowhead scaleUnaspis yanonensisKuwana (Hemiptera: Diaspididae), in order to demonstrate the evolution of antiparasitism behavior of herbivores using parasitoids in the field. We used the following five methods: a comparison of parasitism risk in different settling behaviors‐parasitoid introduction into a parasitoid‐free population; a comparison of the settling behavior between parasitoid‐present and parasitoid‐free populations; a common garden experiment, in which scales were transferred from parasitoid‐present and parasitoid‐free populations into the same garden; and a laboratory observation of the settling behavior of the first instars derived from the two population categories. Both parasitoids were introduced into a parasitoid‐free population in Wakayama in 1987, and the settling mode of the scales was examined in 1987, 1994, and 1995. The introduction of parasitoids modified the scale‐settling mode so that more crawlers settled under another scale (called burrowing), which was consistent with the results observed in parasitoid‐present (including South China) and parasitoid‐free populations. Moreover, only the burrowing scale exhibited a lower parasitism rate compared to scales settling singly and being burrowed. The common garden experiment demonstrated that scales introduced from the parasitoid‐present population had a greater proportion of burrowers than the parasitoid‐free population, even in the same field cage under parasitoid‐free conditions. Laboratory observations demonstrated that the population difference in parasitism rate was principally due to intrinsic differences in the settling behavior of nymphs; some first‐instar nymphs derived from the parasitoid‐present population burrowed under another scale settled. These results strongly suggest that the natural selection pressure imposed by the parasitoids modified the settling behavior of the arrowhead scale.

PREDATION BY NATIVE ARTHROPODS ON THE AFRICAN PARASITOID PROROPS NASUTA (HYMENOPTERA: BETHYLIDAE) IN COFFEE PLANTATIONS OF MEXICO

The establishment or colonization of natural enemies is a critical period of adjustment for the introduced individuals in the target area. Successful colonization and its effectiveness in control, depend on the intrinsic capabilities of the species and the interaction of physical and biotic factors (Callan 1969). Although the concept of establishment is simple, in practice it is a difficult task. From 4,769 introductions of predators and parasitoids made up to 1990, only 1,445 (30.3%) were established (Greathead & Greathead 1992). Diverse reasons have been mentioned of the traits likely to reduce the establishment of biological control agents. Among the most important are: adverse climatic condition, insufficient genetic variation, poor searching capacity, interference from chemicals or cultural practices, inadequate numbers of individuals introduced, lack of synchrony with the host and interference by native organisms (Hopper et al. 1993, Hopper 1996). Prorops nasuta Waterston is an African parasitoid of the coffee berry borer (CBB) Hypothenemus hampei (Ferrari) (Coleoptera: Scolytidae), which is considered as the main pest of coffee worldwide (Le Pelley 1968, Baker 1999). R nasuta females usually spend most of its life inside of a coffee fruit infested by the CBB. The wasp feeds on all juvenile stages, but only paralyses and oviposits on the full-grown larvae and pupae. The larva starts to feed externally after hatching and one host is sufficient for the development of each wasp. When the parasite larva is fully developed, it spins a cocoon and enters to the pupal stage (Hargreaves 1935; Infante 1998). The life cycle of P nasuta form egg to adult lasts 28 days at 220C (Infante 2000), but adults remain in the coffee fruit for a few days more in order to copulate. As with other bethylids, this species has males emerging before their sisters with which they mate. The new generation of wasps leave the berry during the day, searching for infested coffee fruits (Hargreaves 1935, Murphy & Moore 1990). In the last few years this parasitoid has been introduced to Mexico, Guatemala, El Salvador, Honduras, Ecuador, Colombia, Jamaica, Indonesia and India. In all these countries P nasuta has been released and is presently under evaluation as a biological control agent (Klein-Koch et al. 1988, Barrera et al. 1990, Baker 1999). In the case of Mexico, repeatedly releases of parasitoids have been carried out in Chiapas since 1992. Recovery surveys indicated that up to now, there is no evidence of the establishment of P nasuta in the country (Infante et al. 2001). Identifying the factors that interfere in the establishment of P nasuta is essential to the success of biological control programmes for the CBB. For that reason, the present paper reports on some native arthropods that were found predating on this species in coffee plantations of Chiapas. The wasps used in releases were reared in the laboratory on borer infested coffee fruits. Parasitoids were taken to the field as adults and released from one liter plastic jars directly onto the branches of coffee trees. From 1992 to 1996, ca. 156,000 individuals were released in the field usually in the morning (before 12:00 hr). Colonization sites for releases consisted of 22 locations, each approximately one-fourth of a hectare. Because few people observe insects under field conditions (P. S. Baker, personal communication), we stayed in the field for about 1-2 hours following parasitoid liberations, to observe the wasps and any possible interaction with other organisms. The organisms detected as interacting with P nasuta were collected and taken to the laboratory for identification. A list of arthropods preying on adults of P nasuta is presented in Table 1. Meantime females were searching for infested fruits, they were easy prey for ants, which normally were present on coffee trees. It was possible to detect at least five species of ants preying on adults of P nasuta. Also six species of spiders caught parasitoids on their webs. As spiders were collected in alcohol, it was not possible to verify their predation on P nasuta. However, we would assume they do, considering they are generalist predators. Recent studies have reported that spiders, such as, Cyclosa caroli, Leucauge mariana and L. vetusta capture and consume individuals of the CBB and its bethylid parasitoid Cephalonomia stephanoderis (Henaut et al. 2001). Because of the small size of P nasuta (2mm), observations were especially difficult to carry out. We could not measure the intensity in which predators were acting, but presumably they are only imnnrt.nnt diiring releases. or mavbe when the

Introduction of parasitoids has maintained a stable population of arrowhead scales at extremely low levels

AbstractWe previously reported the drastic decline of the arrowhead scale, Unaspis yanonensis Kuwana (Hemiptera: Diaspididae) following the introduction of two parasitoid species, Aphytis yanonensis DeBach et Rosen and Coccobius fulvus Compere et Annecke (Hymenoptera: Aphelinidae), which were used as biological control agents in a Japanese grove of Satsuma mandarin oranges, Citrus unshiu Marc. (Rutaceae). In this study, we examined whether the parasitoids regulated the scale population at lower levels after its initial decline. Specifically, we monitored the population dynamics of the scale and the rates of parasitism by the two parasitoids three times per year for 16 years following the introduction of the wasps. The two parasitoid species maintained a U. yanonensis density at 1/200 of the density prior to their introduction. When we excluded the wasps, the scale population grew at a rate that was more than fivefold that of a control (parasitoid‐infested) group. Although the rates of parasitism by C. fulvus fluctuated, they remained at relatively high levels, whereas those of A. yanonensis were 0% over the last 6 years. A repeated‐measures ANOVA indicated that scale density remained stable subsequent to its rapid decline. This showed that the parasitoids stabilized the scale population at a lower level than host plant limitations would have dictated, and strongly suggests that C. fulvus alone regulates the scale population density at an extremely low level. The latter finding contradicts other studies which have suggested that the two parasitoid species complement each other in regulating scale density. We discuss whether a behavioral refuge used by the scale against parasitoids, which we have demonstrated in an earlier study, might contribute to the observed stable host–parasitoid system at low densities.

Natural enemies of the maize cob borer, Mussidia nigrivenella (Lepidoptera: Pyralidae) in Benin, West Africa.

Mussidia nigrivenella Ragonot is a pest of maize cobs in West Africa. It significantly reduces maize yields and grain quality, with quantitative losses of 2-25%at harvest, and up to 10-15% indirect losses due to an increase in storage pest infestation levels. Infestation by M. nigrivenella also significantly increased the susceptibility of maize to Aspergillus flavus infection and subsequent aflatoxin contamination. Surveys conducted in different agro-ecological zones of Benin on cultivated and wild host plants during 1994-1997 revealed one egg parasitoid, three larval parasitoids and one pupal parasitoid attacking M. nigrivenella. Egg parasitism was scarce on all host plants sampled and in all four agro-ecological zones. Parasitism by larval and pupal parasitoids was usually less than 10%, and varied with host plant species. Both larval and pupal parasitoids were rare or absent in cultivated maize fields. The solitary chalcidid pupal parasitoid, Antrocephalus crassipes Masi, was the predominant species, contributing approximately 53% of the observed mortality. Logistic regression analysis indicated that this parasitoid was more prevalent on fruits of Gardenia spp. (Rubiaceae) than on the other host plant species including maize used by M. nigrivenella, and was most abundant between February and September. The differences in parasitoid diversity and parasitism between Benin and other regions suggest that there are opportunities for biological control through introduction of exotic parasitoids or using the 'new association' approach, which uses natural enemies of closely related host species that occupy similar ecological niches to the target pest.

Potential and Risks of Biological Control of Cactoblastis cactorum (Lepidoptera: Pyralidae) in North America

Cactoblastis cactorum Berg, an invasive moth and famous biological of weeds agent, threatens numerous native and economic prickly pear cacti (Opuntia) in the United States and Mexico. Biological of the moth, using a variety of approaches, is considered including: introduction of parasitoids and pathogens from the moth's native home in South America, introduction of parasitoids from related North American cactus moths (Pyralidae: Phycitnae), inundative releases of parasitoids known to attack the moth in Florida, and inundative releases of mass reared generalists parasitoids. The primary risk of employing biological is the reduction of the many North American cactus moths, some of which probably regulate native Opuntia that can be weedy. The various biocontrol approaches are ranked according to their relative risk to the native cactus moths. The introduction of South American parasitoids or pathogens specific to the genus Cactoblastis (if they exist) may be the least risky approach. The introduction of South American parasitoids that can attack many cactus moths is the most risky approach because it could result in persistent control of these non-target native insects. Biological probably can reduce the abundance of C. cactorum populations but is unlikely to prevent the spread of the moth. The relative benefits and risks of biological need to be carefully assessed prior to any operational biological programs. It will be difficult to reach agreement on acceptable levels of risk, if the likely benefits can't be predicted. Other management options need to be considered.

The effect of natural enemies on the spread of barley yellow dwarf virus (BYDV) by Rhopalosiphum padi (Hemiptera: Aphididae).

The effects of two natural aphid enemies, adult Coccinella septempunctata Linneaus, a predator, and Aphidius rhopalosiphi de Stefani Perez, a parasitoid, on spread of barley yellow dwarf virus (BYDV) transmitted by the bird cherry-oat aphid, Rhopalosiphum padi (Linnaeus) were studied under laboratory conditions. Predators or parasitoids were introduced to trays of durum wheat seedlings and the patterns of virus infection were observed after two, seven and 14 days of exposure. More plants were infected with BYDV in control trays without A. rhopalosiphi than in trays with the parasitoid present, both seven and 14 days after the introduction of parasitoids. Patterns of virus infection were found to be similar over time in trays with a parasitoid present and in control trays. More plants were infected in trays with C. septempunctata present than in control trays, both two and seven days after the introduction of the coccinellid. The spread of virus infections progressed differently over time for the two treatments (predator and parasitoid), differences between treatments being most marked after two days and seven days, when more plants exposed to predators but fewer exposed to parasitoids were infected with BYDV compared to their respective controls. However, by the 14th day 88% of all plants were infected and there was no significant difference between the two treatments. The role of natural enemies in spread of BYDV is discussed.

Influence of Food Deprivation on Foraging Decisions of the Parasitoid <I>Bathyplectes curculionis</I> (Hymenoptera: Ichneumonidae)

As adults, many parasitoid wasps require carbohydrates for reproduction and self-maintenance. Consequently, many adult female parasitoids that require carbohydrate foods located at a distance from host patches face a trade-off between searching for hosts and food. In a series of experiments using a Y-tube olfactometer, we explored how hunger affects the foraging decisions of Bathyplectes curculionis (Thomson), a parasitoid of alfalfa weevil larvae. In particular, we tested whether an unfed parasitoid female is more likely to search for food while a fed female is more likely to initiate host-searching by first orienting to odors from the plants on which the host insect feeds. When offered a choice between odors of the weevil’s host plant foliage (alfalfa, Medicago sativa L.) and a flower commonly found in the alfalfa field habitat (dandelion, Taraxacum officinale Weber), unfed female wasps preferred the floral odor and fed wasps preferred odors of the host plant. The wasps preferred odors of inflorescences of dandelion over those of phacelia, Phacelia tanacetifolia Bentham, a plant not found in alfalfa fields. Both fed and unfed wasps, however, responded positively to phacelia odor when offered against a control. When the wasps were given the choice between phacelia flowers and alfalfa foliage, neither unfed nor fed wasps expressed a preference for either odor. An important consideration in introduction and conservation of parasitoids in biological control is a parasitoid’s varying responsiveness to host-habitat and floral odors as influenced by physiological state.

Parasitoid Population Biology

Preface xi List of Contributors xiii One: Introduction by Michael E. Hochberg and Anthony R. Ives 3 PART ONE: POPULATION DYNAMICS 15 Two: Host Location and Selection in the Field by Jgr6me Casas 17 Three: Effects of Parasitoid Clutch Size on Host-Parasitoid Population Dynamic by George E. Heimpel 27 Four: Host-Parasitoid Models: The Story of a Successful Failure by Carlos Bernstein 41 Five: A Field Guide to Studying Spatial Pattern Formation in Host-Parasitoid Systems by Susan Harrison 58 Parasitoid Spread: Lessons for and from Invasion Biology by Alan Hastings 70 Seven: Landscape Ecology of Parasitism by Jens Roland 83 PART TWO: POPULATION DIVERSITY 101 Eight: The Evolution of Parasitoid Egg Load by Minus van Baalen 103 Nine: Host Resistance, Parasitoid Virulence, and Population Dynamics by H. C. J. Godfray 121 Ten: Developmental Traits and Life-History Evolution in Parasitoids by Michael R. Strand 139 Eleven: Host Specificity and Trophic Relationships of Hyperparasitoids by Jacques Brodeur 163 Twelve: Comparing Parasitoid-Dominated Food Webs with Other Food Webs: Problems and Future Promises by Marcel Holyoak 184 Thirteen: Species Coexistence in Parasitoid Communities: Does Competition Matter? by Bradford A. Hawkins 198 PART THREE: POPULATION APPLICATIONS 215 Fourteen: Biological Control: The Need for Realistic Models and Experimental Approaches to Parasitoid Introductions by Nick Mills 217 Fifteen: Parasitoid Populations in the Agricultural Landscape by Teja Tscharntke 235 Sixteen: Threats, Flies, and Protocol Gaps: Can Evolutionary Ecology Save Biological Control? by Bernard D. Roitberg 254 Seventeen: What, Conserve Parasitoids? by Michael E. Hochberg 266 Eighteen: Conclusions: Debating Parasitoid Population Biology over the Next Twenty Years by Anthony R. Ives and Michael E. Hochberg 278 References 305 Index 359

A spatial model for the successful biological control of Sitona discoideus by Microctonus aethiopoides

Summary Here we describe a new model for the biological control of the pest weevil Sitona discoideus by the parasitoid Microctonus aethiopoides. Based on an earlier empirical model, the new model was expanded to include explicit dispersal in a coupled map lattice metapopulation. Model results were consistent with observed data from New Zealand, mimicking successful biological control with a reduction in host density from 1984 to 1991 and a sustained suppression of around 75% thereafter. The metapopulation model was locally stable because of strong host density‐dependence and a non‐random parasitoid attack function. Metapopulation structure had little effect on the local dynamics, except in transient behaviour such as initial rates of parasitoid spread or the response to a local perturbation. The survival rate of dispersing weevils was nevertheless important in determining overall weevil abundance. Assuming that the observed low survival rate of weevils during dispersal (around 0·3%) was related to the relative scarcity of its host‐plant in the landscape, the model suggested that local weevil density could substantially increase with an increase in area of crop planted. Although the extent of biological control would be sustained in relative terms, increasing the crop abundance could allow a substantial increase in absolute pest density. With appropriate adjustment, the model also simulated the unsuccessful biological control observed in Australia. Advancing weevil oviposition in autumn (reflecting warmer autumn temperatures in Australia) and reducing parasitism rates among aestivating weevils (reflecting a lack of summer development of parasitoids in Australia, compared with the atypical development of a proportion in New Zealand), led to an inability of the parasitoid to significantly reduce weevil populations in the model. This host–parasitoid system is unique for the quality and duration of monitoring conducted before, during and after parasitoid introduction. It also represents one of the few biological control case studies to be thoroughly evaluated through use of empirical models such as the spatial and non‐spatial versions presented here.

Indigenous Natural Enemies Associated with Phyllocnistis citrella (Lepidoptera: Gracillariidae) in Eastern Spain

Abstract The incidence of generalist indigenous natural enemies of the citrus leafminer (CLM), Phyllocnistis citrella Stainton (Lepidoptera; Gracillariidae), was monitored during three growing seasons at two different orchards located in the major citrus-growing area of Spain. Composition of the parasitoid complex changed during the study period. However, the eulophids Cirrospilus near lyncus Walker and Pnigalio pectinicornis L. were consistently the predominant species. Despite the varying composition of the parasitoid complex, oviposition, host feeding, and predatory preferences of the natural enemies of the CLM clearly centered on third instar larvae. Incidence of beneficial fauna increased as the season progressed, reaching maximal values up to 70% of susceptible leafminers (mature larvae) at the end of the summer. Parasitism was significantly related to relative host density. However, predation showed no relationship to host availability but did so to flushing in one of the orchards. Incidence of indigenous natural enemies of the CLM should not be ignored when planning any introduction of exotic parasitoids, and their conservation should be taken into account when planning any citrus IPM strategy.

Parasitoid Drift After Biological Control Introductions: Re-examining Pandora's Box

Howarth (1983) in his influential article “Classical biological control: panacea or Pandora's box” questioned the environmenta safety of biological control introductions. He focused on several important areas of concern including (1) the irreversibility of alien introductions, (2) the possibility of host switching to innocuous native or beneficial species, (3) dispersal of biological control agents to new habitats, and (4) the lack of research on the efficacy and impact of biological control attempts. Heightened concerns over nontarget effects since (Howarth 1991, Simberloff and Stiling 1996, Van Driesche and Hoddle 1997,Follett and Duan 1999) have slowed the pace of biological control introductions through increased regulation and have prompted a moment of reflection on the fate of past releases. The trend in biological control introductions is, perhaps, best exemplified in Hawaii, where more biological control releases have, been made against Insect pests than anywhere else in the world (Debach 1974, Funasaki et al. 1988). Largely in response to concerns over nontarget effects to Hawaii's unique and fragile fauna, introductions of parasitoids and predators against insect pests, which were being made at a rate of 3.8 speciesyr between 1900–1980, slowed to 2.3 speciesyr during 1980–1989 and have slowed further to about one introduction every two years since 1990 (Fig. 1). The lid to “Pandora's box” nearly has been shut tight in Hawaii.