Biological Control of the Cassava Mealybug in Africa: A Review

Among several natural enemies introduced to combat the cassava mealybug, Phenacoccus manihoti (Homoptera: Pseudococcidae), the neotropical parasitoid Apoanagyrus (Epidinocarsis) lopezi (Hymenoptera: Encyrtidae) was the most successful. It established in 26 African countries, causing a satisfactory reduction in the population density of P. manihoti in most farmers' fields. Four conclusions concerning the possible application of the research results to other biological control projects are discussed. (1) Foreign exploration was intensive and should be maintained at this level in other projects, if necessary at the cost of other activities. (2) In the controversy about the amount of research results needed before first releases are made, an understanding of the proper role of quarantine is essential. Whereas quarantine (preferably outside the continent) guarantees nonnoxiousness of natural enemies, only research in the experimental release sites can determine whether a given natural enemy will be efficient. It was confirmed that the released exotic insects did not affect the diversity of the indigenous fauna. Modalities used in this project for the execution of releases, i.e., always on request by and in collaboration with national programs, are recommended for adoption in future projects. (3) Laboratory and field studies established the scientific basis for quantifying the impact of the pest insect and its control by A. lopezi. This was expressed as reduction in pest population levels and yield loss and gain in revenue. Behavior of adult females in searching and choosing hosts was identified as a better predictor of efficiency of a species in the field than life table studies under controlled temperatures. (4) It is concluded that biological control is the basis for integrated pest management. Other interventions, such as cultural methods or the use of resistant varieties, need to be in harmony with biological control because the impact of natural enemies cannot usually be manipulated by the farmer. To achieve sustainability, the aim is to optimize tritrophic interactions among the plant, the phytophagous pest organisms, and their natural enemies, rather than to maximize the effect of a single intervention.     

Influence de l'hyperparasitisme sur les populations d'un hymenoptère encyrtidae,Epidinocarsis lopezi,parasitoide de la cochenille du manioc Phenacoccus manihoti introduit au Congo

Résumé Une étude au champ de la dynamique des populations de la cochenille du manioc Phenacoccus manihoti Matt.-Ferr. (Hom. Pseudococcidae) et des agents biologiques qui lui sont associés a été entreprise dans 4 parcelles de manioc Manihot esculenta Crantz (Euphorbiacée) situées dans 2 localités différents du Congo. Elle a essentiellement montré que les 7 à 16% de parasitisme développés par le parasitoïde exotique Epidinocarsis lopezi (De Santis) (Hym. Encyrtidae), 4 ans après son introduction, n'affectent pas significativement la dynamique des populations du ravageur. Les taux importants d'hyperparasitisme (67 à 100%) dont le parasitoïde primaire est l'objet limitent la reproduction de ses populations. Toutefois il est difficile de conclure quant à l'impact réel des hyperparasites sur l'efficacité de l'auxiliaire dans la lutte contre la cochenille.

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A field study of cassava mealybug Phenacoccus manihoti Mat.-Ferr. (Hom. Pseudococcidae) population dynamics, together with that of associated biological agents was made on 4 sample plots in cultivated manioc Manihot esculenta Crantz (Euphorbiacée) in two different areas of the Congo. It showed that four years after introduction, the 7 to 16% of parasitism attributable to the exotic parasitoid Epidinocarsis lopezi (De Santis) (Hym. Encyrtidae), did not significantly affect pest population dynamics. High levels of hyperparasitism (67% to 100%) to which the parasitoid is itself subject limits its population levels. It is, however, impossible to determine the real effect of hyperparasites on the efficiency of the auxiliary in the biological control of the mealybug.

     

Competition between Gyranusoidea tebygi and Anagyrus mangicola, parasitoids of the mango mealybug, Rastrococcus invadens: interspecific host discrimination and larval competition

The competition between Gyranusoidea tebygi Noyes and Anagyrus mangicola Noyes (both Hymenoptera: Encyrtidae), exotic parasitoids of the mango mealybug, Rastrococcus invadens Williams (Homoptera: Pseudococcidae) was studied in the laboratory. No significant differences were found in the way each parasitoid species examined, attacked, stung, and oviposited into hosts, unparasitized, or previously parasitized by the other species. This suggests that neither species discriminates against each other. The total number of parasitoids of either species emerging did not significantly differ between competition experiments. When A. mangicola was the first parasitoid to attack a host, it had no significant advantage over G. tebygi. However, when A. mangicola followed G. tebygi by either 4 or 24 h, it clearly won. Overall A. mangicola won the competition in 70.9% of all cases. The level of the competition, either at the egg or larval stage, and factors responsible for the elimination of older larvae by younger ones could not be assessed in these experiments. The coexistence of the two parasitoids as complementary for the biological control of the mango mealybug is discussed.     

Guiding Classical Biological Control of an Invasive Mealybug Using Integrative Taxonomy

Delottococcus aberiae De Lotto (Hemiptera: Pseudococcidae) is a mealybug of Southern African origin that has recently been introduced into Eastern Spain. It causes severe distortions on young citrus fruits and represents a growing threat to Mediterranean citrus production. So far, biological control has proven unsatisfactory due to the absence of efficient natural enemies in Spain. Hence, the management of this pest currently relies only on chemical control. The introduction of natural enemies of D. aberiae from the native area of the pest represents a sustainable and economically viable alternative to reduce the risks linked to pesticide applications. Since biological control of mealybugs has been traditionally challenged by taxonomic misidentification, an intensive survey of Delottococcus spp. and their associated parasitoids in South Africa was required as a first step towards a classical biological control programme. Combining morphological and molecular characterization (integrative taxonomy) a total of nine mealybug species were identified in this study, including three species of Delottococcus. Different populations of D. aberiae were found on wild olive trees, in citrus orchards and on plants of Chrysanthemoides monilifera, showing intra-specific divergences according to their host plants. Interestingly, the invasive mealybug populations from Spanish orchards clustered together with the population on citrus from Limpopo Province (South Africa), sharing COI haplotypes. This result pointed to an optimum location to collect natural enemies against the invasive mealybug. A total of 14 parasitoid species were recovered from Delottococcus spp. and identified to genus and species level, by integrating morphological and molecular data. A parasitoid belonging to the genus Anagyrus, collected from D. aberiae in citrus orchards in Limpopo, is proposed here as a good biological control agent to be introduced into Spain.     

No inbreeding depression in laboratory‐reared individuals of the parasitoid wasp Allotropa burrelli

Inbreeding depression is a major concern in almost all human activities relating to plant and animal breeding. The biological control of pests with natural enemies is no exception, because populations of biocontrol agents experience a series of bottlenecks during importation, rearing, and introduction. A classical biological control program for the Comstock mealybug Pseudococcus comstocki (Hemiptera: Pseudococcidae) was initiated in France in 2008, based on the introduction of an exotic parasitoid, Allotropa burrelli Mues. (Hymenoptera: Platygastridae), a haplodiploid parasitoid imported from Japan. We evaluated the sensitivity of A. burrelli to inbreeding, to optimize rearing and release strategies. We compared several morphological and life‐history traits between the offspring of siblings and the offspring of unrelated parents. We took into account the low level of genetic variability due to the relatively small size of laboratory‐reared populations by contrasting two types of pedigree: one for individuals from a strain founded from a single field population, and the other generated by hybridizing individuals from two strains founded from two highly differentiated populations. Despite this careful design, we obtained no evidence for a negative impact of inbreeding on laboratory‐reared A. burrelli. We discussed the results in light of haplodiploid sex determination and parasitoid mating systems, and classical biological control practices.     

Density-Dependent Benefits in Ant-Hemipteran Mutualism? The Case of the Ghost Ant Tapinoma melanocephalum (Hymenoptera: Formicidae) and the Invasive Mealybug Phenacoccus solenopsis (Hemiptera: Pseudococcidae)

Although density-dependent benefits to hemipterans from ant tending have been measured many times, few studies have focused on integrated effects such as interactions between ant tending, natural enemy density, and hemipteran density. In this study, we tested whether the invasive mealybug Phenacoccus solenopsis is affected by tending by ghost ants (Tapinoma melanocephalum), the presence of parasitoids, mealybug density, parasitoid density and interactions among these factors. Our results showed that mealybug colony growth rate and percentage parasitism were significantly affected by ant tending, parasitoid presence, and initial mealybug density separately. However, there were no interactions among the independent factors. There were also no significant interactions between ant tending and parasitoid density on either mealybug colony growth rate or percentage parasitism. Mealybug colony growth rate showed a negative linear relationship with initial mealybug density but a positive linear relationship with the level of ant tending. These results suggest that benefits to mealybugs are density-independent and are affected by ant tending level.     

Suitability of five mealybug species (Hemiptera,Pseudococcidae) as hosts for the solitary parasitoid Anagyrus sp. nr. pseudococci (Girault) (Hymenoptera: Encyrtidae)

Anagyrus sp. nr. pseudococci is an endoparasitoid which has been used as a biological control agent of mealybug pests. In this study, we compared the suitability of five mealybugs species with different phylogenetic relationships and geographical origins as hosts of this parasitoid. The selected mealybugs were: (1) a Mediterranean-native species, Planococcus ficus, sharing a long co-evolutionary history with the parasitoid; (2) three exotic species, the Afrotropical Planococcus citri, the Australasian Pseudococcus calceolariae and the Neotropical Pseudococcus viburni, with a recent history; and (3) the Neotropical Phenacoccus peruvianus, with no previous common history with the parasitoid. Host suitability was assessed based on different fitness parameters, such as body size, developmental time, emergence rate and sex ratio. The parasitoid was able to complete development in all mealybug species. Nevertheless, its emergence rate significantly varied among mealybug species, with the highest values observed in Pl. ficus and Pl. citri, intermediate values in Ps. calceolariae and the lowest ones in Ps. viburni and Ph. peruvianus. The body size of adult wasp females varied with host suitability and was positively correlated with other measures of parasitoid fitness, including the emergence rate and the sex ratio. The parasitoid developmental time differed among mealybug species but did not correlate with any other measure of fitness. A female biased sex ratio was found in the parasitoid progeny emerged from all mealybug species, except in Ps. viburni and Ph. peruvianus. There was a direct relationship between the proportion of females in the parasitoid progeny and the emergence rate.     

Interaction betweenRastrococcus invadens [Hom.: Pseudococcidae] and two natural enemies

Two natural enemies of the mealybugRastrococcus invadens, the parasitoidGyranussoidea tebygi and the pathogenHirsutella cryptosclerotium were tested. Levels of parasitism by the parasitoid were reduced by the pathogen but overall mortality of the mealybug was greater both when agents were acting together.      

Population Dynamics and Life Tables of the Mango Mealybug, Rastrococcus invadens Williams, and its Introduced Natural Enemy Gyranusoidea tebygi Noyes in Benin

Life table data for Rastrococcus invadens and its introduced natural enemy Gyranusoidea tebygi were obtained in the field and in the laboratory. The mealybug population's potential rate of increase ranged from 0.066/day to 0.078/day. The potential for increase of the parasitoid was double that of its host. Seasonal fluctuations in abundance of R. invadens were followed from 1988 to 1992 on mango trees in southern Benin. The population density of R. invadens decreased during the rainy seasons and peaked during the dry seasons. Mealybug field sex ratios were extremely variable, and the impact of such variability on the mealybug's potential rate of increase was analyzed. The populations of the exotic encyrtid G. tebygi, introduced into Benin in 1988 for control of the pest, were synchronized with the host populations. The spatial patterns of parasitism distribution in relation to the host population density were either independent or directly density-dependent, both at the tree level and for larger zones. However, reducing the scale of analysis resulted in different types of relationships. The impact of predators was a minor factor in the population dynamics of the mealybug. Four of the six species of hyper-parasitoids attacking mealybugs parasitized by G. tebygi developed high populations. In the two orchards studied, mealybug populations eventually collapsed and disappeared. This fact is discussed as being an indication that the biological control of the mango mealybug by G. tebygi was achieved by non-equilibrium local dynamics, and should be evaluated in a meta-population perspective.     

Interspecific interference between Apoanagyrus lopezi and A. diversicornis, parasitoids of the cassava mealybug Phenacoccus manihoti

The parasitoids Apoanagyrus lopezi De Santis and A. diversicornis (Howard) (Hymenoptera: Encyrtidae) have been introduced into Africa for the biological control of the cassava mealybug Phenacoccus manihoti Matile-Ferrero (Homoptera: Pseudococcidae). We have studied competition between these species to investigate if they can coexist. Here we report on the influence of the simultaneous presence of non-conspecific adult females on searching efficiency on patches. Wasps of either species foraged on discs of cassava leaf with mealybugs, while at the same time different numbers of non-conspecifics were also depleting the patch. Patch area per parasitoid and number of hosts available to each parasitoid were equal in all treatments.In both species, the presence of other foragers clearly affected several aspects of the parasitoids' behaviour. Patch residence time increased with the number of non-conspecifics in A. diversicornis. In both parasitoid species, the proportion of hosts left unparasitized after the patch visit decreased with increasing numbers of females on the patch. The proportions of super- and multiparasitism did not change with the number of females. Both species produced more offspring during a patch visit in the presence of more non-conspecifics. These behavioural changes did not, however, lead to a change in the offspring production rate on patches. A. diversicornis produced offspring at a rate three times that of A. lopezi when one A. lopezi and one A. diversicornis foraged simultaneously. This is the first report of an aspect of interspecific competition where A. diversicornis has an advantage over A. lopezi. Interference between adult females thus promotes coexistence of the two species on P. manihoti.     

Biological control of cereal stem borers in Kenya: A cost benefit approach

Lepidopteran stem borers are the key pests of maize in Sub-Saharan Africa. In the lowland tropics, dry mid-altitude, dry transitional and the moist mid-altitude zones of Kenya, the invasive crambid Chilo partellus (Swinhoe) (Lepidoptera: Crambidae) causes up to 73% yield loss. The International Centre of Insect Physiology and Ecology (ICIPE) started a biological control (BC) program in 1991 to control stem borers in subsistence agriculture in Africa with emphasis on classical BC of C. partellus. The project released the braconid larval parasitoid Cotesia flavipes Cameron (Hymenoptera: Braconidae) in 1993 in coastal Kenya, where it got established and spread to other regions. This study assesses the economic impact of the introduced parasitoid. Temporal data on percentage parasitism by the introduced parasitoid and on stem borer density were collected between 1995 and 2004. Socio-economic data was collected through administration of questionnaires to 300 farmers. Economic impact of the project was calculated as the value of the yield loss abated by the parasitoid based on a model of expected stem borer density and parasitism level. Average annual parasitism increased linearly from the time of introduction to reach 20% parasitism by 2004. The net reduction in total stem borer density over the last 10 years was 33.7%, thus abating 47.3% of yield loss. The region will accumulate a net present value of US $ 183 million in economic benefits in 20 years since release of the parasitoid. Introduction of other parasitoid species targeting the egg and pupal stages of the stem borer life cycle stages would be required for biological control to push yield loss by stem borers to an insignificant level.     

Host Stage Selection and Sex Allocation by Gyranusoidea tebygi (Hymenoptera: Encyrtidae), a Parasitoid of the Mango Mealybug, Rastrococcus invadens (Homoptera: Pseudococcidae)

Host stage selection and sex allocation by Gyranusoidea tebygi Noyes (Hym,, Encyrtidae) were studied in choice and no-choice experiments in the laboratory. The parasitoid reproduced on first, second, and third instars of the mango mealybug, Rastrococcus invadens Williams (Hem., Pseudococcidae), and it avoided hosts that were already parasitized. Host feeding was occasionally observed. Sex ratios of the offspring produced by individual wasps were highly biased in favor of females, whereas the sex ratio of groups of wasps foraging under crowded conditions varied from male biased in smaller hosts to female biased in larger hosts. Females had longer developmental times than males, developed faster in larger mealybugs than in smaller ones, and were always larger than males emerging from the same host instar. Their size increased with the instar of the host at oviposition. About 90% of all ovipositions in second and third instar nymphs resulted from an attack with multiple stings, starting with a sting in the head of the host for the most part. The function of these head stings is either to assess quality of the host or to subdue hosts prior to oviposition. Encounter rates, number of attacks, and number of stings during one attack increased, while ovipositions decreased with host instar. Time investment per oviposition and time spent preening increased with increasing host age because older hosts defended themselves more vigorously than younger ones. Thus, while fitness of the parasitoid increased with host size, fitness returns per time decreased. The implications of this host selection behavior for the biological control of the mango mealybug are discussed.     

Release and establishment in Nigeria of Epidinocarsis lopezi, a parasitoid of the cassava mealybug, Phenacoccus manihoti

The encyrtid wasp Epidinocarsis (= Apoanagyrus) lopezi (De Santis) was imported from Paraguay into Nigeria for the biological control of the cassava mealybug, Phenacoccus manihoti Matile-Ferrero. It was mass-reared and released at four localities in Nigeria. The parasitoid is now established and it is dispersing throughout cassava growing areas of Nigeria.

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Libération et installation au Nigéria d'Epidinocarsis lopezi, parasitoïde de la cochenille du manioc Phenococcus manihoti

Résumé Epidinocarsis lopezi (Apoanagyrus) lopezi a été introduit du Paraguay au Nigéria pour lutter contre la cochenille du manioc, Phenacoccus manihoti. Il a été lâché dans quatre champs de manioc pour étudier son acclimatation et son installation au Nigéria. Trois ans après les lâchers, les résultats ont permis de conclure que E. lopezi s'est établi avec succès et se disperse dans la plupart des zones de culture du manioc au Nigeria; il a aussi survécu à trois saisons pluvieuses pendant lesquelles les populations de P. manihoti ont été très faibles. Quatorze mois après les premiers lâchers, cet encyrtide a été obtenu à environ 150 km du lieu de libération.

     

Sustained biological control of the cassava mealybugPhenacoccus manihoti [Hom.: Pseudococcidae] byEpidinocarsis lopezi [Hym.: Encyrtidae] in Nigeria

Following the successful introduction ofEpidinocarsis lopezi (De Santis) for biological control of the cassava mealybug (CM)Phenacoccus manihoti Mat.-Ferr. in southwestern Nigeria in 1981 and 1982, 11 groups of cassava fields were sampled every 2 weeks up to 1988 for impact assessment. After 1984, CM populations remained mostly below 10 per tip despite the presence of native hyperparasitoids, demonstrating the long-term success of biological control byE. lopezi in the region. Indigenous polyphagous coccinellids were found only during peak host densities, whereas the specificE. lopezi was common throughout the year. During some periods, percentage parasitism indicated delayed density dependence. Since 89% of all sampled cassava tips had no CM at all and the parasitisme is very mobile, parasitization rates were also calculated for individual infested tips (N=4,878). Parasitism increased slightly with host density on tips having between 1 and 10 CM of the 3^rd and 4^th instars, indicating positive density dependence. Such tips comprised 64% of all infested tips. At higher host densities, parasitism rates fell rapidly. The results are discussed in view of different theories on population regulation by biological control agents.      

Defense Response of Native and Alien Mealybugs (Hemiptera: Pseudococcidae) Against the Solitary Parasitoid Anagyrus sp. nr. pseudococci (Girault) (Hymenoptera: Encyrtidae)

The host behavioral and immune (encapsulation) defenses against the parasitoid Anagyrus sp. nr. pseudococci were compared for five mealybug species with different phylogenetic relationships and geographical origins: i) a Mediterranean native mealybug species, Planococcus ficus, with a long co-evolutionary history with the parasitoid; ii) three alien mealybugs species, Planococcus citri, Pseudococcus calceolariae and Pseudococcus viburni, with a more recent co-evolutionary history; and iii) a fourth alien mealybug species, Phenacoccus peruvianus, with no previous common history with the parasitoid. Three host defense behaviors were registered: abdominal flipping, reflex bleeding and walking away. The native host Pl. ficus and its congener Pl. citri exhibited the lowest probability of defense behavior (0.11?±?0.01 and 0.09?±?0.01 respectively), whereas the highest value was observed in P. viburni (0.31?±?0.02). Intermediate levels of defense behavior were registered for Ps. calceolariae, and Ph. peruvianus. The probability of parasitoid encapsulation was lowest and highest for two alien host species, Ph. peruvianus (0.20?±?0.07) and Ps. viburni (0.86?±?0.05), respectively. The native host Pl. ficus, its congener Pl. citri and Ps. calceolariae showed intermediate values (0.43?±?0.07, 0.52?±?0.06, and 0.45?±?0.09, respectively). The results are relevant with respect to biological control and to understand possible evolutionary processes involved in host range of A. sp. nr. pseudococci.     

红火蚁与扶桑绵粉蚧互惠关系对松粉蚧抑虱跳小蜂和美棘蓟马的影响

蚂蚁与蜜源昆虫互作是物种间重要的关系之一,发挥着重要的生态功能。红火蚁Solenopsis invicta Buren是重要的入侵害虫,对生物多样性的影响已被熟知,但它与蜜源昆虫互作的生态学效应却不被充分理解。本研究评价了红火蚁与扶桑绵粉蚧Phenacoccus solenopsis Tinsley这两种入侵害虫之间的互作对寄生性天敌和粉蚧竞争性昆虫的影响。研究发现红火蚁的照看显著减少了寄主植物上粉蚧重要寄生蜂松粉蚧抑虱跳小蜂Aenasius bambawalei Hayat的种群数量,提高了寄主上粉蚧的存活率,有利于寄主上粉蚧种群的扩增和繁殖。同时红火蚁的存在也显著降低扶桑寄主上粉蚧竞争性昆虫美棘蓟马Echinothrips americanus Morgan成虫和幼虫的数量,抑制了美棘蓟马种群的竞争力,使得粉蚧可以占有更多的寄主植物,为粉蚧种群的繁殖提供了更好的条件。可见,红火蚁与扶桑绵粉蚧的互惠关系的生态效应可能是通过它们与多物种互作综合形成的结果。     

The Cassava Mealybug (Phenacoccus manihoti) in Asia: First Records,Potential Distribution,and an Identification Key

Phenacoccus manihoti Matile-Ferrero (Hemiptera: Pseudococcidae), one of the most serious pests of cassava worldwide, has recently reached Asia, raising significant concern over its potential spread throughout the region. To support management decisions, this article reports recent distribution records, and estimates the climatic suitability for its regional spread using a CLIMEX distribution model. The article also presents a taxonomic key that separates P. manihoti from all other mealybug species associated with the genus Manihot. Model predictions suggest P. manihoti imposes an important, yet differential, threat to cassava production in Asia. Predicted risk is most acute in the southern end of Karnataka in India, the eastern end of the Ninh Thuan province in Vietnam, and in most of West Timor in Indonesia. The model also suggests P. manihoti is likely to be limited by cold stress across Vietnam''s northern regions and in the entire Guangxi province in China, and by high rainfall across the wet tropics in Indonesia and the Philippines. Predictions should be particularly important to guide management decisions for high risk areas where P. manihoti is absent (e.g., India), or where it has established but populations remain small and localized (e.g., South Vietnam). Results from this article should help decision-makers assess site-specific risk of invasion, and develop proportional prevention and surveillance programs for early detection and rapid response.     

Measuring host finding capacity and arrestment of natural enemies of the cassava mealybug,Phenacoccus manihoti, in the field

In unifested fields, 80 cassava tips were artificially infested with 0, 1, 2, 4, 8, 16, 32, or 64 third instars, and 20 or 100 eggs of cassava mealybug,Phenacoccus manihoti Matile-Ferrero (Hom., Pseudococcidae). Another 80 uninfested tips served as a control. Tips were arranged in a circle of 28 m diameter, in the centre of which the following exotic natural enemies ofP. manihoti were released:Apoanagyrus (Epidinocarsis) lopezi De Santis andA. diversicornis (Howard) (Hym., Encyrtidae),Hyperaspis notata (Mulsant) andDiomus hennesseyi Fürsch (Col., Coccinellidae), and others. This experiment was repeated six times. During the 4–14 days following release, all experimental tips were inspected at two-hour intervals during each day and the presence of exotic as well as indigenous natural enemies, likeExochomus troberti Mulsant (Col., Coccinellidae), ants and spiders was noted. The experiment was repeated six times measured the aggregative response by the natural enemies to different host densities, achieved through host attractance and arrestment. All exotic natural enemies, except the males ofApoanagyrus spp., were fast attracted to the host colonies. As compared to the control tips, they concentrated on the infested tips about 50-fold for the twoApoanagyrus spp. and 10 to 20-fold for the exotic coccinellids. By contrast, non-coevolved indigenous coccinellids, as well as generalist predators like ants and spiders were attracted to the infested tips only 2 to 5-fold.A. lopezi responded best to different host densities, followed byA. diversicornis and the coccinellids, followed by ants and spiders. None of the parasitoids or predators was particularly attracted to egg masses. These results correspond closely to the known efficiencies of these natural enemies,A. lopezi standing out among all candidates. The results of such aggregation studies are compared with those of life-table studies.     

Field cage evaluation of interspecific interaction of two aphelinid parasitoids and biocontrol effect on Bemisia tabaci (Hemiptera: Aleyrodidae) Middle East‐Asia Minor 1

To explore sustainably effective biological control measures to suppress the super pest Bemisia tabaci (Gennadius) Middle East‐Asia Minor 1 and better understand the biological control effects of single and multiple releases of parasitoids, we evaluated the performance and interaction of two aphelinid parasitoids of B. tabaci, Eretmocerus hayati Zolnerowich & Rose (an exotic primary parasitoid) and Encarsia sophia (Girault & Dodd) (an autoparasitoid, which is controversial in a biological control program). Single species or two species were jointly (1:1 density ratio) released in field cages on cotton in Hebei province, China, in 2010. Results of the field cage experiment showed that all parasitoid release treatments were successful in reducing the densities of the host B. tabaci relative to the control in which no parasitoid was released. The combined release of two parasitoid species showed the highest control effect among the treatments. Different population growth trajectories indicated asymmetric competitive effects of En. sophia on Er. hayati. The densities of Er. hayati were significantly higher in the Er. hayati alone treatment than in the combined release treatment, while densities of En. sophia were lower in the En. sophia alone treatment than in the combined release treatment. Our results demonstrated interspecific competition between autoparasitoid En. sophia and exotic primary parasitoid Er. hayati. However, no evidence indicated that autoparasitoid En. sophia disrupted the host suppression achieved by primary parasitoid Er. hayati. The release of the autoparasitoid together with the primary parasitoid may not influence host suppression in biological control.     

Laboratory rearing and biological parameters of the eulophid Pnigalio agraules,a parasitoid of Cameraria ohridella

Predators as well as parasitoids native to Europe accept the exotic horse chestnut leafminer, Cameraria ohridella Deschka and Dimi? 1986 (Lepidoptera: Gracillariidae), either as prey or as host. However, the influence of these antagonists on the populations of the pest insect is so far very low. Therefore, efforts to develop an integrated pest management system against C. ohridella should include methods which foster the natural enemy complex. In the present study we developed a laboratory rearing method and investigated several biological parameters of Pnigalio agraules (Walker 1839) (Hymenoptera: Eulophidae), a dominant species in the horse chestnut leafminer’s parasitoid complex in many European regions. This native parasitoid satisfies three basic requirements for successful use as a biocontrol agent with regard to C. ohridella. The parasitoid’s fecundity, longevity and the speed of juvenile development by far exceeds that of the leafminer, enabling the parasitoid population to increase faster than that of the host. Furthermore, our results show that the impact of this species on C. ohridella populations has been previously underestimated, because non‐reproductive killing (i.e. host‐feeding and host‐stinging) of the hosts, resulting in considerable larval mortality of the leafminer, has not been quantitatively assessed. However, naturally occurring parasitoid populations have negligible impact on C. ohridella populations. Further studies, including experimental releases of P. agraules, are necessary to understand the constraints limiting the parasitoid’s performance in the field and to assess the potential benefits of releases for the control of C. ohridella.