A comparison between the amino acid composition of an egg parasitoid wasp and some of its hosts

Amino acid compositions of the eggs of five lepidopteran hosts for Trichogramma minutum were compared with each other and with a non-host species, Rhodnius prolixus, in which T. minutum oviposits but does not develop. Host eggs are quite homogeneous, particularly when compared according to groupings of potentially interconvertible amino acids. Combined mole percent values for glycine, serine and alanine were higher in hosts (27.5–29.2 mole%) than in R. prolixus eggs (21.5 mole%), in bovine serum albumin (14.9%), which has been used as a protein source in artificial diets for T. minutum, or in many of the mixtures used in published diets for this species. Since these three amino acids make up 26.3 mole% of the adult amino acid content of T. minutum, their deficiency in diets could require metabolic compensation detrimental to development.Adult T. minutum arising from eggs of Manduca sexta, Choristoneura fumiferana, and Sitotroga cerealella are similar in amino acid composition to each other and, in general, to their hosts. Variability appears greater in hosts than in adult wasp composition, suggesting some interconversion of host amino acids to accommodate inflexible nutritional requirements of T. minutum.In the three host species tested, free amino acids constituted 15.8–19.3% by weight of the amino acid in egg contents. In M. sexta eggs, glycine, serine and alanine together make up 28.4% by weight of the total free amino acid, a much higher proportion than in many published diets. The four free amino acids (isoleucine, leucine, phenylalanine and histidine) reported to be oviposition stimulants in experiments on encapsulated diets are present in sufficient concentrations to induce oviposition in the host species tested and in R. prolixus. S. cerealella egg contents having approximately 1.8 g amino acid, yield one or rarely two adult T. minutum (1g amino acid/insect). In contrast, M. sexta eggs with 94 g amino acid each yield an average of 10–12 adults (8.2g amino acid/insect). This suggests that small hosts are allocated few eggs which can only develop into small adults because of nutrient supply (parasitoid size in metabolically restricted), whereas much larger hosts are allocated proportionately fewer eggs than the former resulting in larger, and presumably more viable and fecund, adults (parasitoid size is established behaviourally).     

Assessment ofTrichogramma species for biological control of forest lepidopteran defoliators

In a laboratory study, we determined the potential of threeTrichogramma (Hymenoptera: Trichogrammatidae) species,T. brassicae Bezdenko,T. minutum Riley andT. nr.sibiricum Sorokina, for biological control against six species of forest lepidopteran pests, black army cutworm, hemlock looper, eastern spruce budworm, western spruce budworm, white-marked tussock moth, and gypsy moth. Females of each parasitoid species were offered eggs from each of the six host species. Parasitization and the effect of the host species on the emerging progeny were examined and recorded.Trichogramma minutum had the broadest host range and successfully parasitized four host species out of the six offered.Trichogramma nr.sibiricum had the narrowest host range and parasitized only two species of hosts. Of the six host species, black army cutworm was the most preferred by all threeTrichogramma species; white-marked tussock moth and gypsy moth were not parasitized by any parasitoids. There was a positive correlation between the size of female offspring and their corresponding egg complement in all three parasitoid species. The developmental time of parasitoids from egg to adult was influenced by both the parasitoid and host species. Our results suggest thatT. minutum has the greatest potential for biological control against various forest lepidopteran pests and that the black army cutworm may be the best target candidate for further study.     

Releases of Trichogramma platneri (Hymenoptera: Trichogrammatidae) in Apple Orchards under a Sterile Codling Moth Release Program

Based on the premise that augmented host numbers may help multiply and support parasitoid populations, the egg parasitoid Trichogramma platneri Nargarkatti was released in apple orchards which were participating in a sterile codling moth, Cydia pomonella (L.), release program. Nonviable eggs resulting from matings involving at least one sterile codling moth partner can be successfully parasitized by T. platneri. Grain moth-reared, as well as codling moth-reared, T. platneri were released either in the spring or in the spring and summer oviposition period(s) of wild codling moth. Sentinel codling moth eggs were hung weekly, for 3-day periods, from May until September to determine fluctuations in T. platneri populations both during and between releases. Low numbers of wild or nonviable codling moth eggs or other susceptible host eggs resulted in sufficient eggs to maintain low spring- or summer-introduced T. platneri populations. T. platneri reduced codling moth damage in trees in which the Trichogramma were released.     

Influence of environmental conditions and parasitoid quality on field performance of Trichogramma minutum

The effects of weather conditions and two parasitoid quality attributes, realized fecundity and host acceptance, were assessed on the field efficacy of mass-released Trichogramma minutum. Temperature was the most important single variable, explaining up to 75% of the variation in field parasitism. There were significant positive relationships between both the sum of the maximum temperatures and the number of degree-hours above a 15 °C threshold, accumulated in the three days following the release, and parasitism in the field. There was a significant negative relationship between the mean relative humidity and the odds of parasitism in the field. Quality parameters based on parasitoid biology were not effective for predicting field efficacy if poor weather conditions persisted after a release. If weather conditions were good (i.e. accumulated maximum temperatures above 62 °C, in the 3 days following the release), then parameters such as release rate and fecundity in the lab were useful predictors of field performance. There was no relationship between host acceptance measured in the lab and field parasitism. Given the importance of field temperatures for field performance, selection for cold tolerance of T. minutum would be desirable.     

Seasonal pattern of oviposition by the North American grape berry moth (Lepidoptera: Tortricidae)

The seasonal patterns of oviposition by the North American grape berry moth, Paralobesia viteana (Clemens) (Lepidoptera: Tortricidae) were monitored in juice grape (Vitis labrusca) vineyards in southwest Michigan. Egg deposition was recorded throughout the growing season at two vineyards in 2006, and at four vineyards from 2007 to 2009. In each vineyard, a random sample of 100 grape clusters was visually inspected twice‐weekly and the number of newly laid eggs was counted. We found that oviposition was continuous but variable throughout the season. Egg deposition started in early June coinciding with early grape bloom, continued at low level until mid‐ to late July, intensified in August close to veraison, and ended in September often before harvest. There were no consistent periods without oviposition that would indicate distinct generations. To determine the contribution of moth immigration into the vineyard to the pattern of oviposition, six grape plants located at the edge of a vineyard next to woods were covered with field cages and stocked with infested fruit. Oviposition and berry infestation were followed weekly on covered and exposed plants. Although higher numbers of eggs and infested berries were found on fruit of exposed vines than enclosed vines, egg deposition and berry infestation followed the same pattern in both treatments. This result indicates that the seasonal pattern of egg deposition is not dependent on immigration of grape berry moth of wild grape origin. The pattern of oviposition by grape berry moth described here contributes to the difficulty of controlling this pest using conventional insecticides with short residual activity.     

Influence of grapevine cultivars on the leafhopper <Emphasis Type="Italic">Empoasca vitis</Emphasis> and its egg parasitoids

The leafhopper Empoasca vitis (Göthe) (Homoptera: Cicadellidae) can cause economic damage in European vineyards. Egg parasitoids, in particular Anagrus atomus (Linnaeus) (Hymenoptera: Mymaridae), are the most important natural enemies of the leafhopper. In four different years, leaves of ten grapevine cultivars, which were grown in a vineyard of north-eastern Italy, were collected at the end of the leafhopper 2nd generation to determine the total number of E. vitis eggs per leaf and the percentage of the E. vitis eggs parasitized. These data were analysed for correlation with leaf density and foliar pubescence. The E. vitis eggs per leaf and the percentage of eggs parasitized by Anagrus spp. were significantly influenced by the cultivar. The number of E. vitis eggs per leaf was positively correlated to leaf density, but it was not influenced by leaf hair density. The parasitization rate by Anagrus spp. was affected by foliar pubescence, especially by erect hairs on the veins. These findings could be used for integrated pest management. In particular, (1) the more susceptible cultivars can be used as early indicators of leafhopper infestation, (2) agronomic practices, that reduce leaf density, could decrease the E. vitis population level and (3) clones with glabrous leaves would favour egg parasitoid activity.     

The relationship between egg load and fecundity among Trichogramma parasitoids

1. The relationships between parasitoid egg load, size, and age (3–72 h) for Trichogramma minutum, T. platneri, and T. pretiosum, reared from two factitious hosts, Ephestia kuehniella and Sitotroga cerealella, were evaluated to test the hypothesis that 24‐h egg load can be used to estimate the fecundity of Trichogramma parasitoids. 2. Egg load increased in relation to female age over the first 3 days of adult life for all three Trichogramma species to a mean egg storage capacity of 46.7 eggs for T. minutum, 41.1 for T. pretiosum, and 35.7 for T. platneri. At 24 h of age, T. minutum had matured enough eggs to fill 67% of its storage capacity, in comparison with 74% for T. pretiosum and 91% for T. platneri. There was a positive relationship between egg load and parasitoid size for all ages of the three Trichogramma species reared from both hosts (with the exception of T. platneri at 3 h post emergence), accounting for 14–69% of the variance in egg load. 3. The potential fecundity, realised (3 day cumulative) fecundity, and oviposition rate (potential fecundity/longevity) of T. platneri were all related linearly to size‐dependent variation in 24‐h egg load, but only the realised fecundity of T. pretiosum, and none of the reproductive characteristics of T. minutum. It is suggested that 24‐h egg load may not be an accurate measure of egg storage capacity in parasitoids and should be used cautiously to represent fecundity. 4. The potential fecundity of seven Trichogramma species reared from E. kuehniella varied from 55 to 150, but neither potential fecundity nor oviposition rate was related significantly to egg load (represented by eggs laid during first 24 h). Selection to avoid egg depletion in the attack of gregarious hosts appears most likely to account for the variation in potential fecundity among Trichogramma species.     

Influence of Host Pheromone on Egg Parasitism by Scelionid Wasps: Comparison of Phoretic and Nonphoretic Parasitoids

The kairomonal activity of the attractant pheromone for the spined soldier bug, Podisus maculiventris (Hemiptera: Pentatomidae), was investigated by exposing fresh pentatomid egg masses in field traps with or without synthetic pheromone. Predominantly two parasitoids were recovered from exposed eggs of P. maculiventris and Euschistus obscurus: Telenomus podisi Ashmead (a generalist pentatomid egg parasitoid) and Telenomus calvus Johnson (a phoretic specialist on Podisus eggs) (Hymenoptera: Scelionidae). The incidences of T. podisi from P. maculiventris and E. obscurus eggs placed in pheromone-baited and nonbaited traps were not significantly different, suggesting that this oophagous wasp does not use the spined soldier bug attractant pheromone as a kairomone. However, T. calvus was reared almost exclusively from egg masses of P. maculiventris placed inside pheromone-baited traps. These results suggest that T. calvus females orient to volatile chemicals emitted by spined soldier bug males as a searching strategy to find areas likely to contain host eggs, in addition to the previously discovered strategy of using the pheromone to guide their phoretic behavior. The data also indicate that T. calvus can distinguish between the egg masses of these pentatomid hosts at close range.     

Using urea phosphate to enhance the effect of gibberellin A3 on grape size

Gibberellic acid (GA₃) is widely used to enlarge the berries of seedless grapes (Vitis vinifera L). In cv. Sultana (Thompson Seedless) the addition of 1000 mg/L urea phosphate (UP) to GA₃ solutions after fruit set reduced the pH of the solutions to a stable pH 2.9 and enhanced the effect of GA₃ on berry size and delayed maturation. Addition of citrate buffer, pH 2.9, to GA₃ sprays did not affect berry size or maturation. The possibility of improved GA penetration due to the low pH is considered. The nutritional effect of UP and direct enhanced penetration by the urea ion are also discussed.Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel. No. 1735-E, 1986 series.     

Autumnal emergence of Anagrus wasps,egg parasitoids of Empoasca vitis,from grapevine leaves and their migration towards brambles

• 1 The Anagrus‘atomus’ parasitoid group (Hymenoptera: Mymaridae), associated with Empoasca vitis (Göthe) (Homoptera: Cicadellidae), overwinters on vegetation surrounding vineyards. The emergence of parasitoid adults from grapevine leaves in autumn was studied in north‐eastern Italy, both in relation to the E. vitis egg‐laying period and to the presence of leafhoppers overwintering as eggs on Rubus bushes.
• 2 Autumnal peaks of Anagrus captured using yellow sticky traps were observed first on grapevines and then on brambles. Parasitoid captures in vineyards were observed for more than 1 month after the last first‐instar nymphs of the grape leafhoppers were noticed. Two species belonging to the A. ‘atomus’ group, Anagrus atomus and Anagrus ustulatus, were captured both on grapevines and brambles.
• 3 Parasitoids of the A.‘atomus’ group can emerge from third‐generation grape leafhopper eggs in accordance with two different development time patterns (i.e. normal or delayed). Individuals with delayed emergence required up to 2.2‐fold more time to develop from an egg to adult than individuals with normal emergence. This meant that some parasitoid adults emerged in autumn from eggs of grape leafhopper laid in August.
• 4 A delayed emergence as a result of a slower development ensures that the A.‘atomus’ parasitoid group is synchronized with the egg‐laying of leafhoppers that overwinter as eggs on Rubus spp.
• 5 Consequently, leafhoppers overwintering as eggs on brambles play a key role in the ecology of the relationship between grape leafhoppers and the A.‘atomus’ parasitoid group.

     

Development and survival of Telenomus lobatus, a parasitoid of chrysopid eggs: effect of host species

Telenomus lobatus Johnson & Bin (Hymenoptera: Scelionidae), previously known only from the eggs of a berothid species, emerged from field-collected eggs of the chrysopid Mallada macleodi. In the laboratory, host species differentially influenced development, survival, and size of the parasitoid. Females parasitized between 55 and 65% of the available eggs of Chrysoperla (C. carnea, C. harrisii, and C. rufilabris), and these yielded 98 to 100% adult parasitoids within an average of 13 days. In contrast, eggs of Chrysopa were parasitized less frequently, (C. chi: 50%; C. oculata: 16%; C. quadripunctata: 1.3%) and relatively few (C. chi: 5.6%; C. oculata: 21%) or no (C. quadripunctata) parasitoids survived to adult emergence. Preimaginal development of T. lobatus in eggs of C. chi and C. oculata was approximately two days longer than in eggs of Chrysoperla spp. Although eggs of Meleoma dolicharthra were parasitized infrequently (approx. 16%), they yielded 100% adult parasitoids. Anomalochrysa maclachlani eggs were parasitized at low rates (1.8%) and parasitoid survival was intermediate (40.7%). Among all species, size of the host egg was positively related to the size of the emerging parasitoid adult.

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Résumé T. lobatus Johnson & Bin (Hym. Scelionidae) connu jusqu'ici uniquement comme parasitoïde des ufs de Berothidae, a étè obtenu d'ufs du chrysope, Mallada macleodi récoltés dans la nature. Au laboratoire, l'espèce de l'hôte influe sur le développement, la survie et la taille du parasitoïde. Les femellles ont parasité 55 à 65% des ufs disponibles de Chrysoperla (C. carnea, C. harrisii, C. rufilabris) et ceux-ci ont donné 98 à 100% de parasitoïdes adultes en 13 jours en moyenne. Par contre, les ufs de Chrysopa étaient moins souvent parasités,-C. chi: 50%; C. oculata: 16%; C. quadripunctata: 1,3%-, et relativement peu de parasitoïdes avaient survecu jusqu'à l'émergence,-C. chi: 5,6%; C. oculata: 21%; C. quadripunctata: 0. Le développment préimaginal est approximativement 2 jours plus long dans les ufs de C. chi et C. oculata que dans ceux de Chrysoperla spp. Bien que les ufs de Meleoma dolicharthra aient été peu parasités,-environ 16%-, 100% ont donné des parasitoïdes adultes. Les ufs de Anomalochrysa maclachlani ont été peu parasités,-1,8%-, et le taux de survie a été moyen: 40,7%. Pour toutes les espèces, la taille de l'uf de l'hôte était liée positivement à la taille du parasitoïde obtenu.

     

Relative performance of European grapevine moth (<Emphasis Type="Italic">Lobesia botrana</Emphasis>) on grapes and other hosts

The European grapevine moth, Lobesia botrana is a major grapevine pest, but despite the abundance of vineyards it is a generalist and uses either grapes or alternative species. Given the abundance and predictability of grape, L. botrana could be expected to have evolved towards monophagy. In order to understand why this species remains polyphagous, we hypothesized that larvae reared on rare wild host plants should have higher fitness than those reared on the more abundant grape host. For this, we compared larval performance and several life history traits on three alternative host plants (Daphne gnidium, Olea europaea, Tanacetum vulgare) and three Vitaceae (Vitis vinifera), two cultivars and one wild species (Ampelopsis brevipedunculata), and two control groups raised on either a low or a high nutritive value medium. Alternative hosts are more suitable than Vitaceae for the reproductive performance of L. botrana: larval mortality and development time was reduced, while pupal weight, growth rate, female longevity, female fecundity, duration of laying and mating success were increased. High quality food ingested by larvae promotes higher adult body weight and enhances female reproductive output. This suggests that alternative hosts provide greater nutritional value for L. botrana than Vitaceae. The use of alternative host plants could thus be maintained in the host range because they offer L. botrana a better fitness than on the Vitaceae. This could typically represent an advantage for moths behaving in plant diversity grape landscapes.     

Oviposition behavior of grape berry moth

Studies of the oviposition and host-finding behavior of grape berry moth (GBM) (Endopiza viteana Clemens) (Lepidoptera: Tortricidae) were prompted by reports of oviposition exclusively on grape (Vitis spp.) clusters. Eggs were deposited only on grape clusters under field conditions, but under controlled laboratory conditions in paired comparisons, eggs were also deposited on leaves. Oviposition within different areas of grapevines was proportional to the available substrate in those areas. Under natural light conditions, eggs were deposited during the 4 h period from 1900 to 2300 h. Most oviposition occurred during the low light conditions characteristic of dusk, but absence of light resulted in greatly reduced egg deposition. None of the artifical oviposition substrates that were evaluated elicited oviposition at rates comparable to those on unaltered grapes. Though paraffin and ceresin wax coatings made natural grapes unacceptable for oviposition by GBM, covering natural grapes with parafilm^® resulted in oviposition equal to that on unaltered grapes. Comparisons of Parafilm covered wooden models and Parafilm covered natural grapes illustrate that some stimuli from the natural grape are perceived through the Parafilm covering. Whole and crushed Emperor grapes and a mixture of apple esters gave strong antennal responses relative to grape volatiles extracted with hexane and Freon^TM 113 from an air filtration column.

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Zusammenfassung Bericht über die spezifische Natur der nordamerikanischen Traubenmotte bei der Wirtswahl haben eine Studie über die Wirtsuche und Eiablage dieser Reben-schädling veranlasst. Im Freien wurden Eier nur auf Trauben gefunden, aber im Labor unter kontrollierten Bedingungen und mit gepaarten Vergleichen wurden Eier auch auf Blättern gelegt. Die Eiablagen innerhalb verschiedener Höhenstrata der Rebe waren proportional zum verfügbaren Substrat. Bei natürlicher Beleuchtung fand die Eiablage innerhalb einer 4 h Periode zwischen 1900 und 2300 h statt. Die meisten Eier wurden im abendlichen Zwielicht abgelegt, aber in absoluter Dunkelheit wurde die Eiablage stark reduziert. Keine der künstlichen Ovipositionsubstrate die geprüft wurden, hatte einen vergleichbaren Effekt auf die Eiablage, wie die auf natürlichen Trauben. Natürliche Trauben die mit Parafilm überzogen waren, sowie Trauben ohne Parafilm wurden zur Eiablage akzeptiert. Trauben die mit paraffin oder ceresin Wachs überzogen waren wurden hingegen abgelehnt. Vergleiche von hölzernen Parafilm überzogenen Trauben-modellen mit natürlichen Trauben zeigten, dass irgendwelche Stimuli der Traube durch die Parafilm-schicht wahrgenommen wurden. Intakte und gequetschte Emperor Trauben sowie eine synthetische Mischung Apfelestern verursachten relativ starke Elektroantennogramm Reaktionen. In Vergleich dazu waren Traubenduftstoffe von einer Duftstoff-Falle, die mit Hexan und Freon 113 extrahiert wurden, wenig aktiv. Die Ergebnisse könnten für den Einsatz von bestimmten Lockstimuli in Kombination mit Fallen oder künstlichen Ovipositionsubstraten angewendet werden.

     

Efficacy of Trichogramma evanescens in controlling the grape berry moth Lobesia botrana in grape farms in Egypt

Abstract

The present work was conducted to evaluate the efficacy of Trichogramma evanescens (Westwood) in controlling the grape berry moth Lobesia botrana (Schiff) in two grape farms, in El-Beheira and El-Gharbia Governorates, northern Egypt during 2004 and 2005 seasons. T. evanescens was mass produced on Sitotroga cerealella (Olivier) eggs in the National Research Centre in Egypt. The horizontal and vertical searching activity of T. evanescens was studied to determine the proper way of distributing the Trichogramma cards in vineyards. Field experiments were also conducted to evaluate T. evanescens efficacy to control L. botrana on a large scale. Parasitism by T. evanescens on L. botrana eggs was greatly affected with the horizontal or vertical distance from the release points as well as with the rate of release. Parasitism reached over 97% and the percentage of reduction in damage caused by the pest reached 96.8% in treated plots. A significant increase in the crop was achieved in treated plots. T. evanescens could be a potential candidate for biological control of the grape moth in vineyards.     

Occurrence of different development time patterns induced by photoperiod in Anagrus atomus (Hymenoptera: Mymaridae), an egg parasitoid of Empoasca vitis (Homoptera: Cicadellidae)

The wasp Anagrus atomus L. parasitizes eggs of the cicadellid Empoasca vitis (Göthe) on grapevines during the vegetative season. In vineyards, abundant parasitoid emergence occurs in the autumn as a result of a developmental delay in part of the A. atomus population. In this context, physiological times required by the parasitoid to develop in E. vitis eggs are recorded during the summer. In early summer, all individuals develop fully, with physiological times in agreement with those reported in the literature. From early August onwards, an increasing proportion of parasitoids show a delay in development involving pre‐imaginal stages. Under transmission microscopy, larvae of A. atomus inside the eggs of E. vitis can be clearly differentiated as ‘light’ and ‘dark’ types, which are associated with normal and delayed development, respectively. The decreasing photoperiod as autumn approaches appears to promote the retardation of growth. This phenomenon can be considered a typical case of risk spreading because, when the availability of E. vitis eggs in vineyards is high (i.e. in early summer), A. atomus shows (i) only a normal developmental pattern that allows a faster population increase, whereas (ii) when E. vitis egg availability begins to be scarce (i.e. from mid summer), an increasing proportion of individuals having delayed development provides better fitness because it allows the parasitoid to synchronize its life history with leafhopper species that lay overwintering eggs on plants other than grapevines.     

Egg distributions and the information a solitary parasitoid has and uses for its oviposition decisions

Approximately three decades ago the question was first answered whether parasitoids are able to assess the number or origin of eggs in a host for a solitary parasitoid, Leptopilina heterotoma, by fitting theoretically derived distributions to empirical ones. We extend the set of different theoretically postulated distributions of eggs among hosts by combining searching modes and abilities in assessing host quality. In the models, parasitoids search either randomly (Poisson) (1) or by vibrotaxis (Negative Binomial) (2). Parasitoids are: (a) assumed to treat all hosts equally, (b) able to distinguish them in unparasitised and parasitised hosts only, (c) able to distinguish them by the number of eggs they contained, or (d) able to recognise their own eggs. Mathematically tractable combinations of searching mode (1 and 2) and abilities (a,b,c,d) result in seven different models (M1a, M1b, M1c, M1d, M2a, M2b and M2c). These models have been simulated for a varying number of searching parasitoids and various mean numbers of eggs per host. Each resulting distribution is fitted to all theoretical models. The model with the minimum Akaike's information criterion (AIC) is chosen as the best fitting for each simulated distribution. We thus investigate the power of the AIC and for each distribution with a specified mean number of eggs per host we derive a frequency distribution for classification.Firstly, we discuss the simulations of models including random search (M1a, M1b, M1c and M1d). For M1a, M1c and M1d the simulated distributions are correctly classified in at least 70% of all cases. However, in a few cases model M1b is only properly classified for intermediate mean values of eggs per host. The models including vibrotaxis as searching behaviour (M2a, M2b and M2c) cannot be distinguished from those with random search if the mean number of eggs per host is low. Among the models incorporating vibrotaxis the three abilities are detected analogously as in models with random search.Experiments with two species of solitary parasitoids (L. heterotoma and Asobara tabida) are conducted. All theoretically postulated distributions are separately fitted to the resulting experimental egg distributions. The AIC criterion is used to choose the best fitting theoretical distribution. For both parasitoid species the frequency distribution of best fitting models for experimental data is compared to the classification of distributions generated by simulations. This leads to the conclusion that both L. heterotoma and A. tabida are able to distinguish between parasitised and unparasitised hosts. For L. heterotoma the results point to an ability to assess the number of eggs in a host, whereas A. tabida does not seem to have this ability. This difference suggests that an egg is more valuable for L. heterotoma than for A. tabida.     

Parasitism of non-target lepidoptera by mass released Trichogramma brassicae and its implication for the larval parasitoid Lydella thompsoni

The release of high numbers of the eggparasitoid Trichogramma brassicae Bezd.(Hym. Trichogrammatidae) to control theEuropean corn borer (ECB), Ostrinianubilalis Hb. (Lep.: Crambidae) in maize hasraised concerns about potential negativeeffects on native natural enemies. The nativelarval parasitoid Lydella thompsoniHerting (Dipt.: Tachinidae) is the mostfrequent and important ECB parasitoid insouthern Switzerland and can achieve highparasitism rates. Its first generation emergestoo early to find ECB larvae and must rely onalternative hosts living in natural habitatsclose to maize fields. Inundative releases ofT. brassicae coincide with theoviposition period of the alternative hosts ofthe tachinid. T. brassicae moving out ofrelease fields may attack and diminish thepopulation of these hosts, creating abottleneck situation for L. thompsoni inthe subsequent spring. Laboratory hostspecificity tests showed that the tachinid'stwo most abundant spring hosts Archanarageminipuncta Haworth (1809) (Lep.: Noctuidae)and Chilo phragmitellus Hübner (1805)(Lep.: Crambidae) are successfully parasitisedby T. brassicae females in no-choicesituations. Our extensive field surveys,however, showed that the two tested springhosts escape parasitism since their eggs arewell hidden or not attractive. Negativeeffects of inundative releases of T.brassicae on the native tachinid fly L. thompsoni, such as population densityreduction, displacement, or local extinction,are very unlikely.     

Effects of agroforestry on phytoseiid mite communities (Acari: Phytoseiidae) in vineyards in the South of France

The abundance and diversity of phytoseiid mites were surveyed from April to September 2003 to 2005 in vineyards (Grenache and Syrah cultivars) co-planted with rows of Sorbus domestica or Pinus pinea and in monoculture plots of grapes in the South of France. Densities of phytoseiid mites were different on the two tree species, with P. pinea a more suitable host than S. domestica. Typhlodromus (Typhlodromus) exhilaratus was the dominant species occurring on grapes and on co-planted rows of S. domestica and P. pinea, whereas T. (T.) phialatus was the most abundant species in monoculture plots of both S. domestica and P. pinea. Factors determining the dominance of T. (T.) phialatus over T. (T.) exhilaratus in monoculture trees are discussed. In this study, agroforestry management did not affect phytoseiid diversity in vineyards, but did affect phytoseiid density, especially in 2005. The results obtained in 2003 and 2004 are not easy to discuss in this regard because of the low densities of mites observed during these 2 years (very dry climatic conditions and pesticide applications).     

Self-, Intra-, and Interspecific Host Discrimination in Telenomus busseolae Gahan and T. isis Polaszek (Hymenoptera: Scelionidae), Sympatric Egg Parasitoids of the African Cereal Stem Borer Sesamia calamistis Hampson (Lepidoptera: Noctuidae)

Oviposition behavior, intra- and interspecific host discrimination, and super- and multiparasitism by the scelionids Telenomus busseolae and T. isis were studied using batches of eggs of the noctuid stalk borer Sesamia calamistis as the host. Both Telenomus species were able to discern eggs already parasitized. As a result, self-superparasitism was only 4.0% for T. busseolae and 5.8% for T. isis. Likewise, intraspecific superparasitism was avoided by both species and was significantly higher for T. busseolae than T. isis, and higher when parasitized eggs were offered immediately (0 h) and after 48 h than after 24 h; apparently, the recognition of parasitized eggs at 24 and 48 h was based on the presence of parasitoid larvae rather than a specific marking substance. Multiparasitism was avoided if the female had a choice between unparasitized and parasitized eggs. In a choice experiment, it was 10.2 and 2.5% for T. busseolae and T. isis, respectively. In a nonchoice experiment, multiparasitism did not vary between species and time treatment; it was low, varying between 9.6 and 24.1%. In the 0-h treatment, T. busseolae always outcompeted T. isis, accounting for 63.4 or 91.7% of the offspring, when T. isis or T. busseolae, respectively, was the first species. In the 24-h treatment, the first species emerged more often than the second did but the host egg mortality, i.e., eggs from which neither borer larvae nor parasitoid emerged, was >40%. Whereas T. busseolae is ubiquitous in Africa, T. isis has never been reported from eastern Africa, and it has been proposed for introduction against the prevailing noctuid pest Bussoela fusca. Based on earlier life table and host suitability studies and on the present findings, it is concluded that T. isis would establish in the midaltitudes but not the highlands of eastern Africa.     

The dynamics of grape leafhopper Empoasca vitis Göthe populations in southern Switzerland and the implications for habitat management

The life cycle of Empoasca vitis and its most important parasitoid Anagrus atomus in southern Switzerland can be divided into three phases. In phase I the adults of E. vitis move from overwintering sites, i.e. primarily conifers, over deciduous plants into the vineyards. The parasitoid A. atomus on the other hand, appears to overwinter in leafhopper eggs, mainly on roses and blackberries. It subsequently completes one generation in leafhopper eggs primarily on blackberries and hazelnuts, before it attacks E. vitis eggs in the vineyards. For phase II, a population model with time‐varying age structures and stochastic properties was constructed for E. vitis. For this purpose a time‐varying distributed delay model with attrition was constructed. Given the calibrated initial density of overwintering females, the model predicts an unacceptable number of E. vitis for the growing season. However, if egg parasitism of A. atomus and Stethynium triclavatum is introduced into the model as an external variable E. vitis densities are predicted which are economically irrelevant. Inphase III E. vitis adults leave the vineyards for the overwintering sites. The model shows the importance of the parasitoid A. atomus during phase II. A. atomus should be favoured by surrounding the vineyards with host plants carrying leafhoppers’ eggs. Consequently, habitat management measures for E. vitis control could be applied to the surroundings of the vineyards.