Response of the egg parasitoid Trichogramma pretiosum to the sex pheromone of its host Heliothis zea

This paper presents results of olfactometer experiments with the egg parasitoid Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae) and its host the corn earworm moth, Heliothis zea (Boddie) (Lepidoptera: Noctuidae). The sex pheromone of the host significantly reduced the total number of border crossings between odour fields in the olfactometer. Also, female parasitoids made significantly more visits to the calling moth odour field than to the opposite control field in the olfactometer. Further, the wasps spent significantly more time in the olfactometer field containing the sex pheromone released by calling virgin moths, than in control fields. If non-calling virgin moths were used as odour source, the response was reversed and wasps were repelled by the odour of the moths, and the numbers of visits were evenly distributed over the four flow fields. These results are discussed in the context of foraging ecology of egg parasitoids.

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Résumé Des expériences menées en olfactométrie avec le parasite oophage Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae) et son hôte, Heliothis zea (Boddie) (Lepidoptera: Noctuidae) donnent les résultats suivants. La présence de la phéromone sexuelle de l'hôte réduit de façon significative le nombre de passages entre les champs odorisés. De mème, les parasites visitent plus fréquemment le champ qui dispense l'odeur de la femelle en appel que le champ témoin placé à l'opposé. Par ailleurs, le temps passé dans le champ qui contient la phéromone sexuelle émise par les femelles vierges en appel est significativement supérieur à la durée de visite des champs témoins. Si l'on utilise comme source d'odeur des femelles vierges qui ne sont pas en appel, la réponse est inversée, les parasites sont alors repoussés par l'odeur de ces papillons et le nombre de visites est distribué de façon aléatoire entre les quatre champs. Ces résultats sont discutés dans le contexte de l'écologie du comportement de recherche chez les parasites oophages.

     

In vitro culture of Trichogramma pretiosum on an artificial medium

The composition of an artificial medium and environmental conditions are described for the in vitro rearing of the egg parasite Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae). The medium was composed of defined amounts of protein, carbohydrates, lipid, salts, and vitamins, but also contained up to 40% insect hemolymph. The hemolymph was necessary to induce pupation. T. pretiosum eggs were obtained by dissection of Heliothis virescens (F.) (Lepidoptera: Noctuidae) eggs. In vitro reared T. pretiosum were similar in size to H. virescens reared T. pretiosum, and females were fecund.

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Résumé Les oeufs de Trichogramma pretiosum ont été obtenus par dissection d'oeufs d'Heliothis virescens. T. pretiosum Riley (Hymenoptère, Trichogrammatidae) a été élevé avec succès sur un substrat synthétique. Outre des quantités définies de protéines, glucides, lipides, éléments minéraux et vitamines, la ration contenait aussi jusqu'à 40% d'hémolymphe de Manduca sexta. L'hémolymphe était nécessaire pour induire la nymphose. En plus de la nourriture, les conditions d'environnement sont apparues extrêmement importantes pour élever T. pretiosum dans des conditions satisfaisantes. Le contrôle de l'humidité relative, en particulier, était le facteur le plus important. Les adultes produits au cours de cette étude étaient d'apparence normale; ils se sont accouplés sans problèmes, les femelles étaient fécondes et leur taille ne différait pas de celle d'individus élevés sur H. virescens.

     

Oviposition and reproductive performance of a generalist parasitoid (Trichogramma pretiosum) exposed to host species that differ in their physical characteristics

The response of generalist egg parasitoids to alternative natural hosts that are present simultaneously is not well known. We investigated the behavior of Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae) in relation to two field hosts Helicoverpa armigera Hübner and Spodoptera litura Fabricius, in choice and no choice tests. We quantified the effects of natal host species and post-emergence adult age on the oviposition preference of the parasitoids. H. armigera eggs were consistently preferred over S. litura eggs, regardless of the natal host and adult age. When only S. litura eggs were available as hosts, they were parasitized at statistically similar rates to H. armigera eggs (average of 17 ± 2.7 vs. 13 ± 3.0, H. armigera to S. litura). The adult lifespan and lifetime fecundity of T. pretiosum were variable but were affected by natal host species and/or host species to which they were exposed. Mean lifespan and fecundity of parasitoids that had developed in H. armigera eggs and were exposed to H. armigera eggs for oviposition were 13.9 ± 1.8 days and 98.7 ± 11.0 adult offspring. By contrast, those that developed in S. litura eggs and were exposed to S. litura eggs for oviposition lived for 7 ± 0.9 days and produced 53.8 ± 8.0 adult offspring. The ovigeny index (OI) was significantly lower in the parasitoids exposed to H. armigera eggs than in those exposed to S. litura eggs, regardless of the natal host, indicating that H. armigera eggs sustain the adult parasitoids better than S. litura eggs. These results are used to predict parasitoid behavior in the field when both hosts are available.     

Development of a continuous cell line from the insect egg parasitoid,Trichogramma pretiosum (Hymenoptera; Trichogrammatidae)

Summary A cell line (IPLB-TpE1) was established from embryos of the hymenopteran parasitoid,Trichogramma pretiosum Riley. Cultures contain a mixture of attached, elongate spindle-shaped cells and large aggregates of suspended cells. Chromosomes of the cells were typical ofTrichogramma species and isozyme characterization showed patterns similar toT. pretiosum adults, but distinctly different fromHeliothis zea, the lepidopteran host from which parasite eggs were obtained. The cells are capable of growth over a wide range of osmotic pressures with equal growth between 350 and 600 mOsm/kg. Optimal growth was obtained with a pH of 6.5. Doubling time at the 40th passage was 72 h and cultures are currently subcultured at weekly intervals. The mention of a commercial product does not constitute an endorsement by the U. S. Department of Agriculture.     

The effect of host size on quality attributes of the egg parasitoid,Trichogramma pretiosum

In a study of the quality ofTrichogramma pretiosum Riley (Hymenoptera: Trichogrammidae), we compared female wasps emerging from natural hosts, parasitized in the laboratory or the field with those emerging from factitious hosts used for commercial mass production. Females from the natural hosts were larger, more fecund, and longer lived than those from the factitious hosts. Compared to small females, large female wasps are substantially more fecund when honey (carbohydrate) is available but marginally more fecund when honey is unavailable. The size of a femaleT. pretiosum depends on two factors: the size of the host egg from which it emerges even when the wasp was gregarious, and the number of conspecifics that emerge with it. The similarities in the size distribution of female wasps emerging from natural hosts, in conjunction with the mechanism by whichTrichogramma measure host size and allocate eggs accordingly, suggests the hypothesis that size related components of fitness in femaleT. pretiosum are under strong selection in the field.     

Development of an Oligidic Diet forin VitroRearing ofTrichogramma galloiZucchi andTrichogramma pretiosumRiley

The goal of this research was to develop an artificial diet for rearingTrichogramma galloiandTrichogramma pretiosum,which are important egg parasitoids of several pests in Brazil. The diet was based on different proportions of hemolymph ofHelicoverpa zealarvae, chicken egg yolk, powdered milk solutions, bovine fetal serum, and an extract fromHeliothis virescenseggs. The ideal volume of diet for rearingT. galloiwas also evaluated. The parasitoids showed different nutritional requirements for their development. The best proportion of diet components forT. galloiwas 70% hemolymph, 20% egg yolk, 10% fetal serum, and 0.2% streptomycin, and forT. pretiosumit was 70% hemolymph, 20% egg yolk, 5% fetal serum, 5% egg extract, and 0.2% streptomycin. Egg yolk was found to be essential for the development of both parasitoids, and the powdered milk solution was not an important component in the diet. Development was not obtained in diets with hemolymph concentrations lower than 40%. A 3- to 4-μl amount of diet was the ideal volume on which to rearT. galloiwith the techniques reported.     

Comparison of Hemolymph and Holotissues of Different Species of Insects as Diet Components forin VitroRearing ofTrichogramma galloiZucchi andT. pretiosumRiley

The aim of this work was to compare pupal holotissues (Diatraea saccharalis, Anticarsia gemmatalis,andBombyx mori) and larval hemolymph of several moth species (Helicoverpa zeaandBombyx mori) commonly produced in Brazilian laboratories as components of artificial diets forin vitrorearing ofTrichogramma galloiandTrichogramma pretiosum.Diets based on larval hemolymph ofH. zeaproduced the best development of both natural enemies, although a diet with pupal holotissues ofB. moriallowed full development ofT. pretiosum.Amino acid analysis showed qualitative differences among the insect derivates and eggs of the natural and alternative hosts, but with a quantitative similarity. Electrophoretic analysis resulting in a diverse protein-stained bands evidenced the qualitative differences among these components.     

Self and conspecific superparasitism by the egg parasitoid Trichogramma evanescens

Superparasitism is a widespread phenomenon in insect parasitoids and may be advantageous in certain circumstances. In this paper, we distinguish two kinds of superparasitism with different adaptive consequences for an ovipositing parasitoid: self superparasitism, where a parasitoid oviposits in a host in which she has previously oviposited, and conspecific superparasitism, where she oviposits in a host containing egg(s) from a previous oviposition by a conspecific. Our studies on Trichogramma evanescens Westwood show that females lay smaller clutches on parasitized than on healthy hosts but make the same overall allocation of males and females, although the sequence of sexes during oviposition differs. No difference was found between allocation in self and conspecific superparasitism. These results are discussed in the light of theories for progeny and sex allocation.

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Selbst- und konspezifisch-superparasitismus durch die schlupfwespe Trichogramma evanescens

Zusammenfassung Superparasitismus ist ein weitverbreitetes Phänomen in Parasitoiden von Insekten und es kann unter bestimmten Umständen vorteilhaft sein. Diese Arbeit macht Unterschied zwischen zwei Formen von Superparasitismus, jeder mit seiner eigenen adaptiven Konsequenz für die parasitierende Schlupfwespe: Selbst-Superparasitismus, wenn eine Schlupfwespe einen Wirt parasitiert die sie vorher selbst parasitiert hat, und Konspezifisch-Superparasitismus, wenn sie einen Wirt parasitiert die vorher von einem Artgenossen parasitiert worden ist. Unsere Untersuchungen an Trichogramma evanescens zeigen dass die Weibchen auf den belegten Wirten, aber das Gesamtverhältnis von männlichen und weiblichen Brut ist dasselbe, obschon die Reihenfolge in den die Eier der beiden Geschlechte abgelegt werden sich underscheiden. Keinen Unterschied wurde gefunden zwischen die Ablegung während elbst-Superparasitismus und Konspezifisch-Superparasitismus. Diese Ergebnisse werden diskutiert im Rahmen der Theorien für die Belegung des Wirtes in bezug auf die Anzahl und das Geschlecht der Eier.

     

Continuous rearing of the maize stem borerBusseola fusca on an artificial diet

Busseola fusca (Fuller) (Lepidoptera: Noctuidae) is a major pest of maize and sorghum in many countries of tropical Africa. Hitherto, research on this important pest has been hampered by the occurrence of a six-month long diapause in the last larval stage and the lack of an artificial diet for rearing the insect in the laboratory. Incorporating 4 to 8-week-old sorghum powder in a nutritionally adequate diet and rearing larvae individually in vials at ambient laboratory conditions (25–30°C, 50–80% r.h., and L12: D12) have made it possible to rear 15 successive non-diapausing generations ofB. fusca capable of producing between 35 to 40 healthy pupae/litre of diet and upto 70% pupation without loss of vigour or reproductive capacity. Five to six generations were completed per year and the overall mean developmental period (egg-egg) was 68 days (egg 6, larval 45, pre-pupal 1, pupal 14 and pre-oviposition 2 days). Larval period lasted 70 days in the first generation compared to 32.3 days in the fifteenth generation. Average fecundity increased from 158.0 to 394.6 eggs per female with a concomitant increase of egg hatch from 44.8 to 79.6% in the first and fifteenth generation, respectively.     

Artificial diet and rearing methods for Thanasimus dubius (Coleoptera: Cleridae), a predator of bark beetles (Coleoptera: Scolytidae)

Clerid beetles are common natural enemies of bark beetles, and could potentially be used as biological control agents if they could be reared in sufficient numbers. We developed an artificial diet devoid of insect components for rearing Thanasimus dubius (Fabricius), a clerid that attacks several economically important bark beetles in eastern North America. We reared larvae of this predator using the artificial diet, and then used either natural or factitious prey to feed the adults so produced. Two different methods of presenting the diet were also examined. We then compared the performance of T. dubius reared on the artificial diet with newly-emerged wild individuals collected from the field. Our results suggest that adult predators reared on the diet are near in quality to wild ones, and high R₀ values can be obtained. No difference in prey preference was found between wild and diet-reared individuals after five generations in the laboratory. Sufficient numbers of predators could be generated using these techniques to permit limited field trials of augmentative biological control.     

Biological characteristics and thermal requirements of a Brazilian strain of the parasitoid Trichogramma pretiosum reared on eggs of Pseudoplusia includens and Anticarsia gemmatalis

A new strain of the parasitoid Trichogramma pretiosum, was collected in Rio Verde County, State of Goiás, Central Brazil, and designated as T. pretiosum RV. This strain was then found to be the most effective one among several different strains of T. pretiosum tested in a parasitoid selection assay. Therefore, its biological characteristics and thermal requirements were studied, aiming at allowing its multiplication under controlled environmental conditions in the laboratory. The parasitoid was reared on eggs of Pseudoplusia includens and Anticarsia gemmatalis at different constant temperatures within an 18–32 °C temperature range. The number of annual generations of the parasitoid was also estimated at those temperatures. Results have shown that T. pretiosum RV developmental time, from egg to adult, was influenced by all temperatures tested within the range, varying from 6.8 to 20.3 days and 6.0 to 17.0 days on eggs of P. includens and A. gemmatalis, respectively. The emergence of T. pretiosum RV from eggs of A. gemmatalis was higher than 94% at all temperatures tested. When this variable was evaluated on eggs of P. includens, however, the figures were higher than that within the 18–30 °C range (more than 98%), and were also statistically higher than the emergence observed at 32 °C (90.2%). The sex ratio of the parasitoids emerged from eggs of A. gemmatalis decreased from 0.55 to 0.29 at 18–32 °C, respectively. However, for those emerged from eggs of P. includens, the sex ratio was similar (0.73, 0.72 and 0.71) at 20, 28 and 32 °C, respectively. The lower temperature threshold (Tb) and thermal constant (K) were 10.65 °C and 151.25 degree-days when the parasitoid was reared on eggs of P. includens; and 11.64 °C and 127.60 degree-days when reared on eggs of A. gemmatalis. The number of generations per month increased from 1.45 to 4.23 and from 1.49 to 4.79 when the parasitoid was reared on eggs of P. includens and A. gemmatalis, respectively, following the increases in the temperature.     

Effect of artificial diet media, glucose, protein hydrolyzates, and other factors on oviposition in wax eggs by Trichogramma pretiosum

Artificial diet media were clearly inferior to dilute KCl-MgSO₄ solutions as ovipositional stimulants for Trichogramma pretiosum. Depending on their concentrations, glucose, protein hydrolyzates, and free amino acids either had no effect on or were inhibitors of oviposition when they were mixed with KCl-MgSO₄ solutions. Oviposition into artificial eggs containing salt solutions formulated to correspond to the concentration of potassium, magnesium, and sodium in insect components revealed that the hemolymph mimic and the mimic of Sitotroga cerealella eggs were poor, and that the mimic of whole Heliothis spp. larvae, which was similar to the concentration of these cations in Heliothis virescens eggs, was the most active in eliciting oviposition.

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Effet du substrat alimentaire artificiel du glucose, des hydrolysats de protéine et autres facteurs sur la ponte de Trichogramma pretiosum dans des oeufs en paraffine

Résumé La ponte de T. pretiosum Riley dans des milieux de culture contenant des concentrations de K⁺-Mg²⁺ correspondant à celle de l'hémolymphe d'insecte ou à celle des oeufs d'Heliothis virescens Fabricius était nettement inférieure à celle obtenue dans des solutions diluées de KCl, MgSO₄.La ponte dans des solutions de KCl-MgSO₄ était fortement inhibée par le glucose ou par l'hydrolisat de caséine à 2,5%. Le glucose et les hydrolysats de protéine et de levure à 1,3% ou à des concentrations inférieures n'ont pas stimulé la ponte. Des solutions aqueuses (sans KCl-MgSO₄) soit de glucose et d'hydrolysat de caséine, soit d'acides aminés libres ont été des stimulants de ponte extrêmement faibles. Quand des solutions de KCl, MgSO₄ et NaCl sont dosées en fonction des résultats d'analyses élémentaires des constituants de l'insecte, la ponte était très faible dans des oeufs artificiels contenant des solutions correspondant aux concentrations en K, Mg et Na, soit de l'hémolymphe d'Heliothis zea, soit des oeufs de Sitotroga cerealella. La ponte était beaucoup plus élevée dans des solutions correspondant aux analyses du dernier stade larvaire d'Heliothis spp. Par suite de l'activité de ponte plus élevée, du coût beaucoup plus faible et du niveau inférieur en éléments nutritifs disponibles pour entretenir la croissance microbienne, les solutions diluées de KCl-MgSO₄ peuvent être supérieures aux régimes artificiels et à l'hémolymphe pour la récolte d'oeufs de Trichogrammes à utiliser dans des régimes artificiels.

     

Efficacy of inoculative releases of Trichogramma ostriniae (Hymenoptera: Trichogrammatidae) against European corn borer Ostrinia nubilalis (Lepidoptera: Crambidae) in field corn

We evaluated the egg parasitoid Trichogramma ostriniae (Hymenoptera: Trichogrammatidae) to control European corn borer [Lepidoptera: Crambidae: Ostrinia nubilalis (Hübner)] in field corn in 2001 and 2002. Inoculative releases of 75,000 T. ostriniae/ha occurred in New York and Virginia in 5–10 cornfields per state when corn was at mid-whorl. Incidence of egg mass parasitism, number of stalk tunnels, incidence of ear damage, and whole-plant yield were evaluated. Parasitism of European corn borer egg masses ranged from 0 to 75% in release plots and was greater in release plots than in control plots. Individual comparisons between paired release and control plots showed no reductions in either stalk or ear damage. However, when data were combined across both years and fields, stalk and ear damage were significantly reduced in New York. In Virginia, no significant differences were detected using data obtained from one year. There were no differences in yield between release and control plots. Low densities of European corn borer, drought conditions in 1 year, and a larger plant canopy in field corn are possible reasons why T. ostriniae releases provided less control than has been observed in previous trials in sweet corn. Additional research focused on improved timing and frequency and number of releases is warranted.     

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.     

Suitability of some farmscaping plants as nectar sources for the parasitoid wasp, Microplitis croceipes (Hymenoptera: Braconidae): Effects on longevity and body nutrients

In support of an ongoing study to evaluate potential farmscaping plants for utilization in organic vegetable production systems, we examined the effects of the nectar of three flowering plant species, sweet alyssum (Lobularia maritima), buckwheat (Fagopyrum sagittatum), and licorice mint (Agastache foeniculum), on the lifespan and body nutrient levels of the wasp, Microplitis croceipes (Cresson) (Hymenoptera: Braconidae), a key parasitoid of some caterpillar pests of vegetable crops in the USA. The greatest longevity (～16 days) was recorded for honey-fed wasps (positive control). Buckwheat significantly increased the lifespan of female and male wasps by at least two-fold relative to wasps provided water only (longevity = 3–4 days). Licorice mint significantly increased female longevity and numerically increased male longevity. Sweet alyssum slightly increased longevity of both sexes but this was not significantly different from the water only control. Females had a significantly longer longevity than males on all the diet treatments. The greatest carbohydrate nutrient levels (sugar content and glycogen) were recorded in honey-fed wasps followed by wasps fed buckwheat, whereas very little nutrients were detected in wasps provided sweet alyssum, licorice mint or water only. However, female wasps were observed to attempt to feed on all three flowering plant species. Thus, the low nutrient levels detected in wasps provided sweet alyssum or licorice mint may be because the nectars were not accessible or were of poor quality. Further studies will evaluate the effects of the promising farmscaping plants on the beneficial and pest insect communities in the field.     

Development of a chemically defined diet for ants

A chemically defined diet is a useful tool for the study of nutritional physiology of organisms. We have developed such a diet for Camponotus carpenter ants to facilitate experiments on nutritional requirements of these ants. Worker colonies of Camponotus floridanus were fed with a chemically defined diet, containing all essential minerals, amino acids, vitamins, growth factors and sucrose in an agar matrix. After 13 weeks, neither the number of raised pupae, their dry weight, nor the mortality of workers in subcolonies fed with this diet differed significantly from control colonies fed with Bhatkar-Whitcomb-agar, in addition to cockroaches and diluted honey. Therefore, this diet is adequate for a normal brood production and a maximal growth rate of C. floridanus larvae, at least for a period of three months. This diet should be suitable for ants that are able to feed on agar-based food resources in general. Received 6 September 2006; revised 5 October 2006; accepted 18 October 2006. An erratum to this article is available at .     

Changes in host acceptance and host suitability as an effect of rearing Trichogramma maidis on a factitious host

Host acceptance and suitability of Ostrinia nubilalis Hbn. for Trichogramma maidis Pint. et Voeg. (Hymenoptera: Trichogrammatidae) were studied, after rearing the parasitoids on O. nubilalis or Ephestia kuehniella Oliv. (Lepidoptera: Pyralidae) for various numbers of generations. In cages, containing two maize plants with in total 30 egg masses of the natural host (O. nubilalis), wasps continuously reared on either E. kuehniella or O. nubilalis found egg masses in equal proportions. The former however, did not parasitize the eggs successfully, due to either low degree of host acceptance or insufficient host suitability or both. Subsequently, host acceptance behaviour of individual females from different strains was studied by means of direct observations after releasing them into a small arena containing eggs of O. nubilalis or E. kuehniella. Wasps continuously reared on O. nubilalis or 1–3 generations on E. kuehniella accepted egg masses of the natural host better than wasps continuously reared on E. kuehniella. Acceptance of O. nubilalis by the wasps gradually decreased with increasing numbers of generations reared on E. kuehniella. By rearing T. maidis, previously cultured on E. kuehniella, for five generations on O. nubilalis, acceptance of egg masses of this host species did not change. Host suitability of O. nubilalis appears to correspond with host acceptance of the strains. Contrary to the observations on O. nubilalis, acceptance and suitability of E. kuehniella were not influenced by the host on which T. maidis was reared. Results of this study show that host acceptance and suitability of the natural host are important quality factors for T. maidis when mass produced on a factitious host.

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Zusammenfassung Wirtsakzeptanz und Wirtseignung von Ostrinia nubilalis Hbn. für den Eiparasitoiden, Trichogramma maidis Pint. et. Voeg., wurden untersucht nach der Zucht auf dem natürlichen Wirt, O. nubilalis, oder auf dem Ersatzwirt, der Mehlmotte, Ephestia kühniella Zell.. Versuche mit Käfigen, in denen je zwei Maispflanzen mit insgesamt 30 Eigelegen von O. nubilalis und 40 Weibchen von T. maidis eingesperrt waren, zeigten, dass Weibchen, die seit über 150 Generationen auf O. nubilalis bzw. E. kühniella gezüchtet worden waren, die Eigelege gleich gut fanden. Während die auf O. nubilalis gezüchteten Parasitoide die Eigelege zu 80% parasitierten, war die Parasitierungsrate der auf E. kühniella gezüchteten Parasitoide gleich Null. Die Ursachen dieses Phänomens wurden in weiteren Versuchen durch direkte Beobachtungen über Wirtsakzeptanz und Wirtseignung untersucht. Einzelne Weibchen von Stämmen, die nur auf O. nubilalis oder während einer zunehmenden Generationenzahl auf E. kühniella gezüchtet worden waren, untersuchte man während 15 Minuten unter der Stereoskoplupe in einer kleinen Arena, die ein Eigelege des Maiszünslers oder Eier der Mehlmotte enthielt. Dabei zeigte sich, dass Wespen, die ausschliesslich auf Maiszünslereiern oder nur 1–3 Generationen auf Mehlmotteneiern gezüchtet worden waren, die Eigelege von O. nubilalis besser akzeptierten als solche, die seit vielen Generationen auf E. kühniella vermehrt worden waren. Die Wirtsakzeptanz verschlechterte sich mit zunehmender Generationenzahl auf E. kühniella. Wenn T. maidis nach 23 Generationen auf E. kühniella wieder während 5 Generationen auf O. nubilalis gezüchtet wurde, verbesserte sich die Akzeptanz der Eigelege von O. nubilalis nicht. Die Wirtseignung der Eigelege von O. nubilalis, stimmt überein mit der Wirtsakzeptanz der verschiedenen Stämme. Dies ergaben Versuche mit 15 Minuten Direktbeobachtung und bei 24 Stunden Expositionszeit. Im Gegensatz zu den Beobachtungen auf Eigelegen von O. nubilalis wurde die Akzeptanz und Eignung der Eier von E. kühniella durch die Zucht auf verschiedenen Wirten nicht beeinflusst. Das Ergebnis dieser Untersuchung zeigt, dass Akzeptanz und Eignung des natürlichen Wirtes wichtige Qualitätsfaktoren für T. maidis in der Massenzucht auf Ersatzwirten sind.

     

Effects of fine-grain habitat complexity on egg parasitism by three species of Trichogramma

Effects of microhabitat complexity on host foraging by three species of Trichogramma (T. deion, T. ostriniae, and T. pretiosum) were evaluated under simulated stored product conditions. All three species have been considered as potential biological control agents for the Indianmeal moth, Plodia interpunctella, in retail stores and warehouses. Trials were conducted with single naïve female parasitoids in 10-cm Petri dishes that were either empty, contained flour, or contained millet. Empty 15-cm Petri dishes, which served as a surface area control, comprised a fourth treatment. Females were allowed to forage for sentinel egg disks for 2 h, after which percentages of parasitism and egg mortality were computed. In addition, behavioral observations were made on a subset of the trials. Trichogramma deion parasitized more eggs than the other two species in the empty dishes and in the dish containing flour. For T. deion, rates of parasitism and egg mortality were significantly greater in both the small and large empty dishes than in the small dishes containing flour or millet. Parasitism was consistently low for all three species in the grain-filled dishes. Among species, T. ostriniae spent the most time walking, while T. pretiosum was the most sedentary. In addition, T. pretiosum spent significantly more time on the first egg visited compared with subsequent eggs. T. deion may be the best-suited for use as a biological control agent for P. interpunctella. However, the potential negative effects of fine-grain habitat complexity should be taken into account when developing a release protocol for Trichogramma spp.     

In vitro rearing of Edovum puttleri,an egg parasitoid of the Colorado potato beetle,on artificial diets: Effects of insect cell line‐conditioned medium

Effects of conditioned media prepared from cell lines derived from 11 insect species (six families, three orders) on the in vitro growth and development of the egg parasitoid Edovum puttleri were investigated. The parasitoid exhibited significantly different responses to the various insect cell line‐conditioned media that were incorporated into the artificial diets. When cell lines were derived from embryos, higher percentages of 3rd instars and prepupae were observed than when cell lines were derived from fat body or ovaries. Medium conditioned with cell line IPLB‐CPB2 derived from the embryos of the Colorado potato beetle produced the best result. Preconditioning time was important. In general, 5 days of preconditioning appeared to be optimal. The growth‐ and development‐promoting effect may have resulted from growth factors or growth‐supporting factors produced/ released by the insect cell lines into the culture medium. Upon storage at 0–4°C for 7–14 days, the ability of cell line‐conditioned medium to promote development beyond the second instar was greatly reduced (approximately 10–55%). Our studies demonstrated that to support the in vitro growth and development of E. puttleri, insect hemolymph could be successfully replaced with insect cell line‐conditioned medium. These findings should facilitate the development of a cost‐effective mass‐rearing system for E. puttleri and/or other parasitoids. Arch. Insect Biochem. Physiol. 40:173–182, 1999. Published 1999 Wiley‐Liss, Inc. This article is a US Government work and, as such, is in the public domain in the United States of America.