The form and variability of temperature‐dependent development responses were measured for the braconid parasitoid Meteorus trachynotus (Vier.), developing in Choristoneura fumiferana (Clem.) and C. rosaceana (Harr.). It was found that parasitism reduces the duration and variability of postdiapause development in C. rosaceana larvae, and that the development of the parasitoid does not resume until its host emerges from diapause. M. trachynotus development and entry into diapause are controlled by the host. In large, nondiapausing hosts, the parasitoid can complete one generation in about 348 degree‐days above 5.9 °C. Male and female adults live an average of 22.0 and 23.8 days at 20 °C, and the preoviposition period is 1.7 days. Total fecundity averages 194.2 eggs per female and is reduced considerably by low host density. Under our experimental conditions, female M. trachynotus lay a maximum of 14.3 eggs per day, with a maximum of 3.7 eggs per host, on average. Simulations based on degree‐day accumulation in 13 locations in eastern Canada showed that the parasitoid was well synchronized with its two alternative hosts, that M. trachynotus could complete three generations in most locations, and that voltinism was essentially determined by entry of C. rosaceana larvae into diapause. Overlap between adult parasitoids and larvae of the spruce budworm is incomplete, and inadequate synchrony seems to be an important aspect of the ecological interactions between these two organisms. Résumé Nous avons mesuré la forme et la variabilité des réactions de cause à effet entre la température et le développement de la braconide Meteorus trachynotus (Vier.) se développant à l'intérieur de larves de Choristoneurafumiferana (Clem.) et de C. rosaceana (Harr.). Le parasitisme réduit la durée et la variabilité de la postdiapause de C. rosaceana, et le développement du parasitoîde ne reprend qu'une fois l'hôte émergé de diapause. Le développement et l'entrée en diapause de M. trachynotus sont sous le contrôle de l'hôte. Dans des larves‐hôtes agées et non diapausantes, le parasitoîde peut engendrer une génération en moins de 348 degrés‐jours au‐dessus de 5,9 °C. Les adultes mâles et femelles vivent en moyenne 22,0 et 23,8 jours à 20 °C, et la période de préoviposition est de 1,7 jour. La fécondité totale est de 194,2 oeufs par femelle, et une faible densité d'hôtes la réduit considérablement. Dans nos conditions expérimentales, les femelles de M. trachynotus pondent au plus 14,3 oeufs par jour, la moyenne maximale étant de 3,7 oeufs par hôte. Des simulations basées sur l'accumulation de degrés‐jours pour 13 endroits dans l'est du Canada ont indiqué que le parasitoîde est bien synchronisé avec ses deux hôtes alternants, que M. trachynotus peut engendrer jusqu' à trois générations par année dans la plupart des endroits, et que son voltinisme est déterminé essentiellement par l'entrée en diapause des larves de C. rosaceana. Le chevauchement entre la période de vol des adultes du parasitoîde et celle de la disponibilité des larves ...

Tranosema rostrale (Brishke) (Hymenoptera, Ichneumonidae) and Actia interrupta Curran (Hymenoptera: Tachinidae) are the two endoparasitoids most frequently encountered in low-density populations of the spruce budworm, Choristoneura fumiferana (Clemens) (Lepidoptera, Tortricidae), in the Quebec City region. Monitoring of attack rates of implanted C. fumiferana larvae at two different study sites suggested the possible existence of competition between the two parasitoids, with A. interrupta seemingly displacing T. rostrale. Here, we show that multiparasitism involving these two species does occur in the field, but at a frequency too low to explain the seasonal pattern of decline in apparent parasitism by T. rostrale that accompanies the rise of A. interrupta attack rates. We also provide preliminary evidence, from laboratory experiments, that A. interrupta has a competitive advantage over T. rostrale and that the success of parasitism by A. interrupta may be enhanced by prior parasitism by T. rostrale under certain conditions, possibly due to the presence of the latter species' polydnavirus. In addition, we describe a PCR-based method that we developed to help detect the presence of T. rostrale eggs which often escape detection by simple visual examination of the dissected host larvae; DNA sequences specific to the polydnavirus injected by the female wasp at the time of oviposition can be readily amplified from whole host larvae.

The immature stages of Meteorus trachynotus Vier., developing in larvae of Choristoneura fumiferana (Clem.), are described. The egg of M. trachynotus is of the stalked type. There are three larval stages. The first instar has a caudal appendage which stops growing in the second instar and is lost when the larva exits from the host in the third instar. Only the first and third instars have sclerotized structures. The head region of the first instar bears a pair of hooklike appendages which are described for the first time. Cephalic sclerites of the last instar larva of other species of Meteorus are compared with those of M. trachynotus. The average duration of immature development at 23 °C was 18 days, the egg stage lasted 3 days, the first, second, and third instars lasted 5, 2.5, and 2.5 days, respectively, and the pupal stage lasted 5 days.

This article is the third and last of a series of models developed to investigate the impact of climate on the spatiotemporal biology of parasitoids. After two earlier papers investigating Tranosema rostrale and Meteorus trachynotus, this last article concerns the tachinid fly Actia interrupta (Diptera: Tachinidae). An individual-based model of the seasonal biology of A. interrupta was developed to determine the impact of climate on its interactions with two of its hosts, the spruce budworm Choristoneura fumiferana (Lepidoptera: Tortricidae) and the obliquebanded leafroller C. rosaceana in eastern North America. The model is based on the developmental responses of ‘the parasitoid’s successive life stages and the ovipositional response of adult females to temperature. It was found that the number of generations this parasitoid undergoes each year varies geographically from two to four, and that its potential growth rate, as dictated by synchrony with larvae of its overwintering host C. rosaceana, is highly patterned geographically and topographically as a result of phenological matching with larvae of obliquebanded leafroller entering diapause in late summer.

This is the second article of a series of three where we develop temperature-driven models to describe the seasonal interactions between parasitoids and their hosts which we use to explore the impact of climate on their spatiotemporal biology. Here, we model the biology of Meteorus trachynotus (Hymenoptera: Braconidae) with an individual-based model of its daily interactions with two host species. This model predicts the performance of the parasitoid in response to temperature affecting its seasonal development and that of the two hosts. We compare model output with an extensive set of field observations from natural host populations. The predicted activity of the first adult parasitoid generation closely matches the seasonal pattern of attack on the spruce budworm, Choristoneura fumiferana (Lepidoptera: Tortricidae) within the limitations of available data. The model predicts 1–4 full generations of M. trachynotus per year in eastern North America, with generations well synchronized with larvae of a known overwintering host, the obliquebanded leafroller Choristoneura rosaceana. The model predicts the observed density dependence of parasitism on spruce budworm. Predicted performance exhibits spatial variation caused by complex life-history interactions, especially synchrony with the overwintering host. This leads to a better performance in warm but not hot environments at middle latitudes and elevations. The model’s predicted spatial patterns correspond closely to our field observations on the frequency of parasitism on spruce budworm. Under climate change, the model predicts that the performance of M. trachynotus populations will improve in the northern portion of its range.

No abstract