Modeling Climatic Influences on Three Parasitoids of Low-Density Spruce Budworm Populations. Part 1: Tranosema rostrale (Hymenoptera: Ichneumonidae)

Abstract

Despite their importance as mortality factors of many insects, the detailed biology and ecology of parasitoids often remain unknown. To gain insights into the spatiotemporal biology of insect parasitoids in interaction with their hosts, modeling of temperature-dependent development, reproduction, and survival is a powerful tool. In this first article of a series of three, we modeled the biology of Tranosema rostrale at the seasonal level with a three-species individual-based model that took into account the temperature-dependent performance of the parasitoid and two of its hosts. The predicted activity of the first adult parasitoid generation closely matched the seasonal pattern of attack on the spruce budworm, Choristoneura fumiferana (Lepidoptera: Tortricidae). The model predicted 1–4 full generations of T. rostrale per year in eastern North America. The generations were generally well synchronized with the occurrence of larvae of a probable alternate host, the obliquebanded leafroller Choristoneura rosaceana (Lepidoptera: Tortricidae), which could be used as an overwintering host. Spatial differences in predicted performance were caused by complex interactions of life-history traits and synchrony with the overwintering host, which led to a better overall performance in environments at higher elevations or along the coasts. Under a climate warming scenario, regions of higher T. rostrale performance were predicted to generally move northward, making especially lower elevations in the southern range less suitable.

Modeling Climatic Influences on Three Parasitoids of Low-Density Spruce Budworm Populations. Part 2: Meteorus trachynotus (Hymenoptera: Braconidae)

“…However, OBL undergoes at least a partial second generation in Quebec, which suggested the proportion of C. rosaceana larvae entering diapause in August may vary considerably from year to year [26]. A recently-developed model of OBL phenology confirms this convincingly [14].…”

“…This simulation model follows the general design of a model of interactions between Tranosema rostrale (Brischke) (Hymenoptera: Ichneumonidae) and the same two hosts [14]. It is an individual-based model, using the life-cycle modeling approach described by Reference [33].…”

“…Development of the parasitoid does not begin until its overwintering host emerges from the hibernaculum [25]. Model inputs are daily minimum and maximum air temperatures and time-series of abundances of SBW and OBL larvae provided by their respective seasonal biology models [14,32], used by the host-attack component. The model outputs daily, for each generation, the number of parasitoid individuals in each life stage, the number dead from various causes (freezing, adult in old age), as well as the number of host larvae of SBW and OBL (feeding or in diapause).…”

“…We know that parasitoids play a key role in the decline of outbreaks [3,4,7] and during the prolonged period between outbreaks [8][9][10]. Most of those species are poorly understood, and we are just beginning to fill-in these knowledge gaps [11][12][13][14].…”

“…In this paper, we report on the development of an individual-based simulation model of the seasonal biology of M. trachynotus and of its interaction with two of its hosts, SBW and OBL, which is based on data from Reference [25] on the relationships between temperature and development, and the existing seasonality models for SBW [32] and OBL [14]. This is the second of a series of articles using this methodology to study the response of trophic interactions to climate.…”