Megastigmus and conifers: the biology of invasion – MACBI

We address this objective by gathering information at multiple scales from both plant and insect: (1) mechanism of host manipulation by deep-sequencing host and parasite transcripts, (2) microbial associates of Megastigmus, (3) phenologies of Megastigmus species in relation to host ovule phenology, (4) molecular phylogeny of Megastigmus, (5) mecanico-statistical models of invasions, (6) ecological impacts of invasion by seed pests.

(2) host manipulation may not involve microbial associates. In progress.
(3) the fitness of some Megastigmus species does not depend on pollination success of the host ovule.
(4) Molecular systematics and phylogeography studies are still in progress.
(5) Dominant winds are passive dispersal vectors for Megastigmus. in progress.
(6) Invasions may affect both resident fauna and host plant dynamics. In progress

The work accomplished during the first 18 months provided critical novel insights on the problematic. Knowledge on microbial associates of Megastigmus and their role will be increased. Light will be shed on the evolutionary history of Megastigmus by finalizing the molecular phylogenies currently in progress. Diverse modelling approaches will allow testing numerous scenarios on the interactions of invasive Megastigmus species with invaded ecosystem components.

2 publications in peer-reviewed international journals.
3 communications in national and international congresses.

Forests are an enormous economic resource in Canada and France. Not only do they represent an immediately exploitable resource, they are renewable and sustainable. The health of forests is highly susceptible to environmental effects. These range from abiotic factors, such as changes in weather patterns, and biotic factors, such as pests and diseases. Insect invasions due to the global seed trade are now becoming extensive. Seed parasites that destroy conifer seed crops are essentially invisible as the parasites move undetected within seed lots shipped from continent to continent. An added risk is that invasions by one species are often occasions for invasion complexes to develop. Diseases such as fungi travel with new insects, doubling the threat to forest health. Our ability to predict the influence of insects and diseases on future landscapes depends on how well we understand the relationship between immobile trees and highly mobile insects. Tree seed insects damage forests and plantations in both countries, affecting native species of plants as well as the animals that depend on them. The success of seed insects is due to their ability to bypass barriers in the developing plant ovule. If we wish to manage seed insects, we require basic information about how the insect takes over a seed's physiology, then moves through a species into other ones, and finally, how it then moves across a landscape. We will look at the highly invasive species of chalcid wasps in the genus Megastigmus (Hymenoptera; Torymidae), which cause extensive damage. M. spermotrophus is found on Douglas-fir. We will deep sequence the seeds and the insects to determine putative mechanisms of physiological control of the plant by the insect. In addition, we will investigate both the insect's and tree's phenologies to decipher how Megastigmus species are able to infest trees in the Pinaceae and Cupressaceae. This information, coupled with phylogeny of the chalcids, will be used to develop models of future invasion. To tackle these international problems caused by global seed exchange we have assembled a team of Franco-Canadian experts in Megastigmus-conifer seed interactions including those specialized in plant and animal reproduction, forest pest surveys, entomology and modeling.