Retracing the routes of invasions and determining the origins of invading species is often critical in understanding biological invasions. The Western conifer seed bug, Leptoglossus occidentalis, an insect native of western North America, was first accidentally introduced to eastern North America and then to Europe. The colonization of the entire European continent occurred in ca. 10-15 years, probably promoted by independent introductions in different parts of Europe. A multi-marker approach (mtDNA and microsatellites) combined with approximate Bayesian computation analyses was used to track the origin of European populations and to determine whether this rapid invasion was caused by multiple introductions. Our results show that at least two independent introductions of L. occidentalis have occurred in Europe. Moreover, the analyses showed a stronger genetic similarity of European invasive populations with the eastern North American populations than with those of the native range, suggesting that invasive North American population acted as a bridgehead for European invasion. The results also revealed that natural dispersal as well as human-mediated transportations as hitchhikers probably enhanced the rapid spread of this invasive pest across Europe. This study illustrates the complexity of a rapid invasion and confirms that bridgehead and multiple introductions have serious implications for the success of invasion.
Stone cells are a physical defence of conifers against stem feeding insects such as weevils and bark beetles. In Sitka spruce, abundance of stone cells in the cortex of apical shoot tips is associated with resistance to white pine weevil. However, the mode of action by which stone cells interfere with growth and development of weevil larvae is unknown. We developed a bioassay system for testing potential effects of stone cells, which were isolated from resistant trees, on weevil larvae. Bioassays using artificial diet and controlled amounts of stone cells focused on physical defence. We evaluated the effects of stone cells on establishment of neonate larvae, mandible wear and changes in relative growth rates of third instar larvae. Establishment of neonates and relative growth rates of third instars were significantly reduced by stone cells. Stone cells appeared to be indigestible by weevil larvae. Our results suggest that stone cells affect weevil establishment and development by forming a physical feeding barrier against neonate larvae at the site of oviposition, and by reducing access to nutrients in the cortex of resistant trees, which contain an abundance of stone cells in place of a more nutrient rich tissue in susceptible trees.
We report that a chemical stimulus from a herbivore, a galling insect, changes plant morphology and physiology to benefit the herbivore. Previous studies could not determine whether insect galls are induced by mechanical or chemical stimuli because feeding and oviposition both occurred at the site of gall formation. We report that the mouthparts of a spruce‐galling insect, Adelges cooleyi, were inserted in stem phloem cells far from induced galls, that tissues between mouthparts and galls appeared normal, and that the ability to initiate galls was inversely correlated with distance from buds (potential gall sites). Thus the effects of chemical stimuli were unambiguously separated from any mechanical influence of probing stylets or ovipositors. Our results strongly suggest that galls were induced by a chemical stimulus transported to buds via vascular tissue and that its efficacy was dose‐dependent.
The sex pheromone of the fir coneworm moth consists of a blend of (3Z,6Z,9Z,12Z,15Z)-pentacosapentaene and (9Z, 11E)-tetradecadienyl acetate. Analogous blends of polyunsaturated, long-chain hydrocarbons with much shorter chain aldehydes or alcohols recently have been discovered in three other moth species in the superfamily Pyraloidea. These combinations of components from two distinct structural classes may represent an important and widespread new pheromone blend motif within the Lepidoptera.
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