![]() ![]() Groups of mixed elms are much less vulnerable to pests than larger planting areas, and mass propagation will occur much less rapidly there. However, research into this possibility has not yet reached a point where this technique can be applied. One successful strategy could be to use specific parasitoids with a narrow spectrum of hosts. In addition, humans transport these insects long distances. Its natural propagation velocity has been demonstrated to range from 50 to 90 km per year. Furthermore, this invasive species' outstanding ability to fly certainly contributes to its propagation. Using pesticides is not recommended due to the lack of success experienced with these in trials in other countries. The species' use of asexual reproduction means a quick succession of generations (up to four a year). In gardens, parks or public green spaces in the autumn, the fallen leaves along with the attached winter cocoon may be raked together and destroyed in the autumn. However, there have not yet been any recorded cases of whole trees dying because of this pest. Damage caused by the zigzag elm sawfly has been observed in both forests and residential areas (gardens and roads where elms are planted for ornamental purposes or in avenues of trees).Ĭountermeasures are only possible to some extent. If this goes on for a number of years, it reduces tree vitality, thereby making the tree more vulnerable to secondary pests. Newly formed replacement leaves are in turn also attacked, in general killing off the affected twigs and branches. ![]() The larvae of this invasive species feed on elm leaves, causing high crown transparency, ranging from 75% to 100% even by the time summer arrives. Imagos hatch continuously from mid-May to mid-September. It has been shown both out in the open and in laboratory experiments that there may be u p to four generations of zigzag elm sawflies a year. The whole cycle from oviposition to hatching of the females of the next generation only takes one month. Such cocoons spend the winter attached to the leaves on the ground or in plant litter. The only type of cocoon that is more tightly spun is the one for hibernation. The larvae are pupated in a loosely spun, reticular cocoon on the underside of the leaf. In all, six larval stages are completed in the course of two to three weeks. ![]() By continuously feeding on the crown of a tree, larvae can cause high crown transparency, extending to complete defoliation in the worst case. Subsequently, more mature larvae eat away the entire leaf except the midrib, thereby eliminating traces of the zigzag feeding characterising the early larval stages. Larvae hatch from these just under a week later.Īn initial sign of their presence is the typical zigzag frass of the young larvae (giving them their name) which emerges between the lateral veins of the leaves, starting at the margins and moving towards the midrib. The females deposit up to 50 eggs individually at leaf margins. The species appears to only reproduce asexually. ![]()
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