Life histories and host specificities of theEchium flea beetlesLongitarsus echii andL. Aeneus [Col. Chrysomelidae]
Two halticine flea beetles,Longitarsus echiiKoch andLongitarsus aeneusKutsch, occurring on the boraginaceous plantEchium plantagineum L. in the western Mediterranean region are potential biological control agents in Australia where the plant has become a weed (Paterson's curse). The adults of both species feed by making “shot holes” in the leaves. The larvae of both species attack the roots ofEchium, those ofL. echii feeding more centrally in the root than those ofL. aeneus which attack the outer cortex and rootlets. Both species are univoltine. The host restrictions of both flea beetles as adults and as larvae were tested using the criteria already established for theEchium leaf minerDialectica scalariellaZeller (Wapshere & Kirk, 1977). This testing established that it would be safe to introduce the 2 insects into Australia for the biological control ofE. plantagineum and they are now under quarantine.RésuméDeux altises,Longitarsus echiiKoch etLongitarsus aeneusKutsch, vivant surEchium plantagineum L. dans l'ouest de la région méditerranéenne, sont des agents de contrôles biologiques potentiels de cette adventice en Australie. Les adultes des 2 espèces creusent des trous dans les feuilles et leurs larves attaquent les racines de la plante. Les larves deL. echii se nourrissent plus de la partie centrale de la racine, alors que celles deL. aeneus préfèrent le cortex extérieur et les radicelles. Les 2 espèces ont une génération par an. La spécificité d'hôte des 2 espèces, tant adultes que larves, a été étudiée selon les critères déjà établis pourDialectica scalariellaZeller (Wapshere & Kirk, 1977). Ces essais ont confirmé que l'introduction des 2 insectes en Australie pour la lutte biologique contreEchium plantagineum serait sans danger, et cette introduction a eu lieu récemment.
Observations on the heliotrope flea beetle,Longitarsus albineus [Col.:Chrysomelidae] with tests of its host specificity
Longitarsus albineus (Foudras) is a potential agent for the biological control ofHeliotropium europaeum L. in Australia. The adults feed on the leaves and the larvae on the rootlets of the weed. Large populations of the beetle reduce plant vigour but rarely cause death of well established plants in the Mediterranean region. There are 3 beetle generations per year in southern France. Third generation adults overwinter and, at the first appearance of the weed in spring, start to feed and reproduce. Feeding trials of adults and larvae against a range of economically important plants and severalBoraginaceae demonstrated specificity to the genusHeliotropium.RésuméLongitarsus albineusFoudras est un auxiliaire possible de lutte biologique contre l'adventiceHeliotropium europaeumLinnaeus en Australie. Les adultes se nourrissent des feuilles et les larves des radicelles d'héliotrope. Par forte infestation, le longitarse affecte la vigueur de la mauvaise herbe, dont il détermine rarement le dépérissement en région méditerranéenne. Le longitarse a 3 générations annuelles dans le midi de la France. Les adultes de la 3e génération hivernent, s'attaquant aux premières pousses d'héliotrope et se reproduisant dès le printemps. Des essais d'alimentation portant sur une série de plantes cultivées et plusieurs boraginées ont montré que larves et adultes sont spécifiques au genreHeliotropium.
When to Cross the Spread? Trading in Two-Sided Limit Order Books
In this paper the problem of optimal trading in illiquid markets is addressed when the deviations from a given stochastic target function describing, for instance, external aggregate client flow are penalized. Using techniques of singular stochastic control, we extend the results of [F. Naujokat and N. Westray, Math. Financ. Econ., 4 (2011), pp. 299--335] to a two-sided limit order market with temporary market impact and resilience, where the bid ask spread is now also controlled. In addition to using market orders, the trader can also submit orders to a dark pool. We first show existence and uniqueness of an optimal control. In a second step, a suitable version of the stochastic maximum principle is derived which yields a characterization of the optimal trading strategy in terms of a nonstandard coupled forward-backward stochastic differential equation (FBSDE). We show that the optimal control can be characterized via buy, sell, and no-trade regions. The new feature is that we now get a nondegenerate no-...