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New ecological pest management of pernicious scale insects in Mediterranean forest and groves


In maritime pine stands in Portugal and Corsica, pine trees were baited with kairomone lures in order to attract local predators, to speed up the prey recognition and to favour the biological control of pine bast scale populations. In all stands, the increment of larval density was higher in control trees than in baited-trees. For the first time, the activation of kairomone lures has proved to enhance the biological control of an invasive pest by local generalist predators. However, further long-term studies are needed to validate the ability of the method to prevent incipient outbreaks and to test for a prolonged establishment of high populations of the predators in kairomone-baited stands, even after the kairomone lures have been removed.
In none of the low infested stands, where mass-trapping was applied to control M. feytaudi populations, the increment of larval density was lower than in control stand. Trap density was probably too low to catch a sufficient number of males to reduce the mating of a significant proportion of females. This indicate that mass-trapping should not be recommended to control Maritime pine bast scale populations The pheromone mass-trapping system was not sufficient to suppress the number of P. citri males attracted, probably mostly from outside the subplot. By contrast the proportion of infested fruits by the Citrus mealybug was consistently higher in mass-trapping than in control subplots. It is then assumed that only a small part of the attracted males from outside the subplot are trapped, the remaining flyers contributing to increase the percentage of fecundated females and, consequently, to raise the infestation level. A promising tactic to manage Citrus mealybug could rely on the combination of mass-trapping within the Citrus orchard with chemical interventions selectively applied at the edge of the orchard, in order to prevent the adverse effect of male attraction from outside the plot.
The new, scientifically innovative, syntheses of M. feytaudi, M. josephi, M. matsumurae and P. citri sex pheromones allow the use of commercial starting materials, they appears reproducible allowing to manufacture effective attractants at half industrial scale. They are therefore cheaper to produce and can now be extensively used.
Encapsulation is a common defence mechanism exerted by a host insect in response to invasion by parasitoids. It frequently leads to the death of the parasitoid and thus may adversely affect biological control by reducing parasitoid efficacy. New association between allopatric ecotypes of the parasitoid and citrus mealybug can result in low level of encapsulation and therefore more efficient biological control. Better control of the citrus mealybug in Portugal and Sicily could be achieved with the Israel and the Portuguese ecotypes of A. pseudococci, respectively.
Male M. feytaudi captures in one trap per ha, baited with the lowest dose (50µg) of pheromone is significantly correlated with larval densities from the same and the next generation. However, the correlation between trap captures and density of larvae fits a parabolic model, showing a decrease of male catches with very high densities of larvae. In outbreak conditions, females are probably competing with pheromone lures to attract available males. The use of pheromone traps is therefore proposed as an easy and reliable method to monitor and predict M. feytaudi populations trends in forests with low to moderate densities of scales where no symptoms of tree decay are yet observed. A positive relationship was found between citrus mealybug male capture and the percentage of fruits infested with colonies of young nymphs. Pheromone trapping is therefore proposed to figure out a new intervention threshold based on male capture early in the summer, i.e., 20 males/trap/day, one or two weeks after the male peak of the flight in June.