The parasitoid Asecodes mento （Walker, 1839） （Hymenoptera： Eulophidae） is the most important biocontrol agent of the strawberry leaf beetle Galerucella tenella （L.） （Coleoptera： Chrysomelidae） in northern Eu...The parasitoid Asecodes mento （Walker, 1839） （Hymenoptera： Eulophidae） is the most important biocontrol agent of the strawberry leaf beetle Galerucella tenella （L.） （Coleoptera： Chrysomelidae） in northern Europe. Here, I investigated whether natural parasitism in organic strawberry plantations was affected by the presence of the alternative host plant meadowsweet （Filipendula ulmaria）, and whether parasitism rates differed between plantations of different ages （6 to 79 years）. I also investigated whether parasitoid brood size, body size and sex ratio differed between the two host plants in the field. Parasitism was very low （0%） in newly established plantations and increased to a plateau （~40%） in fields where strawberries had been grown for approximately 20 years or longer. Such an extended colonization process is unacceptable for commercial growers. It would thus be desirable to find a method to catalyze parasitoid population buildup in young plantations. Parasitoid brood sizes were larger in beetles collected from meadowsweet, while body size and sex ratio did not differ between parasitoids collected from the two plants. These findings suggest that meadowsweet can export parasitoids to neighboring strawberry fields. Although this is a possibility, I did not find any significant differences in parasitism rates between isolated strawberry fields and fields adjacent to meadowsweet stands, indicating that effects of local vegetation are small on parasitism rates. Releasing parasitoids in newly established strawberry plantations may be a better strategy for quickly obtaining high parasitism than intercropping with meadowsweet.展开更多
文摘The parasitoid Asecodes mento （Walker, 1839） （Hymenoptera： Eulophidae） is the most important biocontrol agent of the strawberry leaf beetle Galerucella tenella （L.） （Coleoptera： Chrysomelidae） in northern Europe. Here, I investigated whether natural parasitism in organic strawberry plantations was affected by the presence of the alternative host plant meadowsweet （Filipendula ulmaria）, and whether parasitism rates differed between plantations of different ages （6 to 79 years）. I also investigated whether parasitoid brood size, body size and sex ratio differed between the two host plants in the field. Parasitism was very low （0%） in newly established plantations and increased to a plateau （~40%） in fields where strawberries had been grown for approximately 20 years or longer. Such an extended colonization process is unacceptable for commercial growers. It would thus be desirable to find a method to catalyze parasitoid population buildup in young plantations. Parasitoid brood sizes were larger in beetles collected from meadowsweet, while body size and sex ratio did not differ between parasitoids collected from the two plants. These findings suggest that meadowsweet can export parasitoids to neighboring strawberry fields. Although this is a possibility, I did not find any significant differences in parasitism rates between isolated strawberry fields and fields adjacent to meadowsweet stands, indicating that effects of local vegetation are small on parasitism rates. Releasing parasitoids in newly established strawberry plantations may be a better strategy for quickly obtaining high parasitism than intercropping with meadowsweet.
