No abstract

We measured the concentrations of radiocesium ((134)Cs and (137)Cs) in a large web spider, Nephila clavata L. Koch (Nephilidae: Arachnida), collected at three sites at different distances from the Fukushima Dai-ichi Nuclear Power Plant about 1.5 y after the accident in March 2011. The radiocesium concentrations in spiders were highest in a streamside secondary forest 33 km northwest of the power plant: mean ± a standard deviation of 2.401 ± 1.197 Bq g(-1) dry for (134)Cs and 3.955 ± 1.756 Bq g(-1) dry for (137)Cs. In a hillside secondary forest 37 km northwest of the power plant, the mean concentrations of (134)Cs and (137)Cs were 0.825 ± 0.247 Bq g(-1) dry and 1.470 ± 0.454 Bq g(-1) dry, respectively. In a pine forest 62 km west of the power plant, very low radiocesium concentrations were detected, but in only a few individuals. The concentrations of (134)Cs and (137)Cs in spiders collected at each site tended to be correlated with the air radiation dose rate at each site. Since spiders are key components of food webs in forests, the high concentrations in this species at contaminated sites suggested that the radiocesium from the accident has transferred through food chains and reached to higher trophic level of the food chains.

No abstract

No abstract

Because insect herbivores generally suffer from high mortality due to their natural enemies, reducing the risk of being located by natural enemies is of critical importance for them, forcing them to develop a variety of defensive measures. Larvae of leaf-mining insects lead a sedentary life inside a leaf and make conspicuous feeding tracks called mines, exposing themselves to the potential risk of parasitism. We investigated the defense strategy of the linear leafminer Ophiomyia maura Meigen (Diptera: Agromyzidae), by focusing on its mining patterns. We examined whether the leafminer could reduce the risk of being parasitized (1) by making cross structures in the inner area of a leaf to deter parasitoids from tracking the mines due to complex pathways, and (2) by mining along the edge of a leaf to hinder visually searching parasitoids from finding mined leaves due to effective background matching of the mined leaves among intact leaves. We quantified fractal dimension as mine complexity and area of mine in the inner area of the leaf as interior mine density for each sample mine, and analyzed whether these mine traits affected the susceptibility of O. maura to parasitism. Our results have shown that an increase in mine complexity with the development of occupying larvae decreases the probability of being parasitized, while interior mine density has no influence on parasitism. These results suggest that the larval development increases the host defense ability through increasing mine complexity. Thus the feeding pattern of these sessile insects has a defensive function by reducing the risk of parasitism.