No abstract

The potential impact of postdispersal seed predation by the field cricket, Teleogryllus emma (Ohmachi et Matsuura), on the seedling emergence of Italian ryegrass (Lolium multiflorum Lam.), a non-native grass weed in Japan, was determined. The relationship between cricket density and the proportion of seedling emergence was investigated by conducting manipulative experiments in duplicate, using enclosures. One-thousand seeds of Italian ryegrass were exposed to adult crickets at different densities (zero, one, two, four and eight individuals per 2.25 m 2 enclosure) for 2 weeks.The proportion of seedling emergence decreased with increasing cricket density. The proportion of seedling emergence in the enclosures without the crickets was 90.9-97.2%, whereas the seedling emergence in the enclosures with eight crickets greatly decreased, to 0.5-2.5%. These results suggest that postdispersal seed predation by T. emma can substantially decrease the abundance of Italian ryegrass at an early life stage and reduce its population in environments with a high density of crickets.

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Denitrification of paddy fields is a key process for improving water quality in fields where nitrate concentrations are high. The objective of the present study was to understand the effects of incorporating organic carbon (C) into soil on the denitrification rate of paddy fields in winter. On 11 December 2007, separate paddy field plots were prepared by incorporating 5 Mg ha )1 of rice straw (RS), 11 Mg ha )1 of rice straw compost (RSC) or a control. A field with a high concentration of nitrate in the water (averaging 18 mg N L )1 ) was irrigated until 29 March. During the experiment, the daily average soil temperature at a depth of 0.05 m ranged between 3 and 15°C. The nitrate concentration in the surface water in the RS plot, where the residence time was 2 days, decreased more than the concentration in the control or RSC plots. The total estimated nitrate removal from each plot in relation to the other plots was RS > RSC = control. Measurements of the soil from each plot on 29 February 2008 showed that incorporation of RS significantly increased the denitrification potential, even at low temperatures (5-10°C). Furthermore, the RS plot contained more dissolved organic C than the control or RSC plots. This result indicates that supplying RS effectively increases denitrification under low-temperature conditions.

We investigated whitefly species and their biotypes, PCR-positive individuals of Tomato yellow leaf curl virus (TYLCV), and leaf curl symptoms by collecting whitefly adults and observing the leaves of various crops in winter greenhouses in Shizuoka Pref., Japan. From January to February 2006, 48 collection sites and 5 kinds of crops were investigated. Leaf curl symptom was observed in 23 out of 36 tomato greenhouses. The whitefly in tomato greenhouses were collected from 23 Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) B biotype populations and 12 Trialeurodes vaporariorum (Hemiptera: Aleyrodidae) populations. The B. tabaci Q biotype was detected in only 2 separate poinsettia greenhouses. From strawberry and melon greenhouses, only Trialeurodes sp. and B. tabaci B biotype, respectively, were collected. TYLCV was detected in 13 out of 30 B. tabaci B biotype populations and in 6 out of 6 T. vaporariorum populations collected from tomato, poinsettia, and melon greenhouses, irrespective of the presence of leaf curl symptom. TYLCV was not detected in any B. tabaci Q biotype individuals.