Dimethylsulfoniopropionate and dimethylsulfoxide in Posidonia oceanica

The present work aims at determining the natural variability of dimethylsulfoniopropionate (DMSP) and dimethylsulfoxide (DMSO) contents in the seagrass Posidonia oceanica, which is the largest producer of these molecules reported to data among coastal autotrophs. Samples were collected during a period of 3.5 years in the pristine Revellata Bay (Calvi, northwestern Corsica, France). The DMSP content ranged from 25 to 265 µmol.gfw−1; DMSO from 1.0 to 13.9 µmol.gfw−1. The dynamics of the two molecules were closely linked, the DMSO content being equivalent to 3.5 % of the DMSP content, all leaf samples considered (n = 423 samples and 414 DMSP(O) data pairs). The annual growth cycle of the seagrass diluted the initial stocks of the two molecules. Temperature indirectly affected molecule content dynamics through their direct effect on the seagrass productivity and biomass. Inter-annual variations in DMSP(O) content in relation to shallow water temperature might further indicate that DMSP(O) could have been involved in the physiological response of P. oceanica to heat-stress. Finally, middle-aged leaf tissues with an organosulfur molecule content similar to the average value calculated for the seagrass leaf bundle appeared to be the best choice of sample material to study DMSP and DMSO in that species. More research is needed to elucidate the biosynthetic pathways of these molecules in seagrasses, the evolutionary reasons for such a high production in P. oceanica and the physiological functions they play.

Role of Leaf Litter in Above-Ground Wood Decay

The effects of leaf litter on moisture content and fungal decay development in above-ground wood specimens were assessed. Untreated southern pine specimens were exposed with or without leaf litter contact. Two types of leaf litter were evaluated; aged (decomposed) and young (early stages of decomposition). The moisture content of specimens was monitored, and specimens were periodically removed for visual evaluation of decay development. In addition, amplicon-based sequencing analysis of specimens and associated leaf litter was conducted at two time points. Contact with either type of leaf litter resulted in consistently higher moisture contents than those not in contact with leaf litter. Visually, evident decay developed most rapidly in specimens in contact with the aged leaf litter. Analysis of amplicon-based sequencing revealed that leaf litter contributes a significant amount of the available wood decay fungal community with similar communities found in the litter exposed wood and litter itself, but dissimilar community profiles from unexposed wood. Dominant species and guild composition shifted over time, beginning initially with more leaf saprophytes (ascomycetes) and over time shifting to more wood rotting fungi (basidiomycetes). These results highlight the importance of the contributions of leaf litter to fungal colonization and subsequent decay hazard for above-ground wood.

Toxicity and Efficacy of Chlorantraniliprole on Pieris rapae (Linnaeus) (Lepidoptera: Pieridae) on Cabbage

Toxicity of chlorantraniliprole was assayed against young (first and second instars) and older larvae (third and fourth instars) of cabbage Pieris rapae (Lepidoptera: Pieridae) on cabbage (Brassicae oleracea), and persistence of field–aged leaf residue of chlorantraniliprole was assayed with 5-old-day larvae of P. rapae on cabbage. Efficacies of chlorantraniliprole and other newer insecticides to P. rapae were tested under field conditions for two seasons in Hubei province in China. The LC50 value of chlorantraniliprole for early and later P. rapae larvae were 7.92 and 11.34 mg/L by contact toxicity, respectively. The LC50 value of chlorantraniliprole for early and later P. rapae larvae were 0.95 and 4.32 mg/L through ingestion, respectively. The toxicity of field-aged leaf residues of chlorantraniliprole (0-, 3-, 5-, 7-, 10-, 14-, 21-, 25-, and 28-day-old residues) declined gradually under the field conditions. Almost all larvae died on day 5 after feeding on the leaves with 0-21-day residue, and the mortalities were as high as 83.3% and 72.5% for the 21- and 25-day-old leaf residues. Chlorantraniliprole application suppressed P. rapae larvae below the economic threshold for 21-28 days. The field efficacy trials show that chlorantraniliprole at 52 mg a.i /L rate was effective against P. rapae larvae on cabbage, providing marketable cabbage with three applications per season. In addition, chlorantraniliprole was as effective as indoxacarb and spinosad and significantly more effective than emamectin benzoate.