Temperature preference and respiration of acaridid mites

The thermal preferences in a grain mass and respiration at various temperatures in mites (Acari: Acarididae) of medical and economical importance [Acarus siro (L. 1758), Dermatophagoides farinae Hughes 1961, Lepidoglyphus destructor (Schrank 1871), and Tyrophagus putrescentiae (Schrank 1781)] were studied under laboratory conditions. Based on the distribution of mites in wheat, Triticum aestivum L., grain along a thermal gradient from 10 to 40 degrees C, L. destructor, D. farinae, and A. siro were classified as eurythermic and T. putrescentiae as stenothermic. The lowest preferred temperature was found for D. farinae (28 degrees C), followed by A. siro (28.5 degrees C), L. destructor (29.5 degrees C), and T. putrescentiae (31.5 degrees C). The relationship between the respiration rate and the temperature was similar for all four mite species. The highest respiration was found in the range from 31 to 33 degrees C. This is approximately 2 degrees C higher than the preferred temperature of these species. The lower temperature threshold of respiration ranged from 1 to 5 degrees C and the upper threshold ranged from 45 to 48 degrees C. Acclimatization of A. siro to temperature regimes of 5, 15, and 35 degrees C resulted in thermal preferences between 9 and 12 degrees C, 9 and 20 degrees C, and 28 and 35 degrees C, respectively. The respiration rate of acclimatized specimens increased with the temperature, reaching a maximum at 29.0 degrees C for mites acclimatized at 5 and 15 degrees C and a maximum at 33.7 degrees C for those acclimatized at 30 degrees C.

Application of ARDRA and PLFA analysis in characterizing the bacterial communities of the food, gut and excrement of saprophagous larvae of Penthetria holosericea (Diptera: Bibionidae): a pilot study

Amplified ribosomal DNA restriction analysis (ARDRA) was used to compare the bacterial communities of the food, the gut sections (ceca, anterior and posterior midgut, hindgut) and the excrement of the litter feeding bibionid larvae of Penthetria holosericea. For universal eubacterial primers ARDRA patterns were complex with only minor differences among samples. Taxon specific primers were also applied to characterize the samples. Fragment composition was transformed to presence/absence binary data and further analyzed. Cluster analysis revealed that bacterial communities of gut highly resembled each other with the exception of the ceca. ARDRA patterns of consumed leaves clustered together with the intact leaves but differed from those of the excrement. ARDRA results were compared with microbial community structure based on phospholipid fatty acid (PLFA) fingerprints. The cluster analysis of PLFA (presence/absence binary) data resulted in a pattern similar to the ARDRA data. The PCA analysis of PLFA relative content separated microbial communities into five groups: (1) anterior and posterior midgut, (2) hindgut, (3) ceca, (4) consumed and intact litter, (5) excrement. Both methods indicated that conditions in the larval gut result in formation of a specific microbial community which differs from both the food and excrement ones. Particularly ceca--(blind appendages, harbor very specific microbial community) are divided from the rest of the gut by perithropic membrane.

Changes in amount of bacteria during gut passage of leaf litter and during coprophagy in three species ofBibionidae (Diptera) larvae

To elucidate the interaction between bacteria and saprophagous Diptera larvae, the amounts of bacteria in leaf litter, individual gut compartments, and feces of three species of Bibionidae (Bibio pomonae, Bibio marci, and Penthetria holosericea), feeding either directly on leaf litter or on fecal pellets produced from leaf litter by larvae of the same species, were assessed by determining total direct counts and viable counts on solid media at different pH. In P. holosericea, the effect of various cultivation temperatures on direct counts of bacteria in individual compartments was also demonstrated. In all species, the amount of bacteria in the anterior mesenteron was lower than in the consumed food, regardless of whether the larvae were feeding on leaf litter or feces, and increased again in the posterior part of the gut. The amount of bacteria in these compartments was generally higher in larvae feeding on feces than in those feeding on leaf litter, whereas the amount of bacteria found in the ceca varied. In B. marci, the amount of bacteria in the mesenteron sections able to grow on alkaline medium (pH 9) was higher than that of bacteria able to grow on slightly acidic medium (pH 5.5) during both the first and the second gut passage. In B. pomonae and P. holosericea, this increase was observed only during the second gut passage. The effect of gut passage in P. holosericea on changes in direct counts of bacteria was more pronounced when the larvae were fed at 5 degrees C as compared to 20 degrees C. Radiolabeled bacteria were digested in the gut and utilized as a source of energy and nutrients by the larvae; digested bacteria represented up to 10% of the material assimilated by the larvae. Lysozyme activity in whole-gut extracts of P. holosericea had a pH optimum of at pH 7, indicating a low in situ activity in the alkaline mesenteron. Proteinase activity, however, had an optimum at pH > 12, suggesting that the digestion of bacteria in the bibionid gut is caused by a combination of digestive proteinases and alkaline pH in the anterior mesenteron.

Temperature dependence and acclimatory response of amylase in the High Arctic springtail Onychiurus arcticus (Tullberg) compared with the temperate species Protaphorura armata (Tullberg)

Amylolytic activity was measured in whole body homogenates of High Arctic (Onychiurus arcticus) and temperate (Protaphorura armata) springtails (Collembola: Onychiuridae) in the temperature range 5-55 degrees C. A pH of ca. 8 was optimum for amylolytic activity in both species. A higher weight-specific amylolytic activity was observed in P. armata. In O. arcticus, amylolytic activity depended on thermal acclimation, which increased during 2 and 9 weeks of cold acclimation (5 degrees C) and decreased over 7 weeks of warming (15 degrees C) of animals that were previously acclimated to cold for 2 weeks. In cold-acclimated O. arcticus, a slower decrease of amylolytic activity occurred with lowering of temperature in the range 5-20 degrees C in comparison with warm-acclimated specimens and P. armata, which resulted in higher activity at 5 degrees C. The activation energy calculated from an Arrhenius plot for P. armata was 68.7 kJ.mol(-1). In O. arcticus it was between 30.2 and 61.5 kJ.mol(-1), being lower in cold-acclimated samples. The temperature optimum for amylolytic activity was higher in the temperate species (40 degrees C), whilst in O. arcticus it depended on the acclimation regime: it rose to 35 degrees C after warm acclimation and decreased to 20 degrees C after cold adaptation. The total soluble protein content of body tissues of O. arcticus also increased during cold acclimation. These differences between the two species suggest that amylolytic activity is an indicator of cold adaptation in the High Arctic O. arcticus.