Community structures of Collembola in sugar maple forests: relations to humus type and seasonal trends

Community structures of Collembola and their seasonal fluctuations were studied in eight southern Quebec sugar maple (Acer saccharum Marsh.) forests growing on mull, moder and mor humus types. Endogeic species were extracted from soil cores using Berlese-Tullgren funnels while epigeic species were collected using pit-light traps (Luminoc®). Comparisons of species presence, abundance, and dominance among sites and seasons were done using Sorensen's similarity coefficients and CANOCO. A total of 92 species from 7 families and 35 genera were identified. Species dominance and community structure differed according to humus types. Two groups of endogeic species were identified. The mor/mor-moder type group included Folsomia penicula, Hypogastrura (Ceratophysella) spp. Que., Micrisotoma achromata, Onychiurus (Protaphorura)? parvicornis, Onychiurus (Onychiurus) sp. A Que. And Onychiurus (Onychiurus) sp. B Que. The mull/mull-moder type group included Isotoma (Desoria) notabilis, Tullbergia (Tullbergia) silvicola, Tullbergia (Tullbergia) clavata, and Pseudosinella alba. Such clear humus type relationships were not found among the epigeic species, but important seasonal changes in community structures were found for these species. Spring species were Sminthurinus (Katiannina) macgillivrayi, Hypogastrura (Ceratophysella) maheuxi, Hypogastrura (Hypogastrura) sp. A Que. and Sminthurinus (Sminthurinus) latimaculosus. Tomocerus (Pogonognathellus) flavescens, Sminthurinus (Sminthurinus) henshawi, and Orchesella hexfasciata appeared in the summer samples while Dicyrtoma (Dicyrtoma) aurata was found only in fall samples where it was dominant in most sites along with either Sminthurides (Sminthurides) lepus or Sminthurinus (Sminthurinus) quadrimaculatus. No strong seasonal trends were found among the dominant endogeic species.     

Biological effects and metabolism of fenoxycarb after treatment of the fourth and the fifth instars of the tobacco budworm,Heliothis virescens F.

Treatment of 4th and 5th instar larvae of Heliothis virescens with different amounts of fenoxycarb induced an increase in weight of the 5th larval instar, prolongation of the 5th larval instar period, or the formation of dauer larvae. No effects were observed during the 4th instar and the moult to the 5th larval instar. To check whether these effects were due to persistence of fenoxycarb in treated larvae, metabolism of this chemical was analysed. Larvae were fed with radio-labelled fenoxycarb at the first day of the 4th or at the first day of the 5th larval instar. Behaviour of the radio-labelled compounds was followed during each instar. At the time of gut purge, the whole of the radio-labelled material was excreted. The effects observed during the 5th instar of 4th-instar-treated larvae do not appear to be due to the persistence of fenoxycarb. The main metabolites of fenoxycarb were identified using coupled gas chromatography and mass spectrometry.     

Interaction of benzimidazole-N-sulfonamides with the cytochrome b/c1 complex of Pythium aphanidermatum

Experiments with intact cells and submitochondrial fractions of Pythium aphanidermatum (Edson) Fitz. indicated an interference of benzimidazole-N-sulfonamides with the NADH- or succinate-driven electron transport system between cytochromes b and c. Comparison with Ustilago maydis (DC) Corda and Botrytis cinerea Pers. ex Fr. revealed that this effect is Oomycetes specific. The molecular interaction between benzimidazole-N-sulfonamides and the mitochondrial cytochrome b/c₁ complex from P. aphanidermatum has been investigated. Binding assays with [¹⁴C]52232 RP (dimefluazole) indicated a time- and dose-dependent labelling of two proteins. The molecular mass of one labelled protein and the competition of the binding with antimycin A suggest that benzimidazole-N-sulfonamides interact with the Q₁-centre of cytochrome b. Furthermore, experiments with doubly labelled [³H][¹⁴C]CGA 323103 revealed a possible irreversible inactivation of the b/c₁ complex leading to covalent linkage of the dimethylsulfonamoyl moiety to the target site.     

Oils for weed control: Uses and mode of action

The role of oils in herbicide treatments is reviewed, both in terms of their own intrinsic activity and of their enhancement of the performance of other herbicides. The phytotoxicity of oils can be related to their physical properties. Their efficacy as adjuvants can vary with the plant/pesticide combination involved, and differences may also be observed between oils of mineral and vegetable origin. The possible mechanisms involved in the enhancement of activity by oils are discussed and areas of work that might elucidate these fun her are indicated.     

Babesia odocoilei infection in elk

Two male North American elk from a commercial herd were evaluated because of a sudden onset of lethargy, anorexia, and voiding of red urine. These 2 elk were kept in the same pen as 4 other male elk that had died during the preceding 2 months. Laboratory analyses revealed anemia and intraerythrocytic parasites, later confirmed as Babesia odocoilei (a protozoal hemoparasite of cervids). Of the 240 elk remaining in the herd, 59 were screened for B odocoilei by microscopic evaluation of blood smears, protozoal culture of blood, and immunofluorescent antibody testing of serum. Of those 59 elk, 34 (58%) were infected with B odocoilei. Babesia odocoilei infection in elk can be fatal and should be considered in cases of sudden death or acute hemolytic anemia. Familiarity with the disease in elk is essential for practitioners because of the increasing popularity of commercial elk farming.     

Controlling Echinococcus multilocularis-ecological implications of field trials

Two field trials to reduce the prevalence of Echinococcus multilocularis in foxes have been conducted in recent years. Although both trials reduced prevalence considerably, they failed to eradicate the parasite in the study region. Following the control trial in northern Germany, prevalence recovered unexpectedly and rapidly, reaching pre-control levels five quarters (15 months) after the end of control. To understand the internal dynamics of the parasite-host system's reaction to control, we developed a spatially explicit simulation model, Echi. The simulation model incorporates the information available concerning fox tapeworm population dynamics.Using epidemiological parameters to adjust pre-control prevalence, the model predicts the temporal evolution of the prevalence of E. multilocularis in controlled foxes without departing from the range of uncertainty of the field data. However, the model does not predict the rapid pre-control recovery observed in the field trial.The deviation of the model's prediction from field data indicates the involvement of processes not yet taken into account. We modified the model step by step to mimic processes with the potential to cause the rapid post-control recovery of the prevalence of E. multilocularis in foxes.Neither the longevity of tapeworm eggs nor the migratory behaviour of foxes showed any influence on the post-control reaction of the parasite-host system. However, landscape structures leading to a heterogeneous distribution of infected foxes have the potential to alter the system's reaction to control. If infected foxes are concentrated in multiple clusters in the landscape, the model prediction tallied with the range of uncertainty of the field data. Such spatial distribution of infected foxes may be caused by differential abiotic conditions influencing the survival of tapeworm eggs.The model was found to comply best with field data if the foxes acquire partial immunity by being exposed to the fox tapeworm.Both hypotheses explaining the rapid post-control recovery of the prevalence of E. multilocularis observed in the fox population were supported by field data.Both hypotheses have far-reaching consequences for future control trials. The spatial aggregation of infected foxes would enable control efforts to be concentrated on these highly infected areas. However, the acquisition of immunity acts as a buffer to control, necessitating intensified control measures.     

苹果叶幕大小对产量的影响

以6个苹果品种为试材,进行苹果的有效负载面积与产量相关性试验.结果表明:在一定条件下,有效负载面积(EBS)越大,产量相应越高.不同纬度对不同品种的EBS和产量的影响不同.土壤中砾石含量对EBS和产量都有影响,但品种和砧木不同,EBS的减少率不同.不同品种对砾石的耐受能力不同.