Review Behaviour and indirect interactions in food webs of plant-inhabiting arthropods

With the increased use of biological control agents, artificial food webs are created in agricultural crops and the interactions between plants, herbivores and natural enemies change from simple tritrophic interactions to more complex food web interactions. Therefore, herbivore densities will not only be determined by direct predator–prey interactions and direct and indirect defence of plants against herbivores, but also by other direct and indirect interactions such as apparent competition, intraguild predation, resource competition, etc. Although these interactions have received considerable attention in theory and experiments, little is known about their impact on biological control. In this paper, we first present a review of indirect food web interactions in biological control systems. We propose to distinguish between numerical indirect interactions, which are interactions where one species affects densities of another species through an effect on the numbers of an intermediate species and functional indirect interactions, defined as changes in the way that two species interact through the presence of a third species. It is argued that functional indirect interactions are important in food webs and deserve more attention. Subsequently, we discuss experimental results on interactions in an artificial food web consisting of pests and natural enemies on greenhouse cucumber. The two pest species are the two-spotted spider mite Tetranychus urticae and the western flower thrips, Frankliniella occidentalis. Their natural enemies are the predatory mite Phytoseiulus persimilis, which is commonly used for spider mite control and the predatory mites Neoseiulus cucumeris and Iphiseius degenerans and the predatory bug Orius laevigatus, all natural enemies of thrips. First, we analyse the possible interactions between these seven species and we continue by discussing how functional indirect interactions, particularly the behaviour of arthropods, may change the significance and impact of direct interactions and numerical indirect interactions. It was found that a simple food web of only four species already gives rise to some quite complicated combinations of interactions. Spider mites and thrips interact indirectly through resource competition, but thrips larvae are intraguild predators of spider mites. Some of the natural enemies used for control of the two herbivore species are also intraguild predators. Moreover, spider mites produce a web that is subsequently used by thrips to hide from their predators. We discuss these and other results obtained so far and we conclude with a discussion of the potential impact of functional indirect and direct interactions on food webs and their significance for biological control.     

Induction of the mRNA for CYP6B2, a pyrethroid inducible cytochrome p450, in Helicoverpa armigera (Hubner) by dietary monoterpenes

A cDNA clone encoding a cytochrome P450 from H. armigera was used to examine the expression of two homologous cytochrome P450 mRNAs, one of which, CYP6B2, is probably involved in pyrethroid metabolism. The mRNA for CYP6B2 in particular can be induced up to tenfold by peppermint oil and the monoterpene α-pinene as well as to a smaller extent by menthol, butylated hydroxyanisole, and piperonyl butoxide. Both mRNAs are present in the major larval tissues, midgut, fat body, and cuticle, although only the mRNAs in the midgut and fat body are inducible by peppermint oil. The induction is a rapid process occurring within a period of 4 h with a similarly rapid rate of decrease in the absence of the inducing compounds. During normal development both mRNAs are absent from eggs and increase during the larval stage, reaching a maximum during mid fifth instar. Both mRNAs then decrease to undetectable levels during pupation and remain undetectable in the adult stage. © 1997 Wiley-Liss, Inc.     

Attraction of a generalist predator towards herbivore-infested plants

The occurrence and strength of interactions among natural enemies and herbivores depend on their foraging decisions, and several of these decisions are based on odours. To investigate interactions among arthropods in a greenhouse cropping system, we studied the behavioural response of the predatory bug Orius laevigatus (Fieber) (Hemiptera: Anthocoridae) towards cucumber plants infested either with thrips (Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae)) or with spider mites (Tetranychus urticae Koch (Acari: Tetranychidae)). In greenhouse release-recapture experiments, the predatory bug showed a significant preference for both thrips-infested plants and spider mite-infested plants over clean plants. Predatory bugs preferred plants infested with spider mites to plants with thrips. Experience with spider mites on cucumber leaves prior to their release in the greenhouse had no effect on the preference of the predatory bugs. However, this experience did increase the percentage of predators recaptured. Y-tube olfactometer experiments showed that O. laevigatus was more attracted to odours from plants infested with spider mites than to odours from clean plants. Thus, O. laevigatus is able to perceive odours and may use them to find plants with prey in more natural conditions. The consequences of the searching behaviour for pest control are discussed.     

Die Cypriniden (Teleostei: Cypriniformes) des oberoligozänen Maares von Enspel nebst Bemerkungen zur Phylogenie und Biogeographie der Phoxininae

Palaeorutilus enspelensis (Böhme 1996), the only fish species from the Upper Oligocene maar lake Enspel (Westerwald), is described and its phylogenetical position within the subfamily Phoxininae is discussed. The cladistic analysis of osteological and lepidological features indicates that the genusPalaeorutilus Gaudant 1988 is a member of the Chub Clade. Furthermore, including of the recent Eurasian taxaLagowskiella andEupallasella in the analysis, the Chub Clade can be divided into two monophyletic Clades: the EurasianPhoxinus Clade (including the holarcticPhoxinus) and the eastern North American Creek Chub Clade which includes the fossil genusPalaeorutilus as its basal sister taxon. These phylogenetical investigation as well as the recent and fossil distribution pattern of the Phoxininae support the following biogeographical hypothesis: The settlement of cyprinids in North America took place in several waves and different directions. The separation of Western Clade and Chub Clade did not occur in North America but in Eocene times in Asia. Members of the Creek Chub Clade migrated from Europe to eastern North America via a transatlantic route prior to the Middle Miocene.     

Tracker: continuous HMMER and BLAST searching

SUMMARY: Tracker is a web-based email alert system for monitoring protein database searches using HMMER and Blast-P, nucleotide searches using Blast-N and literature searches of the PubMed database. Users submit searches via a web-based interface. Searches are saved and run against updated databases to alert users about new information. If there are new results from the saved searches, users will be notified by email and will then be able to access results and link to additional information on the NCBI website. Tracker supports Boolean AND/OR operations on HMMER and BLASTP result sets to allow users to broaden or narrow protein searches. AVAILABILITY: The server is located at http://jay.bioinformatics.ku.edu/tracker/index.html. A distribution package including detailed installation procedure is freely available from http://jay.bioinformatics.ku.edu/download/tracker/.     

Time course and extent of functional recovery during the first postoperative year after minimally invasive total hip arthroplasty with two different surgical approaches--a randomized controlled trial

While others have reported short-term comparisons between various minimally invasive surgical (MIS) approaches to total hip arthroplasty (THA) and their conventional analogues, longer-term data is lacking, as is information indicating whether MIS approaches to THA provide a biomechanically complete recovery. Furthermore, different MIS approaches have not been compared. Our approaches of interest were a one-incision modified Watson-Jones, and a two-incision approach. Hypotheses: (1) There are significant differences in gait recovery patterns between the two surgical groups and (2) THA subjects have significant differences in function one year after surgery compared to control subjects. To test these hypotheses, THA candidates (n=26) were randomized to receive one of these MIS approaches and evaluated preoperatively, and postoperatively at 3 weeks, and at 3, 6 and 12 months. Evaluations included three-dimensional gait analysis and 24-hour step-counts. The same data were obtained from 25 control subjects. Recovery time-course was assessed using repeated measures ANOVA. T-tests were used to compare controls with the pooled group of THA subjects. We found no differences between the two THA surgical groups regarding the time-course of recovery (p≥0.591). Although recovery was statistically complete by 3 months postoperatively for all variables, there were significant differences from controls at 12 months. Most notably, the external hip adduction moment, which reflects hip abductor function, was more than one standard deviation below normal (p<0.001). THA subject inactivity could not explain the gait differences, since one year after surgery daily step counts were not significantly different from controls (p=0.346). More work is necessary to determine ways to improve biomechanical outcomes for today's patients with high expectations for function and implant longevity.