Neonates know better than their mothers when selecting a host plant

Evolutionary ecological theory predicts that among insect herbivores ‘mothers know best’ when selecting a plant to deposit their eggs. Host‐plant selection is usually studied for the adult stage exclusively, although mothers have not always been reported to know best. Here, we investigate the host‐plant selection behaviour of caterpillars, which are considered to be completely dependent on their mothers’ choices. We use a system that offers a biologically relevant framework to compare the degree of participation of adults and juveniles in host‐plant selection. Our results show that neonate Pieris brassicae caterpillars can actively discriminate between conspecific Brassica oleracea plants with or without aphid (Brevicoryne brassicae) infestation. The caterpillars prefer aphid‐infested plants on which their performance is significantly better, while their mothers, the female butterflies, did not discriminate. We compared caterpillar preferences of individuals released individually or in groups, because P. brassicae is a gregarious species. We found that the strength of the preference for aphid‐infested plants was not affected by the degree of grouping. Caterpillar choices were made before contact with the plants, indicating that plant odours were used for orientation. However, the composition of the volatile blends emitted by plants with and without aphids did not show strong differences. Similarly, like with aphid‐infested plants, plants treated with salicylic acid (SA) were also preferred by neonates over untreated control, indicating that the infestation by aphids may have rendered the plants more attractive to the neonates via changes related to interference with JA‐signaling. The main parasitoid of the caterpillars did not discriminate between plants with hosts in the presence or absence of aphids, showing that top–down forces do not influence the relative suitability of the different food sources for the caterpillars. These data are discussed in the context of mothers and offspring having both important, but different roles in the process of host‐plant selection. Butterflies may select the plant species patch, while their offspring adjust and/or update the choices of their mothers at the local scale, within the micro‐habitat selected by the adult.     

Consequences of constitutive and induced variation in plant nutritional quality for immune defence of a herbivore against parasitism

The mechanisms through which trophic interactions between species are indirectly mediated by distant members in a food web have received increasing attention in the field of ecology of multitrophic interactions. Scarcely studied aspects include the effects of varying plant chemistry on herbivore immune defences against parasitoids. We investigated the effects of constitutive and herbivore-induced variation in the nutritional quality of wild and cultivated populations of cabbage (Brassica oleracea) on the ability of small cabbage white Pieris rapae (Lepidoptera, Pieridae) larvae to encapsulate eggs of the parasitoid Cotesia glomerata (Hymenoptera, Braconidae). Average encapsulation rates in caterpillars parasitised as first instars were low and did not differ among plant populations, with caterpillar weight positively correlating with the rates of encapsulation. When caterpillars were parasitised as second instar larvae, encapsulation of eggs increased. Caterpillars were larger on the cultivated Brussels sprouts plants and exhibited higher levels of encapsulation compared with caterpillars on plants of either of the wild cabbage populations. Observed differences in encapsulation rates between plant populations could not be explained exclusively by differences in host growth on the different Brassica populations. Previous herbivore damage resulted in a reduction in the larval weight of subsequent herbivores with a concomitant reduction in encapsulation responses on both Brussels sprouts and wild cabbage plants. To our knowledge this is the first study demonstrating that constitutive and herbivore-induced changes in plant chemistry act in concert, affecting the immune response of herbivores to parasitism. We argue that plant-mediated immune responses of herbivores may be important in the evaluation of fitness costs and benefits of herbivore diet on the third trophic level.     

Prey preference of the phytoseiid miteTyphlodromus pyri 2. Electrophoretic diet analysis

The prey selection of the phytoseiid miteTyphlodromus pyri Scheuten was studied by using polyacrylamide gel electrophoresis to analyse the diet of field-collected predators. The predators were obtained from an orchard where the phytophagous prey mitesPanonychus ulmi (Koch) andAculus schlechtendali (Nalepa) were present in various density ratios.Esterases of both prey species were identified in the predators, but on all sampling datesP. ulmi esterases were discovered much more frequently than those ofA. schlechtendali. The data show thatT. pyri hardly fed onA. schlechtendali over a range of prey density ratios. It is therefore concluded thatT. pyri prefersP. ulmi toA. schlechtendali.     

Gene and domain duplication in the chordate Otx gene family: insights from amphioxus Otx

We report the genomic organization and deduced protein sequence of a cephalochordate member of the Otx homeobox gene family (AmphiOtx) and show its probable single-copy state in the genome. We also present molecular phylogenetic analysis indicating that there was single ancestral Otx gene in the first chordates which was duplicated in the vertebrate lineage after it had split from the lineage leading to the cephalochordates. Duplication of a C-terminal protein domain has occurred specifically in the vertebrate lineage, strengthening the case for a single Otx gene in an ancestral chordate whose gene structure has been retained in an extant cephalochordate. Comparative analysis of protein sequences and published gene expression patterns suggest that the ancestral chordate Otx gene had roles in patterning the anterior mesendoderm and central nervous system. These roles were elaborated following Otx gene duplication in vertebrates, accompanied by regulatory and structural divergence, particularly of Otx1 descendant genes.      

An approach to real-time flexible scheduling

Two types of flexibility are important in manufacturing scheduling in general and in real-time scheduling in particular. The first is flexibility with respect to the criteria that can be considered in the scheduling decisions. The second is flexibility with respect to the trade-off between decision quality and computational burden: that is, the ability to arrive at a solution that makes maximum use of theavailable computational capacity and computation time. This paper describes a procedure which meets the above requirements. The procedure is justified using a theoretical analysis based on probability. Experimental results of the procedure's performance are also presented. The results show that random selection (which is used in the procedure) can play a useful role in the real-time scheduling problem.     

Spider Mite-Induced (3S)-(E)-Nerolidol Synthase Activity in Cucumber and Lima Bean. The First Dedicated Step in Acyclic C11-Homoterpene Biosynthesis

Many plant species respond to herbivory with de novo production of a mixture of volatiles that attracts carnivorous enemies of the herbivores. One of the major components in the blend of volatiles produced by many different plant species in response to herbivory by insects and spider mites is the homoterpene 4,8-dimethyl-1,3(E), 7-nonatriene. One study (J. Donath, W. Boland [1995] Phytochemistry 39: 785-790) demonstrated that a number of plant species can convert the acyclic sesquiterpene alcohol (3S)-(E)-nerolidol to this homoterpene. Cucumber (Cucumis sativus L.) and lima bean (Phaseolus lunatus L.) both produce 4,8-dimethyl-1,3(E),7-nonatriene in response to herbivory. We report the presence in cucumber and lima bean of a sesquiterpene synthase catalyzing the formation of (3S)-(E)-nerolidol from farnesyl diphosphate. The enzyme is inactive in uninfested cucumber leaves, slightly active in uninfested lima bean leaves, and strongly induced by feeding of the two-spotted spider mite (Tetranychus urticae Koch) on both plant species, but not by mechanical wounding. The activities of the (3S)-(E)-nerolidol synthase correlated well with the levels of release of 4, 8-dimethyl-1,3(E),7-nonatriene from the leaves of the different treatments. Thus, (3S)-(E)-nerolidol synthase is a good candidate for a regulatory role in the release of the important signaling molecule 4,8-dimethyl-1,3(E),7-nonatriene.     

Ice premelting during differential scanning calorimetry

Premelting at the surface of ice crystals is caused by factors such as temperature, radius of curvature, and solute composition. When polycrystalline ice samples are warmed from well below the equilibrium melting point, surface melting may begin at temperatures as low as -15 degrees C. However, it has been reported (. Biophys. J. 65:1853-1865) that when polycrystalline ice was warmed in a differential scanning calorimetry (DSC) pan, melting began at about -50 degrees C, this extreme behavior being attributed to short-range forces. We show that there is no driving force for such premelting, and that for pure water samples in DSC pans curvature effects will cause premelting typically at just a few degrees below the equilibrium melting point. We also show that the rate of warming affects the slope of the DSC baseline and that this might be incorrectly interpreted as an endotherm. The work has consequences for DSC operators who use water as a standard in systems where subfreezing runs are important.     

Are herbivore-induced plant volatiles reliable indicators of herbivore identity to foraging carnivorous arthropods?

Plants that are damaged by herbivorous arthropods provide carnivorous enemies of the herbivores with important information. They emit an induced volatile blend that is highly detectable to the carnivores from a distance. Such detectable signals that indicate herbivore presence are important for the carnivores because herbivores themselves are under strong selection not to expose themselves. In addition, carnivores would benefit from a specificity of the induced plant volatiles. Whether herbivore-induced plant volatiles are reliable indicators of herbivore identity, however, has not been resolved unambiguously. Some studies support the reliability of herbivore-induced plant volatiles, while others do not. Different approaches have been used such as chemical analysis, behavioural analysis or a combination of the two. Based on the total of chemical studies one might conclude that in most cases herbivore-induced plant volatiles are not very specific for the herbivore that damages the plant. However, arthropod chemosensors are much more sensitive than the detectors of analytical instruments. Therefore, chemical analyses are not suitable to demonstrate whether or not herbivore-induced plant volatiles are reliable indicators of herbivore identity to carnivores. Behavioural studies should provide this information. In analysing carnivore behaviour it should be realised, however, that arthropod behaviour can be highly variable. Arthropod foraging decisions are affected by external and internal factors such as (a) abiotic environmental factors, (b) presence of competitors or enemies, (c) deprivation of food or oviposition sites, (d) specific deprivation of certain nutrients or (e) learning. In this paper their effect on discrimination of carnivores between volatile blends emitted by plants infested by different herbivores is reviewed. This provides testable hypotheses of why discrimination was not found in some studies. The ability of carnivores to discriminate is likely to be more common than is clear to date, which should invoke functional studies of the conditions that influence the occurrence of this discrimination.