Influence of researcher experience and fieldwork intensity on the probability of brood losses in sensitive species: The case of the Red-backed Shrike Lanius collurio

Minimizing disturbance to animals when studying them should be a major consideration in ecological research design, especially when species are known to be sensitive to disturbances. A basic method in the study of bird reproductive ecology involves nest visits, but these can adversely affect birds’ breeding success. Appropriate fieldwork procedures are therefore highly important, especially in the case of timid and sensitive species. This study aimed to assess the impact of the method of searching for nests of Red-backed Shrike Lanius collurio on the probability of these birds abandoning their broods. Our study revealed that observer experience and nest searching intensity did influence the likelihood of brood desertion by this species. Less field experience and a greater nest searching intensity caused the shrikes to abandon their nests more often. We recommend paying scrupulous attention to the behaviour of the birds when searching for nests and when looking for nests after incubation has started.     

Anatomical defences against bark beetles relate to degree of historical exposure between species and are allocated independently of chemical defences within trees

Conifers possess chemical and anatomical defences against tree‐killing bark beetles that feed in their phloem. Resins accumulating at attack sites can delay and entomb beetles while toxins reach lethal levels. Trees with high concentrations of metabolites active against bark beetle‐microbial complexes, and more extensive resin ducts, achieve greater survival. It is unknown if and how conifers integrate chemical and anatomical components of defence or how these capabilities vary with historical exposure. We compared linkages between phloem chemistry and tree ring anatomy of two mountain pine beetle hosts. Lodgepole pine, a mid‐elevation species, has had extensive, continual contact with this herbivore, whereas high‐elevation whitebark pines have historically had intermittent exposure that is increasing with warming climate. Lodgepole pine had more and larger resin ducts. In both species, anatomical defences were positively related to tree growth and nutrients. Within‐tree constitutive and induced concentrations of compounds bioactive against bark beetles and symbionts were largely unrelated to resin duct abundance and size. Fewer anatomical defences in the semi‐naïve compared with the continually exposed host concurs with directional differences in chemical defences. Partially uncoupling chemical and morphological antiherbivore traits may enable trees to confront beetles with more diverse defence permutations that interact to resist attack.     

Ecological significance of light quality in optimizing plant defence

Plants balance the allocation of resources between growth and defence to optimize fitness in a competitive environment. Perception of neighbour‐detection cues, such as a low ratio of red to far‐red (R:FR) radiation, activates a suite of shade‐avoidance responses that include stem elongation and upward leaf movement, whilst simultaneously downregulating defence. This downregulation is hypothesized to benefit the plant either by mediating the growth‐defence balance in favour of growth in high plant densities or, alternatively, by mediating defence of individual leaves such that those most photosynthetically productive are best protected. To test these hypotheses, we used a 3D functional–structural plant model of Brassica nigra that mechanistically simulates the interactions between plant architecture, herbivory, and the light environment. Our results show that plant‐level defence expression is a strong determinant of plant fitness and that leaf‐level defence mediation by R:FR can provide a fitness benefit in high densities. However, optimal plant‐level defence expression does not decrease monotonically with plant density, indicating that R:FR mediation of defence alone is not enough to optimize defence between densities. Therefore, assessing the ecological significance of R:FR‐mediated defence is paramount to better understand the evolution of this physiological linkage and its implications for crop breeding.     

Roles of plant volatiles in defence against microbial pathogens and microbial exploitation of volatiles

Plants emit a large variety of volatile organic compounds during infection by pathogenic microbes, including terpenes, aromatics, nitrogen‐containing compounds, and fatty acid derivatives, as well as the volatile plant hormones, methyl jasmonate, and methyl salicylate. Given the general antimicrobial activity of plant volatiles and the timing of emission following infection, these compounds have often been assumed to function in defence against pathogens without much solid evidence. In this review, we critically evaluate current knowledge on the toxicity of volatiles to fungi, bacteria, and viruses and their role in plant resistance as well as how they act to induce systemic resistance in uninfected parts of the plant and in neighbouring plants. We also discuss how microbes can detoxify plant volatiles and exploit them as nutrients, attractants for insect vectors, and inducers of volatile emissions, which stimulate immune responses that make plants more susceptible to infection. Although much more is known about plant volatile–herbivore interactions, knowledge of volatile–microbe interactions is growing and it may eventually be possible to harness plant volatiles to reduce disease in agriculture and forestry. Future research in this field can be facilitated by making use of the analytical and molecular tools generated by the prolific research on plant–herbivore interactions.     

Effects of starvation on death‐feigning in adult Eucryptorrhynchus brandti (Coleoptera: Curculionidae)

In insects, death‐feigning is an effective defence strategy. Eucryptorrhynchus brandti, a major borer pest in China, has a weak flight ability and exhibits obvious death‐feigning behaviour when disturbed. Despite a large number of studies of its biological and ecological properties as well as control methods, the death‐feigning behaviour has not been specifically described. In laboratory conditions, we recorded the survival rate under starvation and feeding conditions and evaluated the effect of starvation on the duration and occurrence of death‐feigning. In a continuous experiment, we examined variation in the death‐feigning duration every day over 7 day. Then, we evaluated the effects of starvation for 3, 6 and 9 day in a non‐continuous experiment and further observed variation in the death‐feigning intensity. We found that starvation significantly affected the survival rate. Survival time was significantly longer in the starvation group than in the feeding group, and females had longer survival times than males (female: 14 day, male: 8 day). In the continuous experiment, starved E. brandti had the longest duration of death‐feigning at 2 day, followed by a significant decrease. In the non‐continuous experiment, the duration and proportion of death‐feigning decreased significantly as the duration of starvation increased and were significantly lower than feeding. These observations suggest that starvation is a non‐negligible factor in the death‐feigning behaviour of E. brandti adults, facilitating the interpretation of future ecological and behavioural data of thanatosis.     

Biochemical insights into basal and induced resistance in cabbage to black rot

Black rot, caused by Xanthomonas campestris pv. campestris (Xcc), is the most devastating disease of brassica, but the mechanisms of basal or induced resistance in cabbage remain largely unknown. Here, we performed three experiments to investigate biochemical features associated with cabbage resistance to black rot. In the first experiment, biochemical changes were assessed in plants that were inoculated with a highly (UFPR 5) or a moderately (Xcc 10) aggressive Xcc isolate. In the second experiment, we examined the biochemical responses in two cultivars (Chato de Quintal [CQ] and Louco de Verão [LV], susceptible and moderately resistant to Xcc, respectively). Finally, we examined whether acibenzolar‐S‐methyl (ASM) could induce cabbage resistance to Xcc. Plants inoculated with the Xcc 10 isolate displayed higher activities of superoxide dismutase (SOD), peroxidase (POX) and ascorbate peroxidase (APX), whereas activities of chitinase (CHI), β‐1,3‐glucanase (GLU) and polyphenol oxidase (PPO) as well as the concentrations of hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) were lower compared to plants inoculated with the UFPR 5 isolate. The resistance of the cultivar LV to Xcc was linked to increases in the activities of CHI, GLU, and PPO and decreases in the activities of SOD, POX and APX as well as in the concentrations of H₂O₂ and MDA relative to the cultivar CQ. In general, ASM‐sprayed plants displayed higher activities for the enzymes studied, which was associated with decreased disease symptoms and oxidative stress. Taken together, our results demonstrated that high activities of both defence and antioxidant enzymes played a major role in both basal and induced resistance of cabbage to black rot.     

Nucleotide sequences of four pathogen-induced alfalfa peroxidase-encoding cDNAs

We constructed an alfalfa cDNA library from mRNA extracted from leaves after infection with Pseudomonas syringae (incompatible interaction). Screening with oligodeoxyribonucleotides designed from regions conserved in all known peroxidases allowed the isolation of four cDNAs (MsprxlA, 1B, 1C and 2). Sequence analysis revealed the presence of open reading frames of 351, 355, 358 and 323 amino acids, respectively, with the characteristic consensus sequences of plant peroxidases. Sequence comparison showed that the Msprx2 product is significantly different from the others and, particularly, lacks a C-terminal propeptide which might be required for vacuolar targeting.     

Herbivore‐induced plant responses in Brassica oleracea prevail over effects of constitutive resistance and result in enhanced herbivore attack

1. Plant responses to herbivore attack may have community‐wide effects on the composition of the plant‐associated insect community. Thereby, plant responses to an early‐season herbivore may have profound consequences for the amount and type of future attack. 2. Here we studied the effect of early‐season herbivory by caterpillars of Pieris rapae on the composition of the insect herbivore community on domesticated Brassica oleracea plants. We compared the effect of herbivory on two cultivars that differ in the degree of susceptibility to herbivores to analyse whether induced plant responses supersede differences caused by constitutive resistance. 3. Early‐season herbivory affected the herbivore community, having contrasting effects on different herbivore species, while these effects were similar on the two cultivars. Generalist insect herbivores avoided plants that had been induced, whereas these plants were colonised preferentially by specialist herbivores belonging to both leaf‐chewing and sap‐sucking guilds. 4. Our results show that community‐wide effects of early‐season herbivory may prevail over effects of constitutive plant resistance. Induced responses triggered by prior herbivory may lead to an increase in susceptibility to the dominant specialists in the herbivorous insect community. The outcome of the balance between contrasting responses of herbivorous community members to induced plants therefore determines whether induced plant responses result in enhanced plant resistance.     

昆虫与植物关系的研究进展和前景

本文综述昆虫与植物之间关系的研究概况，包括历史渊源、昆虫选择寄主植物的生理机制，植物对虫害的反应、用抗虫基因在作物中移植以防治害虫和展望。着重叙述昆虫神经中枢对于植物理化特性所产生的感觉内导的综合作用，植物蒙受虫害后的补偿作用及由此诱导所产生的化学防御作用。讨论了以抗虫基因移植于农林作物来防治害虫是否会引起昆虫对这种新育成的植物产生适应或抗性。昆虫与植物之间的关系是一个重要的科研领域，对其发展前景