Experimental assemblage of novel plant–herbivore interactions: ecological host shifts after 40 million years of isolation

Geographic isolation is the first step in insect herbivore diet specialization. Such specialization is postulated to increase insect fitness, but may simultaneously reduce insect ability to colonize novel hosts. During the Paleocene‐Eocene, plants from the order Zingiberales became isolated either in the Paleotropics or in the Neotropics. During the Cretaceous, rolled‐leaf beetles diversified in the Neotropics concurrently with Neotropical Zingiberales. Using a community of Costa Rican rolled‐leaf beetles and their Zingiberales host plants as study system, we explored if previous geographic isolation precludes insects to expand their diets to exotic hosts. We recorded interactions between rolled‐leaf beetles and native Zingiberales by combining DNA barcodes and field records for 7450 beetles feeding on 3202 host plants. To determine phylogenetic patterns of diet expansions, we established 20 experimental plots in the field, in which we planted plots five exotic Zingiberales, recording beetles feeding on these exotic hosts. In the laboratory, using both native and exotic host plants, we reared a subset of insect species that had expanded their diets to the exotic plants. The original plant–herbivore community comprised 24 beetle species feeding on 35 native hosts, representing 103 plant–herbivore interactions. After exotic host plant introduction, 20 percent of the beetle species expanded their diets to exotic Zingiberales. Insects only established on exotic hosts that belong to the same plant family as their native hosts. Laboratory experiments show that beetles are able to complete development on these novel hosts. In conclusion, rolled‐leaf beetles are preadapted to expand their diets to novel host plants even after millions of years of geographic isolation.     

Susceptibility of lady beetles (Coleoptera: Coccinellidae) to entomopathogenic nematodes

We investigated differential susceptibility of lady beetles to entomopathogenic nematodes, for two reasons: (1) to estimate potential nontarget effects on natural lady beetle populations, (2) to compare the susceptibility of exotic versus native lady beetle species. We hypothesize that successful establishment of some exotically introduced arthropods may be due, in part, to a lower susceptibility relative to competing native species. In laboratory studies, we compared the pathogenicity, virulence, and reproductive capacity of Heterorhabditis bacteriophora and Steinernema carpocapsae among two native (Coleomegilla maculata and Olla v-nigrum) and two successfully established exotic (Harmonia axyridis and Coccinella septempunctata) lady beetles, and a known susceptible lepidopteran host, Agrotis ipsilon. After 1 and 2 days of exposure to either nematode species, mortality of A. ipsilon was higher than in all lady beetles. Thus, we predict that nematode field applications would have significantly less impact on lady beetle populations than on a susceptible target pest. Additionally, the impact of soil-applied nematodes may be lower on lady beetles than on soil-dwelling hosts because the former spends relatively less time on the soil. Exotic lady beetles were less susceptible to nematode infection than native species. Reproductive capacity data also indicated lower host suitability in H. axyridis, but not in C. septempunctata. Overall, the hypothesis that low susceptibility to pathogens in certain exotic lady beetles may have contributed to competitive establishment was supported (especially for H. axyridis). Additional studies incorporating different hosts and pathogens from various geographic locations will be required to further address the hypothesis.     

Host-associated differences in fitness within and between populations of a seed beetle (Bruchidae): effects of plant variability

Summary Experiments were conducted with the sexually reproducing seed beetle Stator limbatus and its hosts in north-central Arizona to determine if it was substructured into units, each specialized for higher fitness on a specific host species. Unlike many studies, we incorporated scale, i.e., conducting experiments between and within beetle populations on seeds from within and between plant species. Of particular interest was whether intraspecific plant variability prevented beetle specialization within beetle populations. Results suggest that S. limbatus is specialized to certain hosts. On the palo verde Cercidium floridum, beetles originally reared from this host had significantly higher emergence compared to beetles transferred from other hosts. We did not test directly for a genetic basis for this. Alternative hypotheses of variation in symbiotic microorganisms in larval guts and maternal effects were assessed. Essentially no bacteria, yeast or protozoa were found, and maternal effects as expressed by varying egg weights were not detected; however, other microorganisms might have been present and maternal effects through inducible enzymes was possible. Caution, then, is needed in any genetic interpretations of our results. The differences on C. floridum were detected from tests between and within beetle populations. Evidence for specialization was not detected on the other hosts, Cercidium microphyllum and Acacia greggii. On the other hosts, beetles performed well regardless of their source. Significant differences were detected among individual plants of C. floridum as to the suitability of their seeds for deveoopment of S. limbatus. No such differences were detected among the other host plants. These patterns of conspecific plant variability are opposite of what is expected if plant variability prevents specialization of beetles to particular species of hosts. Thus, the data suggest seed variability among plants does not prevent specialization to host species in this system. We discuss how the patterns of host use in this study relate to the hypothesis of sympatric host race formation.     

Host suitability and diet mixing influence activities of detoxification enzymes in adult Japanese beetles

Induction of cytochrome P450, glutathione S transferase (GST), and carboxylesterase (CoE) activity was measured in guts of the scarab Popillia japonica Newman, after consumption of single or mixed plant diets of previously ranked preferred (rose, Virginia creeper, crape myrtle and sassafras) or non-preferred hosts (boxelder, riverbirch and red oak). The goal of this study was to quantify activities of P450, GST and CoE enzymes in the midgut of adult P. japonica using multiple substrates in response to host plant suitability (preferred host vs non-preferred hosts), and single and mixed diets. Non-preferred hosts were only sparingly fed upon, and as a group induced higher activities of P450, GST and CoE than did preferred hosts. However, enzyme activities for some individual plant species were similar across categories of host suitability. Similarly, beetles tended to have greater enzyme activities after feeding on a mixture of plants compared to a single plant type, but mixing per se does not seem as important as the species represented in the mix. Induction of detoxification enzymes on non-preferred hosts, or when switching between hosts, may explain, in part, the perceived feeding preferences of this polyphagous insect. The potential consequences of induced enzyme activities on the ecology of adult Japanese beetles are discussed.     

Examining the hierarchy threshold model in a no-choice feeding assay

The hierarchy threshold model of individual insect diet predicts the acceptance or rejection of individual hosts when encountered by insects. One assumption of the hierarchy threshold model is that post-discrimination phase insects which accept lower ranked hosts will also accept hosts that are ranked higher. This assumption does not however suggest whether or not such insects behave differently when encountering these two hosts. This question is explored using Zygogramma bicolorata Pallister (Coleoptera: Chrysomelidae). Adult beetles that had just fed, or were one inter-meal interval after feeding, or were deprived for three or six days after feeding, were individually observed on a plant that either ranked high, Parthenium hysterophorus L., or low Xanthium occidentale Bertol. (Heliantheae: Ambrosiinae) in choice tests. Just-fed beetles were generally unresponsive to either host plant and did not feed. Beetles held for one inter-meal interval showed more feeding responses (shorter lag time between sampling and feeding, higher proportions of individuals feeding, and more time feeding) towards the higher ranked plant. As the beetles approached six days deprivation, behaviours of sampling, feeding and locomotion differed less between the two plants, but were still apparent. I conclude that food deprived Z. bicolorata beetles do still discriminate between the two plants. This result partially supports the hierarchy threshold model.     

Predation by and activity patterns of 'parasitic' beetles of the genus Amblyopinus (Coleoptera: Staphylinidae)

This study explores the relationship between staphylinid beetles of the genus Amblyopinus and their small mammal hosts. Previous studies had concluded that these beetles were parasitic and fed directly on blood, skin exudates, or other epidermal derivatives of their hosts. We examined the mode of attachment, behaviour, and feeding activities of 254 Amblyopinus (A. tiptoni and A. emarginatus ) on 69 hosts which were captured in Sherman live traps. In addition, similar information and diurnal activity patterns were monitored for 11 beetles kept on two hosts ( Peromyscus nudipes ) over a period of 14 days. Beetles were found to be attached to the host only by grasping clumps of fur in their mandibles. No sign of damage to the skin of the host could be found. Feeding by the beetles on parasitic arthropods was observed and concluded to be the primary feeding habit. Beetles showed a strong circadian activity pattern, in which they are attached to the host during night-time hours and actively hunt in the nest during daylight hours. Attachment to the host is hypothesized to be primarily a vehicle for tracking prey of the beetles within the variety of nests used by any individual host. We conclude that these beetles are not parasitic but, instead, highly specialized predators on ectoparasitic arthropods, with specialized behavioural and morphological adaptations for their unique life style.     

Wolbachia infections in world populations of bean beetles (Coleoptera: Chrysomelidae: Bruchinae) infesting cultivated and wild legumes

Wolbachia endosymbionts are widespread among insects and other arthropods, often causing cytoplasmic incompatibility and other reproductive phenotypes in their hosts. Recently, possibilities of Wolbachia-mediated pest control and management have been proposed, and the bean beetles of the subfamily Bruchinae are known as serious pests of harvested and stored beans worldwide. Here we investigated Wolbachia infections in bean beetles from the world, representing seven genera, 20 species and 87 populations. Of 20 species examined, Wolbachia infections were detected in four species, Megabruchidius sophorae, Callosobruchus analis, C. latealbus and C. chinensis. Infection frequencies were partial in M. sophorae but perfect in the other species. In addition to C. chinensis described in the previous studies, C. latealbus was infected with two distinct Wolbachia strains. These Wolbachia strains from the bean beetles were phylogenetically not closely related to each other. Among world populations of C. chinensis, some Taiwanese populations on a wild leguminous plant, Rhynchosia minima, exhibited a peculiar Wolbachia infection pattern, suggesting the possibility that these populations comprise a distinct host race or a cryptic species.     

Evolutionary relationships, cospeciation, and host switching in avian malaria parasites

We used phylogenetic analyses of cytochrome b sequences of malaria parasites and their avian hosts to assess the coevolutionary relationships between host and parasite lineages. Many lineages of avian malaria parasites have broad host distributions, which tend to obscure cospeciation events. The hosts of a single parasite or of closely related parasites were nonetheless most frequently recovered from members of the same host taxonomic family, more so than expected by chance. However, global assessments of the relationship between parasite and host phylogenetic trees, using Component and ParaFit, failed to detect significant cospeciation. The event-based approach employed by TreeFitter revealed significant cospeciation and duplication with certain cost assignments for these events, but host switching was consistently more prominent in matching the parasite tree to the host tree. The absence of a global cospeciation signal despite conservative host distribution most likely reflects relatively frequent acquisition of new hosts by individual parasite lineages. Understanding these processes will require a more refined species concept for malaria parasites and more extensive sampling of parasite distributions across hosts. If parasites can disperse between allopatric host populations through alternative hosts, cospeciation may not have a strong influence on the architecture of host-parasite relationships. Rather, parasite speciation may happen more often in conjunction with the acquisition of new hosts followed by divergent selection between host lineages in sympatry. Detailed studies of the phylogeographic distributions of hosts and parasites are needed to characterize these events.     

光肩星天牛与星天牛种间竞争行为研究

光肩星天牛Anoplophora glabripennis和星天牛Anoplophora chinensis是我国两种重要的林业蛀干害虫,存在很多共同的寄主植物。为了阐明两种星天牛之间的物种竞争关系,本文采用行为观察试验,研究两种星天牛寄主危害部位、异种危害寄主识别和种间争斗行为等试验。结果显示,光肩星天牛和星天牛在寄主植物上的取食危害部位有很大差异,光肩星天牛主要取食寄主植物的枝条上部,取食面积为2 390.0 mm²,占整个寄主植物取食面积的69.3%,星天牛主要取食寄主植物的树干上部,取食面积为3 140.0 mm²,占整个寄主植物的96.6%;两种星天牛都能识别异种天牛危害过的寄主,对其具有显著的回避性,其中光肩星天牛对星天牛危害过的寄主取食量平均值为420.8 mm²,显著低于健康寄主取食量平均值2 518.8 mm²,同样,星天牛对光肩星天牛危害过的寄主取食量平均值为436.8 mm²,显著低于健康寄主取食量平均值1 803.5 mm²,而对同...     

The origin and radiation of Macaronesian beetles breeding in Euphorbia: the relative importance of multiple data partitions and population sampling

Species-level phylogenies derived from many independent character sources and wide geographical sampling provide a powerful tool in assessing the importance of various factors associated with cladogenesis. In this study, we explore the relative importance of insular isolation and host plant switching in the diversification of a group of bark beetles (Curculionidae: Scolytinae) feeding and breeding in woody Euphor biaspurges. All species in the genus Aphanarthrumare each associated with only one species group of Euphorbia(succulents or one of three different arborescent groups), and the majority of species are endemic to one or several of the Macaronesian Islands. Hence, putative mechanisms of speciation could be assessed by identifying pairs of sister species in a phylogenetic analysis. We used DNA sequences from two nuclear and two mitochondrial genes, and morphological characters, to reconstruct the genealogical relationships among 92 individuals of 25 species and subspecies of Aphanarthrumand related genera. A stable tree topology was highly dependent on multiple character sources, but much less so on wide population sampling. However, multiple samples per species demonstrated one case of species paraphyly, as well as deep coalescence among three putative subspecies pairs. The phylogenetic analyses consistently placed the arborescent breeding and West African--Lanzarote-distributed species A. armatumin the most basal position in Aphanarthrum, rendering this genus paraphyletic with respect to Coleobothrus. Two major radiations followed, one predominantly African lineage of succulent feeding species, and one island radiation associated with arborescent host plants. Sister comparisons showed that most recent divergences occurred in allopatry on closely related hosts, with subsequent expansions obscuring more ancient events. Only 6 out of 24 cladogenetic events were associated with host switching, rendering geographical factors more important in recent diversification.     

Host plant affects pollen beetle (Meligethes aeneus) egg size

Abstract. In some herbivorous insect species, egg size is larger on low‐quality hosts than on high‐quality hosts and may be related to the prospect that larger offspring are more likely to survive on a poor host. Sizes of eggs laid by pollen beetles [Meligethes aeneus Fab. (Coleoptera: Nitidulidae)] were examined with insects confined on one of two different host plants that had previously shown differences in adult preference and larval performance. Individual females were also exposed sequentially to both the low‐quality host (Sinapis alba L.) and the high‐quality host (Brassica napus L.) and the size of their eggs was determined. Pollen beetles laid shorter eggs on low‐quality hosts both for different females on different host plants and for the same individuals on different host plants, in contrast to the prediction that low‐quality hosts would receive larger eggs than high‐quality hosts. Previously, egg production rate was shown to be reduced when pollen beetles are exposed to low‐quality hosts and it is suggested that oogenesis is incomplete, resulting in shorter eggs. The possibility that this is related to antibiosis on S. alba is discussed.     

Host association influences variation at salivary protein genes in the bat ectoparasite Cimex adjunctus

Parasite–host relationships create strong selection pressures that can lead to adaptation and increasing specialization of parasites to their hosts. Even in relatively loose host–parasite relationships, such as between generalist ectoparasites and their hosts, we may observe some degree of specialization of parasite populations to one of the multiple potential hosts. Salivary proteins are used by blood‐feeding ectoparasites to prevent hemostasis in the host and maximize energy intake. We investigated the influence of association with specific host species on allele frequencies of salivary protein genes in Cimex adjunctus, a generalist blood‐feeding ectoparasite of bats in North America. We analysed two salivary protein genes: an apyrase, which hydrolyses ATP at the feeding site and thus inhibits platelet aggregation, and a nitrophorin, which brings nitrous oxide to the feeding site, inhibiting platelet aggregation and vasoconstriction. We observed more variation at both salivary protein genes among parasite populations associated with different host species than among populations from different spatial locations associated with the same host species. The variation in salivary protein genes among populations on different host species was also greater than expected under a neutral scenario of genetic drift and gene flow. Finally, host species was an important predictor of allelic divergence in genotypes of individual C. adjunctus at both salivary protein genes. Our results suggest differing selection pressures on these two salivary protein genes in C. adjunctus depending on the host species.     

Experimental demography and the vital rates of generalist and specialist insect herbivores on native and novel host plants

1. Colonization success of species when confronted with novel environments is of interest in ecological, evolutionary and conservation contexts. Such events may represent the first step for ecological diversification. They also play an important role in adaptive divergence and speciation. 2. A species that is able to do well across a range of environments has a higher plasticity than one whose success is restricted to a single or few environments. The breadth of environments in which a species can succeed is ultimately determined by the full pattern of its vital rates in each environment. 3. Examples of organisms colonizing novel environments are insect herbivores expanding their diets to novel host plants. One expectation for insect herbivores is that species with specialized diets may display less plasticity when faced with novel hosts than generalist species. 4. We examine this hypothesis for two generalist and two specialist neotropical beetles (genus Cephaloleia: Chrysomelidae) currently expanding their diets from native to novel plants of the order Zingiberales. Using an experimental approach, we estimated changes in vital rates, life-history traits and lifetime fitness for each beetle species when feeding on native or novel host plants. 5. We did not find evidence supporting more plasticity for generalists than for specialists. Instead, we found similar patterns of survival and fecundity for all herbivores. Larvae survived worse on novel hosts; adults survived at least as well or better, but reproduced less on the novel host than on natives. 6. Some of the novel host plants represent challenging environments where population growth was negative. However, in four novel plant-herbivore interactions, instantaneous population growth rates were positive. 7. Positive instantaneous population growth rates during initial colonization of novel host plants suggest that both generalist and specialist Cephaloleia beetles may be pre-adapted to feed on some novel hosts. This plasticity in host use is a key factor for successful colonization of novel hosts. Future success or failure in the colonization of these novel hosts will depend on the demographic rates described in this research, natural selection and the evolutionary responses of life-history traits in novel environments.     

Rapid evolution and specialization following host colonization in a yucca moth

Host shifts followed by specialization can result in sympatric genetic differentiation, and may have fuelled the diversification of phytophagous insects. This study examines a recent colonization of a non‐native host by Prodoxus quinquepunctellus (Lepidoptera: Prodoxidae). Allozyme differentiation was detected among different host feeding populations, yet was nearly absent among similar host feeding populations in sympatry. Geographical patterns of allozyme variation showed a much higher level of population structure among populations feeding on the derived host. Conversely, mtDNA haplotype frequencies were nearly homogeneous in the derived populations compared to the ancestral populations, suggesting a bottleneck and/or rapid fixation of haplotypes following host colonization. Moth emergence coincided with host plant flowering, and phenological differences between host species translated into allochronic isolation between populations feeding on different hosts. Derived moth populations also differed significantly in three ovipositor characters from ancestral populations. These findings suggest rapid host‐specific genetic differentiation, and specialization of moth emergence time and ovipositor morphology following host colonization.     

守瓜属甲虫的取食行为与寄主植物葫芦素种类的关系

黄足黄守瓜和黄足黑守瓜是两个非常相似的守瓜属甲虫,但它们对寄主的选择性和取食行为却完全不同.黄足黄守瓜先用口器在黄瓜或南瓜叶面划圈,然后取食圈内叶组织,但却不取食丝瓜、苦瓜和西瓜,而黄足黑守瓜则只取食丝瓜,且不发生划圈取食行为.研究表明,这两种甲虫的寄主选择性及取食行为与瓜类作物合成的葫芦素种类显著相关.黄瓜和南瓜在黄足黄守瓜取食后能诱导合成抑制取食的葫芦素Ⅰ,使得黄守瓜只能先划圈阻断葫芦素Ⅰ在叶面的迁移才能取食圈内叶组织.而苦瓜和西瓜本身就合成抑制取食的葫芦素D,使得甲虫不选择这两种瓜类作物取食.丝瓜则合成刺激甲虫取食的葫芦素B和E,使得黑守瓜能直接取食.本研究表明,守瓜属甲虫对寄主植物合成的特定次生物质的味觉响应机制在其寄主选择和取食行为方面起着重要作用.     

Species richness and regional distribution of myrmecophilous beetles

Four major hypotheses have been put forward to explain local species richness of commensal or parasitic species. The resource distribution hypothesis predicts that regionally widespread host species are able to support higher local species richness of commensals or parasites. On the other hand, the resource size hypothesis predicts that larger hosts can support more species than smaller hosts, and comparably, the resource abundance hypothesis predicts that hosts that offer more resources are able to support more species. Finally, the resource concentration hypothesis predicts that hosts that occur in high-density patches support higher species richness. In this study, we tested the first three of the above hypotheses with myrmecophilous beetles and their host ants. In addition to species richness of myrmecophilous beetles, we also applied the above hypotheses to explain the distribution of the beetles. Our data are exclusively based on an extensive literature survey. Myrmecophilous beetles live in naturally fragmented environments composed of host ant colonies and they are exclusively dependent on ants. We found that the distribution of the host ants and the colony size of the host ants had a positive effect on both the species richness and the distribution of myrmecophilous beetles. In the same way, we found that myrmecophilous beetle species that are generalists, i.e. have more than one host ant species, and thus have more abundant resources, were more widely distributed than specialist species. Thus, we found support for the hypothesis that resource distribution, resource size and resource abundance have an effect on species richness and on the distribution of species.     

叶甲科昆虫的定殖机制

在复杂的生态环境中,叶甲科昆虫利用寄主植物的挥发物作为嗅觉信号,并协同视觉信号共同作用以提高其远距离搜寻和定位寄主的效率。叶甲科昆虫也释放信息素来调节同种或者异种个体的行为反应;找到寄主植物后,叶子的形态学特性和化学组分的浓度等接触性因素就会影响叶甲科昆虫对寄主植物的最终选择。叶甲对上述这些信号物质的反应也受叶甲本身状态的影响,如生殖、滞育、饥饿、交配以及取食等。叶甲科昆虫对寄主植物的搜寻、辨识和接受、取食以及繁殖的过程受一种或多种因素协同影响。从嗅觉、视觉和触觉等方面对叶甲科昆虫的定殖机制做一综述。     

Semiochemicals and bark beetle populations: Exploitation of natural phenomena by pest management strategists

An analysis of semiochemical communication between host trees, bark beetles and commensal or entomophagous insects discloses five principal means by which semiochemicals can influence the population dynamics of bark beetles. These are: mediation of aggregation and mass attack on new hosts, cessation of aggregation and shifting of attack to uninhabited hosts, induction of aggregation by competing species, inhibition of aggregation by competing species, and mediation of host finding by commensal and entomophagous insects. Further analysis suggests major points of natural vulnerability which lead to six fundamental strategies for potential pest management: prevention of production of aggregation pheromones, sabotage of olfactory perception, exploitation of semiochemical-based secondary attraction, exploitation of antiaggregation pheromones, exploitation of repellent allomones, and exploitation of the kairomonal response by entomophagous insects. Investigations of the many possible tactics arising from these strategies have led to three types of operational pest management programs: prevention of pheromone production by excluding bark beetles from their hosts; suppression of bark beetle populations through the utilization of semiochemical-baited traps, trees or logs; and the use of antiaggregation pheromones to protect vulnerable hosts from attack.     

Olfactory recognition and behavioural avoidance of angiosperm nonhost volatiles by conifer-inhabiting bark beetles

Abstract 1 When searching for suitable hosts in flight, especially in mixed forests, conifer‐inhabiting bark beetles will encounter not only suitable host trees and their odours, but also unsuitable hosts and nonhost trees. Rejection of these trees could be based on an imbalance of certain host characteristics and/or a negative response to some nonhost stimuli, such as nonhost volatiles (NHV). 2 Recent electrophysiological and behavioural studies clearly indicate that conifer‐inhabiting bark beetles are not only able to recognize, but also to avoid, nonhost habitats or trees by olfactory means. Green leaf volatiles (GLV), especially C₆‐alcohols, from the leaves (and partly from bark) of nonhost angiosperm trees, may represent nonhost odour signals at the habitat level. Specific bark volatiles such as trans‐conophthorin, C₈‐alcohols, and some aromatic compounds, may indicate nonhosts at the tree species level. Flying bark beetles are also capable of determining whether a possible host is unsuitable by reacting to signals from conspecifics or sympatric heterospecifics that indicate old or colonized host tree individuals. 3 Combined NHV signals in blends showed both redundancy and synergism in their inhibitory effects. The coexistence of redundancy and synergism in negative NHV signals may indicate different functional levels (nonhost habitats, species, and unsuitable hosts) in the host selection process. Combinations of NHV and verbenone significantly reduced the number of mass attacked host trees or logs on several economically important species (e.g. Dendroctonus ponderosae, Ips typographus, and I. sexdentatus). 4 We suggest a semiochemical‐diversity hypothesis, based on the inhibition by NHV of bark beetle host‐location, which might partly explain the lower outbreak rates of forest insects in mixed forests. This ‘semiochemical‐diversity hypothesis’ would provide new support to the general ‘stability‐diversity hypothesis’. 5 Natural selection appears to have caused conifer‐inhabiting bark beetles to evolve several olfactory mechanisms for finding their hosts and avoiding unsuitable hosts and nonhost species. NHV and unsuitable host signals have potential for use in protecting trees from attack. The use of these signals may be facilitated by the fact that their combination has an active inhibition radius of several metres in trap test, and by the observation of area effects for several trees near inhibitor soruces in tree protection experiments. Furthermore, incorporation of negative signals (such as NHV and verbenone) and pheromone‐based mass‐trapping in a ‘push–pull’ fashion may significantly increase the options for control against outbreaks of conifer‐inhabiting bark beetles, especially in high risk areas.