Role of olfaction in host plant selection and local adaptation of a polyphagous herbivore,Eucolaspis Sharp

Host plant cues are known to shape insect–host plant association in many insect groups. More pronounced associations are generally manifested in specialist herbivores, but little is known in generalist herbivores. We used a polyphagous native beetle from New Zealand, bronze beetle, Eucolaspis sp. ‘Hawkes Bay’ (Chrysomelidae: Eumolpinae) to explore the role of olfaction in locating host plants and local adaptation. We also tested the role of other cues in the degree of acceptance or rejection of hosts. Adult Eucolaspis beetles were attracted to fresh leaf volatiles from apple and blackberry (Rosaceae). Male and female beetles responded similarly to olfactory cues of host plants. An indication of evolutionary affiliation was observed in olfactory preferences of geographically isolated conspecific populations. We found that geographically isolated populations of the beetles differ in their olfactory responses and exhibit some degree of local adaptation. However, irrespective of geographical and ecological associations, blackberry was preferred over apple as a feeding plant, and another novel plant, bush lawyer (Rubus australis), was readily accepted by 53.25% of the tested beetles. We show that plant volatiles play an important role in host location by Eucolaspis, but the acceptance or rejection of a particular host could also involve visual and contact cues.     

Mixing barley cultivars affects aphid host plant acceptance in field experiments

Four barley varieties with no significant difference in aphid acceptance were sown in pure stands and in pairwise combinations with varieties side by side in separate rows. Settling tests were done in situ in the field plots with apterae of Rhopalosiphum padi (L.) (Homoptera:Aphididae) and showed that aphid acceptance was changed in some combinations of cultivars. In a laboratory test, in which plants of one cultivar were exposed to air from the other cultivars, aphid acceptance was significantly reduced in three of the four cultivars when treated with air from certain other cultivars. Two of these three cultivars showed the same reduction under field conditions. This supports the hypothesis that plant/plant communication may release responses in neighbouring plants that change aphid host plant acceptance. The results also show that this mechanism is not restricted to optimal growing conditions in the laboratory, although it may be modified under field conditions depending on plant genotype.     

Biological control of root-rot of Coleus forskohlii Briq. using microbial inoculants

The root-rot or wilt of Coleus forskohlii is a very serious soil-borne disease caused by Fusarium chlamydosporum. A field study was undertaken to study the possibility of controlling the disease using three biocontrol agents viz., Glomus mosseae, Pseudomonas fluorescens, Trichoderma viride, singly and in combination. Planting of coleus cutting was done in wilt sick soil. Inoculation with Trichoderma viride + Glomus mosseae gave the best result in controlling the disease. The same treatment also resulted in maximum growth, yield and root forskolin concentration of coleus. Plants treated with T. viride + G. mosseae showed a disease severity index of 33.28% compared to uninoculated control plants, which had a maximum disease severity index of 85.5%. The fungicide Emisan (0.2%) was not as effective as the biocontrol agents in controlling the pathogen.     

Slow larval growth on a suboptimal willow results in high predation mortality in the leaf beetle Galerucella lineola

The slow growth/high mortality hypothesis predicts that herbivorous insects feeding on suboptimal host plants are subjected to higher predation mortality owing to the longer time spent in the vulnerable juvenile stages compared with conspecifics feeding on optimal plants. We tested this hypothesis for the willow-feeding leaf beetle Galerucella lineola raised on one suitable (Salix viminalis) and one unsuitable (S. dasyclados) willow species as well as on plants from an interspecific cross between the two species. Cohorts of larvae raised on caged plants (protected from enemies) and uncaged plants (exposed to enemies) were monitored daily throughout larval development in two consecutive years. Larvae raised on S. viminalis developed faster, grew larger and survived better than those raised on S. dasyclados. The suitability of the hybrid plants was intermediate to that of their parents. Our results strongly support the slow growth/high mortality hypothesis. In both years, total predation during the larval period was higher on S. dasyclados than on S. viminalis. Furthermore, the daily predation rate (i.e. the proportion of larvae preyed upon per day) was higher on S. dasyclados than on S. viminalis. When hybrid plants were included in the analysis total predation was positively correlated with both larval development time and daily predation rate. We suggest that high predation on beetles on low-quality plants is the combined result of their longer development time and elevated daily predation rate. The results are discussed in relation to the evolution of host plant selection and the paradox of sublethal plant defenses.     

Nutritional suitability and ecological relevance of <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> and <Emphasis Type="Italic">Brassica oleracea</Emphasis> as foodplants for the cabbage butterfly, <Emphasis Type="Italic">Pieris rapae</Emphasis>

The thale cress, Arabidopsis thaliana, is considered to be an important model species in studying a suite of evolutionary processes. However, the species has been criticized on the basis of its comparatively small size at maturity (and consequent limitations in the amount of available biomass for herbivores) and on the duration and timing of its life cycle in nature. In the laboratory, we studied interactions between A. thaliana and the cabbage butterfly, Pieris rapae, in order to determine if plants are able to support the complete development of the herbivore. Plants were grown in pots from seedlings in densities of one, two, or four per pot. In each treatment, one, two, or five newly hatched larvae of P. rapae were placed on fully developed rosettes of A. thaliana. In a separate experiment, the same densities of P. rapae larvae were reared from hatching on single mature cabbage (Brassica oleracea) plants. Pupal fresh mass and survival of P. rapae declined with larval density when reared on A. thaliana but not on B. oleracea. However, irrespective of larval density and plant number, some P. rapae were always able to complete development on A. thaliana plants. A comparison of the dry mass of plants in different treatments with controls (= no larvae) revealed that A. thaliana partially compensated for plant damage when larval densities of P. rapae were low. By contrast, single cress plants with 5 larvae generally suffered extensive damage, whereas damage to B. oleracea plants was negligible. Rosettes of plants that were monitored in spring, when A. thaliana naturally grows, were not attacked by any insect herbivores, but there was often extensive damage from pulmonates (slugs and snails). Heavily damaged plants flowered less successfully than lightly damaged plants. Small numbers of generalist plant-parasitic nematodes were also recovered in roots and root soil. By contrast, plants monitored in a sewn summer plot were heavily attacked by insect herbivores, primarily flea beetles (Phyllotreta spp.). These results reveal that, in natural populations of A. thaliana, there is a strong phenological mismatch between the plant and most of its potential specialist insect herbivores (and their natural enemies). However, as the plant is clearly susceptible to attack from non-insect generalist invertebrate herbivores early in the season, these may be much more suitable for studies on direct defense strategies in A. thaliana.     

檀香与不同豆科植物寄生关系的研究

为了解檀香(Santalum album L.)与不同豆科植物的寄生关系,选取11种具有重要经济价值的豆科植物和檀香一起种植,对檀香叶片的光合特征和株高、地径以及寄主植物根系的吸器大小进行了测定。结果表明,檀香的吸器大小、数量在不同寄主之间存在很大差异,不同寄主对檀香的株高、地径也有显著差异。檀香的优良寄主有美洲合欢(Calliandra haematocephala)、苏木(Caesalpinia sappan)、台湾相思(Acacia confusa)、龙牙花(Erythrina corallodendron);一般的寄主植物有马占相思(Acacia mangium)、降香黄檀(Dalbergia odorifera)、黄槐(Cassia surattensis);不适宜的寄主植物有凤凰木(Delonix regia)、海南红豆(Ormosia pinnata)、银合欢(Leucaena leucocephala)、洋紫荆(Bauhinia blakeana)。同时,檀香的株高、地径及光合特征和吸器数量密切相关。因此,檀香种植时应选择适宜的优良寄主植物。     

Can the Geranium Bronze, <Emphasis Type="Italic">Cacyreus marshalli</Emphasis>, become a threat for European biodiversity?

Cacyreus marshalli Butler is an invasive species in many parts of Europe and Mediterranean area. In Europe, its larvae normally feed on pelargoniums. We investigated its potential to spread to native Geranium spp. and evaluated the conservation risks that such a shift would pose for both native geraniums and cohabitant butterflies. The host plant preferences of the Geranium Bronze were investigated under controlled conditions. Studies included both no-choice and multi-choice tests, respectively using 9 and 6 Italian native Geranium spp. Host plant preferences were evaluated by counting the number of eggs laid on individual plants and following butterfly development until adult emergence. Under no-choice conditions, at least one egg was recorded on each tested plant, except for G. phaeum L. All the plants on which oviposition occurred were fully suitable for larval development. The butterfly, however, clearly preferred three species, i.e. G. pratense L., G. sanguineum L. and G. sylvaticum L. for oviposition. In multi-choice trials, females laid at least one egg on all the tested plants, with a preference for G. pratense and G. sylvaticum. In presence of Pelargonium spp. plants, however, no oviposition was observed on any Geranium spp. We assessed offspring fitness measuring their wingspan. No statistical differences were detected in the wingspan between adults emerged from Geranium and Pelargonium. Cacyreus marshalli represents a potential threat for both native geraniums and for Geranium-consuming lycaenids, such as Aricia nicias Meigen and Eumedonia eumedon Esper.     

Flower form alteration by genetic transformation with the class B MADS-box genes of <Emphasis Type="Italic">Agapanthus</Emphasis><Emphasis Type="Italic">praecox</Emphasis> spp. <Emphasis Type="Italic">orientalis</Emphasis> in transgenic dicot and monocot plants

The class B genes, which belong to the MADS-box gene family, play important roles in regulating petal and stamen development in flowering plants. These genes exist in two different types termed DEF- and GLO-like genes, and the B-function is provided by heterodimers of a DEF- and a GLO-like gene product. In the present study, dicot (tobacco and lettuce) and monocot (Tricyrtis hirta) plants were transformed with the GLO-like gene of Agapanthus praecox ssp. orientalis ApGLO alone or in combination with the DEF-like gene of the same plant ApDEF. In two out of 10 transgenic tobacco plants containing ApGLO, sepals partially converted into petaloid organs. For lettuce, ray florets of four out of nine transgenic plants containing ApGLO also developed additional petaloid organs. In two out of five transgenic T. hirta plants containing both ApGLO and ApDEF, organs developed in whorl 4 showed noticeable morphological alteration: they were much longer compared with carpels of non-transgenic plants, and had purple spots overall on the surface as filaments of non-transgenic plants. No morphological alterations were observed in vegetative organs between transgenic and non-transgenic plants for all the three species. The results obtained in the present study indicate a possibility of molecular breeding for flower form alteration by genetic transformation with the class B MADS-box gene(s) of heterologous plant species.     

The role of Acanthospermum hispidum in the phenology of Euschistus heros and of Nezara viridula

Laboratory, greenhouse, and field studies with Euschistus heros (F.) and Nezara viridula (L.) (Heteroptera: Pentatomidae) in northern Paraná, Brazil, demonstrated greater survival and longevity with E. heros than N. viridula when fed the weed Acanthospermum hispidum DC. (Compositae). E. heros was better adapted to A. hispidum than N. viridula but neither species reproduced on this plant. Stink bugs moved from soybean to A. hispidum mainly during mid-March to mid-April when soybean plants matured. The infestation reached 60 and 100% with a maximum of ca. 3 and 10 stink bugs/plant in 1988 and 1989, respectively. Surprisingly, E. heros and N. viridula, which are normally seed-feeders, strongly preferred the high moisture stems of A. hispidum. Both species demonstrated similar feeding frequencies. These results suggest that in northern Paraná, the common weed, A. hispidum functions as a temporary host providing water and nutrients to those two pentatomid pests of soybean. Finally, both species do not seem to recognize A. hispidum as an unsuitable or perhaps toxic plant.     

The influence of plant species on attraction and host acceptance inCotesia glomerata (Hymenoptera: Braconidae)

Females of the larval parasitoidCotesia glomerata (L.) use plant-associated cues to locate their lepidopteran host,Pieris rapae L. In this study we investigated the influence of four host plant species,Brassica oleracea var.acephala (‘Vates’ kale),Tropaeolum majus (nasturtium),Lunaria annua (honesty), andCleome spinosa (spider flower), on two components of the host selection process inC. glomerata, namely, attraction and host acceptance. Choice tests in a flight tunnel showed that parasitoids were attracted to some host plant species more than to others in the absence of host larvae.B. oleracea was the most attractive plant species, followed byL. annua, T. majus, andC. spinosa. In previous studies it was shown thatB. oleracea carries highly suitable hosts forC. glomerata and that, in the field, parasitization rates on this plant were the highest. When host larvae were reared on the four host plant species and then transferred to a common substrate (B. oleracea var.capitata, cabbage), plant species that had served as diet for the hosts did not have a significant effect on acceptance for parasitization. Thus, parasitoids were attracted to host plant species differentially, but they did not discriminate among host larvae based on the dietary history of their hosts. ForC. glomerata, it appears that phytochemistry mediates host selection more by influencing parasitoid attraction than it does by affecting host acceptance.     

Food acceptance by a monophagous and an oligophagous insect in relation to seasonal changes in host plant suitability

Food acceptance by larvae of two lepidopteran species feeding on Rosaceae, viz. Yponomeuta evonymellus (monophagous) and Y. padellus (oligophagous), was compared. The influence of seasonal changes in plants as food for both insects was examined, in particular, the effects of nitrogen and sorbitol in leaves. In the laboratory, Y. evonymellus accepts Crataegus monogyna, a host plant of Y. padellus, and Y. padellus accepts Prunus padus, the host plant of Y. evonymellus. P. padus is the most suitable food plant for Y. evonymellus. No difference in food-quality for Y. padellus was found between C. monogyna and P. padus. The performance of both species on P. padus is less influenced by seasonal changes than on Crataegus. The suitability of Crataegus decreases during the season. This is probably caused by the decrease of its nitrogen content, and not by the decrease of sorbitol in the plant. The monophagous, Y. evonymellus, is more sensitive to seasonal changes in its food when fed with a non host plant than the oligophagous Y. padellus. In oviposition experiments both species have a preference for their normal host-plants.     

Prefeeding and Acceptance Behavior of an Oligophagous Beetle is Dependent on Plant Suitability and Rearing History

Host prefeeding and acceptance behavior of herbivorous insects may strongly differ depending upon the plant species and previous experience. We examined prefeeding behaviors and acceptance of host and non-host plants by the beetle Phaedon cochleariae in populations with different rearing histories using a camera. Suitable host plants evoked short test biting followed by long feeding durations indicating that these first contacts provide sufficient information to stimulate feeding. In contrast, plants of intermediate quality caused prolonged test biting but feeding duration was rather low. When offered unsuitable plants, beetles showed only rare leaf contacts and test biting, demonstrating that test biting behavior is a useful measure of plant suitability. Rearing history had a minor influence on host plant exploitation behavior.     

Banker plants promote functional biodiversity and decrease populations of the cabbage whitefly Aleyrodes proletella

In this study, potential banker plant systems against the cabbage whitefly Aleyrodes proletella Linnaeus (Hemiptera: Aleyrodidae) were developed under controlled conditions. The two most promising banker plant systems, that is, the parasitoid Encarsia tricolor Förster (Hymenoptera: Aphelinidae) either with Aleyrodes lonicerae Walker on European columbine (columbine system) or with Trialeurodes vaporariorum Westwood (Hemiptera: Aleyrodidae) on Hokkaido squash (pumpkin system), were further evaluated in the field. Although the pumpkin system produced three times more parasitoids than the columbine system, both banker plants led to an 1.5-fold increase in A. proletella parasitism rates. However, only the pumpkin system increased the abundance of syrphid larvae on cabbage by 61.5% and reduced A. proletella populations on average by 4.4%–25.8% depending on the respective assessment date. In conclusion, the pumpkin system revealed to be a promising (supplementary) control measure against A. proletella. Options for further improvement and standardization of the pumpkin system as well as a potential implementation in cabbage production are discussed.     

Differing acceptance of familiar and unfamiliar plant species by an oligophagous beetle

The mustard leaf beetle, Phaedon cochleariae (F.) (Coleoptera: Chrysomelidae), is specialized to feed and develop on various species within the Brassicaceae. In this study, we investigated the acceptance of several host plant species (Brassica rapa L. and Sinapis alba L.), commonly used by the beetle (familiar plants), and of various unfamiliar plants, including systematically and chemically related [Bunias orientalis L. (Brassicaceae) and Tropaeolum majus L. (Tropaeolaceae), both Brassicales], as well as unrelated non‐host plant species [Plantago lanceolata L. (Plantaginaceae); Lamiales]. Emphasis was laid on the acceptance of the neophyte B. orientalis, and on underlying cues responsible for the acceptance of the various species. Behavioural responses to plant volatiles were studied using a static four‐chamber olfactometer. Stimulants and deterrents were investigated by bioassay‐guided solid phase extraction and semi‐preparative high performance liquid chromatography. A difference in acceptance of plant species was found: odours and polar compounds of all Brassicales evoked attraction and feeding stimulation, respectively, in Ph. cochleariae. Glucosinolates and their volatile hydrolysis products could be the main compounds that are involved in attraction of the beetles. In contrast, Ph. cochleariae did not respond to odours of the non‐host P. lanceolata, and some fractions of this plant had feeding‐deterrent effects, due to the presence of iridoid glycosides, among others. Although adult females accepted the neophyte B. orientalis for oviposition, neonate larvae did not survive on it. The flavonoid‐containing fraction of this plant was deterrent, whereas a similar fraction had been shown to cause some feeding stimulation when derived from S. alba. Differences in qualitative and quantitative composition of related metabolites lead to differentiated plant acceptance, proving the complexity of plant cues and of insect responses that determine host acceptance behaviour. The possibility of a diet breadth enlargement to B. orientalis and the role of Ph. cochleariae as a putative native biocontrol agent of this invasive plant are discussed.     

Polyphagy and primary host plants: oviposition preference versus larval performance in the lepidopteran pest Helicoverpa armigera

Oviposition preference and several measures of offspring performance of Helicoverpa armigera (Hübner) were investigated on a subset of its host plants that were selected for their reputed importance in the field in Australia. They included cotton, pigeon pea, sweet corn, mungbean, bean and common sowthistle. Plants were at their flowering stage when presented to gravid female moths. Flowering pigeon pea evoked far more oviposition than did the other plant species and was the most preferred plant for neonate larval feeding. It also supported development of the most robust larvae and pupae, and these produced the most fecund moths. Common sowthistle and cotton were equally suitable to pigeon pea for larval development, but these two species received far fewer H. armigera eggs than did pigeon pea. Mungbean also received relatively few eggs, but it did support intermediate measures of larval growth and survival. Fewest eggs were laid on bean and it was also the least beneficial in terms of larval growth. Among the host plant species tested, only flowering pigeon pea supported a good relationship between oviposition preference of H. armigera and its subsequent offspring performance. Australian H. armigera moths are thus consistent with Indian H. armigera moths in their ovipositional behaviour and larval performance relative to pigeon pea. The results suggest that the host recognition and acceptance behaviour of this species is fixed across its geographical distribution and they support the theory that pigeon pea might be one of the primary host plants of this insect. These insights, together with published results on the sensory responses of the females to volatiles derived from the different host plant species tested here, help to explain why some plant species are primary targets for the ovipositing moths whereas others are only secondary targets of this polyphagous pest, which has a notoriously broad host range. Handling Editor: Joseph Dickens     

Survival and behavior of Plutella xylostella larvae on cabbages with leaf waxes altered by treatment with S-ethyl dipropylthiocarbamate

Cabbages (Brassica oleracea L.) treated with S-ethyl dipropylthiocarbamate (EPTC) herbicide had reduced amounts of leaf surface waxes (40.6% of controls) and reduced densities of leaf surface wax crystallites (20.8% of controls). Leaf waxes of EPTC-treated plants chemically and morphologically resembled leaf waxes of genetically glossy cabbages resistant to the diamondback moth Plutella xylostella (L.) (Lepidoptera: Plutellidae). Survival of larvae was significantly reduced on EPTC-treated cabbage plants in three out of four experiments (62.0–15.3% of survival on controls). P. xylostella neonates also moved more rapidly on EPTC-treated plants than on untreated controls (1.84±0.16 cm/min on controls vs. 3.94±0.24 cm/min on treated plants; P=0.0001). These results support the hypotheses that reduction in leaf waxes is the basis of resistance to P. xylostella in genetically glossy plants and that reduced acceptance by larvae is associated with this resistance. Modification of leaf surface waxes with EPTC or similar compounds may have potential as an economic control for P. xylostella in Brassica crops.     

“HAIRY CANOLA” – Arabidopsis GL3 Induces a Dense Covering of Trichomes on Brassica napus Seedlings

Transformation with the Arabidopsis bHLH gene 35S:GLABRA3 (GL3) produced novel B. napus plants with an extremely dense coverage of trichomes on seedling tissues (stems and young leaves). In contrast, trichomes were strongly induced in seedling stems and moderately induced in leaves of a hairy, purple phenotype transformed with a 2.2 kb allele of the maize anthocyanin regulator LEAF COLOUR (Lc), but only weakly induced by BOOSTER (B-Peru), the maize Lc 2.4 kb allele, or the Arabidopsis trichome MYB gene GLABRA1 (GL1). B. napus plants containing only the GL3 transgene had a greater proportion of trichomes on the adaxial leaf surface, whereas all other plant types had a greater proportion on the abaxial surface. Progeny of crosses between GL3⁺ and GL1⁺ plants resulted in trichome densities intermediate between a single-insertion GL3⁺ plant and a double-insertion GL3⁺ plant. None of the transformations stimulated trichomes on Brassica cotyledons or on non-seedling tissues. A small portion of bHLH gene-induced trichomes had a swollen terminal structure. The results suggest that trichome development in B. napus may be regulated differently from Arabidopsis. They also imply that insertion of GL3 into Brassica species under a tissue-specific promoter has strong potential for developing insect-resistant crop plants. Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.     

Transformation of the tropane alkaloid-producing medicinal plant Hyoscyamus muticus by particle bombardment

We report an efficient whole plant transformation system for Hyoscyamus muticus, an important medicinal plant of the Solanaceous family. We developed a system using a plasmid carrying the nptII and gusA genes, which was delivered into leaf explants by particle bombardment. Ten percent of bombarded leaf explants formed kanamycin-resistant callus, from which putative transgenic plants were recovered. The nptII gene conferring kanamycin resistance was found to be incorporated into the genome of all transgenic plants screened. Over 50% of the kanamycin resistant plants showed strong expression of the non-selected gusA gene. The majority of transgenic plants reached maturity, could be self pollinated, and produced fertile seed. A simple and efficient whole plant transformation system for this medicinal plant is an important step in furthering our understanding of tropane alkaloid production in plants.     

Abundances of thrips on plants in vegetative and flowering stages are related to plant volatiles

Western flower thrips (WFTs), Frankliniella occidentalis Pergrande, and onion thrips (OTs), Thrips tabaci Lindeman, are two cosmopolitan insect pests of agricultural and horticultural plants. Understanding the occurrence and development of thrips on plants is crucial for identifying suitable plants that can be used for developing a “push-pull” strategy against thrips. In this study, the dynamics of WFTs and OTs on plants (Allium fistulosum L., Medicago sativa L., Luffa cylindrica (L.) Roem., Ocimum basilicum L., and Schizonepeta tenuifolia (Benth.) Briq.) were investigated for two consecutive years (2018–2019). Throughout the survey, the abundances of both thrips species were strongly associated with plant species and plant phenology; both thrips species were present at relatively high densities on M. sativa but very low densities on O. basilicum and S. tenuifolia. Populations of both thrips species greatly increased during plant flowering. A Y-tube olfactory test was used to study the effects of plant volatiles in mediating thrips behaviour and showed that volatiles of M. sativa were attractive to both thrips species whether emitted by the plant in the vegetative or flowering stage, while volatiles of O. basilicum and S. tenuifolia were repellent to thrips. Additionally, because of the presence of a high number of floral chemicals, both thrips species exhibited a greater preference for volatiles emitted by plants in the flowering period over those emitted by plants in the vegetative period. Our observations indicate that plant species and flowering status play an important role in the abundance dynamics of thrips and that the volatiles of flowering plants attract thrips more strongly than volatiles emitted by vegetative plants. These findings can facilitate the screening of attractive/unattractive plants for developing push-pull strategies to control thrips.