The Effect of Cucurbitacin E Glycoside, a Feeding Stimulant for Corn Rootworm, on Biocontrol Fungi: Beauveria bassiana and Metarhizium anisopliae

Corn rootworms compulsively feed on cucurbitacins (bitter compounds found in many cucurbits), while most other pest insects are repelled by them. Several hypotheses have been proposed for this activity, but the results have been equivocal. One recent hypothesis suggested that cucurbitacin may provide protection against soil borne fungal entomopathogens, both in the adult corn rootworm and in the eggs laid in the soil. Any antifungal activity would preclude the use of this feeding stimulant to enhance the activity of fungal pathogens used in biocontrol. To test this hypothesis, we exposed two fungal pathogens of corn rootworm, Beauveria bassiana and Metarhizium anisopliae , to an extract from a bitter mutant of Hawkesbury watermelon, which contained about 0.05% cucurbitacin E glycoside. The extract inhibited the growth of both fungi. However, when the extract was sterilized by passing through a 0.45 micron filter, this inhibitory activity disappeared. Purified cucurbitacin E glycoside did not inhibit the growth of either fungus. Four Bacillus isolates (identified as Bacillus subtilis var. globigii and B. amyloliquefaciens ) were isolated from this extract which were able to inhibit the growth of both fungi. All of these bacteria excreted the inhibitory activity into the medium. Thus, the inhibition of fungal growth attributed to cucurbitacin may actually be due to bacteria incidentally associated with cucurbits.     

Molecular phylogeny of rootworms and related galerucine beetles (Coleoptera: Chrysomelidae)

The Galerucinae (Coleoptera: Chrysomelidae) sensu stricto (true galerucines) comprise a large assemblage of diverse phytophagous beetles containing over 5000 described species. Together with their sister taxon, the flea beetles, which differ from true galerucines by having the hind femora usually modified for jumping, the Galerucinae sensu lato comprises over 13 000 described species and is the largest natural group within the Chrysomelidae. Unlike the flea beetles, for which robust hierarchical classification schemes have not been erected, an existing taxonomic structure exists for the true galerucines, based mostly on the works of the late John Wilcox. In the most recent taxonomic list of the Galerucinae sensu stricto, five tribes were established comprising 29 sections housing 488 genera. The majority of the diversity within these tribes is found within the tribe Luperini, in which two genera, Monolepta and Diabrotica, are known to contain over 500 described species. Here, we extend the work from previous phylogenetic studies of the Galerucinae by analysing four amplicons from three gene regions (18S and 28S rRNA; COI) representing 249 taxa, providing the largest phylogenetic analysis of this taxon to date. Using two seven‐state RNA models, we combine five maximum likelihood models (RNA + DNA for the rRNAs; three separate DNA models for the COI codon positions) for these partitions and analyse the data under likelihood using Bayesian inference. The results of these two analyses are compared with those from equally weighted parsimony. Instead of choosing the results from one optimality criterion over another, either based on statistical support, tree topology or philosophical predisposition, we elect to draw attention to the similar results produced by all three analyses, illustrating the robustness of the data to these different analytical methods. In general, the results from all three analyses are consistent with each other and previous molecular phylogenetic reconstructions for Galerucinae, except that increased taxon sampling for several groups, namely the tribes Hylaspini and Oidini, has improved the phylogenetic position of these taxa. As with previous analyses, under‐sampled taxa, such as the Old World Metacyclini and all sections of the subtribe Luperina, continue to be unstable, with the few taxa representing these groups fluctuating in their positions based on the implemented optimality criterion. Nonetheless, we report here the most comprehensive phylogenetic estimation for the Galerucinae to date.     

Effect of Bacillus thuringiensis cry3Bb1 protein on the feeding behavior and longevity of adult western corn rootworms (Coleoptera: Chrysomelidae)

The first transgenic corn hybrids expressing the Bacillus thuringiensis (Bt) Cry3Bb1 protein to control corn rootworm (Diabrotica spp.) larvae were registered for commercial use in 2003. This study was conducted to investigate the effect of Cry3Bb1 protein in combination with a cucurbitacin bait on adult feeding and longevity of both organophosphate-resistant and -susceptible western corn rootworms, Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae). In choice and no-choice tests, possible repellency to the Bt protein was quantified by comparing beetle consumption of cellulose disks treated with three concentrations of Bt in combination with a feeding stimulant (Invite EC) to disks treated with stimulant alone. A lethal-time assay also was conducted to examine survival of beetles exposed to Bt protein in their diet. Results from these assays indicate that adult rootworms are not significantly deterred by the presence of Cry3Bb1 on the treated discs and that ingestion of toxin does not adversely affect adult longevity.     

A review of the natural enemies of beetles in the subtribe Diabroticina (Coleoptera: Chrysomelidae): implications for sustainable pest management

Diabroticina is a speciose subtribe of New World Chrysomelidae (Subfamily Galerucinae: Tribe Luperini) that includes pests such as corn rootworms, cucumber beetles and bean leaf beetles (e.g. Diabrotica, Acalymma, Cerotoma species). The evolution and spread of pesticide resistance, the European invasion of Diabrotica v. virgifera LeConte, and possible development of resistance due to the large-scale deployment of Diabrotica-active Bt maize in North America have generated a sense of urgency in developing biological control options against Diabroticina pests. In the present study, we review available knowledge on biological control options, including 290 publications on natural enemy–Diabroticina associations in the New World. Several natural enemy species or groups appear to be promising candidates for control strategies with different ecological rationales. We propose that future research should pursue: (1) development of inundative biological control products, particularly mass-produced entomopathogenic nematodes and fungi, (2) understanding of specific natural enemies of Diabroticina larvae throughout the Americas and of adults particularly in higher altitudes of Central America or northern South America including potential classical biological control agents against D. v. virgifera; (3) enhancement of natural enemies through cultural practices, i.e., reduced tillage, reduced weed control, cover crops, diversified crop rotations or soil amendments. Research and action must be coordinated to accelerate the exploration of biological control options.     

Mexican diabroticite beetles: I. Laboratory test on host breadth of Acalymma and Diabrotica spp.

Choice tests were conducted to determine relative degree of specialization of feeding behavior of 11 Mexican diabroticite species in the genera Acalymma and Diabrotica (Chrysomelidae: Luperini). Adult beetles were offered a choice between cotyledons of a non-bitter (not containing cucurbitacin) cucurbit (C. pepo L. var. Crookneck), corn (Zea mays L.), and beans (Phaseolus vulgaris L.). In a second assay a bitter (containing cucurbitacin) cucurbit (C. pepo L. var. Ambassador) was added to the array of plants offered. Neonates of two species of Acalymma and one species of Diabrotica were offered a choice between roots of a non-bitter and a bitter cucurbit, and between a bitter cucurbit and corn.Adult insects showed distinct preferences in the first assay. All Acalymma spp. tested accepted only the non-bitter cucurbit as host, whereas Diabrotica spp. preferred either the cucurbit or the noncucurbit hosts. When the bitter cucurbit was offered together with the other three hosts, all species changed their host choice and significantly preferred the bitter cucurbit. Neonates of all three species tested significantly preferred the bitter cucurbit roots over the non-bitter roots, and the corn roots over the bitter cucurbit.The observation that all Mexican diabroticite species tested left suitable hosts when bitter cucurbits were offered in a choice situation supported the hypothesis that the association between diabroticites and Cucurbitaceae is mediated by plant chemical compounds. For both, the Acalymma spp., which were found to be cucurbit specialists, as well as for the polyphagous Diabrotica spp., cucurbitacin B acted as a strong feeding arrestant which implies that the chemical mediation of this interaction might be an evolutionary conservative trait within the tribe.     

Effects of age, sex, and dietary history on response to cucurbitacin in Acalymma vittatum

The chrysomelid Acalymma vittatum is stenophagous, subsisting almost entirely on plants in the Cucurbitaceae, which generally contain cucurbitacins. Cucurbitacins are extremely bitter tetracyclic triterpenoids that are toxic to most organisms. As do other diabroticite beetles, A. vittatum sequester cucurbitacins, which have been shown to act as phagostimulants and arrestants. Our results reveal, however, that for A. vittatum the response to cucurbitacin diminishes with continued sequestration. Colony-reared A. vittatum were fed only roots (as larvae) and foliage of either `Marketmore 76' (which contains a normal amount of cucurbitacin, `bitter') or `Marketmore 80' (a near isogenic line that contains no cucurbitacin, `non-bitter') cucumber. Over 1200 individual beetles from the day of adult emergence to 15 days following emergence were placed in choice and no-choice arenas containing potted cotyledons of the two cucumber varieties for 24 h. In choice tests, overall preference for the bitter cucumber cultivar was maintained, but degree of preference changed with age and became significantly less for beetles reared on bitter diets. Furthermore, in no-choice tests, age, sex, dietary history, and interactions among these variables all significantly affected the feeding response to cucurbitacin. For A. vittatum reared without cucurbitacin, total consumption of the bitter cultivar increased over time. For beetles reared with cucurbitacin, total foliage consumption of the bitter cultivar declined, within nine days, to equal that of the non-bitter cultivar. Feral A. vittatum, unexpectedly, consumed more of the non-bitter than the bitter cultivar in no-choice tests. Ecological and applied implications of this variation in response to cucurbitacin are discussed.     

Consumption of residue containing cucurbitacin feeding stimulant and reduced rates of carbaryl insecticide by western corn rootworm (Coleoptera: Chrysomelidae).

Application of insecticide at a reduced rate with a cucurbitacin-based feeding stimulant is a viable alternative to a broadcast insecticide application for control of adult western corn rootworms, Diabrotica virgifera virgifera, LeConte. Because of the small amount of material applied, it is conceivable that a high density of beetles could consume all of the spray residue before economic control is achieved. A laboratory experiment was conducted to determine the amount of cucurbitacin-based spray residue consumed by beetles. Dried residue of four treatments were exposed to three groups of 10 rootworm beetles for 1 h each. Treatments consisted of a cucurbitacin-based adjuvant (Cidetrak CRW, Trécé, Salinas, CA) with carbaryl insecticide (Sevin XLR Plus, Rhone Poulenc, Research Triangle Park, NC) mixed at 0, 0.12, 1.2, and 12 g (AI)/liter. For the treatment with cucurbitacin adjuvant only (no insecticide), beetles consumed 0.029 mg beetle(-1) h(-1) of exposure. Approximately 54% of the beetles were recorded as feeding at any given time during the 60-min feeding period. However, when the spray residue contained carbaryl, no weight loss of treatment residue was measured, though the beetles were observed to feed from the residue during the first few minutes of exposure. When residue included insecticide, beetles quickly ceased feeding (within 20 min), and toxicity behavior was observed 30 min after initial exposure for up to 75% of the beetles, which were classified as moribund (unable to stand upright). Beetle mortality was recorded 24 h after exposure and demonstrated that male beetles (53% dead for three insecticide treatments) were more susceptible to carbaryl toxicity than female beetles (28% dead for three insecticide treatments). Regression analysis showed a significant positive relationship between mortality of female beetles and ovarian development. Based on the measurements of this experiment, it is unlikely that realistic beetle densities would consume enough spray residue to prevent economic control of the beetle population.     

Inhibition of seed germination by extracts of bitter Hawkesbury watermelon containing cucurbitacin, a feeding stimulant for corn rootworm (Coleoptera: Chrysomelidae)

Cucurbitacins are feeding stimulants for corn rootworm used in baits to control the adults of this insect pest. Corn rootworm larvae also feed compulsively on cucurbitacins. Cucurbitacins are reported to be gibberellin antagonists that may preclude their use as seed treatments for these soil-dwelling insects. The crude extract of a bitter Hawkesbury watermelon containing cucurbitacin E-glycoside significantly inhibited germination of watermelon, squash, and tomato seeds. Although the germination of corn seed was not significantly inhibited, root elongation was inhibited by crude extracts, but not by high-performance liquid chromatography-purified cucurbitacin E-glycoside. Therefore, the effects of the major components in the bitter watermelon extract (e.g., sugars) on seed germination and root elongation were determined. Pure sugars (glucose and fructose), at concentrations found in watermelon extract, mimicked the inhibition of seed germination and root elongation seen with the crude bitter Hawkesbury watermelon extract. Removal of these sugars may be necessary to use this extract as a bait for corn rootworm larvae as a seed or root treatment.     

Effects of host plant and cucurbitacin on growth of larval Diabrotica undecimpunctata howardi

The effects of host plant and dietary cucurbitacin on the growth of larval southern corn rootworm (SCR), Diabrotica undecimpunctata howardi Barber (Chrysomelidae: Luperini), were investigated. SCR were reared on four hosts: corn, Zea mays; peanuts, Arachis hypogaea; and two squash varieties, Cucurbita pepo cv. Ambassador (containing cucurbitacin D (0.08 mg g^–1 fr.wt.) = bitter), and C. pepo cv. Early Yellow Crookneck (lacking cucurbitacin = non-bitter). Larval growth was significantly greater on corn and peanuts than on either squash variety. After four weeks, adults had emerged from corn and peanut plants, while squash-reared larvae had not yet entered the pupal stage. There was no difference in larval growth on the two varieties of squash. Primary metabolite measurements showed no nutritional differences between the two squash varieties. Artificial diet experiments were used to test the effect of three concentrations of cucurbitacin D (0.0, 0.1, and 0.6 mg g^–1 diet) on growth of larval SCR. Larvae reared on diet containing 0.6 mg g^–1 cucurbitacin weighed significantly less than larvae reared on diet containing 0.1 mg g^–1 or no cucurbitacin after 10 d. No significant difference in growth was measured between the 0.1 mg g^–1 diet and the 0.0 mg g^–1 diet. Results are discussed relative to theories about the relationship between diabroticites and cucurbitacins.     

On the origin of the desert locust Schistocerca gregaria (Forskål) (Orthoptera: Acrididae: Cyrtacanthacridinae)

The locust genus Schistocerca (Stål) has a transatlantic disjunction, which has been controversial for more than a century. Among 50 species within the genus, only one species, the desert locust (S. gregaria Forskål), occurs in the Old World, and the rest occur in the New World. Earlier taxonomists suggested that the desert locust is a migrant from America, but this view was strongly challenged when a large swarm of the desert locust successfully crossed the Atlantic Ocean from West Africa to the West Indies in 1988. The currently accepted view, supported by this incident, is that the New World species are descendants of a gregaria-like ancestor, and the desert locust would be ancestral to the rest of the genus. However, there is surprisingly little evidence to support this view other than the 1988 swarm. I present the most comprehensive phylogenetic study that suggests that the desert locust originated from the New World, contrary to the accepted view. I also present a hypothesis about how the ancestral Schistocerca might have colonized the New World in the first place in light of phylogenetic relationships with other cyrtacanthacridine genera.     

Genetic Detection and Characterization of Lujo Virus,a New Hemorrhagic Fever–Associated Arenavirus from Southern Africa

Lujo virus (LUJV), a new member of the family Arenaviridae and the first hemorrhagic fever–associated arenavirus from the Old World discovered in three decades, was isolated in South Africa during an outbreak of human disease characterized by nosocomial transmission and an unprecedented high case fatality rate of 80% (4/5 cases). Unbiased pyrosequencing of RNA extracts from serum and tissues of outbreak victims enabled identification and detailed phylogenetic characterization within 72 hours of sample receipt. Full genome analyses of LUJV showed it to be unique and branching off the ancestral node of the Old World arenaviruses. The virus G1 glycoprotein sequence was highly diverse and almost equidistant from that of other Old World and New World arenaviruses, consistent with a potential distinctive receptor tropism. LUJV is a novel, genetically distinct, highly pathogenic arenavirus.     

Systematics and origin of moths in the subfamily Arctiinae (Lepidoptera,Erebidae) in the Neotropical region

The availability of standard protocols to obtain DNA sequences has allowed the inference of phylogenetic Hypotheses for many taxa, including moths. We here have inferred a phylogeny using maximum‐Likelihood and Bayesian approaches for a species‐rich group of moths (Erebidae, Arctiinae), with strong emphasis on Neotropical genera collected in different field campaigns in the Atlantic Forest of Brazil, eastern Amazon and southern Ecuador. A total of 277 species belonging to 246 genera were included in the analysis. Our main objectives were to shed light on the relationships between suprageneric groups, especially subtribes, and hypothesize colonization events in and out of the Neotropics. The monophyly of Arctiinae and its four tribes (Lithosiini, Amerilini, Syntomini and Arctiini) was recovered in the ML and Bayesian trees. Three Lithosiini subtribes previously found and two additional species groups were recovered monophyletic in both phylogenetic estimation methods. In Arctiini, the monophyly of Spilosomina and Arctiina was highly supported in the ML and Bayesian trees, but the monophyly of Ctenuchina and Echromiina was weakly supported in the ML tree and absent in the Bayesian tree; the remaining subtribes were paraphyletic and, in the case of Phageopterina, formed several species groups. The mapping of species occurrence in our ML tree suggests that Arctiinae have an Old World origin and that the Neotropical region was colonized at least six times independently. Our analysis also suggests that a number of species that occur in Neotropical and other zoogeographic regions may have originated in the Neotropics, although further taxon sampling is required to support this hypothesis. To our knowledge, this is the first time that a highly speciose group of tropical moths is well covered in a phylogeny, and it seems plausible that the results reported here may be extendable to other species‐rich tropical undersampled moth taxa.     

A molecular phylogenetic analysis of the vampire moths and their fruit-piercing relatives (Lepidoptera: Erebidae: Calpinae)

Within butterflies and moths, adult hematophagy is limited to species within the vampire moth genus Calyptra. These moths are placed within the subfamily Calpinae, whose other members are known to exhibit a broad range of feeding behaviors including those that can be considered 'piercers' of fruits or other hosts and 'tear feeders'. Here, we reconstruct a phylogenetic hypothesis of Calpinae using molecular data to test whether hematophagy in Calyptra arose from plant or animal-related behaviors. We use a Bayesian method of ancestral state reconstruction to determine the most likely feeding behaviors for the subtribes and genera within this lineage.     

Phylogeny of West AfricanCaryedon(Coleoptera: Bruchidae): Congruence between Molecular and Morphological Data

Seed beetles belonging to the Old World genusCaryedonfeed in the seeds of various Caesalpinioideae, Mimosoideae, and Combretaceae. In an attempt to resolve broad phylogenetic relationships within the genus, we obtained 332 base pair sequences of mitochondrial 12S ribosomal DNA and morphological data for the 16 West AfricanCaryedonspecies. Morphological characters were analyzed under maximum parsimony and sequences were compared under maximum parsimony, maximum likelihood, and neighbor joining. Using a partition homogeneity test, we determined that morphological and molecular data sets were combinable. Combined data were analyzed under maximum parsimony. Morphological and molecular trees were congruent at the species group level and total evidence analyses yielded the same topologies as molecular data with each of the three outgroups used. Four main terminal clades are recognized, each corresponding with a group of species generally feeding on the same host plant family, subfamily, genus, or species. The monophyly of legume feedingCaryedonis supported by both data sets, and Combretaceae feeders split in two monophyletic assemblages.     

Maxillary appendages used by western corn rootworms, Diabrotica virgifera virgifera, to discriminate between a phagostimulant and -deterrent

Ablation of maxillary appendages on western corn rootworm, Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae), were used to determine which mouthparts were involved in discrimination between the phagostimulant, cucurbitacin B, and the phagodeterrent, strychnine. Strychnine deterred feeding in unablated beetles when its concentration on disks was equal to or higher than cucurbitacin B. Unilateral or bilateral lacinea ablation did not affect discrimination between cucurbitacin B and strychnine. Galeal ablations abolished strychnine deterrence at equimolar concentrations of both compounds but not at higher strychnine concentrations, whereas maxillary palp ablation had no effect. However, bilateral ablation of both galea and maxillary palps resulted in a loss of deterrence at all strychnine concentrations. These results indicated strychnine sensitive chemoreceptors were primarily located on the galeae and maxillary palps. However, beetles without galeae and palps still feed on disks suggesting that cucurbitacin B sensitive chemoreceptors were located on other mouthparts and contributed to cucurbitacin B phagostimulation.     

A Molecular Phylogeny of the Tiger Beetles (Cicindelidae): Congruence of Mitochondrial and Nuclear rDNA Data Sets

As a basis for comparative studies in the family Cicindelidae (tiger beetles), a phylogenetic hypothesis for major groups was established based on molecular data, focusing on the taxa of the New World. Two markers, mitochondrial 16S rRNA and nuclear 18S rRNA, were sequenced for a total of 912 nucleotides and 30 taxa. All Cicindelidae were inferred to be a monophyletic group by the presence of a segment in the 5′ region of the 18S rDNA which is predicted to fold into a single stem-loop structure not present in the outgroup. The total number of variable and potentially informative positions was smaller in the 18S data set, but their higher internal consistency resulted in a strong phylogenetic signal. Inferred relationships were stable over a wide range of alignment parameters, but the inclusion of alignment-sensitive positions and presumptive gap characters added substantially to the resolution and overall support of the tree. Both data sets were in general congruence. The combined evidence suggests that relationships in Cicindelidae as currently recognized have to be reconsidered. No convincing evidence could be found for the traditional subdivision into two subfamilies, Cicindelinae and Collyrinae. The latter is embedded within the Cicindelinae and clearly not the sister to all other cicindelids. Most of the current tribes and subtribes, particularly in the Megacephalini, are paraphyletic groups, whereas monophyly of the large tribe Cicindelini is well supported by the molecular data.     

Repeated trans-Atlantic dispersal catalysed a global songbird radiation

Aim Turdus thrushes are one of the most speciose and widespread songbird genera, comprising nearly 70 species that combined have a near‐global distribution. Herein, we use molecular phylogenetic, molecular clock and behavioural evidence to examine the historical biogeography of the genus. Ancestral area reconstructions in conjunction with divergence estimates and palaeoclimatogical data are used to test whether the long‐standing paradigm of Beringian colonization or trans‐Atlantic dispersal best explains modern distributions in the New and Old Worlds. Location Worldwide, with emphasis on New World–Old World biotic interchange. Methods Using a molecular phylogenetic hypothesis of Turdus thrushes, we reconstructed ancestral area relationships utilizing the five major continental or regional areas occupied by species in the genus. We also examined the evolution of behaviours on the phylogeny, and estimated the timing of major lineage divergences via a molecular clock. Results Turdus originated in Eurasia, and following the colonization of Africa underwent a series of five trans‐Atlantic sweepstake dispersals. The data reject the alternative hypothesis that connections between Old and New World Turdus species can be attributed to movement through Beringia with subsequent extinction. Divergence estimates indicate that these dispersals all occurred near the Miocene–Pliocene boundary, 5 Ma. A significant phylogenetic correlation between migratory and flocking behaviour is evident in the genus. Main conclusions The initial divergence of Turdus in the Old World was followed by a series of trans‐Atlantic sweepstake dispersal events. These dispersals are temporally correlated with a specific palaeoclimatic system, which would have facilitated transport of Turdus from the Caribbean to the Old World across the Atlantic. Uplift of the Central American Seaway 4.7 Ma effectively shut down the palaeoclimatic system, and no additional trans‐Atlantic dispersals are evident in Turdus after this time. Migratory movements by ancestral lineages in flocks, rather than as single individuals, suggest an increased likelihood of successfully colonizing new areas, post‐dispersal.     

Examining Cuphea as a potential host for western corn rootworm (Coleoptera: Chrysomelidae): larval development

In previous crop rotation research, adult emergence traps placed in plots planted to Cuphea PSR-23 (a selected cross of Cuphea viscosissma Jacq. and Cuphea lanceolata Ait.) caught high numbers of adult western corn rootworms, Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae), suggesting that larvae may have completed development on this broadleaf plant. Because of this observation, a series of greenhouse and field experiments were conducted to test the hypothesis that Cuphea could serve as a host for larval development. Greenhouse-grown plants infested with neonates of a colonized nondiapausing strain of the beetle showed no survival of larvae on Cuphea, although larvae did survive on the positive control (corn, Zea mays L.) and negative control [sorghum, Sorghum bicolor (L.) Moench] plants. Soil samples collected 20 June, 7 July, and 29 July 2005 from field plots planted to Cuphea did not contain rootworm larvae compared with means of 1.28, 0.22, and 0.00 rootworms kg(-1) soil, respectively, for samples collected from plots planted to corn. Emergence traps captured a peak of eight beetles trap(-1) day(-1) from corn plots on 8 July compared with a peak of 0.5 beetle trap(-1) day(-1) on 4 August from Cuphea plots. Even though a few adult beetles were again captured in the emergence traps placed in the Cuphea plots, it is not thought to be the result of successful larval development on Cuphea roots. All the direct evidence reported here supports the conventional belief that rootworm larvae do not survive on broadleaf plants, including Cuphea.     

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.     

Field studies of the temporal response patterns of male Diabrotica virgifera virgifera LeConte and D. barberi Smith and Lawrence to 8R-methyl-2R-decyl propanoate

ABSTRACT. Variations in the diel response of male northern and western corn rootworms attracted to a synthetic pheromone source were examined in southwestern Ontario. Activity was measured by the number of males caught at hourly intervals in sticky traps baited with 8 R -methyl-2 R -decyl propanoate. Northern corn rootworm males were attracted to the pheromone between 22.30 and 0330 hours and were unresponsive at all other times at temperatures above 15°C. Western corn rootworm males had a bimodal response with peaks in attraction from 08.30 to 12.30 hours and again from 15.30 to 18.30 hours. While the period of peak attraction for northern corn rootworm males was well defined, the pattern for western corn rootworm males was erratic and many beetles were caught throughout the day. Evening temperatures below 15°C suppressed the activity of both northern and western corn rootworms. While the nightly period of activity for the northern corn rootworms was shifted by low temperatures to the following morning, that of the western corn rootworm was not altered substantially. As a result, peaks in the response of northern and western corn rootworm males occurred simultaneously under these conditions, suggesting strongly that temporal separation of activity periods was not an important factor in maintaining sexual isolation for these species in Ontario.