Adult Flea Beetles Research Articles

Evaluation of spring-type and winter-type Brassica napus germplasm for genetic diversity in response to flea beetle herbivory in typical and atypical planting windows

Current practices of flea beetle ( Phyllotreta spp.) control in Brassica napus L. rely heavily on seed treatments and due to growing concerns regarding the safety of such treatments on non-target and beneficial insect populations, genetic resistance would be beneficial for a more balanced integrated pest management strategy. However, none of the registered B. napus. canola varieties exhibit measurable resistance to flea beetle injury. To this end, an evaluation of 14 winter-type B. napus breeding lines and 15 spring-type B. napus breeding lines for resistance to flea beetle feedings was conducted, as it was found that at least one line in each family exhibited noticeably reduced flea beetle damage compared to sister lines in a breeding nursery. The study revealed natural genetic variation within B. napus for flea beetle antixenosis which could be used by dedicated breeders to develop canola varieties with higher levels of flea beetle resistance. Data indicated that host plant resistance did not vary between feeding by newly emerged adult flea beetles in the fall and the overwintered adults in the spring in either winter-type or spring-type canola, as well as for adult feeding preferences. This indicates that favourable genes identified in in either habitat-type could be used interchangeably to confer resistance even though the flea beetle life cycle is different for each planting period, while either overwintered adults or newly emerged adults can be used to evaluate feeding damage.

First record of <em>Microctonus brassicae</em> in Czechia, a potential biological control agent against a primary oilseed rape pest

After the ban on treating oilseed rape seeds with neonicotinoids in European Union, cabbage stem flea beetles (Psylliodes chrysocephala Linnaeus, 1758) again became one of its main pests. In Czechia, the impact of this pest increases every year, given with the narrowing spectrum of suitable insecticides and growing damage to oilseed rape plants in autumn. Based on this scenario, it is appropriate to look for alternative options to control oilseed rape pests. One option could be supporting beneficial organisms. One of these organisms is the hymenopteran braconid parasitoid Microctonus brassicae (Haeselbarth, 2008), which parasitizes adult cabbage stem flea beetles. Its occurrence has now been confirmed outside Great Britain in Czechia and continental Europe respectively. Five male specimens of M. brassicae emerged from 50 collected adults of cabbage stem flea beetle by sweep netting from two localities in central Bohemia. This parasitoid of adult cabbage stem flea beetles and its larval parasitoids probably play an important role in the life cycle and population dynamics of this pest. Current knowledge about the biology, taxonomic classification and identification of this parasitoid is summarized in this paper.

Effect of immigration time and beetle density on development of the cabbage stem flea beetle, (Psylliodes chrysocephala L.) and damage potential in winter oilseed rape

In a semi-field net cage experiment set up in three growing seasons (2015–2018) at Julius-Kühn Institute Braunschweig, Germany, the influence of different release times of adult cabbage stem flea beetles, Psylliodes chrysocephala (early September, mid-September, early October) and different beetle densities (6.7, 13.3 and 20 beetles/m2) on reproduction and damage potential in winter oil seed rape was investigated. In parallel to the cage trials, the number of deposited eggs was assessed in small boxes exposed in the field. Beetles released in early September laid significantly more eggs compared to beetles released early October, with a maximum of 270 eggs per female. The early release of beetles resulted in significantly higher numbers of larvae in autumn, but this differed significantly between the years. Warm autumn or winter conditions led to continued egg laying and development, whereas cold conditions stopped the reproduction. Significant yield losses (25%) and significant plant losses during winter were only found in 2016/17 in treatments with an early release of high numbers of beetles (20 beetles /m2). The German damage threshold of 3–5 larvae per plant was reached when 13 beetles/m2 were released before 20th September and 20 beetles per m2 after 20th September. Data of this study can be used for a better damage prediction and a more targeted beetle control.

Host Range of Cotton Flea Beetle (Podagrica puncticollis) in a Hot Dry Tropical Environment of Ethiopia

Cotton flea beetle, Podagrica puncticollis is the most destructive insect pest of cotton in north-western part of Ethiopia. This study was conducted to identify and determine the host range of cotton flea beetle in Metema area. The field survey was undertaken from June 27, 2015 to January 9, 2016 in ten kebele administrations of the district. At least three fields were prospected after every 15 days, in each kebele for host plants as well as to determine population density and percent leaf damage by adult cotton flea beetle, at different growth stages of cotton plant. The composition of plant species with damaged symptom or infested by flea beetle was analysed using quantitative means and identified by comparing specimens with description of identification manuals. A total of 11 host plant species of cotton flea beetle were identified in the cotton growing areas of Metema throughout a season. Indigofera longibarbata (Fabaceae), Hibiscus articulatus, H. cannabinus, H. vitifolius, Abutilon figarianum, Sida alba and S. urens (Malvaceae), Bidens pilosa and B. setigera (Asteraceae), Corchorus olitorius and C. trilocularis (Tiliaceae) found to be common host plants of cotton flea beetle. Thus, among the host plants, H. vitifolius, H. cannabinus, H. articulatus, C. olitorius and C. trilocularis were the most suitable hosts for adult cotton flea beetle in respect of the number of adults per plant and percent foliage damage they sustained. These findings could aid in developing longterm management strategies for this important insect pest existing in a hot dry tropical environment of north-western Ethiopia.

The potential of the solitary parasitoid Microctonus brassicae for the biological control of the adult cabbage stem flea beetle, Psylliodes chrysocephala.

The cabbage stem flea beetle (CSFB), Psylliodes chrysocephala L. (Coleoptera: Chrysomelidae), is a major pest of oilseed rape, Brassica napus L. (Brassicaceae), within the UK and continental Europe. Following the withdrawal of many broad‐spectrum pesticides, most importantly neonicotinoids, and with increased incidence of pyrethroid resistance, few chemical control options remain, resulting in the need for alternative pest management strategies. We identified the parasitoid wasp Microctonus brassicae (Haeselbarth) (Hymenoptera: Braconidae) within CSFB collected from three independent sites in Norfolk, UK. Parasitism of adult CSFB was confirmed, and wasp oviposition behaviour was described. Moreover, we show that within captive colonies parasitism rates are sufficient to generate significant biological control of CSFB populations. A sequence of the M. brassicae mitochondrial cytochrome oxidase 1 (MT‐CO1) gene was generated for rapid future identification. Moroccan specimens of Microctonus aethiopoides (Loan), possessing 90% sequence similarity, were the closest identified sequenced species. This study represents the first description published in English of this parasitoid of the adult cabbage stem flea beetle.

Two methods for rearing the striped flea beetle Phyllotreta striolata (Coleoptera: Chrysomelidae) under laboratory conditions

AbstractThe striped flea beetle, Phyllotreta striolata (Fabricius) (Coleoptera: Chrysomelidae), is a major pest of canola (Brassica Linnaeus, Brassicaceae) on the Canadian prairies. The previously published methods to rear striped flea beetles under laboratory conditions are not sufficient to maintain laboratory colonies over a sustained period of time. Here, we describe two methods to rear striped flea beetles in the laboratory. The first method produces both immature stages and adult flea beetles using Napa cabbage (Brassica napa subsp. pekinensis (Loureiro) Hanelt) and canola as food sources. Beetles reared using this method produced an average of 9.7 ± 4.5 eggs, had a juvenile development period of between 26 and 33 days, and had an adult longevity between 17 and 55 days. Between 62% and 90% of the colony-reared eggs resulted in the successful development to an adult beetle. The second method uses canola as the only host, and facilitates easy access to high quantities of adult beetles. This method resulted in a six-fold to nine-fold increase in adult numbers per generation. Developmental time from adult to adult ranged from 25 to 30 days. Our two methods facilitated rearing striped flea beetles for several generations in the laboratory with or without hibernation.

Efficacy of Entomopathogenic Nematodes and Sprayable Polymer Gel Against Crucifer Flea Beetle (Coleoptera: Chrysomelidae) on Canola.

The crucifer flea beetle, Phyllotreta cruciferae (Goeze), is a key pest of canola (Brassica napus L.) in the northern Great Plains of North America. The efficacies of entomopathogenic nematodes (Steinernema spp. and Heterorhabditis spp.), a sprayable polymer gel, and a combination of both were assessed on canola for flea beetle management. Plots were treated soon after colonization by adult flea beetles, when canola was in the cotyledon to one-leaf stage. Ten plants along a 3.6-m section of row were selected and rated at pre-treatment and 7 and 14 d post treatment using the damage-rating scheme advanced by the European Plant Protection Organization, where 1 = 0%, 2 = 2%, 3 = 5%, 4 = 10%, and 5 = 25% leaf area injury. Under moderate flea beetle feeding pressure (1-3.3% leaf area damaged), seeds treated with Gaucho 600 (Bayer CropScience LP Raleigh, NC) (imidacloprid) produced the highest yield (843.2 kg/ha). Meanwhile, Barricade (Barricade International, Inc. Hobe Sound, FL) (polymer gel; 1%) + Scanmask (BioLogic Company Inc, Willow Hill, PA) (Steinernema feltiae) resulted in the highest yields: 1020.8 kg/ha under high (2.0-5.3% leaf area damaged), and 670.2 kg/ha at extremely high (4.3-8.6 % leaf area damaged) feeding pressure. Our results suggest that Barricade (1%) + Scanmask (S. feltiae) can serve as an alternative to the conventional chemical seed treatment. Moreover, Scanmask (S. feltiae) can be used to complement the effects of seed treatment after its protection has run out.

Flea beetle (Chrysomelidae: Alticinae) species composition and abundance in different cruciferous oilseed crops and the potential for a trap crop system

Flea beetles are significant insect pests of cruciferous oilseed crops in northern Europe. A two-year small-scale field experiment was performed to determine the species complex and abundance of flea beetles (Chrysomelidae: Alticinae) associated with eight cruciferous oilseed plants: Brassica juncea (L.) Czern., Brassica napus L. var. oleifera subvar. annua, Brassica nigra (L.) Koch, Brassica rapa L. var. oleifera subvar. annua, Camelina sativa (L.) Crantz, Eruca sativa Mill., Raphanus sativus L. spp. oleifera (DC) Metzg. and Sinapis alba L. Their relative attractiveness to flea beetles was compared to assess their potential for use within a trap crop system for spring oilseed rape. Adults of six species of flea beetles were found on the test plants. Phyllotreta undulata Kutsch. was the most abundant species followed by Phyllotreta nigripes (Fabr.), Phyllotreta nemorum L. and Phyllotreta vittata (=striolata) (Fabr.), while Phyllotreta atra (Fabr.) and Chaetocnema concinna Marsh. were occasionally present. The species composition of flea beetles on seven of the investigated plant species was fairly similar but differed significantly on C. sativa. The flea beetle species discriminated between the tested host plants, with a general gradient in attraction from E. sativa > B. juncea > B. nigra > R. sativus > S. alba > B. rapa > B. napus through to C. sativa. Brassica juncea and B. nigra developed faster and at early growth stages were more attractive to overwintered adult flea beetles than B. napus and therefore had potential as trap plants to protect spring rape. R. sativus and E. sativa, despite their development rate being slower than B. napus were also more attractive to flea beetles. Thus, further experiments with a complex of attractive early season and late-season plant species (multiple trap crops) should be undertaken.

The invasive flea beetle Luperomorpha xanthodera (Coleoptera: Chrysomelidae: Alticinae), potentially noxious to ornamental plants – first record in Poland

Abstract A specimen of a flea beetle collected by plant sweeping from an experimental plot of oregano in Warsaw showed characteristics of the invasive species Luperomorpha xanthodera. This beetle, originating from Far East, appeared in Europe at the beginning of this century and seems to extend its range continuously. So far, it has been noted from England, Italy, France, The Netherlands, Germany, Austria and Hungary but not from Poland. Being polyphagous, adult flea beetles of this species may appear in numbers on flowers of various ornamental plants causing considerable damage.

Physiological Response of Okra to Flea Beetle Herbivory as Measured by Leaf Loss, Chlorophyll Disruption, and Dry Matter Yield

Okra, Abelmoschus esculentus (L.) Moench, is attacked by the adult chrysomelid flea beetles, Podagrica spp. Information on physiological disruptions that occur due to flea beetle infestation affecting okra yield loss is incomplete. Screenhouse and field experiments were established to examine the effects of insect populations on leaf abscission, chlorophyll concentration, and biomass partitioning. Okra plants were grown in wire mesh screen cages and artificially infested with flea beetles, P. uniforma Jac., at population densities of 0, 5, 10, 20, 30, and 40 pairs per plant at 3 weeks after sowing (1 pair = 1 male and 1 female). In both experiments, okra plants had increased leaf abscission up to 100% at the 40-pair level in response to P. uniforma–induced injury. There were no significant differences in chlorophyll concentrations of plants at 0-, 5-, and 10-pair levels of infestation, suggesting the use of a compensatory mechanism by plants; at the 20-pair level a significant reduction occurred. Number of leaves per plant, shoots, roots, and dry fruit and total dry matter yield were reduced with infestation above the 20-pair level. More biomass was partitioned into roots at the 5- and 10-pair levels, but insect damage at populations beyond these levels completely suppressed the plant's ability to partition biomass. Dry fruit yields were reduced more than 50% when beetle populations increased beyond 20 pairs in both experiments. There was a correlation between insect density and number of leaves per plant and shoot, root, dry fruit, and total dry matter yield. The reduction in okra leaf production and chlorophyll content and increase in leaf abscission as a result of flea beetle infestation apparently resulted in a reduction in dry matter yield. The 20-pair level appeared to be the damage threshold of the insects. Physiological disruptions induced by the flea beetle at this level overcame the plants' ability to compensate for damage and caused significant reductions in leaf production, chlorophyll content, and dry matter yield and an increase in leaf abscission.

Leaf ageing promotes the shift in defence tactics in Mallotus japonicus from direct to indirect defence

Summary1. Most plant species rely upon multiple lines of defence that develop or change functions with leaf age. To date, the effects of leaf age on multiple defence traits have been insufficiently elucidated. For Mallotus japonicus (Euphorbiaceae), we report a shift from direct to indirect defence against herbivory. That shift occurs gradually during leaf ageing.2. First, the densities of trichomes and pellucid dots, the numbers of extrafloral nectaries (EFNs) and pearl bodies, and the number of ants on leaves of M. japonicus were examined in the field at weekly intervals. Secondly, herbivore species and the degree of herbivory were examined. Thirdly, the effects of ants on herbivore exclusion were investigated experimentally in the field. Finally, to confirm the effectiveness of trichomes and pellucid dots for defence against two herbivore species [the adult flea beetle, Aphthona strigosa (Coleoptera: Chrysomelidae), and the inchworm, Ascotis selenaria (Lepidoptera: Geometridae)], both young and middle‐aged leaves were tested using laboratory bioassay.3. On newly emerged leaves, densities of trichomes and pellucid dots were extremely high, but they decreased rapidly with leaf age. The respective quantities of EFNs that were actually secreting nectar, the pearl bodies, and the ants on middle‐aged leaves were greater than those on leaves of other ages. On M. japonicus, we found 11 herbivorous insects, among which Ap. strigosa and As. selenaria were the principal herbivores.4. The damaged leaf areas of ant‐excluded plants were much larger than those of control plants. Most herbivory was attributable to As. selenaria. Laboratory bioassay revealed that against Ap. strigosa and small As. selenaria larvae, trichomes and pellucid dots in young leaves functioned well, although those in middle‐aged leaves did not.5. Synthesis. Young M. japonicus leaves are defended against herbivores through the use of direct defence traits such as trichomes and pellucid dots. However, the plant uses indirect defence traits for middle‐aged leaves. This shift from direct defence to indirect defence with leaf ageing supports the ‘optimal defence theory’: plants have evolved multiple defence traits to maximize their fitness.

Laboratory Toxicity Profile of an Organic Formulation of Spinosad against the Eggplant Flea Beetle, Epitrix Fuscula Crotch

The eggplant flea beetle, Epitrix fuscula Crotch, is a major insect pest of eggplant, Solanum melongena L. var. esculentum (Solanaceae), produced in the south central United States and often requires management with insecticides immediately following setting of transplants into the field. Few insecticides approved for use in organic production have provided effective management of the beetles. The study reported herein demonstrates the effectiveness of Entrust, a new organic approved formulation of spinosad. Following exposure on eggplant foliage, Entrust was shown to be toxic to adult flea beetles with LC50 and LC95 values of 42.9 and 296.7 ppm, respectively. Although mortality following exposure was sometimes delayed until six days, the effects on flea beetle behavior were observed in as little as six hours following exposure. Feeding was significantly reduced one day after exposure to both the highest recommended field rate and to a 25% concentration of the high rate. Persistence in the field was short. No significant differences in mortality were detected for beetles transferred to treated and water-treated eggplant foliage taken three days after application. Of the insecticides approved for use in organic production, Entrust likely offers an excellent choice for management of eggplant flea beetles on eggplant.

Insights Into Flea Beetle (Coleoptera: Chrysomelidae: Galerucinae) Host Specificity From Concordant Mitochondrial and Nuclear DNA Phylogenies

Abstract Flea beetles in the genus Altica are herbivorous, urban agricultural pests that are morphologically difficult to distinguish. Host plant associations, therefore, have been used as an important species character in field studies. Indigenous weeds in the Onagraceae, genus Oenothera, are known to serve as developmental hosts for the flea beetle Altica litigata Fall. Although host plant specificity in herbivorous beetles is labile and adult A. litigata have been reported to aggregately feed on plants in the nonindigenous Lythraceae, genus Lagerstroemia, there is no evidence that these ornamental trees serve as developmental hosts. Because adult A. litigata feed on host plants from species in two plant genera, this study was designed to test two hypotheses. The first hypothesis that was tested was whether adult flea beetles collected from primrose and crape myrtle plants across four ecoregions are phenotypically (morphology) and genotypically (genotype) A. litigata. The second hypothesis that was tested was whether two unlinked loci, cytochrome oxidase subunit I and internal transcribed spacer, are phylogenetically concordant for flea beetle species. If so, they could be used to determine the intraspecific geographic history of A. litigata collected from Oenothera and Lagerstroemia species. We discuss how these markers, in conjunction with morphology and host plant feeding behavior, can not only help to validate morphologically difficult taxa but also can illuminate herbivore-plant genetic structure through phylogeny analyses.

Impact of entomopathogenic nematodes on adults of Phyllotreta spp. (Coleoptera: Chrysomelidae) under laboratory conditions

In 2005, preparations of four species of the entomopathogenic nematodes Steinernema feltiae, S. carpocapsae, Heterorhabditis bacteriophora, and H. megidis, were tested under laboratory conditions for their ability to kill adult flea beetles, Phyllotreta spp. (Coleoptera: Chrysomelidae). The nematode preparations were tested at doses of 200, 1000, and 2000 IJs per adult and at temperatures 15°C, 20°C, and 25°C. The numbers of beetles killed were recorded two, four, six, and eight days after treatment. The nematodes were more effective at 20°C and 25°C than at 15°C. At 20°C, the nematodes had killed between 44% (H. megidis at the lowest dose tested) and 77% (S. feltiae at the lowest dose tested) of the beetles eight days after treatment. At the two highest doses tested, the S. feltiae, S. carpocapsae, and H. bacteriophora preparations each killed at least 74% of the beetles at 25°C. Steinernema feltiae was the most effective nematode (LC50=483–1467 IJs/adult) and, as an alternative to chemical insecticides, appears to have the highest potential for controlling overwintered flea beetles (May) under field conditions. The nematodes S. feltiae, S. carpocapsae and H. bacteriophora would all be suitable for controlling adult flea beetles during warm summer months, when flea beetles occur in high numbers in Slovenia.

Differential Resistance Among Crape Myrtle (Lagerstroemia) Species, Hybrids, and Cultivars to Foliar Feeding by Adult Flea Beetles (Altica litigata)

Field (choice) and laboratory (no choice) studies were conducted to evaluate the susceptibility of 12 crape myrtle (Lagerstroemia) cultivars, representing two species and their interspecific hybrids, to feeding damage by the flea beetle (Altica litigata Fall). The results indicate that as a group, the L. indica L. cultivars were more susceptible to attack and significant herbivory damage by Altica beetles, whereas all the L. fauriei Koehne cultivars and most of the interspecific L. indica × fauriei hybrids were resistant. Significant differences in feeding damage were observed between the new and older leaves in the susceptible hybrid ‘Biloxi’ and L. indica ‘Whit IV’, but not in the rest of the cultivars. Mineral nutrient content differences were observed between species with L. indica cultivars having a significantly contrasting nutrient status profile compared with the L. fauriei and interspecific hybrid cultivar groups. The results indicate that the factors influencing Altica flea beetle-feeding preferences and damage are inherited and therefore will allow the implementation of pest management practices that minimize damage and optimize chemical control strategies. In addition, opportunities may exist for breeding and selection efforts that could lead to superior cultivars with insect resistance.

Heterogeneity of plant phenotypes caused by herbivore‐specific induced responses influences the spatial distribution of herbivores

Abstract 1. Herbivory can induce resistance in a plant and the induced phenotype may be disfavoured by subsequent herbivores. Yet, as the distance between plants in a population increases, limited mobility may make a herbivore more likely to feed and oviposit on host plants in its immediate surroundings.2. The present study tested whether a herbivore’s preference and distribution across plants with different induced phenotypes was influenced by the spatial distribution of plants. A fragmented population of Solanum dulcamara plants was created. This consisted of discrete, spatially separated patches with different histories of damage, either herbivory from adult flea beetles (Psylliodes affinis), tortoise beetles (Plagiometriona clavata), or mechanical damage. Each patch was separated by 7 m and consisted of 12 plants that were spaced 30 cm apart. Then a fixed number of adult tortoise beetles were introduced to each patch, and movement and oviposition within and between spatially separate homogeneous patches (receiving one type of damage) were compared with movement and oviposition within heterogeneous patches (containing all three types of damage) over the growing season.3. Flea beetle and tortoise beetle herbivory consistently induced different phytochemical responses in S. dulcamara (polyphenol oxidase and peroxidase), and adult tortoise beetles avoided oviposition on the flea beetle induced plants within heterogeneous patches. However, between homogeneous patches, plant phenotype did not influence oviposition. Colonisation by naturally occurring flea beetle adults followed a similar pattern.4. These results suggest that the heterogeneity of plant phenotypes can influence herbivore choice and distribution at small but not large spatial scales.

Comparisons of Ecorational and Chemical Insecticides Against Crucifer Flea Beetle (Coleoptera: Chrysomelidae) on Canola

Studies were done comparing the insecticides SpinTor (spinosad), BotaniGard (Beauveria bassiana), Neemix (azadirachtin), and Surround (kaolin, a clay) with conventional chemical insecticides Capture (bifenthrin) and Helix XTra (thiamethoxam), all applied at seven rates in a 7-d assay to assess their impact on adult crucifer flea beetle, Phyllotreta cruciferae (Goeze) (Coleoptera: Chrysomelidae). Lethal time (LT) required for 25, 50, and 75% mortality (LT25, LT50, and LT75) and relative potencies for the insecticide concentration groupings (0, 1X-1.5X, and 2X- 4X) were estimated for each treatment by using survival functions. P. cruciferae mortality increased in response to increasing concentrations, especially for Helix XTra, Capture and SpinTor. After 2 d of exposure in 2002, mortality ranged from 54 to 78% for Helix XTra, from 60 to 94% for Capture, and from 66 to 92% for SpinTor across concentrations. In 2003, flea beetle mortality ranged from 37 to 60%, from 29 to 63%, and from 23 to 52% on exposure to Helix XTra, Capture, and SpinTor, respectively, for 2 d. The LT50 and relative potencies of the insecticides were in the order of Helix XTra, Capture, and SpinTor > BotaniGard, Neemix, and Surround. In 2002, LT50 values were 1 and 2 d for Capture and SpinTor, 2 d for BotaniGard, and 3 d for Neemix and Surround. In 2003, LT50 values occurred between 2 and 4 d after exposure to Helix XTra, Capture, and SpinTor, with LT50 values of 5-7 d on exposure to BotaniGard, Neemix, and Surround. SpinTor seems to be a suitable ecorational insecticide in canola, Brassica napus L., for P. cruciferae management.

Bioassay for assessing resistance of Arabidopsis thaliana L. (Heynh.) to the adult crucifer flea beetle, Phyllotreta cruciferae (Goeze) (Coleoptera: Chrysomelidae)

A bioassay arena and a laboratory screening protocol were developed for assessing lines of Arabidopsis thaliana L. (Heynh.) for feeding damage by the adult crucifer flea beetle, Phyllotreta cruciferae (Goeze). The arena consists of a 96-well microtitre plate with a modified top to contain flea beetles and allow ventilation. Eight lines of A. thaliana, arranged in an 8 × 8 Latin square design, were screened simultaneously in each arena using 50 starved flea beetles. Two cotyledons and the first pair of true leaves per plant were rated visually under a dissecting microscope using a visual damage rating scale. The protocol was used to screen 29 wild ecotypes, eight mutant lines and a single transgenic line of A. thaliana. Discrimination between both cotyledon and leaf tissue was apparent for young beetles that were both non-reproductive or reproductive, but not for old reproductive beetles. Differences were observed between Asian and European ecotypes of A. thaliana, suggesting that geographic origin may play a role in susceptibility of Arabidopsis ecotypes to flea beetle feeding. The transparent testa regulatory gene mutants (lines 82, 111, 164) were most susceptible to flea beetle feeding, possibly indicating a role for anthocyanins and/or flavonoids in governing flea beetle susceptibility. Significant variation in damage levels indicates that expression of flea beetle resistance in the A rabidopsis genome is plastic, and that potential exists to use the wide array of publicly available Arabidopsis germplasm as tools in the transfer of resistance to agronomically important host plants. Key words: Seedling bioassay, Arabidopsis thaliana, wild ecotypes and mutants, crucifer flea beetle, Phyllotreta cruciferae, host plant resistance

Prefeeding Behavior of the Crucifer Flea Beetle, Phyllotreta cruciferae, on Host and Nonhost Crucifers

The prefeeding behaviours of adult crucifer flea beetles, Phyllotreta cruciferae (Coleoptera: Chrysomelidae: Alticinae), were determined on seedlings of the host plant, Brassica napus, and compared to behaviors on seedlings of the nonhost crucifers, Crambe abyssinica, Sinapis alba, and Camelina sativa. Three stages of prefeeding behaviour, i.e., acclimation, stimulation, and initial feeding, were distinguished through observation of filmed beetles. Both antennal and tarsal chemoreceptors are important in determination of host plant quality by the crucifer flea beetle. The results of this study suggest that the sequence of prefeeding behaviors plays a crucial role in the onset of feeding. Differences in time spent on plant tissue and the frequency and duration of prefeeding behaviors provide insight into possible mechanisms of resistance to flea beetles in the non-Brassica crucifers. The nonpreferred hosts C. abyssinica and S. alba contain deterrent phytochemicals that partially inhibit feeding. These deterrent compounds appear to be volatile in nature in S. alba but nonvolatile in C. abyssinica. CFB resistance in the nonhost C. sativa may result from either the presence of repellent or the absence of stimulatory volatile phytochemicals.

Action spectra of phototactic responses of the flea beetle, Phyllotreta striolata

Abstract. Adult flea beetles, Phyllotreta striolata, show a strong positive phototactic response. The action spectrum of phototaxis of dark‐adapted beetles was measured with minimal required light intensity between the wavelength range of 300 nm and 600 nm. Male and female flea beetles showed identical phototacitc behaviours. The beetles were most sensitive to light with peak wavelengths between 350 nm and 430 nm in the morning. In the afternoon and evening, the sensitivity to wavelengths shorter than 430 nm decreased, but they remained most sensitive to 430 nm. These results suggest that changes in sensitivity of the photoreceptors or nervous integration influence the phototactic responses, and that the blue wavelengths are more attractive than others.