Individual variation in two host plants of the ladybird beetle,Epilachna pustulosa (Coleoptera: Coccinellidae)

Individual variation in two species of host plants (thistle,Cirsium kamtschaticum, and blue cohosh,Caulophyllum robustum) of the herbivorous ladybird beetleEpilachna pustulosa was examined under laboratory conditions for their acceptability to adult beetles as a food resource, for adult preference and for larval performance. When clones of these plants were subjected to non-choice tests using posthibernating female beetles, there was found to be significant intraspecific variation among clones in terms of their acceptability, but interspecific variation was not detected. Significant intraspecific as well as interspecific variation were frequently detected in the two host plants when clones of these plants were subjected to choice tests using posthibernating female beetles; the magnitude of interspecific plant variation for beetle preference is not necessarily larger than that of intraspecific plant variation. Individual variation across plant species with respect to beetle larval performance was also significant. A positive correlation between adult preference and larval performance is suggested across the two taxonomically remote host plant species, thistle and blue cohosh, although this needs further investigation.     

Eucalypt responses to fertilization and reduced herbivory

Summary We manipulated soil fertility and insect attack for two species of Eucalyptus in natural stands of subalpine woodland on shallow, infertile granitic soils. E. pauciflora and E. stellulata responded in similar ways to simultaneous insecticide and fertilizer treatments. Eliminating herbivorous insects produced the largest changes — improved plant growth, increased leaf N and P, and reduced leaf specific density. Fertilizer regime modified some leaf properties, but had little effect on tree growth. E. stellulata trees were initially shorter than E. pauciflora, but grew faster without herbivores; by the end of the experiment both species were the same size when herbivores were removed. Foliage N and P levels increased most in trees with the most balanced fertilizer addition (NPK), and increased in all trees protected from insects, regardless of fertilizer regime. In this system, herbivorous insects exacerbated the effects of nutrientpoor soils, and may affect dominance of Eucalyptus species in mature forests.     

The role of aggregation in the response of Mexican bean beetles to host-plant density

Summary According to the resource concentration hypothesis, specialized insect herbivores predominantly attack host plants growing in pure, large, and/or dense stands because they are more likely to find and less likely to leave such stands. This study examines movement of a herbivorous beetle, Epilachna varivestis, in an attempt to understand why the beetle's numbers per plant increase with plant density. I studied immigration into, emigration from, and movement within host patches by following movements of individually marked beetles, while experimentally varying host-plant density. In order to study the effect of conspecifics on movement, I varied the number of beetles released on the same plant.The probability of intrapatch movement decreased, and the probability of emigration increased when plant density was reduced. Both immigration rate and intrapatch movement were strongly affected by presence or absence of conspecifics. Beetles were much more likely to stop at plants with a high number of beetles, compared to plants without beetles.On the basis of these results I advance a model that provides a mechanistic explanation of why dense patches should acquire high herbivore loads in the E. varivestis-garden bean system. Movement in Mexican bean beetles is strongly aggregative, and in dense patches frequent intrapatch movement provides ample opportunity for beetle aggregations to build up. In sparse patches, however, intrapatch movement is virtually absent and such aggregations are less likely to arise.     

Biological control of <Emphasis Type="Italic">Lantana camara</Emphasis> in South Africa: targeting a different niche with a root-feeding agent, <Emphasis Type="Italic">Longitarsus</Emphasis> sp.

The root-feeding flea beetle, Longitarsus sp. (Coleoptera: Chrysomelidae: Alticinae), was studied as a potential biological control agent for Lantana camara L. (Verbenaceae) in South Africa. Host range tests were carried out on 52 plant species in 11 families. Although 11 plant species, all in the family Verbenaceae, supported complete development of Longitarsus sp. during no-choice tests, the beetles showed very strong preferences for L. camara during paired-choice and multi-choice tests. The results confirm that the beetles have a narrow host range, and that under natural conditions they are highly unlikely to utilise plants other than L. camara. In the unlikely event that some of the Lippia spp. are attacked in the field, they are not expected to sustain populations of the flea beetle over time. Attributes that should enhance the biocontrol potential of Longitarsus sp. include: the adults are long-lived and highly mobile; and, the larvae cause extensive direct damage to the roots of L. camara, which could in turn expose the plants to soil-born pathogens. All indications are that Longitarsus sp. could make a substantial contribution to the biological control of L. camara in many countries around the world because the beetles pose no threat to non-target plant species and they damage a part of the plant (i.e. roots) not yet affected by any other agent species.     

Patch colonization by Trirhabda canadensis (Coleoptera: Chrysomelidae): effects of plant species composition and wind

Summary The goldenrod leaf beetle, Trirhabda canadensis, is known to respond to odors of host and non-host species in the laboratory. Here we report movements of T. canadensis in the field in response to volatile odors from monocultures and polycultures of host plants. Overall, beetles preferentially colonized plots with a higher density of host plants and lower diversity of allelochemicals, but under some wind conditions there were marked exceptions. At high windspeeds, they colonized whichever plot(s) was upwind. At low windspeeds, beetles colonized preferred plots even when they were not upwind. The data suggest that odor dispersion varies in a complex way with windspeed: at low windspeeds beetles received information from a wide are of vegetation and made choices while at high windspeeds information was available only from upwind plot(s).     

Plant stress and insect performance: cottonwood,ozone and a leaf beetle

Summary Leaf area consumption rates, development rates, survivorship, and fecundity of the imported willow leaf beetle (Plagiodera versicolora Laich) were examined on two clones of eastern cottonwood which were previously exposed to ozone or charcoal-filtered air. P. versicolora consumed more ozone treated foliage, but were more fecund when reared on charcoal-filtered air treated plants. Beetle development rates and survivorship were not significantly different on treated and control cottonwoods. We concluded that: 1) Ozone fumigation of cottonwood reduced foliage quality, and the reproductive success and overall performance of P. versicolora. 2) increased foliage consumption by beetles was probably a mechanism compensating for decreases in foliage quality. 3) Reductions in beetle fecundity were due to an initial reduction in oviposition rates. 4) Beetle feeding preference did not correlate with the suitability of foliage for beetle performance. These results are discussed in relation to the impact of air pollution on plant-insect interactions.     

The effects of wilt symptom development and peroxidase induction on interactions between vascular wilt bacteria and cucumber beetles

Infection of cucumber (Cucumis sativus L.) with the bacterial pathogen Erwinia tracheiphila E. F. Smith causes vascular wilt disease in leaves, which may alter the suitability of the host plant for insects and other pathogens. In this study, densities of spotted (Diabrotica undecimpunctata howardi Barber) and striped (Acalymma vittata (Fab.) cucumber beetles (Coleoptera: Chrysomelidae) were higher on wilted leaves of mature and seedling field plants inoculated with E. tracheiphila. Bacterial infection or feeding by D. undecimpunctata howardii beetles increased total peroxidase enzyme activity in inoculated or infested leaves of greenhouse seedlings, but only beetle feeding induced higher activities in untreated systemic leaves on the same plants. Neither bacterial infection nor beetle infestation led to the development of systemic acquired resistance (SAR) to the fungal pathogen Colletotrichum orbiculare (Berk & Mont.) Arx. Susceptibility to this fungus was greater on E. tracheiphila-infected plants than on controls. The positive association between leaf wilt symptom development and beetle occurrence thus occurs in the presence of an oxidative but not anti-pathogenic response induced by both the insect and the pathogen.     

Whorl and pollen-shed stage application of Beauveria bassiana for suppression of adult western corn rootworm

The corn rootworm complex is the most damaging insect pest of corn (Zea mays L.). This study was conducted to determine the efficacy of whorl and pollen-shed stage applications of a granular formulation of Beauveria bassiana (Balsamo) Vuillemin for control of adult western corn rootworm (Diabrotica virgifera virgifera Le Conte). The effect of application time (whorl-stage, pollen-shed) and plant surface exposed (leaves and leaf collars; silks; leaves, leaf collars, and silks) on level of beetle fungal infection were investigated. In addition, the number of colony forming units of B. bassiana in the corn leaf collar area was quantified. In the three years (1998–2000) of the study, application of B. bassiana at whorl-stage did not significantly increase beetle fungal infection. Beauveria bassiana applied to plants at pollen-shed in 1998 resulted in a significant increase in beetle infection with 51% of beetles from treated plants infected and 6.0% from control plants. Similar applications at pollen-shed in 1999 and 2000 resulted in very low infection levels. Beauveria bassiana application at pollen-shed stage significantly increased the number of colony forming units per leaf collar during all years of the study. Beetle infection with B. bassiana did not differ consistently among plant surface to which beetles were exposed for either application. Increased fungal load in leaf collars was not correlated with increased levels of adult infection. Increased rates of B. bassiana and application when beetles are present on the plants are likely needed to significantly increase infection rates.     

Sequential flowering of neighboring goldenrods and the movements of the flower predator Epicauta pennsylvanica

Summary As neighboring plants flower sequentially, do flower feeders preferentially remain in the area, rather than move to another area with flowering plants? I examined the movements of the meloid beetle Epicauta pennsylvanica, a flower predator specializing on Solidago, in four types of replicated experimental plots — monocultures of Solidago altissima, or S. altissima interplanted with members of the same genus, same family, or different taxonomic orders. I released marked beetles only in the genus plots, which contained four species of Solidago, two that bloom before S. altissima. The number of beetles in the genus plots declined steadily as S. altissima came into flower in all the plots; the total number of beetles in all the plots remained fairly constant. I found no evidence that plant neighborhoods affected beetle distribution. Beetles foraging on the early blooming Solidago species did not remain in the genus plots as S. altissima came into flower. In addition, beetles that left the genus plots did not differentially accumulate in any of the other plot types, even though one type of plot was a monoculture with four times the density of S. altissima than the other plots.     

Host finding and recognition by Altica carduorum, a defoliator of Cirsium arvense

Altica carduorum Guer. (Coleoptera: Chrysomelidae) populations aggregate on vigorously growing stands of its host, the thistle Cirsium arvense (L.) Scop. (Asteraceae). The beetle needs contact to recognize a Cirsium species and biting to distinguish its host C. arvense. Feeding or mechanical damage on C. arvense, but not other Cirsium species, aggregates the beetles. Also feces from feeding on C. arvense, but not other Cirsium species, aggregates the opposite sex. Adults also aggregate on larval feces. We suggest that initial host location in the spring depends on random encounter by beetles overwintering in a stand of C. arvense. The beetles commonly make short flights after feeding and either land on another C. arvense plant, which establishes a secondary aggregation centre, or return to the original one. In this manner beetles released on a stand of C. arvense in China spread a radius of 600 m in a year, but those released 35 m away from their host failed to find it. Altica carduorum will develop on any Cirsium species to which it is confined, but is monophagous in the field because host finding is dependent on aggregation to wound and feces substances that are specific to C. arvense.     

Movement patterns of Cetonia beetles (Scarabaeidae) among flowering Viburnum opulus (Caprifoliaceae)

The movement patterns of flower-visiting Cetonia (Coleoptera, Scarabaeidae) were studied in central Sweden over 4 years, providing the first quantitative study of beetle pollination behaviour conducted in a temperate zone. The beetles were marked individually and tracked throughout their visits to Viburnum opulus L. (Caprifoliaceae), a partly beetle-pollinated shrub displaying large umbel-like, creamy-white blossoms. Beetle abundance differed greatly between study years. Of marked beetles observed on V. opulus flowers, an average of 26% returned each year. The beetles performed frequent inter-plant flights, and showed fidelity to particular V. opulus individuals at the study site. Furthermore, they preferred V. opulus to other plants flowering concomitantly and showed considerable constancy in this habit. Movements were mostly between individuals from unshaded locations with high inflorescence and flower number. Normally, the beetles flew on average about 4 times the horizontal nearest-neighbour distance between flowering V. opulus (c. 18 m). From these observations it is concluded that Cetonia beetles are powerful long-distance dispersal agents for V. opulus pollen, perhaps leading to an enhanced gene flow not possible with the plant's other pollinators.     

Influence of Forest Types and Effects of Forestry Activities on Species Richness and Composition of Chrysomelidae in the Central Mountainous Region of Japan

Species richness and composition of the Chrysomelidae (Coleoptera) were studied in larch (Larix kaempheri [Lamb.] Carrière) plantations, secondary forests, and primary forests. In addition, the effects of forest management practices, such as thinning and long rotation, were examined in the larch plantation. The species richness of Chrysomelidae was higher in the larch plantation than in the secondary forest or in the primary forest. Among the larch plantations, the species richness in old-aged plantations was higher than that in middle-aged plantations. The composition of the beetle assemblages in the larch plantation differed from that in the secondary forest or in the primary forest. Exosoma akkoae (Chujo), Batophila acutangula Heikertinger, and Calomicrus nobyi Chujo were caught with a bias toward the larch plantation. Longitarsus succineus (Foudras) and Sphaeroderma tarsatum Baly were caught more in the secondary forest and the primary forest, respectively. More B. acutangula and S. tarsatum were caught in stands where their host plants occurred at higher rates. Species richness of understory plants was an important factor for chrysomlid species richness, and frequency of host occurrence affected the number of individuals of leaf beetles examined. It seems that forest types and forest management practices affect host plants as well as Chrysomelidae, and that these effects on the host plants also influence chrysomelid assemblages.     

Fine‐scale heterogeneity in beetle assemblages under co‐occurring Eucalyptus in the same subgenus

Aim Insect biodiversity is often positively associated with habitat heterogeneity. However, this relationship depends on spatial scale, with most studies focused on differences between habitats at large scales with a variety of forest tree species. We examined fine‐scale heterogeneity in ground‐dwelling beetle assemblages under co‐occurring trees in the same subgenus: Eucalyptus melliodora A. Cunn. ex Schauer and E. blakelyi Maiden (Myrtaceae). Location Critically endangered grassy woodland near Canberra, south‐eastern Australia. Methods We used pitfall traps and Tullgren funnels to sample ground‐dwelling beetles from the litter environment under 47 trees, and examined differences in diversity and composition at spatial scales ranging from 100 to 1000 m. Results Beetle assemblages under the two tree species had distinctive differences in diversity and composition. We found that E. melliodora supported a higher richness and abundance of beetles, but had higher compositional similarity among samples. In contrast, E. blakelyi had a lower abundance and species richness of beetles, but more variability in species composition among samples. Main conclusions Our study shows that heterogeneity in litter habitat under co‐occurring and closely related eucalypt species can influence beetle assemblages at spatial scales of just hundreds of metres. The differential contribution to fine‐scale alpha and beta diversity by each eucalypt can be exploited for conservation purposes by ensuring an appropriate mix of the two species in the temperate woodlands where they co‐occur. This would help not only to maximize biodiversity at landscape scales, but also to maintain heterogeneity in species richness, trophic function and biomass at fine spatial scales.     

The effect of host size on the sex ratio of Syngaster lepidus, a parasitoid of Eucalyptus longhorned borers (Phoracantha spp.)

The solitary larval ectoparasitoid, Syngaster lepidus Brullé, parasitizes the cryptic larvae of two wood-boring beetles, Phoracantha recurva Newman and Phoracantha semipunctata F. The objective of this study was to determine how the female parasitoids allocated the sex of progeny when presented with larval hosts of uniform size classes. Host size was directly correlated with age of the Phoracantha larval hosts. Groups of Phoracantha larvae of a single age class (2-, 3-, 4-, or 5-week-old) were exposed to parasitoids, and sex ratios of the resulting parasitoid progeny from each host age class were determined. A significant relationship was observed among the sizes of P. recurva and P. semipunctata hosts and the sex ratio of emerging parasitoids. Parasitized 2-week-old beetle larvae of both Phoracantha spp. produced only male S. lepidus progeny, whereas older larval hosts produced increasing proportions of female parasitoids (up to 80% females from 5-week-old hosts). Two-week-old Phoracantha larvae of both species produced fewer parasitoids than host larvae 3–5-week-old. The size of parasitoid progeny consistently increased with host larval age (size), and female parasitoids were larger than males across all host size classes. Male S. lepidus developed in approximately 25 days from 2-week-old hosts, and 19–21 days in 3–5-week-old hosts. Female S. lepidus developed in 22–25 days, with developmental time increasing with host size.     

Confinement Behavior of Cape Honey Bees (Apis mellifera capensis Esch.) in Relation to Population Densities of Small Hive Beetles (Aethina tumida Murray)

We quantified the effects of increasing small hive beetle (Aethina tumida Murray) populations on guarding behavior of Cape honey bees (Apis mellifera capensis, an African subspecies). We found more confinement sites (prisons) at the higher (50 beetles per colony) rather than lower (25 beetles per colony) beetle density. The number of beetles per prison did not change with beetle density. There were more guard bees per beetle during evening than morning. Neither guard bee nor beetle behavior varied with beetle density or over time. Forty-six percent of all beetles were found among the combs at the low beetle density and this increased to 58% at the higher one. In neither instance were beetles causing depredation to host colonies. Within the limits of the experiment, guarding behavior of Cape honey bees is relatively unaffected by increasing beetle density (even if significant proportions of beetles reach the combs).     

Natural flightless morphs of the ladybird beetle Adalia bipunctata improve biological control of aphids on single plants

The challenge of using ladybird beetles for biological control of insect pests such as aphids is that the adult beetles tend to fly away from the host plants. Therefore, flightless ladybirds might improve biocontrol. There are several artificial ways to obtain flightless beetles, but it may be preferable to use natural variation in flight ability. We investigated, for the first time, biocontrol by inundative augmentation of natural flightless morphs of the ladybird beetle Adalia bipunctata. Microcosm experiments using single leaves with one of three species of aphid revealed no differences in consumption behavior between flightless and winged beetles. Monitoring for 48 h of single, caged pepper plants infested with aphids of Myzus persicae nicotianae or Aulacorthum solani showed that flightless beetles had a longer residence time on the plants than winged beetles. This only translated into significantly better biocontrol of M. persicae. Despite their difference in residence time, both beetle morphs reduced the population growth of A. solani. This is probably explained by the tendency of A. solani to drop from the plant upon disturbance, and we predict that flightless beetles may outperform winged ones in the long term. Overall, our results provide a proof of principle that natural flightless A. bipunctata can improve biocontrol of aphids by ladybird beetles. However, we recognize that the effect of biocontrol will vary with the species of aphid used and that further examination in long term and large scale experiments is required.     

Lack of evolution in a leaf beetle that lives on two contrasting host plants

The interactions between plant‐eating insects and their hosts have shaped both the insects and the plants, driving evolution of plant defenses and insect specialization. The leaf beetle Trirhabda eriodictyonis (Chrysomelidae) lives on two shrubs with differing defenses: Eriodictyon crassifolium has hairy leaves, whereas E. trichocalyx has resinous leaves. We tested whether these beetles have differentiated onto the two host plants, and if not, whether the beetles prefer the better host plant and prefer mates who are from that host plant. In feeding tests, adult beetles strongly preferred eating E. trichocalyx regardless of which host they came from. In addition, females laid more eggs if they ate E. trichocalyx than E. crassifolium. So, E. trichocalyx is generally the better host. However, beetle mate preference was not in line with food choice. Males did not prefer to mate with females from E. trichocalyx. Females from E. crassifolium did prefer males from E. trichocalyx over males from E. crassifolium, but did not lay more eggs as a result of these matings. We conclude that the beetle populations we studied have not differentiated based on their host plants and may not have even adapted to the better host. Although to humans these host plant defenses differ dramatically, signs that they have caused evolution in the beetles are lacking. The case of T. eriodictyonis stands counter to many other studies that have seen the differentiation of ecotypes and/or adaptive coordination of an herbivore's life cycle based on host plant differences.     

Aggregation and Mate Location in the Red Milkweed Beetle (Coleoptera: Cerambycidae)

We examined behavioral mechanisms underlying aggregation and mate location in the red milkweed beetle, Tetraopes tetrophthalmus (Forster) (Coleoptera: Cerambycidae). Larvae of this species feed on rhizomes of common milkweed, Asclepias syriaca L., and adults feed on the flowers and foliage, aggregating on individual stems within milkweed patches. Adults preferred to aggregate on milkweeds that had multiple, large inflorescences. Males actively searched for females, often flying between host plants. Mate location did not appear to involve long-range pheromones or vision, but rather males landed on milkweed stems arbitrarily, whether or not females were present. Males remained for longer periods, and so tended to accumulate, on milkweed stems that had female-biased sex ratios. We conclude that aggregation of T. tetrophthalmus is cued by host plant characteristics but dynamically influenced by the sex ratio of conspecifics present on individual stems.     

Explaining differences in flea beetle Phyllotreta cruciferae goeze densities in simple and mixed broccoli cropping systems as a function of individual behavior

Diversification of habitat has proved to be an efficient way to reduce insect pest levels in agroecosystems. Some general theories used to explain this fact, such as the natural enemies and the resource concentration hypotheses, do not always clearly apply because, in many cases, pest individuals and population response seem controlled by more specific insect-plant interactions. In non replicated plots, we found substantially lower flea beetle densities in mixed broccoli-Vicia cropping systems compared to broccoli monoculture. These results were consistent with those from controlled experiments reported in the literature. To investigate if beetle behavior was related to such population reduction, the movement behavior of marked individuals of Phyllotreta cruciferae Goeze released in plots composed solely of broccoli plants and of broccoli mixed with Vicia faba or Vicia sativa plants, was followed and analyzed. The mean tenure time of beetles was longer in simple than in mixed cultures. Also, more beetles tended to fly out and leave mixed cultures compared to monoculture. This resulted in faster reduction of artificially introduced flea beetle populations in the mixed systems.Flea beetles landing on cover crop plants spent considerable time entangled in Vicia sativa branches or attempting to reach the upper part of the tall Vicia faba plants from which they could fly away. It is possible that the beetles characteristic movement on these two species of cover crops increased their risk of predation and the time and energy expended before they reached suitable host plants. Nevertheless, it seems that the detected flea beetle emigration rates were more than sufficient to account for the population trends observed.     

Effects of leaf and sap feeding insects on photosynthetic rates of goldenrod

Summary Herbivory can alter the balance between sources and sinks within a plant, and changes in the source-sink ratio often lead to changes in plant photosynthetic rates. We investigated how feeding by three insect herbivores affected photosynthetic rates and growth of goldenrod (Solidago altissima). One, a phloem-sap feeding aphid (Uroleucon caligatum), creates an additional sink, and the other two, a leaf-chewing beetle (Trirhabda sp.) and a xylem-sap feeding spittlebug (Philaenus spumarius) both reduce source supply by decreasing leaf area. Plants were grown outside in large pots and insects were placed on them at predetermined densities, with undamaged plants included as controls. All insects were removed after a 12-day feeding period. We measured photosynthetic rates both of damaged leaves and of undamaged leaves that were produced after insect removal. Photosynthetic rates per unit area of damaged leaves were reduced by spittlebug feeding, but not by beetle or aphid feeding. Conductance of spittlebugdamaged leaves did not differ from controls, but internal carbon dioxide concentrations were increased. These results indicate that spittlebug feeding does not cause stomatal closure, but impairs fixation within the leaf. Effects of spittlebug feeding on photosynthetic rates persisted after the insects were removed from the plants. Photosynthetic rates per unit area of leaves produced after insect removal on spittlegug-damaged plants were lower than control levels, even though the measurements were taken 12 days after insect removal. The measurement leaf on spittlebugdamaged plants was reduced in area by 27% relative to the controls, but specific leaf area (leaf area/leaf weight) was increased by 18%. Because of the shift in specific leaf area, photosynthetic rates were also examined per unit leaf weight, and when this was done there were no significant differences between control and spittlebug-damaged plants. Beetle and aphid feeding had no effects on the photosynthetic rate of the leaves produced after insect removal. Plant relative growth rates (in terms of height) were reduced by spittlebugs during the period that the insects were feeding on the plants. Relative growth rates of spittlebug-damaged plants were increased above control levels after insect removal, but these plants were still shorter than controls 17 days after insect removal. Beetles and aphids did not affect plant relative growth rates or plant height. Feeding by both spittlebugs and beetles reduced leaf area, and the effect of the spittlebug was more severe than that of the beetle. These results show that effects of herbivory on photosynthetic rates cannot be predicted simply by considering changes in the source-sink ratio, and that spittlebug feeding is more damaging to the host plant than beetle or aphid feeding.