Leaf-feeding Beetle Research Articles

On integrating molecular and ecological studies of plant resistance: variety of mechanisms and breadth of antagonists

We are grateful that an attempt has been made (Heil 1999) to place the issue of systemic acquired resistance (SAR) within an ecological context. However, although this review raises some interesting points for further action and provides food for thought, we believe that the author may have underestimated both the changes in conceptual frameworks that are needed in order to incorporate SAR within such a context, and the efforts already being made in this area. The investigation of induced resistance mechanisms in plants is a fast-moving area of research and several excellent reviews on aspects considered in Heil (1999) have subsequently appeared (e.g. Agrawal et al. 1999; Bostock 1999; Maleck & Dietrich 1999; Pieterse & van Loon 1999). Indeed, a further review could usefully explore the evidence available for the points that Heil raises at the beginning of his article. Our article does not purport to be such a review; rather we wish to raise, in reply, two important points that have been generally overlooked in this debate. First, any understanding of SAR in its ecological context involves integrating this resistance within the framework of the other mechanisms by which the plant modifies its interactions with consumers. Second, this wider context for SAR must consider the potential for very broad interphylumn effects. We demonstrate these points from our studies on the interactions between the large perennial herb Runmex obtusifolius and its consumers, notably the leaf-feeding chrysomelid beetle Gastrophysa viridula and the leaf-infecting rust fungus Uromyces rumnicis. This is one of the few tripartite systems that has been intensively studied and that can also provide information on multiple, interacting resistances in plants.

Impact of defoliation by the biocontrol agentZygogramma bicolorataon the weed Partheniumhysterophorus in Australia

The leaf-feeding beetle Zygogrammabicolorata Pallister was introduced from Mexico intoAustralia in 1980 as a biocontrol agent for the weedParthenium hysterophorus L. (Asteraceae). Z. bicolorata became abundant in 1990, and since 1992there has been regular outbreaks resulting in thedefoliation of the weed in central Queensland. In thisstudy we evaluated the impact of defoliation by Z. bicolorata on P. hysterophorus from 1996 to1998. Z. bicolorata caused 91–100% defoliationresulting in reductions in weed density by 32–93%,plant height by 18–65%, plant biomass by 55–89%,flower production by 75–100%, soil seed-bank by13–86% and seedling emergence in the following seasonby 73–90%. At sites with continued outbreaks ofZ. bicolorata, it is expected that the existing soilseed-bank will be minimised, resulting in reduceddensity of parthenium in 6 to 7 years.

Plant Development Affects Arthropod Communities: Opposing Impacts of Species Removal

We examined the hypothesis that developmental phase changes from juvenile to mature growth in plants affect the distribution of common herbivores, which in turn affect the rest of the arthropod community. Using naturally occurring clones of cottonwoods, we compared the arthropod communities found in the mature zones of upper tree canopies, in juvenile zones at the base of mature trees, and in juvenile ramets that have suckered from the roots of mature trees. Mature zones were shown to support 23% greater species richness and 108% greater relative abundance than juvenile ramets. Of 17 common arthropod taxa, 8 showed significantly higher abundances on one developmental zone over another; 4 had higher abundances on mature zones, and 4 had higher abundances on juvenile ramets. The juvenile zones of mature trees resembled a transition zone, supporting intermediate species richness and relative abundance. We also detected a significant clone effect on arthropod relative abundance, indicating that plant development varies among clones. Because developmental-based resistance directly affects the distributions of the two dominant insect herbivores, we then removed these insects to quantify the indirect impacts of development on the rest of the arthropod community. The gall-forming aphid Pemphigus betae was removed from susceptible mature branches (juvenile branches and ramets are resistant), and the leaf-feeding beetle Chrysomela confluens was removed from susceptible juvenile ramets (mature branches are resistant). We found opposite impacts of removal: aphid removal decreased species richness and abundance in mature zones by 32 and 55%, respectively, while beetle removal increased species richness and abundance on juvenile ramets by 120 and 75%, respectively. These studies suggest that plant development is an important factor that contributes to the structuring of insect communities, and that the indirect impacts of plant development acting through common herbivores may rival direct impacts (e.g., competition and predation) in their overall importance. Furthermore, the habitat mosaic created by developmental processes provides a mechanism for understanding the commonly observed pattern of higher biodiversity in mixed-aged stands of trees and forest edges than in even-aged stands or forest interiors.

Host Specificity of Altica carduorum Guer. Chrysomelidae: Coleoptera , a Defoliator of Cirsium arvense L. Scop. Asteraceae from North-western China

Traditionally, insects are not approved for release in North America as agents for the biological control of weeds if the larvae complete development on desirable plants in no-choice tests. This criterion excludes the use of the leaf-feeding beetle Altica carduroum Guer. since it can complete development on all Cirsium spp., including rare North American species, although in nature it is only known from the target weed Cirsium arvense. Host suitability is the result of a sequence of selection factors, and this study shows that most discrimination between thistle species is the result of host finding and egg production, and not larval developmental ability. In no-choice tests, the larvae completed development on 18 Cirsium species in five sections of the genus that were tested and on Silybum marianum, but not on other genera in the tribe Cardueae or more distantly related Asteraceae. The adult food consumption on C. arvense was two to eight times greater than on other Cirsium species, many of which, such a...

AreAltica carduorumandAltica cirsicola(Coleoptera: Chrysomelidae) Different Species? Implications for the Release ofA. cirsicolafor the Biocontrol of Canada Thistle in Canada

Altica carduorumandAltica cirsicolaare two species of leaf-feeding beetle (Coleoptera: Chrysomelidae) which appear to be morphologically indistinguishable and reportedly hybridize in the laboratory. A European population ofA. carduorumwas previously screened for host-plant specificity and released in North America for the control of Canada thistle,Cirsium arvense.A population ofA. cirsicolafrom China is currently being considered as a biocontrol agent forC. arvenseand, as a different beetle species, must be screened using host-specificity tests similar to those used forA. carduorum.IfA. carduorumandA. cirsicolaare, in fact, one species, the screening requirements forA. cirsicolacould be significantly reduced. Hence, we investigated the taxonomic relationship betweenA. carduorumandA. cirsicolausing morphometric analyses, hybridization experiments, and DNA fingerprinting using random amplified polymorphic DNA (RAPD) analysis. Discriminant function analyses indicate thatA. carduorumandA. cirsicolacannot be reliably distinguished by their morphologies, and interspecific matings produce fertile F1offspring. However, because interspecific matings produce significantly fewer offspring than intraspecific matings, and because of clear differences in their DNA profiles, we conclude thatA. carduorumandA. cirsicolaare separate species. This study serves to highlight the value of genetic analyses in taxonomic studies and their role in biological control programs.

Biology and Host Range of Gratiana spadicea (Klug, 1829) (Coleoptera: Chrysomelidae: Cassidinae), a Potential Biological Control Agent for the Weed Solanum sisymbriifolium Lamarck (Solanaceae) in South Africa

Abstract A leaf-feeding tortoise beetle (Gratiana spadicea) was screened as a potential biological control agent for the invasive exotic weed Solanum sisymbriifolium in South Africa. Favorable biological characteristics of G. spadicea include a high rate of increase, long-lived and mobile adults, several generations per year, and a high per capita feeding rate. Host range was investigated in larval survival tests and adult choice tests under laboratory conditions. Larvae were successfully reared on 8 of 11 indigenous Solanum species, on 4 of 5 exotic Solanum species (apart from S. sisymbriifolium), and on economically important S. melongena (eggplant) but not on any of the species of Datura, Nicandra, and Physalis tested. Very limited adult feeding and oviposition occurred on several of the indigenous Solanum species and on eggplant. These trials were conducted under quarantine conditions with the potential for laboratory artifacts. The poor larval survival on nonhosts and the inability of the agent to recognize nonhosts as oviposition sites supported a request for release of this agent, which was subsequently granted.

Aphid-ant interaction reduces chrysomelid herbivory in a cottonwood hybrid zone.

In a cottonwood (Populus) hybrid zone, Chaitophorus aphids attract aphid-tending ants which subsequently reduce herbivory by the leaf-feeding beetle, Chrysomela confluens. Observations and experimental manipulations of aphids and beetle larvae on immature cottonwood trees demonstrated that: 1) via their recruitment of ants, aphids reduced numbers of beetle eggs and larvae on the host; 2) these interactions occurred within a few days of the host being colonized by aphids; and 3) although aphid colonies were ephemeral, their presence resulted in a 2-fold reduction in beetle herbivory. The aphid-ant interaction is most important in the hybrid zone where 93% of the beetle population is concentrated (for reasons unrelated to aphids and ants). Because beetle defoliation of immature trees is high (ca. 25%), the indirect effect of aphids in reducing herbivory is likely more beneficial to trees in the hybrid zone than in adjacent pure zones where beetle herbivory is virtually absent. Tree genotype likely affects the impact of the aphid-ant interaction on trees within the hybrid zone, since levels of herbivory differ between sympatric Fremont and hybrid cottonwoods.

Biological control of St. John's Wort, Hypericum perforatum (Clusiaceae), in South Africa

Hypericum perforatum L. is a herbaceous perennial plant that was first noticed as an invader in the Southwestern Cape of South Africa in 1945. Following an unsuccessful chemical control programme, a leaf-feeding beetle, Chrysolina quadrigemina Suffrain, was introduced in 1960, which almost completely destroyed dense stands of the weed. In 1972, a gall-midge, Zeuxidiplosis giardi Kieffer, was released and has proved valuable in damaging seedlings in moist habitats. Attempts to establish three other insect herbivore species failed. Hypericum perforatum is now considered to be under satisfactory control in the Southwestern Cape. Although C. quadrigemina, together with Z. giardi, has been pivotal in eliminating the dense stands of H. perforatum, other factors, such as climate, unsuitable habitats and a lack of dispersal agents, have probably also contributed to containing the weed.

Biological control of Lantana camara (Verbenaceae) in South Africa

Lantana camara L., a fast-growing verbenaceous shrub from Central and South America, is a toxic invasive weed in many countries. Taxonomically, L. camara is a complex of several cultivars (forms) whose diversity has frustrated attempts at biological control by insect natural enemies that show preferences for some cultivars and an inability to survive on others. Of the 16 insect herbivore species imported into South Africa for biological control of L. camara, six have become established and two were already present. Two leaf-feeding chrysomelid beetle species, Octotoma scabripennis Guèrin-Mèneville and Uroplata girardi Pic, usually in association with the tingid bug, Teleonemia scrupulosa Stål, are exerting some degree of control. A seed-feeding agromyzid fly, Ophiomyia lantanae (Froggatt), may be contributing to the overall stress on the plant, but its contribution to biocontrol has not been determined. A flower-feeding pyralid moth, Salbia haemorrhoidalis Guenèe, is established in low numbers at isolated sites over a wide area. A noctuid moth, Hypena strigata (F.), an African species that was mistakenly ‘imported’ into South Africa, contributes little to biocontrol of L. camara in this country, although it was very successful in Hawaii. The biocontrol of L. camara in South Africa, with its problems and shortcomings, is reviewed and the future of the programme is discussed. A better understanding of the functional relationships and interactions between the various cultivars of L. camara and insect herbivores may improve the chances of succeeding with biological control.

Developmental Changes in Resistance to Herbivory: Implications for Individuals and Populations

The hypothesis that individual plants undergo predictable changes in their resistance to herbivory as they mature was experimentally tested. The performance of two species of insects transferred onto different—aged trees of the same naturally occurring clones of narrowleaf cottonwood, Populus angustifolia, showed opposing and significant changes in host resistance as a function of tree age. The gall—forming aphid Pemphigus betae was 70 times as common on mature trees as on juvenile trees. Transfer experiments demonstrated that this pattern is adaptive; survivorship on mature trees was 50% higher than on juvenile trees. The leaf—feeding beetle Chrysomela confluens exhibited opposite distribution on hosts, with densities 400 times as high on juvenile as on mature trees. This is also adaptive; larvae transferred to mature hosts had 50% lower survival and took 25% longer to reach adulthood than those transferred to juvenile trees. These survivorship and performance data and our inability to support the hypotheses of other mechanisms that would produce the observed distributions suggest that the distributions result from the insects' preferences for different—aged hosts. Several basic implications emerge. (1) Developmental changes in resistance and susceptibility of hosts are important components in determining the distribution of herbivores. (2) A single plant can change rapidly in its resistance traits with age such that a 10—fold change in resistance can occur over a 2—yr period. (3) As trees mature, increased and decreased resistances to different herbivores can produce nonoverlapping herbivore distributions that could be misinterpreted as being the result of competition (e.g., in this study, beetle abundance was strongly, negatively correlated with aphid abundance). (4) While host maturation processes have large effects on within— and between—tree variation in resistance to herbivores, the implications for herbivore population dynamics and community structuring have not been generally appreciated.

Tolerance of Adult Drosophila melanogaster to Sub-Freezing Temperatures

The effects of exposure to sub-freezing temperatures on the survival of insects have been studied experimentally mainly in three types of insect. One is the beetles associated with stored products, including Bruchus obtectus (Carter, 1925), and Tribolium confusum (Nagel and Shepard, 1934, and Salt, 1936). A leaf feeding beetle, Popillia japonica (Payne, 1928) has also been studied. The emphasis of these studies has been on the possibility of physical control of these pests. The second type includes the hitch-hikers on aircraft. Knippling and Sullivan (1957) studied the survival of six species of insects and a tick which were exposured to 0, −5, −10, −15, −20, and −30°C. for one hour, and that of one of the insects, the house fly, to −20° for different durations up to 60 minutes. Their objective was to determine the possibility of these arthropods being transported alive by aircraft. Thus, the conditions which they tested were those which may be encountered by the arthropods in the unheated parts of jet aircraft during flights in the stratosphere. The third type of insects is Drosophila, mainly D. melanogaster. Since the present paper deals also with this insect, pertinent facts reported by earlier authors are summarized in Table I.

Editor's Error: The Effect of a Leaf Feeding Beetle on Big Sagebrush in British Columbia

Editor's Error: The Effect of a Leaf Feeding Beetle on Big Sagebrush in British Columbia

The Effect of a Leaf Feeding Beetle on Big Sagebrush in British Columbia

This is a report of a startling natural phenomenon that occurred when an insect population multiplied to such proportions that it all but eliminated a common range plant over a very large area. This does not presume to give any final answers or explain why or how this situation developed, or where it will eventually end. It is designed primarily to relate what has happened to date regarding the sagebrush that has been affected. If it does nothing else it should impress upon us that nature herself sometimes takes matters into her own hands to help right the wrongs caused by man. In July 1954 a beetle identified as Trirhabda pilosa Blake, hereafter referred to as T. pilosa, was discovered by the author on big sagebrush (Artemisia tridentata Nutt) near Kamloops, British Columbia. At this time a patch of sagebrush less than two acres in extent was seen to have turned a rusty brown color. C 1 o s e r examination revealed myriads of small metallic blue larvae stripping the surface layers from the leaves. A few mature insects were collected and subsequently i d e n t i f i e d through the Field Crops Insect Laboratory, Science Service in Kamloops. Final identification was made by Mrs. D. H. Blake, who originally named the species.