The disease complex of the gypsy moth: I. Major components
Abstract
A study was undertaken to elucidate the impact of the various components of disease on natural populations of the gypsy moth, Porthetria dispar. Diseased larvae from both sparse and dense populations were examined and categorized on the basis of etiologic and nonetiologic mortality factors. Results indicated a significantly higher incidence of parasitoid involvement—but virtual nonexistence of polyhedral viroses—in the relatively stable sparse populations. Nuclear polyhedrosis probably represented the primary mortality factor in the dense populations. Many insects examined from both population types revealed no infectious agent or overt cause of disease, a fact that may indicate a major regulatory role of noninfectious disease in natural populations. Variation in the disease complex within the populations that have been studied indicates that minor causes of disease in one may well predominate in others. Thus, to fully understand this complex, it must be studied across a number of years within a series of populations from different geographical areas.
References (3)
- R.W. Campbell
The role of disease and desiccation in the population dynamics of the gypsy moth Porthetria dispar (L.) (Lepidoptera: Lymantriidae)
Can. Entomol
(1963)
Cited by (32)
Microsporidian Entomopathogens
2012, Insect Pathology, Second EditionBaculoviruses and Other Occluded Insect Viruses
2012, Insect Pathology, Second EditionHost specificity of microsporidia pathogenic to forest lepidoptera
2000, Biological ControlThe host specificity of microsporidian pathogens of Lepidoptera was studied in Bulgaria where native populations of Lymantria dispar and their endemic microsporidia occur. L. dispar and sympatric lepidopteran larvae were collected from four sites in central and western Bulgaria. Three species of microsporidia, Vairimorpha sp., Nosema sp., and Endoreticulatus sp. are known to be endemic in three L. dispar populations, with one species in each population. No microsporidia were found in a fourth L. dispar population. In addition to the L. dispar microsporidia, 11 isolates of microsporidia were recovered from the 1494 individual lepidopteran hosts collected in these sites. When fed to L. dispar, 3 isolates produced infections that were atypical of infections in the natural hosts; one additional isolate produced an atypical infection in Spodoptera exigua. A Nosema sp. isolated from a noctuid host produced heavy infections in L. dispar larvae. Sequencing revealed that the noctuid microsporidium and the closely related Vairimorpha sp. and Nosema sp. microsporidia from L. dispar are distinctly different isolates. These investigations strengthen previous laboratory predictions of narrow host ranges for the Nosema and Vairimorpha microsporidia recovered from L. dispar in Europe. In addition, the Endoreticulatus sp., which was predicted from laboratory studies to be a generalist, was not found in Lepidoptera species sympatric with L. dispar. The results from our study indicate that laboratory testing may considerably underestimate the host specificity of many terrestrial microsporidia. Nevertheless, infectivity to nontarget hosts in the laboratory may set the stage for understanding the evolution of closely related microsporidia found in different host species.
Physiological Host Specificity of Microsporidia as an Indicator of Ecological Host Specificity
1998, Journal of Invertebrate PathologyFor most groups of biological control agents the relationship between laboratory (physiological) host range and the host range in the field (ecological host range) has not been explored empirically. The objective of our study was to investigate this relationship using the North America gypsy moth,Lymantria dispar,as a model nontarget host for microsporidia from native North American Lepidoptera. The gypsy moth,L. dispar,a native of Europe, has been established in North America for nearly 130 years and presumably exposed to many species of microsporidia from sympatric native Lepidoptera. Nevertheless, microsporidia have never been observed in North American populations ofL. dispar.We conducted traditional laboratory feeding experiments using microsporidia from 20 lepidopteran host species and 1 coleopteran host species againstL. dispar.Microsporidia from 18 native hosts infectedL. disparlarvae. Although some of the infections were not typical of infections in the indigenous natural hosts, mature spores were produced in most of these infections. Horizontal transmission experiments, based on exposure of uninfectedL. disparlarvae to infectedL. disparlarvae, demonstrated that the microsporidia were far more host specific than the direct feeding experiments suggested. Of the three microsporidian biotypes that were horizontally transmitted between the nontargetL. disparlarvae, all were transmitted at very low levels. The results of our experiments provide additional evidence that the ecological host specificity of terrestrial microsporidia is much narrower than the physiological host specificity. Our studies establish the validity of using nonindigenous insect species with long-term data sets on natural enemies associated with them as a tool for testing hypotheses about host specificity.
Host Specificity of Microsporidia (Protista: Microspora) from European Populations of Lymantria dispar (Lepidoptera: Lymantriidae) to Indigenous North American Lepidoptera
1997, Journal of Invertebrate PathologyResults of traditional laboratory bioassays may not accurately represent ecological (field) host specificity of entomopathogens but, if carefully interpreted, may be used to predict the ecological host specificity of pathogens being considered for release as classical biological control agents. We conducted laboratory studies designed to evaluate the physiological host specificity of microsporidia, which are common protozoan pathogens of insects. In these studies, 49 nontarget lepidopteran species indigenous to North America were fed five biotypes of microsporidia that occur in European populations ofLymantria disparbut are not found in North American populations ofL. dispar.These microsporidia,Microsporidiumsp. from Portugal,Microsporidiumsp. from Romania,Microsporidiumsp. from Slovakia,Nosema lymantriae,andEndoreticulatussp. from Portugal, are candidates for release as classical biological control agents intoL. disparpopulations in the United States. The microsporidia produced a variety of responses in the nontarget hosts and, based on these responses, the nontarget hosts were placed in the following categories: (1) no infection (refractory), (2) atypical infections, and (3) heavy infections.Endoreticulatussp. produced patent, host-like infections in nearly two-thirds of the nontarget hosts to which it was fed. Such generalist species should not be recommended for release. Infections comparable to those produced inL. disparwere produced in 2% of the nontarget hosts fedMicrosporidiumsp. from Portugal, 19% of nontarget hosts fedMicrosporidiumsp. from Romania, 13% fed spores ofMicrosporidiumsp. from Slovakia, and 11% of nontarget species fedN. lymantriae.The remaining nontarget species developed infections that, despite production of mature spores, were not typical of infection inL. dispar.We believe it is very unlikely that these atypical infections would be horizontally transmitted within nontarget insect populations in the United States.
Diversification of biological control strategies in agriculture
1991, Crop ProtectionThe factors that cause pest outbreaks depend on the complex nature of crops, pests, physical habitats and the natural biota. Despite all efforts to control pests, approximately 35% of all crop production is lost to pests. Thus, the biological controls used to control the 67 000 pest species that exist world wide should be expanded and diversified. Host-plant resistance plus natural parasites and predators are the two dominant measures that regulate plant-feeding organisms. At present these two types of biological controls dominate pest control in agriculture. One of the major problems with the use of host-plant resistance in agricultural crops is that a single gene for resistance is bred into the crop. It is therefore relatively easy for the pest species to evolve and to overcome the resistance in the crop. In nature, however, most host-plant resistance is based on multiple genes and a diverse set of resistant factors. This diverse, polygenic resistance system helps to prevent plant-feeding species from overcoming the resistance in the host plant. Increasing diversity in host-plant resistance could improve stability of crop resistance in agriculture. The selection of parasites and predators from relatives of the target pest for introduction instead of introducing natural enemies from the native home of the pest for biological control improves the success rate of this technology. The use of this ‘new association’ approach takes advantage of diversity and has been shown to increase threefold the effectiveness of biological control. Furthermore, it is a way to control native pests, which make up the largest portion of crop pests. Equally important, this technique increases the arsenal of natural enemies that can be successfully employed in biological control. Finally, combining the use of host-plant resistance and use of natural enemies via the ‘new association’ technique enhances the effectiveness of both biological controls. These methods are compatible and the diversity they contribute increases the success and stability needed for effective control.