Phytophagous Insect Species Research Articles

Putative protein digestion in a sap-sucking homopteran plant pest (rice brown plant hopper; Nilaparvata lugens: Delphacidae)—identification of trypsin-like and cathepsin B-like proteases

Sap-sucking phytophagous insect species of the order Hemiptera have been assumed not to carry out digestive proteolysis, but instead to rely on free amino acids in the phloem and xylem saps for their nutritional requirements. Extracts prepared from isolated guts of rice brown planthopper ( Nilaparvata lugens), a homopteran crop pest, were shown to contain protease activity, with hydrolysis of both protein and synthetic peptide substrates being observed. Assays with specific inhibitors suggested that a trypsin-like serine protease was responsible for most of hydrolytic activity against synthetic substrates. A cDNA library was prepared from RNA extracted from N. lugens gut tissue, and screened for protease-encoding sequences. cDNAs for a cathepsin B-like protease and a trypsin-like protease were isolated and fully characterised; the latter exhibits a novel C-terminal region and an unusual activation mechanism, and represents a small gene family. Soya bean Kunitz trypsin inhibitor (SKTI) is an effective inhibitor of protein hydrolysis by N. lugens gut extracts in vitro, explaining why transgenic rice plants expressing this protein are partially resistant to the insect (Mol. Breed. 5 (1999) 1). It is suggested that digestive proteolysis may be widespread in sap-sucking homoptera, and can make a significant contribution to nutrition.

A method for laboratory studies on the polyphagous predator Macrolophus pygmaeus (Hemiptera: Miridae).

A method for studying the life history parameters of Macrolophus pygmaeus Rambur was developed and described. Fecundity of the predator was studied by placing one female and one male in a plastic cylinder in which a stem piece was used as an ovipositional substrate. Smaller cylinders were used to study the percentage of egg hatch of M. pygmaeus. Results demonstrated that this method is suitable for studying the fecundity and egg eclosion of M. pygmaeus. Allowing for easy modification, the method offers suitable conditions for maintenance of both insect and plant material and can be inexpensively modified for different experiments and the parts are easily constructed. The proposed method could also be employed for similar studies on other predatory hemipterans such as mirids and anthocorids and very likely on other phytophagous insect species that lay their eggs in or on plant stems.

Cry1Ab protein levels in phytophagous insects feeding on transgenic corn: implications for secondary exposure risk assessment

AbstractEnzyme‐linked immunosorbent assays (ELISA) and bioassays were used to estimate levels of Cry1Ab protein in four species of phytophagous insects after feeding on transgenic Bt‐corn plants expressing Cry1Ab protein or artificial diets containing Cry1Ab protein. The level of Cry1Ab in insects feeding on sources containing the Cry1Ab protein was uniformly low but varied with insect species as well as food source. For the corn leaf aphid, Rhopalosiphum maidis (Fitch), feeding on diet solutions containing Cry1Ab protein, the level of the protein in the aphid was 250–500 times less than the original levels in the diet, whereas no Cry1Ab was detected by ELISA in aphids feeding on transgenic Bt‐Corn plants. For the lepidopteran insects, Ostrinia nubilalis (Hübner), Helicoverpa zea (Boddie), and Agrotis ipsilon (Hufnagel), levels of Cry1Ab in larvae varied significantly with feeding treatment. When feeding for 24 h on artificial diets containing 20 and 100 ppm of Cry1Ab, the level of Cry1Ab in the larvae was about 57 and 142 times lower, respectively, than the original protein level in the diet for O. nubilalis, 20 and 34 times lower for H. zea, and 10 to 14 times lower for A. ipsilon. Diet incorporation bioassays with a susceptible insect (first instar O. nubilalis) showed significant Cry1Ab bioactivity present within whole body tissues of R. maidis and O. nubilalis that had fed on diet containing a minimum of 20 ppm or higher concentrations (100 or 200 ppm) of Cry1Ab, but no significant bioactivity within the tissues of these insects after feeding on transgenic Bt‐corn plants. The relevance of these findings to secondary exposure risk assessment for transgenic Bt crops is discussed.

Effect of different host substrates on hemipteran salivary protein profiles*

Three species of phytophagous insects (Empoasca fabae, E. abrupta and Lygus hesperus) and one species of entomophagous insect (Podisus maculiventris) were transferred from rearing hosts to treatment hosts (THs). After feeding on the THs, the insects were transferred to collection diet sachets (CD) for saliva recovery. The collected salivary proteins were analysed by gel electrophoresis. Different salivary protein profiles were observed for E. fabae and E. abrupta when fed on the same diet. Within species, in the protein profile of E. fabae, more bands were visible from insects fed on broad bean [faba bean] than those fed on a simple diet (SD) [composition not specified]. Also, one band of about 45 kDa was present at much greater percentage composition from insects on the broad bean diet than on SD. E. abrupta demonstrated more bands after being fed SD than pinto bean (PB, Phaseolus vulgaris). For L. hesperus, different banding patterns were observed with insects fed on different diets. More bands were observed for insects that fed on an artifical Lygus-rearing diet than on cotton or PB. More bands were observed after insects fed on cotton compared to PB. Starved insects fed and salivated more than the non-starved insects, yet the protein components of the saliva were similar. In contrast to the phytophagous insects, P. maculiventris showed minimal differences in salivary protein profiles after feeding on Trichoplusia ni or an artificial diet.

The Phytophagous Arthropods Associated with Senna obtusifolia (Caesalpiniaceae) in Mexico and Honduras and Their Prospects for Utilization for Biological Control

A survey of the phytophagous arthropod fauna associated with sicklepod, Senna obtusifolia, was undertaken between 1991 and 1993 to find biological control agents for this increasingly serious weed in Australia and its closely related congener, Senna tora. The survey concentrated in Mexico on the Gulf coast, the Pacific coast, and the Yucatan peninsula. Additional searching was undertaken in the state of Morelos, Mexico and Honduras. Some 108 phytophagous insect species were found. Literature searches and preliminary observation indicated that 10 species were sufficiently stenophagous to warrant further consideration as potential biocontrol agents. Two species, Mitrapsylla albalineata (Homoptera: Psyllidae) and Conotrachelus sp. ‘Morelos’ (Coleoptera: Curculionidae), have been brought to Australia for further study.

Phytophagous Insects Associated withHieracium pilosella(Asteraceae) in Hungary, Central Europe

During a 3-yr survey to find potential biological control agents against Hieracium pilosella L. (Asteraceae), a serious weed in many parts of the world, 130 phytophagous insect species were collected at 7 sites in Hungary. Most species belonged to the order Heteroptera (30 species, 23.1% of species), Homoptera (29, 22.3%), and Coleoptera (33, 25.4%). Most species were present in low numbers. Only 2 endophagous species (1.5%) were found. The percentage of rare species was high (66%), and the species turnover between years (74–83% at different sites) were high as well. These suggest an unstable insect assemblage. In comparison with other Asteraceae species, the phytophagous insect assemblages of H. pilosella contained few host-specific species. Only 4 species were genus-specific, and 2 of them, a gall wasp [ Aulacidea pilosellae (Kieffer)] and a tephritid fly [ Tephritis ruralis (Loew)] may be potential biological control agents.

Einfluß des Verhaltens adulter Insekten auf Ressourcen-Nutzung und Populationsdynamik: Ein Drei-Komponenten-Modell der Populationsdichte-Steuerung

Bottom-up processes (limitation by resources) and top-down processes (limitation by antagonists) are usually considered to be the driving forces in the population dynamics of insects. This view implies that a permanent underutilization of resources by phytophagous insects or parasitoids is due to population control by natural enemies and/or disease organisms. Our contribution presents examples of phytophagous insects and parasitoids with a level of resource utilization which cannot be satisfactorily explained by the dichotomy of bottom-up and top-down processes. We start by defining the term available resources. We then bring an evaluation of the success rate of biocontrol agents introduced against allochthonous noxious weeds in Canada. A recent status report [Harris 1995] shows that a considerable number of phytophagous insect species established in Canada without their specialized natural enemies exploit only a small proportion of the available biomass of host plants. For one of these species, the tephritid gallformer Urophora cardui, we show that its host selection behaviour leads to a spatial dispersion pattern of galls resulting in a strongly inverse density dependence of resource utilization. Further examples of an underutilization of hosts are given for parasitoids attacking Urophora species in flower heads of Centaurea and for parasitoids of aphids. Neither a bottom-up nor a direct top-down process, but rather specific behaviour patterns are involved in these cases of resource underutilization. These patterns may be adaptive in the sense of spreading the risk, of escaping enemies operating in a density-dependent manner or as a trade-off between host quality and host quantity. They may also be historically constrained. To account for the possible impact of behaviour, we propose to replace the dichotomy of bottom-up and top-down processes by a triangle scheme where changing combinations of resource limitation, limitation by antagonists and specific behaviour patterns control population densities.

The structure of the phytophagous insect fauna on the introduced weed Solidago altissima in Switzerland

AbstractSolidago altissima L. was introduced into Europe as an ornamental plant from North America more than 100 years ago and the phytophagous insect fauna of it was recently examined in Switzerland where it has become an important weed in disturbed habitats. Rhizomes and aerial parts were examined and all insects collected in summer were tested in a no‐choice feeding test. 18 out of 55 phytophagous insects were found feeding on S. altissima in Switzerland and for the remaining 37 the relation with the plant was not determined. The insects that have expanded their host range to feed on S. altissima since its introduction to Switzerland are almost solely opportunistic, unspecialized ectophages not closely attuned to the growth cycle of S. altissima. Only 4% of the insects were specialists and 9% endophagous. In contrast in North America S. altissima supports 25% specialists and 17% endophages. The native Solidago virgaurea L. in Switzerland supports many more specialists (28%) and endophages (23%) than S. altissima here. Possible reasons why almost none of these have switched to S. altissima are discussed. A comparison is made between the number of insects recruited by S. altissima in Switzerland with the number recruited by the exotic plants Heracleum mantegazzianum Som. & Lev. (Apiaceae) in Switzerland and Xanthium occidentale Bertol. (Asteraceae) in Australia. Reasons for different levels of insect recruitment are discussed. The high number of phytophagous insect species found on S. altissima in North America shows that there should be no shortage of possible control agents and any insects imported into Switzerland for the biological control of S. altissima would find largely unexploited food sources awaiting them.

Investigations on the Phytophagous and Predator Insect Species on Stone-Fruits in North-East Agricultural Region of Turkey

Phytophagous and predator insect species were investigated on apricot, peach, plum, morello cherry, and cherry in the North-east Agricultural Region of Turkey during 1991 and 1992. The samples were taken in orchards in Erzurum, Artvin, Erzincan, Igdir and Kars provinces. At the result of this study, 123 phytophagous and 41 predators totally 164 species were recorded in various orders, families and genera. Among phytophagous species, Hyalopterus pruni (Geoffroy) (Aphididae), Pterochloroides persicae (Cholodkovsky) (Lachnidae), Rynchites auratus (Scop.), R. bacchus (L.) (Attelabidae), Anthonomus pomorum (L.) (Curcilionidae), Cydia pomonella (L.) (Tortricidae), Lyonetia clerckella L. (Lyonetidae), Rhagoletis cerasi L. (Tephritidae), and Eurytoma schreineri Schreiner (Eurytomidae) have economic importance as pest on various stone fruits in this region. E. schreineri detected as a new apricot pest in Turkey and infested 20-25% of apricot fruits. R. auratus is the most serious pest of the morello cherry fruits and the rate of infestation is 10-85% . Adults of R. bacchus feed on the apricot fruits and make several holes, in addition, this species nibbles fruit steams and cause drop off up to 90% of fruits in some localites. This study brought out that R. auratus and R. bacchus have economic importance in this region. On the other hand, although Acronicta tridens (D. & S.) (Noctuidae) and Caliroa limacina Retz. (Tenthredinidae) show local distribution they cause important damages in infested orchards. Psylliodes kasyi Lopatin (Chrysomelidae) and E. schreineri are new records for Turkish fauna. Moreover, the larva of Gypsonoma rosaecolana Dbld. (Tortricidae), bore through the flesh of the apricot fruits. Syndemis musculana Hb. (Tortricidae) and Ypsolopha persicella F. (Yponomeutidae) feed on apricot and peach leaves, respectively. Among predator species, Nagusta goedeli (Klt.) (Reduviidae), Anthocoris nemoralis (F.), A. sibiricus Rt. (Anthocoridae), Chrysoperila carnea (Stephens) (Chrysopidae), Scymnus subvillosus (Goeze), Stethorus punctillum Ws. (Coccinellidae), Episyrphus balteatus (DeGeer), Melanostoma mellinum (L.), Metasyrphus corollae (F.) and Sphaerophoria scripta L. (Syrphidae) were dominant species in this region. In addition, preys of some species were also determined.

The spatial population dynamics of insects exploiting a patchy food resource : II. Movements between patches.

The population dynamics of ten species of phytophagous insects and seven parasitoids inhabiting the flowerheads of two herbaceous plants, Centaurea nigra and Arctium minus, were studied, and three main aspects of their ecology were examined, namely, rates of population extinction, density dependence in population changes from one generation to the next, and movements between populations. The study was based on monitoring the insect populations on more than 50 patches of each plant, scattered over 5 km2 of arable farmland and the results were used to test the relative importance of immigration and population regulation to the persistence of these populations. This paper describes the study of movements between patches of food plant. Experimentally planted new patches of plants were rapidly colonised by all species and this appeared to be unaffected by distance from a source population, up to the maximum distance of 800 m considered in the experiment. Large patches tended to be colonised more readily than small ones. Movements between plant patches were studied with the use of chemical markers (Rb, Sr, Dy and Cs) which were applied as chloride salts to individual patches, and which were translocated to the flowerheads and so to insects feeding on the seed, and to their parasitoids. Initial experiments in the laboratory showed that these elements could be readily detected by ICP (Inductively Coupled Plasma) mass spectrometry in the bodies of all species reared on potted plants sprayed with solutions containing them. Background levels of strontium were patchily high on the study area, but the other elements were naturally either absent or in very low concentrations. Four patches of each plant were marked with a different element in 1991. In 1992, samples of four species of tephritid fly and two parasitoids were collected from all patches, and analysed for the four elements. These analyses showed that individual of all species moved considerable distances, with movements of up to 2 km being commonly recorded. Estimates of rates of immigration to patches showed that movement plays an important role in the population dynamics of these insects. There was some evidence that immigration was density-dependent: it was highest when the resident populations (numbers per flowerhead) were low.

Behavioral adaptations of two phytophagous insects feeding on two species of phototoxic Asteraceae

Two phototoxic plants of the Asteraceae family were studied in relation to species of phytophagous insects for which they are hosts:Argyrotaenia velutinana Wlk. feeding onChrysanthemum leucanthemum L. andChlorochlamys chloroleucaria (Guenee) colonizingRudbeckia hirta L. The toxicity of these two plants is related to the presence of acetylenes and thiophenes that induce a light-mediated production of deleterious singlet oxygen and other free radicals (phototoxicity). Results showed that females ofA. velutinana laid their eggs preferentially in the shade and the larvae adopted hiding behaviors, such as bending of ligulate corollas and silk spinning to build opaque shelters. By avoiding direct exposure to the sun, both behaviors may reduce phototoxicity associated with ingested plant materials. Furthermore, larvae ofC. chloroleucaria demonstrated a preference in the field for pollen, which constitutes a nonphototoxic tissue of their host plant. Experimental alterations of these specific behaviors induced important biological consequences for larvae of both insects such as mortality or reduction of larval growth rate. These results reinforce the idea that behavior may constitute an efficient adaptation to avoid phototoxicity.

The Phytophagous Arthropods Associated with Lantana camara, L. hirsuta, L. urticifolia, and L. urticoides (Verbenaceae) in North America

A survey of the phytophagous arthropod fauna associated with four closely related species of Lantana (L. camara, L. urticifolia, L. urticoides, and L. hirsuta) was undertaken in Mexico and the southern United States between 1988 and 1992 to find biological control agents for L. camara, a serious weed in Australia and elsewhere. Some 261 phytophagous insect or mite species (and two rust fungi) were found. Records of species collected during three previous entomological surveys were added to produce a more complete data set of 550 phytophagous species collected throughout North America. Twenty-six of these were considered to have host ranges confined to the subfamily Verbenoideae and thus to be prospective or actual biological control agents.

Biocontrol-Parasite: Parasitoid–Host and Crop Loss Assessment Simulation Model

A model (BIOCONTROL-PARASITE) that simulates host and parasitoid population interactions, parasitism rates, and plant damage is described. BIOCONTROL-PARASITE can simulate many different species of phytophagous insects, parasitoids, and plants because specifics of the insect and plant biology are entered through menus at the beginning of a simulation. Augmentative releases of egg and nymphal parasitoids also can be simulated. The accuracy of BIOCONTROL-PARASITE predictions was tested by comparing them with field estimates of Lygus hesperus (Knight), in an alfalfa agroecosystem with Anaphes iole (Girault), and Leiophron uniformis (Gahan) as egg and nymphal parasitoids, respectively. BIOCONTROL-PARASITE predicted L. hesperus nymphal and adult populations, egg and nymphal parasitism rates, and plant state with reasonable accuracy. Simulations with and without parasitoids predicted that egg and nymphal parasitoid populations created by way of augmentative releases would reduce the L. hesperus population, but would not greatly decrease feeding damage and subsequent loss of alfalfa seed. Simulations predicted that releasing both egg and nymphal parasitoids would decrease L. hesperus egg, nymphal, and adult populations slightly below levels achieved by releasing only egg parasitoids. Estimates of seed yields from simulations with and without L. hesperus indicated that about one-third of the alfalfa seed crop would be eaten by L. hesperus. Using BIOCONTROL-PARASITE as a tool for identifying parasitoid species that might be candidates for mass rearing and release as biocontrol agents and to test the applicability and realism of data collected from laboratory experiments of host-parasitoid interactions is discussed. The assumptions and limitations of the model also are described.

Insect Herbivory in a River Red Gum (Eucalyptus camaldulensis Dehnh.) Forest in Southern New South Wales

ABSTRACTThe influence of insect herbivory on tree growth was examined in a river red gum (Eucalyptus camaldulensis) forest in southern New South Wales. Mature E. camaldulensis trees treated with the systemic insecticide monocrotophos lost an average of 13.9%± 1.6 of potential leaf area from current season's foliage compared with 22.3%± 1.6 from untreated trees. the most common form of damage was caused by leaf‐chewing insects. Leaf tissue lost by sap‐sucking, leafmining or galling insects was minimal. A total of 49 species of phytophagous insects were collected from the E. camaldulensis canopies. the insecticide‐treated trees had significantly higher rate of diameter increment (2.9 cm ± 1.1 vs. 0.7 cm ± 0.1). They also possessed healthier crowns and significantly larger leaf length/width ratios. the insecticide treatment had no significant effect on potential area per leaf or mean specific mass of the sampled foliage. the level of insect herbivory in nearby saplings was not significantly different to that of the mature trees.

The biological control of Centaurea spp. In North America: Do insects solve the problem

AbstractSpoiled and diffuse knapweed, Centaurea maculosa Lam. and C. diffusa Lam., both of European origin, are two of the most important rangeland weeds in North America. Surveys for potential biological control agents started in 1961, and agents were first introduced in 1970. So far, 11 phytophagous insect species of European origin have been released in North America. Despite legislation (restricted transport), large‐scale application of herbicides and reductions in seed production of up to 95% by the existing seed‐feeding biocontrol agents established, knapweed infestation has further increased during the last decade, covering nearly 2‐8 and 13 million ha for spotted and diffuse knapweed, respectively. In this paper, the biocontrol programme is reviewed critically and the present status analysed. To reach a break‐through in knapweed control, a cumulative stress approach is now envisaged, by extending the stress imposed by the biocontrol agents to increasing competition by the other vegetation through grazing regimes and reseeding programmes. Four steps to optimize the biocontrol effect and which lead to the integration of biocontrol into range management are described and suggestions, both scientific and political, are presented to render biological control more efficient and predictive.

Interspecific and Intraspecific Interactions Via Plant Responses to Folivory: An Experimental Field Test

I tested the hypothesis that phytophagous insect species compete interspecifically on shared host plants by inducing chemical, physical, and phenological changes in the plant that either directly reduce insect growth and survival or indirectly alter attack by natural enemies. I manipulated levels of simulated folivory on branches within eight trees of Quercus emoryi in a complete randomized block design. Survival and causes of mortality, including attack by natural enemies, of a dominant leafminer, Cameraria sp. nov., were monitored over two growing seasons. Survival varied significantly among trees but not among treatments. Causes of mortality also varied significantly among trees. Death from premature leaf abscission increased significantly with increasing levels of branch damage, while mortality from other causes, including death from bacterial and fungal attack, declined significantly with increasing levels of damage. However, neither of these changes in mortality was sufficient to cause changes in overall survival. Leaf damage did not influence attack by macroscopic natural enemies (hymenopteran parasitoids or vertebrate and invertebrate predators). By far, the most important factor affecting survival and causes of mortality within trees was the presence of co—occurring larvae on leaves (i.e., intraspecific competition). Simulated folivory in the first growing season did not affect folivory by Cameraria or other folivorous arthropods in the next season. Colonization, survival, rate of attack by natural enemies, and amount of herbivory by other arthropods in the second growing season were not affected by levels of leaf damage in the first one. Neither survival nor causes of mortality of Cameraria in the second growing season were associated with folivory by endemic leafchewing arthropods. Simulated folivory in the first growing season did, however, reduce leaf production in the second season. These results do not support the hypothesis that insect species complete interspecifically via induced plant responses and their effects on the third trophic level (natural enemies of the herbivores). The effects of simulated (first growing season) and insect (second growing season) folivory via induced plant responses on the Cameraria population was negligible relative to intraspecific interactions. Further, my results do not support the notion that folivore—induced responses are defensive and that plants have evolved these responses to manipulate the third trophic level. In natural settings, other factors that influence population dynamics of phytophagous insects, such as intraspecific competition and interactions with microparasites, may obscure any negative effects of herbivore—induced plant responses on interactions among herbivore species and their macroscopic natural enemies.

Phytophagous insects collected fromParkinsonia aculeata [Leguminosae: Caesalpiniaceae] in the Sonoran desert region of the southwestern United States and Mexico

Parkinsonia aculeata L. (Leguminosae: Caesalpiniaceae), a weed in northern Australia, was the target of a biological control programme from 1983–1987. Sixty-five phytophagous insect species were collected fromP. aculeata growing in the Sonoran desert region of the southwestern United States and Mexico. Six orders (Coleoptera, Diptera, Hemiptera, Lepidoptera, Orthoptera and Thysanoptera) and 30 families were represented. Of the 12 species with potential as biological control agents, only one has passed specificity testing and has been released in Australia.

Accumulation of Cadmium, Copper, and Zinc in Five Species of Phytophagous Insects

Concentrations of cadmium, copper, and zinc were determined in adults, larvae, larval faeces, and host plants of four monophagous and one oligophagous phytophagous insect species. In this way, transport of these metals from the plants via the larvae to the adults could be followed. The influence of metamorphosis on heavy metal concentrations was also studied. In general, metal concentrations tended to be lowest in plants, intermediate in larvae, and highest in adult insects. The exception was cadmium, concentrations of which were higher in larvae than in adult insects. Concentrations of cadmium were higher in faeces than in food plants, whereas no such difference was found for copper and zinc.

Fate of quinolizidine alkaloids through three trophic levels:Laburnum anagyroides (Leguminosae) and associated organisms

The quinolizidine alkaloids (QA) of golden rain,Laburnum anagyroides, and those of phytophagous insects associated with the plant, as well as of parasitoids of the latter, were analyzed by capillary GLC and GLC-MS. The alkaloid content in samples of vegetative plant parts was high at the beginning of the season, then decreased, while that of reproductive organs was high throughout flowering, pod formation, and maturation. The analyses showed that the QA of the plant passed through two higher trophic levels (herbivorous insects and their parasitoids) and that the alkaloid pattern changed little during the passage. The alkaloids were present in two phytophagous insect species associated with golden rain: the predispersal seed predator,Bruchidius villosus [5-13μg/g fresh weight (fw)], andAphis cytisorum (182-1012μg/g fw), an aphid that feeds on shoots, leaves, and inflorescences. Braconid and chalcidoid parasitoids emerging from the bruchid host also contained alkaloids (1.3-3μg/g fw), as did three foraging ant species,Lasius niger, Formica rufibarbis, andF. cunicularia (45μg/g fw), that visited the aphid colonies or honeydew-covered leaves of aphid-infested plants. The hypothesis that developing bruchid larvae and/or the plant "manipulate" QA supply to infested seeds was not supported, because QA content of leftover endosperm in seeds after bruchid development was similar to that of uninfested seeds. The frass of developing bruchid larvae was rich in QA (31μg/ g dry weight). While aphids sequestered, the bruchid larvae took up and eliminated QA with the frass without chemical transformation.

Density Dependence in the Mortality of Phytophagous Insects on Goldenrod ( Solidago altissima )

Field censuses were combined with laboratory rearing and dissection to investigate the frequency of density-dependent predation and parasitism of 13 phytophagous insect species associated with the goldenrod, Solidago altissima . Only 11% of the correlations between mortality and density were statistically significant. However, of those relationships that were significant, all were positive in sign, indicating a trend toward direct density dependence. Mortality of nonoutbreak species, with their potentially more stable dynamics, was not more likely to be density dependent than was that of outbreak species. Predation and parasitism showed no difference in the frequency of positive relationships, nor were suites of parasitoids more likely to exhibit direct density dependence than individual parasitoid species.