Fly Eurosta Solidaginis Research Articles

Loss of Ice-Nucleating Activity and Avoidance of Inoculative Freezing with Puparium Formation Induced by 20-Hydroxyecdysone in Eurosta solidaginis(Diptera:Tephritidae)

Overwintering larvae of the goldenrod gall fly Eurosta solidaginis begin to freeze at temperatures above -10°C. The initiation of freezing at relatively high subzero temperatures may involve multiple ice nucleation mechanisms to protect the insect from lethal intracellular freezing. In spring, the insect changes the mode of its cold-hariness from freeze-tolerant to freeze-susceptible type, with the metamorphosis from larva to pupa. The change is accompanied by a lowering of the supercooling points (spontaneous freezing points) and an increase in the resistance to inoculative freezing. The present study demonstrated that the change in cold-hardiness accompanied by puparium formation is artificially induced by 20-hydroxyecdysone treatment. In the beginning of the puparium formation, the insects lowered their supercooling points and lost their freeze tolerance, becoming resistant to inoculative freezing. At 25°C, the serial changes were completed within a week of the hormonal treatment.

GENOTYPIC VARIATION AND INTEGRATION IN HISTOLOGICAL FEATURES OF THE GOLDENROD BALL GALL

The herb Solidago altissima (Compositae) forms a gall when attacked by the fly Eurosta solidaginis (Diptera: Tephritidae). We performed an experiment to determine how histological features of gall morphology contribute to previously observed genetic variation in gall diameter. Galls induced on 10 replicated plant clones were sectioned, and their internal tissues and cells measured. Four concentric tissue zones were identified, including a cytoplasmically rich tissue lining the insect's central chamber, and a cytoplasmically poor cortex. As expected, outer gall diameter differed among clones, with a broad sense heritability of 0.29. However, clonal differences for component tissue thicknesses were found for only two of the zones; cortex thickness showed the greater genotypic variation, with a broad sense heritability of 0.30. Path analysis was used to examine the contribution of the zone thicknesses, vascular supply and cell sizes to outer gall diameter at the phenotypic, genotypic and environmental‐developmental levels. These showed that cortex thickness was the single greatest determinant of gall size. At the phenotypic level, the single most important determinant of cortex thickness was the number of cortical cells, whereas the amount of cortical vascularization was second in importance. But, at the genotypic level of analysis, vascularization was the single most important determinant of genotypic differences in gall size. The larger the gall, the greater the protection to the inducing insect. Since the bulk of the gall consists of large, cytoplasmically poor cells, the insect gains protection while imposing a small cost on the plant.

Can there be an escalating arms race without coevolution? Implications from a host-parasitoid simulation

Under a restricted set of conditions, predator-prey or parasite-host systems may exhibit an escalating arms race over several generations that is not coevolutionary. Preconditions for such a process include high correlation between prey/host quality and defensive capability, and phenotypic plasticity in predator/parasite-counter defenses that responds to quality. We present simulation models based on the parasitoid waspEurytoma gigantea, which lays its egg in the goldenrod gall induced by the flyEurosta solidaginis. For the parasitoid to successfully lay an egg, the gall walls must be thinner than the parasitoid's ovipositor is long. Wall thickness is highly correlated with gall size, so probability of successful attack declines with gall size. However, since the parasitoid eats the gall tissue, individuals developing in small galls have little food and mature with shorter ovipositors than those which develop in large galls. The simulation showed that the population mean parasitoid size is set by mean gall size. Since small galls are more frequently parasitized, there is a selection pressure on the gallmaker to induce larger galls. But, an additional simulation showed that since parasitoid ovipositor length depends on gall size, an evolutionary increase in gall size will also result in a non-evolutionary increase in parasitoid body size and ovipositor length over several generations.

Variation in selection pressures on the goldenrod gall fly and the competitive interactions of its natural enemies.

Larvae of the tephritid fly Eurosta solidaginis induce ball-shaped galls on the stem of tall goldenrod, Solidago altissima. Survival probability depends on gall size; in small galls the larva is vulnerable to parasitoid oviposition, whereas larvae in large galls are more frequently eaten by avian predators. Fly populations from 20 natural old fields in central Pennsylvania were monitored in 1983 and 1984 to examine the distribution of the selection intensity imposed by natural enemies, the parasitoids Eurytoma gigantea and E. obtusiventris, the inquiline Mordellistena unicolor, and the predatory birds Dendrocopus pubescens and Parus atricapillus. Mordellistena and E. obtusiventris are able to attack galls of all diameters while E. gigantea and the predatory birds preferentially assaulted small and large diameter galls, respectively. Eurosta in intermediate sized galls had the highest survivorship, hence selection had a stabilizing component. However, parasitoid attack was more frequent than bird attack, and the two did not exactly balance, thus there was also a directional component. The mean directional selection intensity on gall size was 0.21 standard deviations of the mean, indicating that larger gall size was favored. Interactions among the insect members of the Eurosta natural enemy guild are complex and frequent.

Induction of a 58,000 dalton protein during goldenrod gall formation

Despite the widespread occurrence of plant-gallmaker interactions, little is known about the actual mechanisms of gall formation. To further characterize this type of parasite-host interaction, the mechanism of gall formation in Solidago altissima, tall goldenrod, by the larva of the tephritid fly Eurosta solidaginis was studied. Proteins produced by galled and ungalled tissues were examined, and the hyperinduction of a 58 kilodalton protein was observed in galled tissues for the second and third week of gall growth. The presence of this protein suggests that a substance secreted by the larva may function as a trans-acting gene regulator.

Metabolic response to temperature pulsing in the goldenrod gall fly Eurosta solidaginis: Cryoprotectant synthesis and catabolism

Metabolic response to temperature pulsing in the goldenrod gall fly Eurosta solidaginis: Cryoprotectant synthesis and catabolism

Winter survival of the gall fly larva, Eurosta solidaginis: Profiles of fuel reserves and cryoprotectants in a natural population

Larvae of the freeze-tolerant gall fly Eurosta solidaginis were sampled from outdoor populations over the course of a winter season and levels of cryoprotectants (glycerol, sorbitol), sugars, fuel reserves (glycogen, glycerides, protein), and lactate were monitored and correlated with the ambient temperature profile. Glycerol production was first stimulated in response to average daily temperatures of 10–15°C with highest rates of synthesis during early October when average temperatures were cooler and minimal daily temperatures did not exceed 8°C. Sorbitol production was initiated in mid-November in response to minimal daily temperatures below 3°C. Winter accumulations of cryoprotectants averaged 360 ± 27 and 119 ± 18 μmol/g wet weight for glycerol and sorbitol, respectively. Loss of cryoprotectants began first with sorbitol whose levels started to decline in February as maximal daily temperatures began to exceed 0°C. Loss of glycerol began in mid-March when average daily temperatures were well above 0°C but significant amounts (125 ± 23 μmol/g) still remained in pupae sampled in mid-April. During early autumn, larvae increased glycogen and protein content by 9- and 2-fold, respectively and increased total glyceride content by 50%. Glycogen was then rapidly depleted and quantitatively converted into polyols as autumn progressed. However lipid and protein reserves remained stable over the winter. Glycogen also appeared to be the fuel reserve supporting basal metabolic rate throughout the winter. During the spring, sorbitol pools were reconverted to glycogen stores but glycerol carbon was not. Lactate levels were fairly constant at 1–2 μmol/g in larvae over the winter suggesting that periods of freezing, necessitating anaerobic carbohydrate fermentation, did not produce a cumulative stress on larvae.

Goldenrod Ball Gall Effects on Solidago altissima: 14C Translocation and Growth

The purpose of this investigation was to determine whether the effects of the goldenrod ball gall on carbon translocation and growth in ramets of Solidago altissima can account for changes in biomass allocation and total biomass observed in galled ramets. To do this, individual leaves of S. altissima were labeled with carbon—14 introduced as CO2. The 14C was introduced into ramets that had ball galls caused by the fly Eurosta solidaginis and into ungalled control ramets; gall size (large vs. small) and point of introduction of the label (above vs. below the gall) were experimental factors. After 5 d the ramets were harvested and their component organs were assayed for 14C using liquid scintillation. In addition, a field cohort of 359 galled and ungalled was followed during the period of gall growth to determine the effect of the gal on stem height growth. Gall size and labeling position had no effect on the percent of 14C translocated out of the labeled leaf but did affect the distribution of translocated 14C. Translocation to underground organs was reduced when the label was introduced above the gall, the reduction being related to gall size. Large galls reduced translocation to the apical bud when the label was introduced below the gall, but small galls did not. Translocation to underground organs was not affected by the gall when the label was introduced below the gall and translocation to the apical bud was not affected by the gall when the label was introduced above the gall; these results indicate that the goldenrod ball gall is a nonmobilizing gall. The presence of a gall did not significantly affect final stem height but did slow the growth of ramets during the period of most rapid gall growth. The observed effects of the gall probably explain changes in resource allocation shown by other studies but do not account for the overall decrease in biomass of galled ramets.

Potential Selective Pressures by Parasitoids on a Plant‐Herbivore Interaction

The potential role of the third trophic level in the evolution of plant—herbivore relationships was examined in the case of the goldenrod Solidago altissima, and the fly Eurosta solidaginis, which forms a round stem gall. Previous observation had shown that galls attacked by parasites are significantly smaller than those in which the gall maker survives. Two different mechanisms could cause such as pattern: parasite attack could occur before galls reach full size and the attacks could cause early cessation of growth, or attack could occur after galls reach their mature size, but with inherently small galls being more prone to attack. In the first instance, parasite attack would diminish the cost of the gall to the plant, and thus favor plant genotypes that facilitate parasites. In the second instance, parasites would exert selection pressure on the gall marker to induce larger galls. Monitoring of marked plants in the field, and field experiments in which parasites were excluded from gall—bearing plants except during controlled periods, showed that parasite attack does not stop gall growth. The parasitoid wasp Eurytoma gigantea is limited to attacking small galls because of the limited reach of its ovipositor. This created a selection intensity of 0.50, favoring Eurosta that induce larger galls. Evolutionary response to selection could be realized directly through change in the gall marker's stimulus ability, or less directly through phenological changes. Plant activity to the gall marker declined with plant age, so that late—starting galls were more vulnerable to parasite attack.

Characterization of mitochondria isolated from the freezing-tolerant larvae of the goldenrod gall fly (Eurosta solidaginis): substrate preferences, salt effects, and pH effects on warm- and cold-acclimated animals

The mitochondria of the freezing-tolerant larvae of the goldenrod gall fly (Eurosta solidaginis) have been isolated and characterized. Proline is the preferred substrate of mitochondria from both warm- and cold-acclimated animals based on state 3 rates. Lipid is used as a substrate by warm- and cold-acclimated mitochondria assayed at 20 °C, but not by the mitochondria from cold-acclimated animals assayed at 1 °C. Cold-acclimated mitochondria assayed at 1 °C have a higher and broader optimal range of salt concentration for the oxidation of proline based on the respiratory control ratio (RCR) than those from warm-acclimated animals oxidizing the same substrate at 20 °C. The optimal pH for warm-acclimated mitochondria oxidizing proline at 20 °C is low (6.2) based on the RCR, but rises to pH 7.0 in cold-acclimated animals at 1 °C. It is suggested that the broad optimal salt concentration in the cold-acclimated animals and the very low optimal pH in warm-acclimated animals are adaptations for survival in this freezing-tolerant larva.

Relationship between temperature and juvenile hormone in the control of cold hardiness in the gall fly Eurosta solidaginis

Relationship between temperature and juvenile hormone in the control of cold hardiness in the gall fly Eurosta solidaginis

On the Origin of the Field Plants of the Northeastern United States

Old fields have dominated studies of terrestrial plant succession in the eastern United States. In spite of the tremendous amount of work on old field succession, fundamental questions remain. One such question is the subject of the present paper: In the primeval landscape, where were the plants that are abundant today in old fields? The question holds interest not only for interpretation of the northeastern landscape but also for understanding of the habitats in which field plants evolved. The plants of fallow agricultural fields are widely assumed to be early successional species, i.e., plants adapted to move from one temporary opening to another, but did they really evolve as successional plants? Many of the plants that grow in abandoned fields today are not native to North America and were thus not part of the landscape prior to European settlement. Bard (1952) reported that between one fifth and one third of the plant species in old fields in New Jersey were alien to North America. It is of the remaining two thirds (roughly 100 species) that we can ask, Where was a sun-loving field flora growing in a landscape that was heavily forested? According to Braun (1950, p. 7), "When the first settlers colonized the Atlantic seaboard ... they found an endless expanse of forest broken only by swamps and bogs, by cliffs or river bluffs too steep for forest, by windfalls and burns, by small grassy openings such as the serpentine barrens of the northern Piedmont, and by the prairie patches and 'barrens' of the interior.' Four hypotheses can be suggested to account for the location of native field plants in the presettlement landscape. (1) They evolved on agricultural land abandoned by Indians far back in time. (2) Native field plants migrated eastward from prairies and savannas at the western margin of the deciduous forest with the onset of extensive clearing for settlement and agriculture and with the development of continuous east-west corridors of open field habitat along railroads and canals. (3) Native field plants were true pioneer or early successional species that colonized temporary forest openings caused by wind, fire, and other kinds of

Nucleator activity in two populations of the gall fly Eurosta solidaginis

Nucleator activity in two populations of the gall fly Eurosta solidaginis

Environmental triggers to cryoprotectant modulation in separate populations of the gall fly, Eurost a solidaginis (Fitch)

Northern and southern populations of the gall fly Eurosta solidaginis utilize quantitatively distinct adaptive strategies when exposed to a laboratory simulation of winter temperatures. Both populations are freezing tolerant and rely in part on the temperature-dependent accumulation of glycerol and sorbitol, and static but elevated levels of trehalose for protection. The accumulation triggers are time-temperature dependent. For northern and southern populations, exposure to 5°C for periods exceeding 24 hr, but less than 5 days or 5°C with a gradual reduction (1°C/day) results in the accumulation of sorbitol at 1.5 μg/mg/day. Glycerol levels remain essentially constant between 10° and −25°C in each population. However, the concentration of glycerol in the Minnesota population is 3–4 times greater that that of the Texas specimens. Haemolymph melting points varied quantitatively with changing cryoprotectant levels. No significant difference was noted between the supercooling points of each population. This suggests that ice-nucleator levels were comparable throughout the exposure period.

Environmental triggers to cold hardening

1. 1. Evidence is presented that indicates that the primary environmental cue to antifreeze/ cryoprotectant accumulation and increased ice nucleator activity is temperature-dependent in various insect species. 2. 2. In the freeze-tolerant, Nearctic carabid beetle Pterostichus brevicornis, first exposure to 0 results in the induction of glycerol synthesis independent of short daylength. 3. 3. In the freeze-tolerant larvae of the Antarctic midge Belgica antarctica, antifreeze/cryoprotectant modulation is dependent in part on temperature and on dietary carbon source and independent of extremes in daylength. 4. 4. Both northern (45 N) and southern (25 30'N) populations of the freeze-tolerant third instar of the fly Eurosta solidaginis depend on near-freezing exposures for the triggering and sorbitol synthesis and the increased activity of hemolymph-borne ice nucleators. 5. 5. The relative advantages of temperature vs photic cues to winter hardening is discussed.