Fly Eurosta Solidaginis Research Articles

Histone H3 and H4 Modifications Point to Transcriptional Suppression as a Component of Winter Freeze Tolerance in the Gall Fly Eurosta solidaginis.

The goldenrod gall fly (Eurosta solidaginis) is a well-studied model of insect freeze tolerance. In situations of prolonged winter subzero temperatures, larvae of E. solidaginis accept ice penetration throughout extracellular spaces while protecting the intracellular environment by producing extreme amounts of glycerol and sorbitol as cryoprotectants. Hypometabolism (diapause) is implemented, and energy use is reprioritized to essential pathways. Gene transcription is one energy-expensive process likely suppressed over the winter, in part, due to epigenetic controls. The present study profiled the prevalence of 24 histone H3/H4 modifications of E. solidaginis larvae after 3-week acclimations to decreasing environmental temperatures (5 °C, -5 °C and -15 °C). Using immunoblotting, the data show freeze-mediated reductions (p < 0.05) in seven permissive histone modifications (H3K27me1, H4K20me1, H3K9ac, H3K14ac, H3K27ac, H4K8ac, H3R26me2a). Along with the maintenance of various repressive marks, the data are indicative of a suppressed transcriptional state at subzero temperatures. Elevated nuclear levels of histone H4, but not histone H3, were also observed in response to both cold and freeze acclimation. Together, the present study provides evidence for epigenetic-mediated transcriptional suppression in support of the winter diapause state and freeze tolerance of E. solidaginis.

Genomic Assessment of the Contribution of the Wolbachia Endosymbiont of Eurosta solidaginis to Gall Induction.

We explored the genome of the Wolbachia strain, wEsol, symbiotic with the plant-gall-inducing fly Eurosta solidaginis with the goal of determining if wEsol contributes to gall induction by its insect host. Gall induction by insects has been hypothesized to involve the secretion of the phytohormones cytokinin and auxin and/or proteinaceous effectors to stimulate cell division and growth in the host plant. We sequenced the metagenome of E. solidaginis and wEsol and assembled and annotated the genome of wEsol. The wEsol genome has an assembled length of 1.66 Mbp and contains 1878 protein-coding genes. The wEsol genome is replete with proteins encoded by mobile genetic elements and shows evidence of seven different prophages. We also detected evidence of multiple small insertions of wEsol genes into the genome of the host insect. Our characterization of the genome of wEsol indicates that it is compromised in the synthesis of dimethylallyl pyrophosphate (DMAPP) and S-adenosyl L-methionine (SAM), which are precursors required for the synthesis of cytokinins and methylthiolated cytokinins. wEsol is also incapable of synthesizing tryptophan, and its genome contains no enzymes in any of the known pathways for the synthesis of indole-3-acetic acid (IAA) from tryptophan. wEsol must steal DMAPP and L-methionine from its host and therefore is unlikely to provide cytokinin and auxin to its insect host for use in gall induction. Furthermore, in spite of its large repertoire of predicted Type IV secreted effector proteins, these effectors are more likely to contribute to the acquisition of nutrients and the manipulation of the host's cellular environment to contribute to growth and reproduction of wEsol than to aid E. solidaginis in manipulating its host plant. Combined with earlier work that shows that wEsol is absent from the salivary glands of E. solidaginis, our results suggest that wEsol does not contribute to gall induction by its host.

Sensory co‐evolution: The sex attractant of a gall‐making fly primes plant defences, but female flies recognize resulting changes in host‐plant quality

Abstract Tall goldenrod plants Solidago altissima appear to eavesdrop on the communication of a specialist gall‐inducing fly Eurosta solidaginis by detecting the volatile emissions of male flies and priming anti‐herbivore defences. However, the effects of defence priming on fly fitness have not previously been demonstrated, despite some evidence that female flies avoid ovipositing on primed plants in the field. To explore how priming affects female preferences and galling success, we manipulated exposure to the priming cue in multiple genotypes of S. altissima and assessed rates of oviposition and gall development. Priming reduced gall formation overall; however, its effect varied across plant genotypes, as well as by the age of the male flies used for priming, possibly reflecting dosage effects (older flies produce lower emissions). Priming by younger males significantly reduced galling success, while priming by older males slightly improved it. Remarkably, female flies accurately assessed host‐plant quality by avoiding plants primed by young males while preferring those primed by older males. Synthesis. Our results suggest that defence priming in S. altissima in response to the volatile emissions of E. solidaginis males does affect fly fitness; however, the effect of priming varied by plant genotype, suggesting that there may be variation in defensive strategies against the fly. Female flies have, in response to this defence, evolved a sophisticated ability to evaluate the quality of primed plants.

Distribution of the Specialist Aphid Uroleucon nigrotuberculatum (Homoptera: Aphididae) in Response to Host Plant Semiochemical Induction by the Gall Fly Eurosta solidaginis (Diptera: Tephritidae).

Many plants use terpenoids and other volatile compounds as semiochemicals. Reception of plant volatiles by conspecifics may trigger a defensive phytochemical response. These same compounds can also function as host recognition signals for phytophagous insects. In this experiment, we find that when the specialist gall-forming fly Eurosta solidaginis (Fitch; Diptera: Tephritidae) attacks its tall goldenrod (Solidago altissima (L.; Asterales: Asteraceae)) host plant, the fly indirectly induces a phytochemical response in nearby tall goldenrod plants. This phytochemical response may, in turn, act as a positive signal attracting the goldenrod specialist aphid Uroleucon nigrotuberculatum (Olive; Hemiptera: Aphididae). Laboratory-based experiments exposing ungalled tall goldenrod plants to the volatiles released by E. solidaginis galls demonstrated a consistent increase in foliar terpenoid concentrations in ungalled plants. Analysis of tall goldenrod stem and gall tissue chemistry revealed induction of terpenoids in gall tissue, with a simultaneous decrease in green leaf volatile concentrations. Field experiments demonstrated a consistent spatial relationship in tall goldenrod foliar terpenoid concentrations with distance from an E. solidaginis gall. Both laboratory and field experiments establish consistent induction of the terpene β-farnesene, and that this compound is a strong positive predictor of U. nigrotuberculatum aphid presence on goldenrod plants along with plant biomass and several other foliar terpenoids. These findings suggest E. solidaginis induced phytochemistry, especially β-farnesene, may be acting as a kairomone, driving aphid distribution in the field.

Are Eurosta solidaginis on Solidago rugosa a divergent host-associated race?

The ball-gall fly Eurosta solidaginis is considered a classic example of host-race formation in herbivorous insects, with host-associated races evolving at least twice, including the well-known pair on Solidago altissima and S. gigantea. Yet E. solidaginis has been occasionally observed galling other Solidago species. Here, we explore the origins of E. solidaginis on Solidago rugosa. We hypothesize that flies associated with S. rugosa are derived from the S. altissima host-race, and ask whether S. rugosa-associated flies have initiated host-race formation. We compared genetic variation among seventeen E. solidaginis populations collected from S. rugosa, S. altissima, and S. gigantea, in an adjacent COI/COII region of the mitochondrial genome. Across the study area, E. solidaginis flies from S. rugosa were as diverged from S. altissima-flies as they were from S. gigantea-flies (pairwise ΦPT 0.075 and 0.78 respectively) but S. altissima and S. gigantea-flies appeared considerably less diverged (0.002). This pattern was driven by the majority of flies, regardless of host-plant, sharing the same haplotype across the study area. However, we detected several site/region-specific haplotypes, not shared among host species. At the local site scale we were able to distinguish S. gigantea-associated fly haplotypes from either S. altissima or S. rugosa haplotypes, but the majority of S. altissima and S. rugosa-flies shared the same haplotype locally. These patterns of haplotype diversity support existing evidence of host-associated divergence in S. altissima- and S. gigantea-associated flies, and suggest that S. rugosa flies are either the same host-race as, or are recently derived from, S. altissima flies. Successful development on S. rugosa and the use of S. rugosa in the absence of use on sympatric S. altissima suggests that E. solidaginis either has a single oligophagous race using both S. altissima and S. rugosa or is in the earliest stages of host-associated differentiation.

Repeated freezing induces a trade-off between cryoprotection and egg production in the goldenrod gall fly, Eurosta solidaginis.

Internal ice formation leads to wholesale changes in ionic, osmotic and pH homeostasis, energy metabolism, and mechanical damage, across a small range of temperatures, and is thus an abiotic stressor that acts at a distinct, physiologically relevant, threshold. Insects that experience repeated freeze-thaw cycles over winter will cross this stressor threshold many times over their lifespan. Here, we examined the effect of repeatedly crossing the freezing threshold on short-term physiological parameters (metabolic reserves and cryoprotectant concentration) as well as long-term fitness-related performance (survival and egg production) in the freeze-tolerant goldenrod gall fly, Eurosta solidaginis We exposed overwintering prepupae to a series of low temperatures (-10, -15 or -20°C) with increasing numbers of freezing events (3, 6 or 10) with differing recovery periods between events (1, 5 or 10 days). Repeated freezing increased sorbitol concentration by about 50% relative to a single freezing episode, and prompted prepupae to modify long-chain triacylglycerols to acetylated triacylglycerols. Long-term, repeated freezing did not significantly reduce survival but did reduce egg production by 9.8% relative to a single freezing event. Exposure temperature did not affect any of these measures, suggesting that threshold crossing events may be more important to fitness than the intensity of stress in overwintering E. solidaginis.

Characterization of cold-associated microRNAs in the freeze-tolerant gall fly Eurosta solidaginis using high-throughput sequencing

Significant physiological and biochemical changes are observed in freeze-tolerant insects when confronted with cold temperatures. These insects have adapted to winter by retreating into a hypometabolic state of diapause and implementing cryoprotective mechanisms that allow them to survive whole body freezing. MicroRNAs (miRNAs), a family of short ribonucleic acids, are emerging as likely molecular players underlying the process of cold adaptation. Unfortunately, the data is sparse concerning the signature of miRNAs that are modulated following cold exposure in the freeze-tolerant goldenrod gall fly Eurosta solidaginis. Leveraging for the first time a next-generation sequencing approach, differentially expressed miRNAs were evaluated in 5°C and −15°C-exposed E. solidaginis larvae. Next-generation sequencing expression data was subsequently validated by qRT-PCR for selected miRNA targets. Results demonstrate 24 differentially expressed freeze-responsive miRNAs. Notable, miR-1-3p, a miRNA modulated at low temperature in another cold-hardy insect, and miR-14-3p, a miRNA associated with stress response in the fruit fly, were shown to be significantly up-regulated in −15°C-exposed larvae. Overall, this work identifies, for the first time in a high-throughput manner, differentially expressed miRNAs in cold-exposed E. solidaginis larvae and further clarifies an emerging signature of miRNAs modulated at low temperatures in cold-hardy insects.

Expression of miRNAs in response to freezing and anoxia stresses in the freeze tolerant fly Eurosta solidaginis

Insect cold hardiness is associated with substantial metabolic rate suppression, often including developmental diapause as well as metabolic suppression imposed by freezing and freeze-associated oxygen limitation. MicroRNAs, small non-coding transcripts that bind to mRNA, are known modulators of hypometabolism in freeze tolerant insects. To further contribute to the growing signature of stress-responsive miRNAs, this study amplified and quantified changes in the expression levels of four microRNA species, miR-8, miR-9, miR-92b and miR-277, in response to freezing or anoxia exposures of freeze tolerant gall fly larvae, Eurosta solidaginis. MiR-92b levels were significantly elevated by 1.57-fold in frozen E. solidaginis at −15°C as compared with 5°C controls, whereas miR-92b levels were significantly reduced in anoxic E. solidaginis to levels that were 0.77-fold as compared with larvae held under normoxic conditions. The other miRNAs investigated showed no significant changes in stressed larvae. These data demonstrate differential miR-92b expression in frozen/anoxic versus control insect larvae and position this miRNA as a stress responsive marker in this model insect.

The limits of drought-induced rapid cold-hardening: Extremely brief, mild desiccation triggers enhanced freeze-tolerance in Eurosta solidaginis larvae

Rapid cold-hardening (RCH) is a highly conserved response in insects that induces physiological changes within minutes to hours of exposure to low temperature and provides protection from chilling injury. Recently, a similar response, termed drought-induced RCH, was described following as little as 6h of desiccation, producing a loss of less than 10% of fresh mass. In this study, we investigated the limits and mechanisms of this response in larvae of the goldenrod gall fly Eurosta solidaginis (Diptera, Tephritidae). The cold-hardiness of larvae increased markedly after as few as 2h of desiccation and a loss of less than 1% fresh mass, as organismal survival increased from 8% to 41% following exposure to −18°C. Tissue-level effects of desiccation were observed within 1h, as 87% of midgut cells from desiccated larvae remained viable following freezing compared to 57% of controls. We also demonstrated that drought-induced RCH occurs independently of neuroendocrine input, as midgut tissue desiccated ex vivo displayed improved freeze-tolerance relative to control tissue (78–11% survival, respectively). Finally, though there was an increase in hemolymph osmolality beyond the expected effects of the osmo-concentration of solutes during dehydration, we determined that this increase was not due to the synthesis of glycerol, glucose, sorbitol, or trehalose. Our results indicate that E. solidaginis larvae are extremely sensitive to desiccation, which is a triggering mechanism for one or more physiological pathways that confer enhanced freeze-tolerance.

Repeated freezing induces oxidative stress and reduces survival in the freeze-tolerant goldenrod gall fly, Eurosta solidaginis

Freeze tolerant insects must not only survive extracellular ice formation but also the generation of reactive oxygen species (ROS) during oxygen reperfusion upon thawing. Furthermore, diurnal fluctuations in temperature place temperate insects at risk of being exposed to multiple freeze–thaw cycles, yet few studies have examined metrics of survival and oxidative stress in freeze-tolerant insects subjected to successive freezing events. To address this, we assessed survival in larvae of the goldenrod gall fly Eurosta solidaginis, after being subjected to 0, 5, 10, 20, or 30 diurnally repeated cold exposures (RCE) to −18°C or a single freeze to −18°C for 20days. In addition, we measured indicators of oxidative stress, levels of cryoprotectants, and total aqueous antioxidant capacity in animals exposed to the above treatments at 8, 32, or 80h after their final thaw. Repeated freezing and thawing, rather than time spent frozen, reduced survival as only 30% of larvae subjected to 20 or 30 RCE successfully pupated, compared to those subjected to fewer RCE or a single 20d freeze, of which 82% pupated. RCE had little effect on the concentration of the cryoprotectant glycerol (4.26±0.66μgglycerol·ngprotein−1 for all treatments and time points) or sorbitol (18.8±2.9μgsorbitol·mgprotein−1 for all treatments and time points); however, sorbitol concentrations were more than twofold higher than controls (16.3±2.2μgsorbitol·mgprotein−1) initially after a thaw in larvae subjected to a single extended freeze, but levels returned to values similar to controls at 80h after thaw. Thawing likely produced ROS as total aqueous antioxidant capacities peaked at 1.8-fold higher than controls (14.7±1.6mmoltrolox·ngprotein−1) in animals exposed to 5, 10, or 20 RCE. By contrast, aqueous antioxidant capacities were similar to controls in larvae subjected to 30 RCE or the single 20d freeze regardless of time post final thaw, indicating these animals may have had an impaired ability to produce primary antioxidants. Larvae lacking an antioxidant response also had elevated levels of oxidized proteins, nearly twice that of controls (21.8±3.2mmolchloramine-T·mgprotein−1). Repeated freezing also lead to substantial oxidative damage to lipids that was independent of aqueous antioxidant capacity; peroxides were, on average, 5.6-fold higher in larvae subjected to 10, 20 or 30 RCE compared to controls (29.1±7.3mmolTMOP·μgprotein−1). These data suggest that oxidative stress due to repeated freeze–thaw cycles reduces the capacity of E. solidaginis larvae to survive freezing.

6. Characterization of a cold-associated miRNA signature in a freeze tolerant insect

Methods to preserve organs, whether destined for transplants or long-term storage, involve maintaining life at non-physiological temperatures. While our molecular understanding of the freezing process has improved the field of cryopreservation, much remains to be done to comprehend life in the cold and to translate this knowledge to known biomedical applications. Natural models of hypometabolism exist in nature and hold keys to our understanding of biochemical processes at play during freezing. Freeze tolerant insects are examples of such models as they survive the low temperatures associated with winter. Overwintering strategies employed include decreased metabolic rate, reduction in heart rate and significant down-regulation of energy-consuming processes. To gain new perspectives on freeze tolerance, we studied differential expression of members of a novel family of nucleic acids named the microRNAs (miRNAs) in the freeze tolerant fly Eurosta solidaginis . miRNAs are small ribonucleic acids capable of regulating protein translation by silencing expression of selected transcripts. Expression of miRNAs was assessed in control (+5 °C) and frozen (−15 °C) insects by miRNA microarray. Several miRNAs were identified as differentially expressed in cold insects and were subsequently sequenced in E. solidaginis . This cold-induced signature of miRNAs could yield crucial information about how they can help cope with temperature stress and how this strategy could be transposed to higher organisms.

In Cold‐Hardy Insects, Seasonal, Temperature, and Reversible Phosphorylation Controls Regulate Sarco/Endoplasmic Reticulum Ca2+‐ATPase (SERCA)

Winter cold hardiness of insects typically involves one of two major strategies for survival below 0 degrees C: freeze avoidance and freeze tolerance. The two strategies have some common features, including the accumulation of high concentrations of cryoprotectant polyols and the frequent occurrence of diapause. Entry into the hypometabolic state of diapause requires coordinated suppression of major ATP-consuming metabolic processes, and ion motive ATPases are important targets for regulation. This study documents the suppression of sarco/endoplasmic reticulum Ca(2+)-ATPase (SERCA) activity in the overwintering larvae of two cold-hardy species, the freeze-avoiding gall moth Epiblema scudderiana and the freeze-tolerant gall fly Eurosta solidaginis. Activity was reduced despite a lack of change in SERCA protein levels in E. solidaginis larvae over the winter and a six- to eightfold increase in SERCA protein in E. scudderiana. This implicated posttranslational modification as the mechanism of SERCA suppression, and in vitro incubations indicated that enzyme phosphorylation by protein kinases A, G, or C strongly reduced enzyme activity. A stable reduction in SERCA activity was also seen in cold-acclimated larvae of both species compared with 15 degrees C controls, with significant changes in the kinetic parameters of the E. scudderiana enzyme (e.g., K(m) ATP was 3.2-fold higher in -20 degrees C-acclimated larvae) that were consistent with reduced enzyme function at low temperature. Epiblema scudderiana SERCA was also subject to regulation by differential temperature effects (Arrhenius activation energy increased by approximately threefold below 10 degrees C) and by seasonal changes in the levels of a SERCA inhibitor protein, phospholamban.

The role of nodding stems in the goldenrod–gall–fly interaction: A test of the “ducking” hypothesis

Herbivores are among the most pervasive selective forces acting on plants, and the number of plant chemicals that presumably evolved for defense against herbivory is immense. In contrast, biologists are only beginning to appreciate the important roles that architectural traits can play in antiherbivore defense. One putative architectural-resistance trait is the nodding stem apex of some goldenrods (Solidago; Asteraceae). Individuals of S. altissima genets that undergo temporary nodding in the late spring (i.e., "candy-cane" ramets) have been shown to be more resistant than individuals of erect-stemmed genets to certain apex-attacking herbivores. We tested the hypothesis that the greater resistance of candy-cane ramets is accomplished by the ramets' "ducking" from the herbivores. In a greenhouse experiment, nodding candy-cane ramets were significantly more resistant to oviposition by the gall-inducing fly Eurosta solidaginis than were ramets of the same genets that had been experimentally straightened. The straightened candy-cane stems were just as susceptible to ovipositions as were ramets of erect-stemmed genets. Thus, ducking indeed appears to confer a resistance advantage to candy-cane genets of S. altissima.

In vivo assessment of cold adaptation in insect larvae by magnetic resonance imaging and magnetic resonance spectroscopy.

BackgroundTemperatures below the freezing point of water and the ensuing ice crystal formation pose serious challenges to cell structure and function. Consequently, species living in seasonally cold environments have evolved a multitude of strategies to reorganize their cellular architecture and metabolism, and the underlying mechanisms are crucial to our understanding of life. In multicellular organisms, and poikilotherm animals in particular, our knowledge about these processes is almost exclusively due to invasive studies, thereby limiting the range of conclusions that can be drawn about intact living systems.MethodologyGiven that non-destructive techniques like 1H Magnetic Resonance (MR) imaging and spectroscopy have proven useful for in vivo investigations of a wide range of biological systems, we aimed at evaluating their potential to observe cold adaptations in living insect larvae. Specifically, we chose two cold-hardy insect species that frequently serve as cryobiological model systems–the freeze-avoiding gall moth Epiblema scudderiana and the freeze-tolerant gall fly Eurosta solidaginis.Results In vivo MR images were acquired from autumn-collected larvae at temperatures between 0°C and about −70°C and at spatial resolutions down to 27 µm. These images revealed three-dimensional (3D) larval anatomy at a level of detail currently not in reach of other in vivo techniques. Furthermore, they allowed visualization of the 3D distribution of the remaining liquid water and of the endogenous cryoprotectants at subzero temperatures, and temperature-weighted images of these distributions could be derived. Finally, individual fat body cells and their nuclei could be identified in intact frozen Eurosta larvae.ConclusionsThese findings suggest that high resolution MR techniques provide for interesting methodological options in comparative cryobiological investigations, especially in vivo.

High resistance to oxidative damage in the Antarctic midge Belgica antarctica, and developmentally linked expression of genes encoding superoxide dismutase, catalase and heat shock proteins

Intense ultraviolet radiation, coupled with frequent bouts of freezing–thawing and anoxia, have the potential to generate high levels of oxidative stress in Antarctic organisms. In this study, we examined mechanisms used by the Antarctic midge, Belgica antarctica, to counter oxidative stress. We cloned genes encoding two key antioxidant enzymes, superoxide dismutase (SOD) and catalase (Cat), and showed that SOD mRNA was expressed continuously and at very high levels in larvae, but not in adults, while Cat mRNA was expressed in both larvae and adults but at a somewhat reduced level. SOD mRNA was expressed at even higher levels in larvae that were exposed to direct sunlight. Catalase, a small heat shock protein, Hsp70 and Hsp90 mRNAs were also strongly upregulated in response to sunlight. Total antioxidant capacity of the adults was higher than that of the larvae, but levels in both stages of the midge were much higher than observed in a freeze-tolerant, temperate zone insect, the gall fly Eurosta solidaginis. Assays to measure oxidative damage (lipid peroxidation TBARS and carbonyl proteins) demonstrated that the Antarctic midge is highly resistant to oxidative stress.

Stealth tactics of galling parasites and their potential indirect effects

Stealth tactics of galling parasites and their potential indirect effects

Gall insects can avoid and alter indirect plant defenses

Parasitic species can dramatically alter host traits. Some of these parasite-induced changes can be considered adaptive manipulations that benefit the parasites. Gall-inducing insects are parasites well known for their ability to alter host-plant morphology and physiology, including the distribution of plant defensive compounds. Here it was investigated whether gall-inducing species alter indirect plant defenses, involving the release of volatile compounds that are attractive to foraging natural enemies. Using field and factorial laboratory experiments, volatile production by goldenrod (Solidago altissima) plants was examined in response to attack by two gall-inducing species, the tephritid fly Eurosta solidaginis and the gelechiid moth Gnorimoschema gallaesolidaginis, as well as the meadow spittlebug, Philaenus spumarius, and the generalist caterpillar Heliothis virescens. Heliothis virescens elicited strong indirect defensive responses from S. altissima, but the gall-inducing species and spittlebugs did not. More significantly, infestation by E. solidaginis appeared to suppress volatile responses to subsequent attack by the generalist caterpillar. The extensive control that E. solidaginis apparently exerts over host-plant defense responses may reduce the predation risk for the gall inducer and the subsequent herbivore, and could influence community-level dynamics, including the distribution of herbivorous insect species associated with S. altissima parasitized by E. solidaginis.

Seasonal Changes in Phospholipid Class and Class‐Specific Fatty Acid Composition Associated with the Onset of Freeze Tolerance in Third‐Instar Larvae ofEurosta solidaginis

Abstract Third-instar larvae of the goldenrod gall fly Eurosta solidaginis (Diptera: Tephritidae) are freeze tolerant in winter. During freezing, cell membranes must compensate for both low temperature and partial dehydration. Documented adaptations to low temperature include increased fatty acid unsaturation and enrichment of cone-shaped phosphatides, both of which inhibit formation of gel phase lipid domains. These changes appear inconsistent with adaptations known to prevent formation of the hexagonal II phospholipid phase at low water activities, namely, increased fatty acid saturation and increased proportions of cylindrical phosphatides. To address these inconsistencies, changes in E. solidaginis phospholipid composition and class-specific fatty acid composition were studied from August to November 2002. Cylindrical phosphatides, mostly phosphatidylcholine (PC), increased transiently and significantly, from 35% of the total to nearly 50%, during the transition from freeze susceptible to freeze tolerant. Monoenes in both PC and phosphatidylethanolamine (PE) represented 35% of total fatty acids in freeze-susceptible larvae but accumulated in PC to 48% and in PE to 42% in freeze-tolerant larvae. Moreover, PC accumulated the most unsaturated acid in this species, 18:3(n-3), to a significantly greater degree than PE. This combination of changes may represent a finely tailored response to both low temperatures and freeze-induced dehydration.

Good mothers, bad mothers, and the nature of resistance to herbivory in Solidago altissima

Evidence of poor correspondence between an insect herbivore's oviposition preferences and the performance of its offspring has generally been attributed either to maladaptive behavior of the insect mother or inadequate measurement by the researcher. In contrast, we hypothesize that many cases of "bad mothers" in herbivores may be a byproduct of the hierarchical way natural selection works on resistance in host plants. Epistatic selection on the components of resistance (i.e., antixenosis and antibiosis) may generate negative genetic correlations between the resistance components, which could counteract the efforts of herbivores to oviposit on the best hosts for the performance of their offspring. In common garden and greenhouse experiments, we measured aspects of antixenosis and antibiosis resistance in 26 genets of tall goldenrod, Solidago altissima, against two common herbivores: the gall-inducing fly Eurosta solidaginis and the spittlebug Philaenus spumarius. Goldenrod antixenosis and antibiosis were positively correlated against E. solidaginis and negatively correlated against P. spumarius. Analogously, population-wide preference-performance correlations were positive for the gall flies and negative for the spittlebugs. Several natural history differences between the two insects could make gall flies better mothers, including better synchrony of the phenologies of the flies and the host plant, the much narrower host range of the gall flies than the spittlebugs, and the more sedentary lifestyle of the gall fly larvae than the spittlebug nymphs. If these results are typical in nature, then negative genetic correlations in antixenosis and antibiosis in plants may often result in zero or negative population-wide correlations between preference and performance in herbivores, and thus may be an important reason why herbivorous insects often appear to be bad mothers.

Evidence for a novel cryoprotective protein from freeze-tolerant larvae of the goldenrod gall fly Eurosta solidaginis

Third-instar larvae of the goldenrod gall fly Eurosta solidaginis (Diptera: Tephritidae) from populations in northern North America transition from freeze-susceptible to freeze-tolerant just prior to the onset of winter. While studies have documented the accumulation of carbohydrate cryoprotectants during this transition, protein cryoprotectants common to other freeze-tolerant species have not been reported in the gall fly. Using larvae collected from a population in Madison County, NY, which changes from freeze-susceptible to freeze-tolerant in early October, we assayed for the presence of factors that could preserve the catalytic activity of the cold-labile enzyme, rabbit muscle lactate dehydrogenase. Freezing this enzyme with a heat-stable, hydrophilic fraction derived from homogenates of both freeze-tolerant larvae and those in the process of becoming freeze-tolerant preserved between 70% and 80% of this enzyme’s activity. Neither a comparable solution of bovine serum albumin nor the naturally-occurring carbohydrates (glycerol, sorbitol, or trehalose) conferred this level of cryoprotection. The putative cryoprotective protein from gall fly larvae did not bind to a weak anion exchanger, implying that its character may be cationic.