César R. Nufio

Host marking behavior in phytophagous insects and parasitoids

Oviposition behavior in phytophagous insects and entomophagous parasitoids is often modified by the presence of conspecific brood (eggs and larvae). Often, females avoid laying eggs on or in hosts bearing brood, a behavior that acts to reduce the level of competition suffered by their offspring. Avoidance of occupied hosts is typically mediated by cues and/or signals associated with brood. In this article, we review the role of Marking Pheromones (MPs) as signals of brood presence in both phytophagous and entomophagous insects. We place information about the function and evolution of MPs in the context of recent theory in the field of animal communication. We highlight the dynamics of host‐marking systems and discuss how effects of MPs vary according to factors such as female experience and egg load. We also examine variation in the form and function of MP communication across a variety of insect taxa. While studies of MP communication in phytophagous insects have focused on the underlying behavioral mechanisms and chemistry of MP communication, studies in entomophagous insects have focused on the functional aspects of MPs and their role in ‘decision‐making’ in insects. We argue that an approach that incorporates the important contributions of both of these somewhat independent, but complementary areas of research will lead to a more complete understanding of MPs in insects. Finally, we suggest that MP systems are model systems for the study of animal signaling and its evolution.

Elevation-Dependent Temperature Trends in the Rocky Mountain Front Range: Changes over a 56- and 20-Year Record

Determining the magnitude of climate change patterns across elevational gradients is essential for an improved understanding of broader climate change patterns and for predicting hydrologic and ecosystem changes. We present temperature trends from five long-term weather stations along a 2077-meter elevational transect in the Rocky Mountain Front Range of Colorado, USA. These trends were measured over two time periods: a full 56-year record (1953–2008) and a shorter 20-year (1989–2008) record representing a period of widely reported accelerating change. The rate of change of biological indicators, season length and accumulated growing-degree days, were also measured over the 56 and 20-year records. Finally, we compared how well interpolated Parameter-elevation Regression on Independent Slopes Model (PRISM) datasets match the quality controlled and weather data from each station. Our results show that warming signals were strongest at mid-elevations over both temporal scales. Over the 56-year record, most sites show warming occurring largely through increases in maximum temperatures, while the 20-year record documents warming associated with increases in maximum temperatures at lower elevations and increases in minimum temperatures at higher elevations. Recent decades have also shown a shift from warming during springtime to warming in July and November. Warming along the gradient has contributed to increases in growing-degree days, although to differing degrees, over both temporal scales. However, the length of the growing season has remained unchanged. Finally, the actual and the PRISM interpolated yearly rates rarely showed strong correlations and suggest different warming and cooling trends at most sites. Interpretation of climate trends and their seasonal biases in the Rocky Mountain Front Range are dependent on both elevation and the temporal scale of analysis. Given mismatches between interpolated data and the directly measured station data, we caution against an over-reliance on interpolation methods for documenting local patterns of climatic change.

Grasshopper community response to climatic change: variation along an elevational gradient.

Background The impacts of climate change on phenological responses of species and communities are well-documented; however, many such studies are correlational and so less effective at assessing the causal links between changes in climate and changes in phenology. Using grasshopper communities found along an elevational gradient, we present an ideal system along the Front Range of Colorado USA that provides a mechanistic link between climate and phenology. Methodology/Principal Findings This study utilizes past (1959–1960) and present (2006–2008) surveys of grasshopper communities and daily temperature records to quantify the relationship between amount and timing of warming across years and elevations, and grasshopper timing to adulthood. Grasshopper communities were surveyed at four sites, Chautauqua Mesa (1752 m), A1 (2195 m), B1 (2591 m), and C1 (3048 m), located in prairie, lower montane, upper montane, and subalpine life zones, respectively. Changes to earlier first appearance of adults depended on the degree to which a site warmed. The lowest site showed little warming and little phenological advancement. The next highest site (A1) warmed a small, but significant, amount and grasshopper species there showed inconsistent phenological advancements. The two highest sites warmed the most, and at these sites grasshoppers showed significant phenological advancements. At these sites, late-developing species showed the greatest advancements, a pattern that correlated with an increase in rate of late-season warming. The number of growing degree days (GDDs) associated with the time to adulthood for a species was unchanged across the past and present surveys, suggesting that phenological advancement depended on when a set number of GDDs is reached during a season. Conclusions Our analyses provide clear evidence that variation in amount and timing of warming over the growing season explains the vast majority of phenological variation in this system. Our results move past simple correlation and provide a stronger process-oriented and predictive framework for understanding community level phenological responses to climate change.

Role of colour and shape stimuli in host‐enhanced oogenesis in the walnut fly, Rhagoletis juglandis

This study aimed to quantify effects of the host plant on oogenesis in the walnut‐husk‐infesting fly, Rhagoletis juglandis Cresson (Diptera: Tephritidae), and to assess the role of physical cues in those effects.

Phenotypic clines, energy balances and ecological responses to climate change

The Metabolic Theory of Ecology has renewed interest in using energetics to scale across levels of ecological organization. Can scaling from individual phenotypes to population dynamics provides insight into why species have shifted their phenologies, abundances and distributions idiosyncratically in response to recent climate change? We consider how the energetic implications of phenotypes may scale to understand population and species level responses to climate change using four focal grasshopper species along an elevation gradient in Colorado. We use a biophysical model to translate phenotypes and environmental conditions into estimates of body temperatures. We measure thermal tolerances and preferences and metabolic rates to assess rates of energy use and acquisition. Body mass declines along the elevation gradient for all species, but mass-specific metabolic rates increases only modestly. We find interspecific differences in both overall thermal tolerances and preferences and in the variation of these metrics along the elevation gradient. The more dispersive species exhibit significantly higher thermal tolerance and preference consistent with much of their range spanning hot, low elevation areas. When integrating these metrics to consider metabolic constraints, we find that energetic costs decrease along the elevation gradient due to decreasing body size and temperature. Opportunities for energy acquisition, as reflected by the proportion of time that falls within a grasshoppers thermal tolerance range, peak at mid elevations. We discuss methods for translating these energetic metrics into population dynamics. Quantifying energy balances and allocation offers a viable approach for predicting how populations will respond to climate change and the consequences for species composed of populations that may be locally adapted.

Superparasitism of larval hosts by the walnut fly, Rhagoletis juglandis, and its implications for female and offspring performance

The oviposition-preference–offspring-performance hypothesis predicts that female insects should prefer to deposit clutches on or in hosts that maximize offspring performance. An important assumption behind this prediction is that female fitness is tightly correlated with the fitness of any one offspring. In this study, we evaluate offspring performance in the walnut fly, Rhagoletis juglandis Cresson (Diptera: Tephritidae), in relation to a previously described oviposition preference for previously exploited host fruit. In particular, we examined how superparasitism of walnut hosts influences offspring survival and weight at pupation under field conditions. We found that superparasitism was common and that increases in larval densities within fruit were associated with reduced larval survival and weight at pupation. In a laboratory experiment, female size was correlated with lifetime fecundity. In this system, oviposition preference is therefore negatively, not positively, correlated with offspring performance. We argue that patterns of female preference in this system reflect direct benefits to females that are traded off against costs in terms of offspring fitness. Because female fitness is a product not only of offspring quality but also of the total number of offspring produced, female walnut flies may be optimizing their fitness by producing many less fecund offspring. Studies examining the preference-performance hypothesis should consider the reproductive conflicts between parents and offspring as potential factors that influence the congruence between parental preference and offspring performance.

How Physical Characteristics of Beetles Affect their Fossil Preservation

Abstract Although insect size and robustness often have been hypothesized to be factors that lead to taphonomic bias in the insect fossil record, no studies have examined how these factors directly affect an insects preservation potential. In this study, laboratory experiments were performed on modern Coleoptera (beetles) to examine the importance of insect morphology on preservation potential. A rotary tumbling barrel was used to determine how insect size and robustness would influence sinking and disarticulation rates. Although size and robustness were not correlated directly, beetles that were larger and more robust were more resistant to disarticulation than smaller, less-robust beetles. Waterlogged specimens gained increased flexibility in their exoskeletons, and were difficult to puncture. Sinking and disarticulation rates were correlated, although it took fewer days for beetles to sink than it took to begin disarticulating. A white-colored film was apparent on all specimens within a few days of their introduction to the tumbling barrel; however, major disarticulation did not occur until the specimens sank to the bottom. An examination of the fossil-beetle literature also suggests the importance of hardness in preservation potential. Although often considered fragile, given the right physical characteristics and environmental conditions, insects can be resistant to disarticulation and decay.

Host-marking behaviour as a quantitative signal of competition in the walnut fly Rhagoletis juglandis

Abstract.  1. Walnut‐infesting flies in the Rhagoletis suavis species group actively re‐use hosts for oviposition despite engaging in a genus‐typical host‐marking behaviour which, in other Rhagoletis groups, deters oviposition. In a study of the walnut fly, R. juglandis (Cresson), alternative hypotheses for the putative marking behaviour were evaluated.

Determining the effects of habitat fragment area on grasshopper species density and richness: a comparison of proportional and uniform sampling methods

Abstract.  1. The sampling methodology used in diversity studies may at times define perceived biological patterns. In this study we used urban grassland fragments in the Front Range of northern Colorado, USA, to determine whether grasshoppers exhibit a species–area relationship (SAR) and to examine the potential effects of sampling protocol, namely uniform and proportional sampling, and sampling biases on our ability to detect such a relationship.

Host Utilization by the Walnut Fly, Rhagoletis juglandis (Diptera: Tephritidae)

Abstract Rhagoletis juglandis Cresson is a specialist that deposits its eggs into the husks of developing walnut fruit. Like other walnut infesting flies in the R. suavis group, R. juglandis actively superparasitizes its larval hosts. However, little is known regarding the degree to which hosts are reused and the ecological context under which host reuse occurs. This field study examined the pattern of host utilization by R. juglandis and how fruit variables such as volume and penetrability affect the degree that hosts are reused. Fruit on four of five study trees were synchronously infested and within 2–2.5 wk all fruit on these trees were infested. Fruit on a fifth tree were significantly less penetrable than those found among the other trees in the study and this may explain why fruit on this tree were rarely used throughout the season. Walnut hosts were commonly multiply infested and reuse of hosts occurred in as few as 1–2 d after first infestion. Infestation levels within fruit appeared to stabilize 4–5 d after fruit were first used. Fruit volume was positively correlated with both the number of punctures on hosts and the infestation levels within hosts that had been infested for either 1–2 or 4–9 d. Large fruit were infested more quickly than small fruit, although this trend was stronger on some trees than others. Finally, despite a size-penetrability correlation among two of the five trees, penetrability itself did not explain either which fruit were preferentially used throughout the season or the infestation levels within fruit.