THE author of this book ranks as the foremost American worker on insect morphology. His contributions on the subject are notable for their clarity and originality of thought, and the appearance of a volume, embodying his ideas in comprehensive form, is sure of a hearty welcome. In its preparation, Mr. Snodgrass has incorporated the results of much first-hand study with those of many recent investigators in the same field. He has produced an outstanding book wherein knowledge of facts is combined with that of function and, at the same time, theoretical conceptions of the origins and relationships of organs and parts are not overlooked. Principles of Insect Morphology
 By R. E. Snodgrass. (McGraw-Hill Publications in the Zoological Sciences.) Pp. ix + 667. (New York and London: McGraw-Hill Book Co., Inc., 1935.) 36s. net.

Principles of Insect Morphology

Nuptial feeding encompasses any form of nutrient transfer from the male to the female during or directly after courtship and/or copulation. In insects, nuptial gifts may take the form of food captured or collected by the male, parts, or even the whole of the male's body, or glandular products of the male such as salivary secretions, external glandular secretions, the spermatophore and substances in the ejaculate. Over the past decade, there has been considerable debate over the current function of nuptial feeding in insects. This debate has centred on the issue of whether nuptial gifts function as paternal investment (i.e. function to increase the fitness and/or number of the gift-giving male's own offspring) or as mating effort (i.e. function to attract females, facilitate coupling, and/or to maximize ejaculate transfer), although the two hypotheses are not mutually exclusive. In the present article, evidence for the potential of nuptial gifts to function as either paternal investment, mating effort, or both is reviewed for each form of nuptial feeding in each insect taxon for which sufficient data are available. Empirical evidence suggests that many diverse forms of nuptial feeding in different insect taxa function, at least in part, as mating effort. For example, nuptial prey and salivary masses in the Mecoptera, regurgitated food in Drosophila (Diptera), hind-wing feeding in Cyphoderris (Orthoptera) and the secretion of the male's cephalic gland in Neopyrochroa (Coleoptera) and Zorotypus (Zoraptera) appear to function to entice females to copulate and/or to facilitate coupling. Nuptial prey and salivary masses in the Mecoptera also appear to function to maximize ejaculate transfer (which is also a form of mating effort), as do nuptial prey in Empis (Diptera), external glandular secretions in Oecanthus and Allonemobius (Orthoptera) and the spermatophylax in gryllids and tettigoniids (Orthoptera). Large spermatophores in, for example, the Lepidoptera and Coleoptera, also appear to be maintained by selection on the male to maximize ejaculate transfer and thereby counter the effects of sperm competition. In contrast to the large amount of evidence in support of the mating effort hypothesis, there is a relative lack of good evidence to support the paternal investment hypothesis. Certain studies have demonstrated an increase in the weight and/or number of eggs laid as a result of the receipt of larger gifts, or a greater number of gifts, in tettigoniids, gryllids, acridids, mantids, bruchid beetles, drosophilids and lepidopterans. However, virtually all of these studies (with the possible exception of studies of the spermatophylax in tettigoniids) have failed to control adequately for hormonal substances in the ejaculate that are known to affect female reproductive output. Furthermore, in at least four tettigoniids (but not in the case of two species), three lepidopterans, a drosophilid and probably also bruchid beetles and bittacids, evidence suggests that the male has a low probability of fertilising the eggs that stand to benefit from his nuptial gift nutrients. Therefore, the hypothesis that paternal investment might account for the function of nuptial gifts in general is not supported.

The function of nuptial feeding in insects: a review of empirical studies

A number of aposematic butterfly and diurnal moth species sequester unpalatable or toxic substances from their host plants rather than manufacturing their own defensive substances. Despite a great diversity in their life histories, there are some general features in the selective utilization of plant secondary metabolites to achieve effective protection from predators. This review illustrates the biochemical, physiological, and ecological characteristics of phytochemical-based defense systems that can shed light on the evolution of the widely developed sequestering lifestyles among the Lepidoptera.

Sequestration of defensive substances from plants by Lepidoptera.

▪ Abstract Inherited environmental effects are those components of the phenotype that are derived from either parent, apart from nuclear genes. Inherited environmental effects arise as the product of parental genes and the parental environment, or their interation, and can include contributions that reflect the abiotic, nutritional, and other ecological features of a parental environment. Separating the impact of inherited environmental effects from inherited genetic effects on offspring phenotype variation has been and continues to be a challenge. This complexity is represented in the presentation of a qualitative model that distinguishes the possible paths of nongenetic cross-generational transmission. This model serves as the framework for considering the nature, in published works, of what was actually measured. Empirical evidence of inherited environmental effects arising from these pathways is documented for a diversity of plant and animal taxa. From these results one can conclude that the impact of...

Incidence and consequences of inherited environmental effects

Summary
1Resource acquisition and allocation are the physiological mechanisms integrating foraging and life-history traits. An understanding of the patterns of acquisition and allocation in different environments and organisms is critical to a predictive theory of life history.
2Here I develop an allocation framework, which provides a template for conceptualizing the interactions among resource acquisition, allocation and life-history traits. The framework describes the process through which food is taken in by an organism at specific life stages, then allocated to growth, survival (including maintenance, defence, dispersal, etc), reproduction and further foraging.
3I use the allocation framework to examine allocation to life-history traits in insects under both benign and stressful environments. Stressful environments result from resource scarcity or harsh environmental conditions. I consider effects of consistent stress or variable stress across time.
4Several broad generalizations emerge from empirical studies, viewed in the allocation framework. First, resource congruence, or the requirement for specific nutrient ratios in, for example, eggs, results in different limiting nutrients for each life-history trait. Second, the timing of resource acquisition affects both allocation patterns and the identity of limiting nutrients for a given life-history trait. Third, physiological trade-offs may occur across, not just within, life stages. Fourth, apparent trade-offs may be driven by differences among traits in resource congruence constraints and deleterious effects of excess nutrients on a particular trait. Fifth, allocation response to environmental stress shows age-specific and sex-specific patterns. Sixth, physiological trade-offs are often more pronounced under environmental stress. Finally, even within insects, there is considerable variability in allocation response to environmental stress. We do not yet have sufficiently diverse and thorough case studies to understand why this is so. Studies in the wild, or relating laboratory conditions to wild environments, are also needed.
5Senescence can also be understood in an allocation framework. The present approach provides a necessary functional basis for understanding patterns of senescence in diverse organisms and environments.
6The allocation framework fosters a mechanistic understanding of life-history patterns, and the beginning of an understanding of the processes underlying those patterns.

https://besjournals.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-2435.2009.01527.x

Understanding insect life histories and senescence through a resource allocation lens.

. Adults of many species of Lepidoptera, principally the males, frequent mud puddles, edges of streams, carrion and animal excreta where they imbibe moisture, an activity referred to as ‘puddling’ Sodium ions are the only known stimulus present which cause males of at least two lepidopteran species to drink for extended periods. In the European skipper Thymelicus lineola (Ochsenheimer) (Lepidoptera: Hesperiidae), only males puddle, even though they have concentrations of abdominal sodium 2–3 times that of females at emergence. During their first mating, males transfer 32% of their abdominal sodium to females. This could be of considerable importance given that an average egg complement contains >50% of the total body sodium of females at emergence. Virgin females, as well as having reduced fecundity, have reduced longevity. This is attributed to virgins not obtaining important nutrients which males transfer to females during mating. Access to sodium ions increases the total number of matings by c. 50% for males living >15 days. Access to sodium ions by once-mated males increases the percentage of males which re-mate on the day following first mating; the percentage of females, mated to the twice-mated males, which lay >50% fertile eggs; and the drought resistance of eggs laid by those females.

Puddling in butterflies : sodium affects reproductive success in Thymelicus lineola

Field observations of the adult European skipper, Thymelicus lineola (Ochs), feeding on concentrated nectars (40-65% sucrose) from a variety of flower species led us to question recent literature stating that butterflies feed primarily, and most effectively, on dilute nectars. Rate of sucrose solution intake, volume consumed and feeding duration were measured for males and females at 25 and 35°C under laboratory conditions. As sucrose concentration increased, the volume of solution ingested per meal first increased and then decreased gradually, while sucrose intake was highest at concentrations ≧40%. Females fed more than males at all concentrations >10% while temperature had no significant effect on meal size. Feeding duration increased with concentration, was shorter at 35 than at 25°C, and was longer for females than males.The rate of volume intake decreased as concentration incresed, but not nearly as rapidly as predicted by earlier models. Rates did not differ between the sexes but were faster at 35 than 25°C. This increase was contributed to equally by a reduction in viscosity and an increase in power output of the cibarial pump. The form of the relations was similar, with maximum rate of sucrose intake occurring at 40% sucrose.A new mathematical model was developed to describe the rate - concentration relation based on the Hagen-Poiseuille equation for laminar fluid flow through pipes. Our model differs from previous models principally in that the power output of the insect's cibarial pump remains relatively constant while the pressure drop created by the pump to induce suction is highly variable. This change results in a very different feeding rate - sucrose concentration function with the optimal rate of sucrose intake at a concentration of approximately 40%. The model indicates that the same relation should hold for a wide range of proboscis shape and size and type of suction pump, and should therefore be applicable to all other nectar feeders with sucking mouth parts. Independent verifications of the model were carried out by measuring the rate of uptake of sucrose solutions of the adult common armyworm, Pseudaletia unipuncta (Haw.), and of human subjects using a volumetric pipette, both of which gave an excellent fit.Nectar concentrations which correspond to optimal rates of sucrose intake should be highly preferred by insects with high feeding costs, those which are time-limited, or which are very vulnerable while feeding. High transport costs and severe water stress may shift preferences to higher and lower concentrations respectively.

https://www.jstor.org/stable/pdfplus/4217617.pdf

Effects of nectar concentration on butterfly feeding: measured feeding rates for Thymelicus lineola (Lepidoptera: Hesperiidae) and a general feeding model for adult Lepidoptera.

Sexual differences in thermoregulation and activity under different weather conditions were observed in field populations of the European skipper, Thymelicus lineola. The proximal causes of these differences were studied under both field and laboratory conditions and their possible im- portance for the mating strategy of this species was examined. Males had a longer daily period of activity than did females, which was related to the ability of males to fly in cooler conditions than females. In the laboratory, in the absence of a radiant heat source, both sexes began basking at body temperatures of 1 90-250C. However, males were able to fly at body temperatures 30 lower than females, which we attribute to a lower wing loading in males. Male mass is 42-62% of female mass, while their wing area is 86% of that of females. This difference should theoretically allow males to fly with a lower wingbeat frequency, and hence, at a lower temperature, since wingbeat frequency is temperature dependent. The body temperature of both male and female dead T. lineola pinned in the basking position rose faster and to a higher level than that of individuals pinned in the resting position with the wings folded, when exposed to an artificial radiant heat source. The thoracic temperature of males at equilibrium was ;40 higher than that of females, despite their smaller size. Males also had higher heating and cooling rates, particularly of the abdomen, which heated and cooled two to four times faster than the female abdomen. In the field, females spent more time basking than males, yet female and male thoracic temperatures did not differ significantly. However, abdominal temperatures, which were always lower than thoracic temperatures in both sexes, were higher in females than in males. As a result, the difference between thoracic and abdominal temperatures was smaller in females than in males. The greater thorax-abdomen temperature differential in males can be explained by their higher rate of abdominal cooling and lower incidence of basking. We suggest that these sexual differences reflect sexual selection favoring males that have superior flight capability in marginal weather con- ditions.

Sexual Differences in the Thermoregulation of Thymelicus Lineola Adults (Lepidoptera: Hesperiidae)

 1 Daily patterns of activity, thoracic temperature (Tth) and thermoregulatory behaviour in relation to environmental conditions were studied in the European skipper Thymelicus lineola (Ochsenheimer) adults



2 Daily activity was limited mainly by Tth, which in turn was dependent on air temperature (Ta) and sunlight However, when light intensity fell to < 100 W m−2, skippers also became inactive



3 Tth was sometimes as much as 12°C above Ta, and this was most pronounced under cool conditions when basking activity predominated



4 Black globe temperature (Tbg) which, in the absence of wind, is influenced by both Ta, and radiant heat load in a manner similar to a basking butterfly, was used to approximate the maximum Tth attained by Tlineola through basking



5 Both males and females basked at Tbg >20°C, and if this temperature was not attained, skippers remained inactive As Tbg increased, basking activity declined more rapidly in males than in females Basking bouts were also shorter in males



6 Males also flew, fed and courted females at Tbg >20°C, while females only fed and flew at Tbg >22°C The percentage of both sexes feeding and flying, and courting in the case of males, were positively correlated with Tbg



7 In warm weather, males divided their time equally between flying and feeding, while females spent the majority of their time feeding Feeding bouts were shorter and flying bouts were longer in males than in females Flight duration in males was positively correlated with Tbg



8 Skippers avoided, and, consequently laid fewer eggs in, shady areas



9 Sexual differences in activity patterns in relation to weather reflect differences in the reproductive requirements of the two sexes

Diel patterns of activity of Thymelicus lineola adults (Lepidoptera: Hesperiidae) in relation to weather *

. Laboratory experiments were carried out to determine the role and characteristics of male scent scales (androconia), located in patches (stigmata) on the forewings of Thymelicus lineola (Ochsenheimer) (Lepidoptera: Hesperiidae).



In behavioural tests, there were 30—40% fewer matings of virgin females by males with the stigmata removed or where females had their antennal sensilla covered with nail polish, when compared to sham-treated controls. These reductions occurred despite a large increase in male courtship activity. No physical contact was observed between male wings and female antennae during mating.



A scanning electron microscope study of male wings and female antennae showed that: (1) lysis zones form over time on the androconia and pieces (osmo-phores) distal to these zones break off; (2) while few of these zones are present at emergence they are numerous in-day-old males; (3) during a single episode of courtship and mating approximately two-thirds of the available osmophores break off, yet the commonly observed courtship between males does not appear to result in osmophore release; and (4) osmophores were never observed on the female antennae.



Electroantennogram recordings (EAGs) indicated that: (1) female antennae responded strongly to odours from male forewings but not from other parts of either males or females; (2) female antennae responded more strongly to young field-collected males than to newly-emerged or old, field-collected males; (3) female antennal response to male forewings was reduced if the androconia were scraped off, and was eliminated if the stigmata were removed; (4) male antennae gave weak EAG responses to both male and female forewings.



We conclude that males release pheromone via the breakage of osmophores during courtship. We propose that the frequently observed refusals by females of courting males are at least partially dependent on the quantity or quality of male pheromone released, which are in turn correlated with the male's age and mating status.

Kenneth A. Pivnick

Papers

Puddling in butterflies : sodium affects reproductive success in Thymelicus lineola

Effects of nectar concentration on butterfly feeding: measured feeding rates for Thymelicus lineola (Lepidoptera: Hesperiidae) and a general feeding model for adult Lepidoptera.

Sexual Differences in the Thermoregulation of Thymelicus Lineola Adults (Lepidoptera: Hesperiidae)

Diel patterns of activity of Thymelicus lineola adults (Lepidoptera: Hesperiidae) in relation to weather *

The role of the androconia in the mating behaviour of the European skipper, Thymelicus lineola, and evidence for a male sex pheromone