Flight energetics in sphinx moths: heat production and heat loss in Hyles lineata during free flight

Eat, Drink, Live: Foraging behavior of a nectarivore when relative humidity varies but nectar resources do not

To meet energetic and osmotic demands, animals make dynamic foraging decisions about food quality and quantity. In the wild, foraging animals may be forced to consume a less preferred or sub-optimal food source for long periods of time. Few choice feeding assays in laboratory settings approximate such contingencies. In this study the foraging behaviors of the hawkmoth Manduca sexta were measured when adult moths were placed within different relative humidity (RH) environments (20%, 40%, 60% and 80% RH) and provided with only one of the following experimental nectars: 0% (water), 12% or 24 % w/V sucrose solutions. Overall, ambient humidity influenced survivorship and foraging behaviors. Moth survivorship increased at higher ambient humidity regardless of experimental nectar. Moths that had access to experimental nectar imbibed large volumes of fluid regardless of what nectar was offered when placed at the lowest humidity (20% RH). However, when placed at the highest humidity (80% RH), moths imbibed higher volumes of fluid when given access to experimental nectar with sucrose in comparison with water. RH also influenced daily foraging behaviors: peak nectar consumption occurred earlier at lower RH levels. Consistent with previous studies in which moths could choose among nectar solutions, total energy intake was not affected by ambient RH under no-choice conditions. However, the proportion of time spent foraging and total energy consumption were significantly reduced across all RH levels in no-choice assays, when compared with previous studies of choice assays under the same conditions. Our results show that even when M. sexta moths are presented with limited options, they can alter their foraging behavior in response to environmental changes, enabling them to meet osmotic and/or energetic demands.

Body size allometry impacts flight-related morphology and metabolic rates in the solitary bee Megachile rotundata

Body size is related to many aspects of life history, including foraging distance and pollination efficiency. In solitary bees, manipulating the amount of larval diet produces intraspecific differences in adult body size. The goal of this study was to determine how body size impacts metabolic rates, allometry, and flight-related morphometrics in the alfalfa leafcutting bee, Megachile rotundata. By restricting or providing excess food, we produced a range of body sizes, which allowed us to test the effect of body size on allometry, the power required for flight, and amount of energy produced, as measured indirectly through CO₂ emission. The power required during flight was predicted using the flight biomechanical formulas for wing loading and excess power index. We found larger bees had higher absolute metabolic rates at rest and during flight, but smaller bees had higher mass-specific metabolic rates at rest. During flight, bees did not have size-related differences in mass-specific metabolic rate. As bees increase in size, their thorax and abdomens become disproportionately larger, while their wings (area, and length) become disproportionately smaller. Smaller bees had more power available during flight as demonstrated by flight biomechanical formulas. Smaller body size was advantageous because of a reduced power requirement for flight with no metabolic cost.

Dual fitness benefits of post-mating sugar meals for female hawkmoths (Hyles lineata)

The white-lined sphinx moth (Hyles lineata: Sphingidae) is the most widespread and abundant hawkmoth pollinator in North America and plays a major role in the reproductive biology of many plant species. H. lineata visits a wide range of plants, which differ in the quality and quantity (e.g. caloric content, volume) of the nectar reward that they offer in exchange for pollination services. Some of these plants represent a suitable oviposition substrate as well as a profitable nectar source, allowing mated H. lineata females to mix foraging and oviposition bouts. We investigated the effects of post-mating nectar intake on the reproductive success of female H. lineata. While all experimental females had access to a 20% sucrose solution during the pre-mating phase (avg. 2.7 days) we manipulated the post-mating diet, assigning mated females to three experimental groups (sucrose fed, water fed, or unfed). Mated females with access to sucrose lived twice as long and produced more fertile eggs at double the rate of control moths that were starved or water-fed after mating. Thus, the sugar component of floral nectar positively affects the physiology of mated H. lineata at multiple levels, which translates into strong selection for mated females to continue nectar foraging during or between oviposition bouts.

Evidence of different thermoregulatory mechanisms between two sympatric Scarabaeus species using infrared thermography and micro-computer tomography

In endotherms insects, the thermoregulatory mechanisms modulate heat transfer from the thorax to the abdomen to avoid overheating or cooling in order to obtain a prolonged flight performance. Scarabaeus sacer and S. cicatricosus, two sympatric species with the same habitat and food preferences, showed daily temporal segregation with S. cicatricosus being more active during warmer hours of the day in opposition to S. sacer who avoid it. In the case of S. sacer, their endothermy pattern suggested an adaptive capacity for thorax heat retention. In S. cicatricosus, an active 'heat exchanger' mechanism was suggested. However, no empirical evidence had been documented until now. Thermographic sequences recorded during flight performance showed evidence of the existence of both thermoregulatory mechanisms. In S. sacer, infrared sequences showed a possible heat insulator (passive thermal window), which prevents heat transfer from meso- and metathorax to the abdomen during flight. In S. cicatricosus, infrared sequences revealed clear and effective heat flow between the thorax and abdomen (abdominal heat transfer) that should be considered the main mechanism of thermoregulation. This was related to a subsequent increase in abdominal pumping (as a cooling mechanism) during flight. Computer microtomography scanning, anatomical dissections and internal air volume measurements showed two possible heat retention mechanisms for S. sacer; the abdominal air sacs and the development of the internal abdominal sternites that could explain the thermoregulation between thorax and abdomen. Our results suggest that interspecific interactions between sympatric species are regulated by very different mechanisms. These mechanisms create unique thermal niches for the different species, thereby preventing competition and modulating spatio-temporal distribution and the composition of dung beetle assemblages.

Keeping a cool head: honeybee thermoregulation

At high ambient temperatures, honeybees regulate head teriperature by evaporative cooling of regurgitated honeycrop contents. Thoracic temperature is secondarily stabilized as heat flows from thorax to head by means of passive conduction and physiological facilitation resulting from accelerated blood flow. The mechanism permits flight at the extraordinarily high ambient temperature of 46 degrees C without overheating the head and thorax despite prodigious amounts of heat produced as a by-product of flight metabolism. In contrast, at low ambient temperatures, thoracic rather than head temperature is regulated; no liquid is regurgitated, and the head is heated passively by conduction both in flight and while stationary.

Effects of corrugation of the dragonfly wing on gliding performance

We investigate the aerodynamic performance of the dragonfly wing, which has cross-sectional corrugation, via a static 2-dimensional unsteady simulation. Computational conditions are Re=150, 1400, and 10,000 with angles of attack ranging from 0 degrees to 40 degrees . From the computational results, lift coefficients are increased by the wing corrugation at all Reynolds number. However, the corrugation has little influence on the drag coefficients. The flows such as vortex in the valley of corrugation and near the edge of the corrugation are locally different from those of an elliptic wing. However, such local flows have little influence on the time averaged wing performance. From the numerical experiment presented in this study, it is determined that suction side corrugations of the wing have very little influence on increase of the lift coefficient at a positive angle of attack.

Estimation of thermal constants: the importance of using equilibrium temperature rather than ambient temperature demonstrated with hoverflies (Diptera, Syrphidae, genus Eristalis)

Water evaporation has a marked effect on the passive rates of body temperature change of eristaline hoverflies. It results in the equilibrium temperature of these flies being significantly lower than ambient temperature. Different values for the cooling and warming constants are therefore obtained depending on whether equilibrium or ambient temperature is used as the baseline. Hence, care must be taken when estimating these constants with all animals, especially those of moderate to high permeability. It is recommended that equilibrium temperature be used in such situations. Evaporative cooling is probably also responsible for cooling constants being higher than warming constants in this and other studies.