Flight Performance of Mamestra brassicae (Lepidoptera: Noctuidae) Under Different Biotic and Abiotic Conditions

Environmental, Developmental, and Genetic Conditions Shaping Monarch Butterfly Migration Behavior

Monarch butterflies in North America migrate south each autumn, but the mechanisms that initiate their migratory flight remain incompletely understood. We investigated environmental, developmental, and genetic factors that contribute to directional flight by testing summer and autumn-generation monarchs in three flight simulators: two at ground level (with and without wind blockage) and a novel balloon-based system that raised butterflies 30 meters into the air. Monarchs reared under autumn-like conditions in a growth chamber during the summer were also tested to explore the influence of developmental cues. Autumn generation monarchs demonstrated significant southwestern flight orientation, observed exclusively in the balloon simulator, underscoring the importance of high-altitude flight for migratory behavior. Summer generation monarchs reared under autumn-like conditions displayed southward orientation, larger wing sizes, and partial reproductive diapause, indicating specific seasonal environmental cues that are sufficient to induce migratory traits. In contrast, a lab line of monarchs reared in captivity since 2016 exhibited diminished wing size and reduced orientation ability, even when raised outdoors in the autumn, consistent with a loss of migratory traits in the absence of migration. Surprisingly, butterflies in the balloon simulator tended to orient upwind, which suggests that wind may also serves as a directional cue during migration. These findings highlight the critical roles of altitude, wind, and environmental cues in monarch migration and validate the balloon flight simulator as a powerful tool for studying migratory behavior. This research advances our understanding of the initiation of monarch migration and informs strategies for conservation efforts amidst environmental change.

Studies on Lygus pratensis' (Hemiptera: Miridae) Flight Ability

Lygus pratensis (Linnaeus) is an important agricultural pest with a strong ability to move and spread between hosts. However, L. pratensis' flight potential and factors affecting its flight ability are unclear. We used the insect flight information system (flight mill) to determine the effects of temperature, humidity, age, sex, and mating on L. pratensis' flight ability in an artificial climate chamber. Temperature and relative humidity significantly affected L. pratensis' flight ability; however, low and high temperature, as well as low humidity, were unsuitable, and the optimal flight environment was 20-28 °C and 60-75% RH. Lygus pratensis' flying ability initially increased and then decreased with age and was highest at 10 days old (flight rate: 71.43%; total flight distance: 18.63 ± 1.89 km; total flight time: 6.84 ± 0.60 h). At 15 days old, flight speed was the highest (3.36 ± 0.18 km h-1). Sex had little effect on L. pratensis' flying ability; it was marginally stronger for females than males, but the difference was insignificant. Mating increased female flying ability but decreased that of males, but the difference was insignificant. Overall, L. pratensis had strong flight dispersal ability, was largely unaffected by sex and mating, and optimal flight conditions were mild temperature and humidity. This knowledge provides a scientific basis for L. pratensis outbreak prediction, prevention, and control.

Flight capacity and behavior of Ephestia kuehniella (Lepidoptera: Pyralidae) in response to kairomonal and pheromonal stimuli

Flight behavior is an important component to understand in the context of pest management. However, because of their small size, little is known about the flight capacity of most stored-product insects, and when a flight has been assessed, it usually consists of a propensity for initiating flight. Despite a priori expectations of the importance of flight for moths, there are no data about the flight capacity and little on the flight behavior of the Mediterranean flour moth, Ephestia kuehniella Zeller (Lepidoptera: Pyralidae). As a result, the objective of the current study was to (i) characterize the baseline flight capacity of E. kuehniella and (ii) determine how flight capacity is affected by the presence of kairomonal, pheromonal, or no stimuli. We found adult E. kuehniella flew a mean of 24-34 km in a 24-h period, and the distance flown per bout increased from 91 to 207 m in the presence of pheromones but decreased to 41 m when food was nearby compared to a negative control. The total number of flight bouts was 1.6-fold higher in the presence of pheromone compared to the negative control, but E. kuehniella flew significantly slower with pheromone and food cues present, suggesting they may be exhibiting an optimal foraging strategy. Our data on flight capacity results in qualitatively and quantitatively different conclusions about flight than those conclusions formed if only flight initiation is considered. Overall, this novel information is useful for understanding the spread within facilities and in the landscape (between facilities), as well as parameterizing ecological modeling.

The cost of movement: assessing energy expenditure in a long-distant ectothermic migrant under climate change

Migration is an energetically taxing phenomenon as animals move across vast, heterogeneous landscapes where the cost of transport is impacted by permissible ambient conditions. In this study, we assessed the energetic demands of long-distance migration in a multigenerational ectothermic migrant, the monarch butterfly (Danaus plexippus). We tested the hypotheses that temperature-dependent physiological processes reduce energy reserves faster during migration than previously estimated, and that increasing climatic temperatures resulting from the climate crisis will intensify baseline daily energy expenditure. First, we reared monarchs under laboratory conditions to assess energy and mass conversion from fifth instar to adult stages, as a baseline for migratory adult mass and ontogenetic shifts in metabolic rate from larvae to adult. Then, using historical tag-recapture data, we estimated the movement propensity and migratory pace of autumn migrants using computer simulations and subsequently calculated energy expenditure. Finally, we estimated the energy use of monarchs based on these tag-recapture data and used this information to estimate daily energy expenditure over a 57 year period. We found support for our two hypotheses, noting that incorporating standard metabolic rate into estimates of migratory energy expenditure shows higher energy demand and that daily energy expenditure has been gradually increasing over time since 1961. Our study shows the deleterious energetic consequences under current climate change trajectories and highlights the importance of incorporating energetic estimates for understanding migration by small, ectothermic migrants.

Physiological and Environmental Influences on Wingbeat Frequency of Oriental Armyworm, Mythimna separata (Lepidoptera: Noctuidae)

The oriental armyworm, Mythimna separata (Walker, 1865) (Lepidoptera: Noctuidae), is a serious global migratory insect pest of grain crops. Although its migratory biology has been studied for a long history, the factors affecting wingbeat frequency (WBF), which is closely related to the flight activity of the insect, remain unclear. In this study, the WBFs of both cultured and migrating moths were tested under different conditions in the laboratory using a stroboscope. The results indicated that age and mating status significantly influenced WBF. One day old adults had the lowest WBF, and unmated females had a significantly higher WBF than that of mated females. In general, the WBF of males was significantly higher than that of female individuals. The WBF decreased gradually with increasing environmental humidity, and WBF had a significant negative binomial regression relationship with temperature change. The WBF of moths that fed on hydromel was much higher than those of the controls that fed on water or without diet. However, wind speed and air pressure had no significant effects on the moth WBF in the test environments. These findings provide a deeper understanding of factors that affect flight ability in M. separata, which will be helpful for developing a regional migratory monitoring and warning system of the pest, such as identifying target insect species based on the WBF from radar observation.

Visiting Plants of Mamestra brassicae (Lepidoptera: Noctuidae) Inferred From Identification of Adhering Pollen Grains

Numerous lepidopteran adults frequently pick up plant pollen when feeding. Identifying plant species visited by Mamestra brassicae moths could further strengthen our knowledge of their migratory trajectory and the interactions of M. brassicae moths with these plant species. Here, with morphological analysis and DNA metabarcoding of pollen carried by the moths, we determined these plant species visited by M. brassicae during 2015-2018. Pollen grains removed from M. brassicae moths were identified from 25 species (18 were identified to genus), representing at least 19 families, including Pinaceae, Oleaceae, Rosaceae, and Asteraceae, but mainly belonging to Angiospermae, Dicotyledoneae. There were noticeable interannual differences (maximum value: 35.31% in 2018) and seasonal differences (maximum value: 33.28% in April-(including May)-June) in the frequency of M. brassicae moths with adhering pollen, but no noticeable difference based on sex. Meanwhile, we also found pollen from some species such as Citrus sinensis (Rutales: Rutaceae) and Melia azedarach (Rutales: Meliaceae) that grow in southern China, indicating that M. brassicae moths might migrate northward in spring. Our results demonstrate that the M. brassicae moth visits a variety of plant species during migration, and these findings promote our understanding of the interaction between moths and these plant species.

Thermal and Oxygen Flight Sensitivity in Ageing Drosophila melanogaster Flies: Links to Rapamycin-Induced Cell Size Changes

Simple Summary

Cold-blooded organisms can become physiologically challenged when performing highly oxygen-demanding activities (e.g., flight) across different thermal and oxygen environmental conditions. We explored whether this challenge decreases if an organism is built of smaller cells. This is because small cells create a large cell surface, which is costly, but can ease the delivery of oxygen to cells’ power plants, called mitochondria. We developed fruit flies in either standard food or food with rapamycin (a human drug altering the cell cycle and ageing), which produced flies with either large cells (no supplementation) or small cells (rapamycin supplementation). We measured the maximum speed at which flies were flapping their wings in warm and hot conditions, combined with either normal or reduced air oxygen concentrations. Flight intensity increased with temperature, and it was reduced by poor oxygen conditions, indicating limitations of flying insects by oxygen supply. Nevertheless, flies with small cells showed lower limitations, only slowing down their wing flapping in low oxygen in the hot environment. Our study suggests that small cells in a body can help cold-blooded organisms maintain demanding activities (e.g., flight), even in poor oxygen conditions, but this advantage can depend on body temperature.

Abstract

Ectotherms can become physiologically challenged when performing oxygen-demanding activities (e.g., flight) across differing environmental conditions, specifically temperature and oxygen levels. Achieving a balance between oxygen supply and demand can also depend on the cellular composition of organs, which either evolves or changes plastically in nature; however, this hypothesis has rarely been examined, especially in tracheated flying insects. The relatively large cell membrane area of small cells should increase the rates of oxygen and nutrient fluxes in cells; however, it does also increase the costs of cell membrane maintenance. To address the effects of cell size on flying insects, we measured the wing-beat frequency in two cell-size phenotypes of Drosophila melanogaster when flies were exposed to two temperatures (warm/hot) combined with two oxygen conditions (normoxia/hypoxia). The cell-size phenotypes were induced by rearing 15 isolines on either standard food (large cells) or rapamycin-enriched food (small cells). Rapamycin supplementation (downregulation of TOR activity) produced smaller flies with smaller wing epidermal cells. Flies generally flapped their wings at a slower rate in cooler (warm treatment) and less-oxygenated (hypoxia) conditions, but the small-cell-phenotype flies were less prone to oxygen limitation than the large-cell-phenotype flies and did not respond to the different oxygen conditions under the warm treatment. We suggest that ectotherms with small-cell life strategies can maintain physiologically demanding activities (e.g., flight) when challenged by oxygen-poor conditions, but this advantage may depend on the correspondence among body temperatures, acclimation temperatures and physiological thermal limits.

Unique Members of the Adipokinetic Hormone Family in Butterflies and Moths (Insecta, Lepidoptera)

Lepidoptera is amongst one of the four most speciose insect orders and ecologically very successful because of their ability to fly. Insect flight is always aerobic and exacts a high metabolic demand on the animal. A family of structurally related neuropeptides, generically referred to as adipokinetic hormones (AKHs), play a key role in triggering the release of readily utilizable fuel metabolites into the hemolymph from the storage forms in the fat body. We used mass spectrometry to elucidate AKH sequences from 34 species of Lepidoptera and searched the literature and publicly available databases to compile (in a phylogenetic context) a comprehensive list of all Lepidoptera sequences published/predicted from a total of 76 species. We then used the resulting set of 15 biochemically characterized AKHs in a physiological assay that measures lipid or carbohydrate mobilization in three different lepidopteran species to learn about the functional cross-activity (receptor-ligand interactions) amongst the different butterfly/moth families. Our results include novel peptide structures, demonstrate structural diversity, phylogenetic trends in peptide distribution and order-specificity of Lepidoptera AKHs. There is almost an equal occurrence of octa-, nona-, and decapeptides, with an unparalleled emphasis on nonapeptides than in any insect order. Primitive species make Peram-CAH-II, an octapeptide found also in other orders; the lepidopteran signature peptide is Manse-AKH. Not all of the 15 tested AKHs are active in Pieris brassicae; this provides insight into structure-activity specificity and could be useful for further investigations into possible biorational insecticide development.