Aare Kuusik

Predation selects for low resting metabolic rate and consistent individual differences in anti-predator behavior in a beetle

Significant between-individual variation in resting metabolic rate (RMR) of animals is a widespread phenomenon that may have important implications for our understanding of variation in behavior and animal personality. By using wild caught mealworm beetles, Tenebrio molitor, we examined the relationships among survival rate under predator tests, individual response latency time to become immobile under the risk of predation, duration of immobility time, and RMR. Individuals with higher levels of RMR were bold, and bold individuals were found to be more exposed to the risk of bird predation. We found that RMR was positively correlated with the latency of immobility response and negatively correlated with the total duration of immobility. The correlation between behavioral responses suggests a behavioral syndrome in the anti-predator behavior of T. molitor. The results indicate that energy metabolism may be part of a syndrome that involves behavior and life history traits in animals.

Diversity in gas exchange and muscular activity patterns in insects studied by a respirometer‐actograph

Different events in insect gas exchange and muscular activity are described by a new system of automatic respirometers, a differential electrolytic microrespirometer‐actograph. This is very sensitive to volumetric changes caused by insect respiration and/or body movements. In this system, oxygen generation and its regulation are combined in the same current circuit. According to this principle, the oxygen consumed by the insect is continuously replaced by equal amounts of electrolytically produced oxygen. This simple laboratory‐made apparatus records simultaneously metabolic rate, the cyclicity of external gas exchange, rhythms of muscular ventilating and the pattern of other body movements, including abdominal pulsations not observable with the naked eye. The respirometer‐actograph described here is applicable also to the recording of the respiration of other terrestrial arthropods or other living organisms or tissues.

Abdominal movements, heartbeats and gas exchange in pupae of the Colorado potato beetle, Leptinotarsa decemlineata

The rhythms of abdominal movements, heartbeats and gas exchange in the pupae of Leptiontarsa decemlineata (Say) were recorded simultaneously using an electrolytic respirometer and infrared gas analyser, both combined with contact thermography.

Periodic muscular activity and its possible functions in pupae of Tenebrio molitor

Abstract. During pupal development, Tenebrio molitor L. show regular periods of rhythmic muscular contractions and associated body movements. These periods of activity last 2.5‐5.8 min and are more frequent in newly ecdysed pupae (c. 3h‐1). They become less frequent (c. 1.5 h‐1) when the basal metabolism reaches its lowest level. In the pharate adult stage the clear pattern of muscular activity disappears.

Studies on insect growth regulating (IGR) and toxic effects of Ledum palustre extracts on Tenebrio molitor pupae (Coleoptera, Tenebrionidae) using calorimetric recordings

Abstract Insect growth regulating (IGR) and toxic effects evoked by Ledum palustre extracts on the metamorphosis stages of Tenebrio molitor were studied using differential thermocouple calorimeters. The timing of normal and failed ecdysis as well as the length of interecdysial periods were measured exactly from calorimetric recordings. Respiratory and muscular responses of poisoned insects were also reflected by characteristic patterns on the recordings.

Predation promotes survival of beetles with lower resting metabolic rates

The energetic definition of fitness predicts that natural selection will maximize the residual energy available for growth and reproduction suggesting that energy metabolism might be a target of selection. In this experimental study, we investigated whether female and male yellow mealworm beetles, Tenebrio molitor L. (Coleoptera: Tenebrionidae), differ in their hiding behaviour, individual response latency time, and duration of immobility to treatments mimicking an approaching predation threat. We experimentally tested whether consistently repeatable anti‐predatory responses and resting metabolic rates (RMR) correlated with survival rates of individuals exposed to a nocturnal predator, the brown rat, Rattus norvegicus (Berkenhout) (Rodentia: Muridae). Resting metabolic rate was part of a syndrome involving anti‐predator behaviour. Individuals with lower RMR concealed themselves against predators in substrate more successfully than individuals with higher RMR, and hiding was associated with longer periods of immobility. Ultimately, mortality was higher in the high‐RMR beetles compared to the low‐RMR beetles. Our results provide direct evidence of natural selection against mobility, i.e., for reduced RMR in T. molitor beetles.

Body movements and their role as triggers of heartbeats in pupae of the Colorado potato beetle Leptinotarsa decemlineata

Rhythmic body movements and their role as triggers of intermittent heartbeats were studied in pupae of Leptinotarsa decemlineata Say. Heartbeats and body movements were recorded simultaneously by means of an optical method (infra‐red cardiography) combined with respirometry. IR‐cardiography allows heartbeats and body movements to be distinguished on the basis of their different rates (40–80 min−1 and 4–8 min−1, respectively) and amplitude.

Gas exchange patterns of bumble bee foragers before and after exposing to lowered temperature

The gas exchange patterns are known to vary between insect species, individuals and even intra-individually. Using volumetric-manometric and flow-through respirometry combined with IR-actography we studied how periods of low temperature affect the respiratory patterns of bumble bee Bombus terrestris foragers. We have shown, in this study, that there is a change in the respiratory patterns of individual B. terrestris foragers after exposing to low temperatures. The bumble bees seemed to become more inactive. The different respiratory patterns appeared in succession and the transition from one pattern to another was associated with the change from an active to a resting state. Typical patterns after exposition to low temperature were discontinuous gas exchange cycles (DGCs).

Monitoring of gas exchange cycles and ventilatory movements in the pine weevil Hylobius abietis : respiratory failures evoked by a botanical insecticide

The large pine weevil, Hylobius abietis (L.) (Coleoptera: Curculionidae), is the most important insect pest of young coniferous plants. The implementation of new control methods requires not only a profound knowledge of the ecology and behaviour of the pest, but particularly of its physiology. Standard metabolic rate (SMR) and discontinuous gas exchange cycles (DGCs) were recorded in parallel with abdominal ventilation movements in adults of H. abietis using a differential electrolytic respirometer‐actograph. Quiescent weevils displayed DGCs of the constriction, flutter, and ventilation phases of the CFV type, while bursts of carbon dioxide were always accompanied by abdominal pumping movements, i.e., muscular ventilation in the closed subelytral cavity (SEC). In some beetles the C phase was absent and thus (C)FV cycles were recorded. In addition, at the beginning and often at the end of a burst, the SEC was rhythmically opened and closed by movements of the last abdominal segments. Continuous pumping movements and an absence of DGCs were signs of stress imposed by handling or by a new environment, even if the beetle was not moving. All individuals showed clear DGCs after recovering from handling and apparatus stress lasting 2–3 h. The results show that in the monitoring of DGCs, it is essential to determine whether they are of the constriction, flutter, and open phases (CFO), or the CFV subtype of the constriction, flutter, and burst (CFB) cycles. Use of our simple closed‐system respirometer enables non‐invasive simultaneous recording of SMR, oxygen uptake, DGCs, and active ventilation in H. abietis and other beetles.

Calorimetric investigations on physiological stress in Tenebrio molitor (Coleoptera, Tenebrionidae) pupae

Abstract Individual variation in the susceptibility to handling stress (mechanical irritation) in laboratory-reared pupae of yellow mealworm, Tenebrio molitor , was studied by means of simple thermocouple twin set-up calorimeters. The stress condition was characterised by disturbances in normal rhythms of gas exchange and body stereotyped movements well distinguishable from calorimetric recordings. Recovering time from stress, induced by the device, was 10–15 min. In every newly established population, a portion of pupal individuals (13–15%) was highly sensitive to handling and these pupae lost significantly more water than the pupae exhibiting no symptoms of stress.