Different functions of two alarm substances in the honeybee.

In the honeybee, isopentyl acetate and 2-heptanone are described as alarm substances. We asked whether both substances have a similar role by testing the effect of their exposure on the appetitive proboscis extension reflex and on the aversive stinging reflex. In the appetitive context of sucrose stimulation no differences were found between isopentyl acetate and 2-heptanone. Small amounts of isopentyl acetate or 2-heptanone (3 microl of 1:9 dilution) yielded a response similar to that of a non-exposed control. Larger amounts of both substances (125 microl of 1:9 dilutions) as well as mixtures led to a decrease of responsiveness to sucrose. In the aversive context of electrical stimulation, significant differences between isopentyl acetate and 2-heptanone were found. Exposure to a small amount of isopentyl acetate (3 microl of 1:9 dilution) or to a large amount of 2-heptanone (125 microl of 1:9 dilution) led to an increase of responsiveness to the electric shock. Larger quantities of isopentyl acetate (125 microl of 1:9 dilution) decreased the responsiveness to the shock. 2-Heptanone never decreased the responsiveness to the shock. Our results indicate that isopentyl acetate and 2-heptanone have different functions even if both are capable of evoking deterrent responses in a defensive context.

Alarm pheromone induces stress analgesia via an opioid system in the honeybee.

Changes of the stinging response threshold of Apis mellifera scutellata were measured on foragers fixed on a holder and stimulated with an electric shock as a noxious stimulus. The threshold of responsiveness to the noxious stimulus increased when bees were previously stimulated with isopentyl acetate, which is a main component of the alarm pheromone of the sting chamber. This effect is antagonised by previous injection of naloxone-hydrochloride (Endo Laboratories Inc.). Results suggest that in the honeybee an endogenous opioid system activated by isopentyl acetate is responsible for modulation of perception for nociceptive stimuli. The resulting stress-induced analgesia in the defender bee would reduce its probability of withdrawal thus increasing its efficiency against enemies.

Metabolic rate during foraging in the honeybee.

The metabolic rate of free-flying honeybees, Apis mellifera ligustica, was determined by means of a novel respirometric device that allowed measurement of CO2 produced by bees foraging under controlled reward at an artificial food source. Metabolic rate increased with reward (sugar flow rate) at the food source. In addition, there was no clear-cut dependence of metabolic rate on load carried during the visit, neither as crop load nor as supplementary weights attached to the thorax. The hypothesis that metabolic rate, as well as foraging and recruiting activities, depend on the motivational state of the foraging bee determined by the reward at the food source is discussed.

[Antidiuretic mechanism in Rhodnius prolixus (Stal, 1859) (Hemiptera, Reduviidae)]. / Mecanismo antidiurético en Rhodnius prolixus (Stal, 1859) (Hemiptera, Reduviidae).

An antidiuretic mechanism is proposed for Rhodnius prolixus, whose activity is manifested when the diuretic phase has terminated and is maintained until the insect has fed again. Presumably this mechanism acts at the level of the proximal rectal sphincter and is inhibited by ingestion, mechanical distension of the gut and central disinhibition by decapitation. It is suggested that the antidiuretic activity is maintained by the nervous system and is modified when there is distention of the gut or when the nervous signal is interrupted by decapitation. It is demonstrated that the excretion of urine in R. prolixus is not controlled exclusively by the diuretic hormone, but rather that factors not linked to the haemolymph maintain the insects in a diuretic or nondiuretic state.

The stinging response of the honeybee: effects of morphine, naloxone and some opioid peptides.

Changes in responsiveness for the stinging reaction of honeybees fixed in a holder after receiving 3 electrical shocks delivered with 1 min interval, was registered and used as measurement for the effect of 2 microliter of different solutions injected. Every shock consisted of a train of pulses of 1 msec each, delivered for 2 sec at a frequency of 100 Hz. Injection of morphine-HCl (50 to 200 n-moles/bee) produced a dose dependent reduction of the honeybee stinging response to the electrical shocks. The morphine dose that produced a 50% inhibition of the response (D50) was 148 n-moles/bee (927 micrograms/g), i.e., a value far greater than that reported for vertebrates in behavioral test of analgesia. Naloxone 1.1 micrograms/g produces a significant reduction of morphine D50 effect and at 4-5 micrograms/g, a full disinhibition. Thus, whereas the D50 of morphine for honeybees is far greater than that for vertebrates, the doses of naloxone that antagonize morphine are similar for bees and vertebrates. Possible explanations of this difference are mentioned. Injections of met-enkephalin, leu-enkephalin, kyotorphin and (D-Ala2) methionine-enkephalinamide, given in doses of 200 n-moles/bee, an amount greater than that of the morphine D50, exhibited no effect on the stinging response.