Citrinin interferes with spiracle control in the cockroach, Periplaneta americana

A preparation of citrinin from an isolate of Penicillium citrinum disrupted the spiracle control mechanism of the cockroach, resulting in excessive evaporation of water. The insect rapidly lost body weight and died due to dehydration within 48 h of treatment with citrinin. Presumptive evidence is given here for the neurotoxic nature of the mycotoxin.     

Classical olfactory conditioning in the cockroach Periplaneta americana

We established a classical conditioning procedure for the cockroach, Periplaneta americana, by which odors were associated with reward or punishment. Cockroaches underwent differential conditioning trials in which peppermint odor was associated with sucrose solution and vanilla odor was associated with saline solution. Odor preference of cockroaches was tested by allowing them to choose between peppermint and vanilla sources. Cockroaches that had undergone one set of differential conditioning trials exhibited a significantly greater preference for peppermint odor than did untrained cockroaches. Memory formed by three sets of differential conditioning trials, with an inter-trial interval of 5 min, was retained at least 4 days after conditioning. This conditioning procedure was effective even for cockroaches that had been harnessed in plastic tubes. This study shows, for the first time in hemimetaborous insects, that both freely moving and harnessed insects are capable of forming olfactory memory by classical conditioning procedure. This procedure may be useful for future electrophysiological and pharmacological studies aimed at elucidation of neural mechanisms underlying olfactory learning and memory.     

Motion analysis of leg joints associated with escape turns of the cockroach,Periplaneta americana

Considerable information is now available on the neural organization of the escape system of the American cockroach. To relate these data to the behavior, we need detailed information on the movements made at the principle leg joints that produce the turn. We used motion analysis of high speed video records to acquire such information. Records from both free ranging and tethered animals were analyzed. 1. We analyzed individual joint movements using a tethered preparation. Stimuli from 4 different angles around the animal were used. For all wind angles, the femur-tibia (FT) joint on the mesothoracic leg that is ipsilateral to the wind source extended while the contralateral mesothoracic FT joint flexed. This moved both of these legs laterally toward the wind source. In freely moving animals the FT movements provide forces that turn the animal away from the wind source. 2. The ipsilateral mesothoracic coxa-femur (CF) joint extended for all wind angles. The contralateral mesothoracic CF joint extended in response to most winds from the rear, but switched to flexion in response to wind from the side and front. As a result of these joint movements, rear wind resulted in rearward movements of the contralateral mesothoracic leg, while side and front wind resulted in more forward movements of that leg. 3. The CF and FT joints for both ipsilateral and contralateral metathoracic legs extended to wind from the rear and switched to flexion as the wind was placed at more anterior positions around the animal. In freely moving animals, extension of these joints would push the animal forward. Flexion would pull the animal backward. 4. Several of the joints showed correlations between rate of movement and initial joint angle. That is, joints that were already flexed at the onset of stimulation tended to move at a faster rate to a final position than joints that started at a more extended position. 5. Metathoracic FT and CF joints showed a high degree of positive correlation during the escape movements. Indeed, many curves showing movement of metathoracic FT and CF joints with time were virtually identical.     

Certain functional connections of neurons control the walking of the cockroach Periplaneta americana

On isolated abdominal nervous chain of the cockroach studies have been made of the responses of motoneurones of the thoracic ganglion to electrical stimulation of afferent axons of the leg nerve under normal conditions and during application of an anticholinesterase drug, GD-7. Depending on the type of stimulated axons, monosynaptic response, as well as polysynaptic phasic and tonic responses of motoneurones were recorded. A scheme of activation of motoneurones is suggested which evokes slow contractions of muscles in cockroach extremities.     

Adipokinetic hormones control amylase activity in the cockroach (Periplaneta americana) gut

This study examined the biochemical characteristics of α‐amylase and hormonal (adipokinetic hormone: AKH) stimulation of α‐amylase activity in the cockroach (Periplaneta americana) midgut. We applied two AKHs in vivo and in vitro, then measured resultant amylase activity and gene expression, as well as the expression of AKH receptor (AKHR). The results revealed that optimal amylase activity is characterized by the following: pH: 5.7, temperature: 38.4 °C, K_m (Michaelis–Menten constant): 2.54 mg starch/mL, and V_max (maximum reaction velocity): 0.185 μmol maltose/mL/min. In vivo application of AKHs resulted in significant increase of amylase activity: by two‐fold in the gastric caeca and 4–7 fold in the rest of the midgut. In vitro experiments supported results seen in vivo: a 24‐h incubation with the hormones resulted in the increase of amylase activity by 1.4 times in the caeca and 4–9 times in the midgut. Further, gene expression analyses reveal that AKHR is expressed in both the caeca and the rest of the midgut, although expression levels in the former were 23 times higher than levels in the latter. A similar pattern was found for the amylase (AMY) gene. Hormonal treatment did not affect the expression of either gene. This study is the first to provide evidence indicating direct AKH stimulation of digestive enzyme activity in the insect midgut, supported by specific AKHR gene expression in this organ.     

Wing receptors of the American cockroach Periplaneta americana]

Wing receptors of the cockroach have been studied using staining technique with methylene blue in living animals. Five types of the receptors were found: trychoid hairs, bristles, complaniform sensillae, chordotonal organs and multiterminal neurons. The majority of the receptors is located at the lower surface of the wing, especially along its ribs. Together with primitive features in the structure (polyneuronal origin of hairs and bristles, poor content of chordotonal organs, absence of distinct groups of companiform sensillae), some specialization of wing receptors with respect to flight function is noted (concentration of proprioceptors along the main mechanical axis of the wing and formation of distinct rows by the companiform sensillae).     

Aminergical regulation of pheromone sensillae in the cockroach Periplaneta americana

Vast adaptability of insects is provided substantially by fast tining of physiological functioning of an organism to conform to the permanently changing environmental conditions. One of the mechanisms of plasticity in insects is modulation of performance of their sense organs by neurohormones. Activity of at least three out of four receptor cells located in cockroach pheromonesensitive sensilla is under influence of octopamine. Increase in firing rate of pheromone receptor cells and decrease in electroantennogram amplitude is accompanied by enhanced behavioural responses of male cockroaches to sex pheromone. The effect of octopamine on reception of a repellent (1,8-cineole) by an insect is reported for the first time. Simultaneous modulation of responses of receptor cells located in sex specific sensilla to semantically different odorants implies their cooperation in formation of insect's behaviour.     

Biosynthesis of 3-methylpentacosane in the cockroach Periplaneta americana.

The biosynthesis of 3-methylalkanes was investigated in the cockroach $\text{Periplaneta americana}$. Between 0.2 and 0.3 percent of the labelled acetate and propionate injected into the insect was incorporated into the cuticular hydrocarbons, compared to 0.01 percent for labelled isoleucine. Twenty-three ± four percent of the [2-¹⁴C]acetate, 42 ± 3 and 44 ± 4 percent of the [2-¹⁴C] and [3-¹⁴C]propionate, and 75 ± 5 percent of the [1-¹⁴C]propionate incorporated into the cuticular hydrocarbons was found in 3-methylpentacosane. These results indicate that propionate serves as the source of the branching methyl group, suggesting a pathway in which this precursor is incorporated during the penultimate step in 3-methylalkane biosynthesis in insects.     

Metabolism of propionate to acetate in the cockroach Periplaneta americana

Carbon-13 NMR and radiotracer studies were used to determine the precursor to methylmalonate and to study the metabolism of propionate in the cockroach Periplaneta americana. [3,4,5-13C3]Valine labeled carbons 3, 4, and 26 of 3-methylpentacosane, indicating that valine was metabolized via propionyl-CoA to methylmalonyl-CoA and served as the methyl branch unit precursor. Potassium [2-13C]propionate labeled the odd-numbered carbons of hydrocarbons and potassium [3-13C]propionate labeled the even-numbered carbons of hydrocarbons in this insect. This labeling pattern indicates that propionate is metabolized to acetate, with carbon-2 of propionate becoming the methyl carbon of acetate and carbon-3 of propionate becoming the carboxyl carbon of acetate. In vivo studies in which products were separated by HPLC showed that [2-14C]propionate was readily metabolized to acetate. The radioactivity from sodium [1-14C]propionate was not incorporated into succinate nor into any other tricarboxylic acid cycle intermediate, indicating that propionate was not metabolized via methylmalonate to succinate. Similarly, [1-14C]propionate did not label acetate. An experiment designed to determine the subcellular localization of the enzymes involved in converting propionate to acetate showed that they were located in the mitochondrial fraction. Data from both in vivo and in vitro studies as a function of time indicated that propionate was converted directly to acetate and did not first go through tricarboxylic acid cycle intermediates. These data demonstrate a novel pathway of propionate metabolism in insects.