Joseph R. Larsen

Ultrastructure of the contact chemoreceptors of Apis mellifera L. (Hymenoptera : Apidae)

Abstract Sensilla chaetica of different sizes were found by scanning electron microscopy on the glossa, labial palps, galeae, antennae and tarsi of the worker honey bee. Sensilla basiconica also were found on these structures, except the antennae and glossa. With the exception of the mandibles, whose sensilla are all innervated by one sensory neuron, transmission electron microscope studies showed these receptors are similar in ultrastructure to taste receptors previously described in other insects. It was determined that sensilla on the mouthparts and tarsi possess 5 sensory neurons, one of which ends at the sensilla base as a mechanoreceptor, the other 4 extending up the lumen of a two-chambered hair. Many of the sensilla are tipped with either a pore or a papilla. About half of the sensilla observed on the antennae are innervated by 6 sensory neurons. A peculiarly shaped sensillum trichodeum occurs on the mandible which breaks off at pupal eclosion. A spatulate peg on the tarsal claw is also present.

Electrophysiological responses of galeal contact chemoreceptors of Apis mellifera to selected sugars and electrolytes

Using conventional electrophysiological methods, the galeal sensilla chaetica of the honey bee, Apis mellifera, responded linearly to the log of solute concentrations of sucrose, glucose, fructose, NaCl, KCl, and LiCl but not to CaCl2 or MgCl2, which failed to give consistent responses. These sensillae had much higher firing rates for sugar than salt solutions; their relative responses to lower concentrations being NaCl < KCl < LiCl ⪡ fructose < glucose ⪡ sucrose. At higher concentrations NaCl < LiCl < KCl ⪡ glucose < fructose ⪡ sucrose. Four different spike types were seen. The first type had the highest amplitude and resulted from sugar stimulation. The second type had a lower height and occurred in the first 30 sec of salt stimulation. A third type with the lowest height appeared with those of the second type after prolonged stimulation with KCl. A fourth type with a high amplitude resulted from mechanical stimulation. The sensilla adapted to sugar solutions linearly to the logarithm of time and non-linearly to the log of salt concentrations. Glucose-fructose mixed-sugar solution effected synergism of response while sucrose solutions caused inhibition when mixed with glucose and/or fructose. Responses of the sensilla to mechanical stimulation showed phasic-tonic characteristics. None of the sensilla tested responded to water.

Effect of photoperiod and temperature on ovarian development in Culex pipiens pipiens

Abstract Culex pipiens pipiens is one member of the C. pipiens complex which diapauses as an adult. Experiments show that photoperiod and temperature both affect the development of the ovarian follicles. Females reared at a 15 hr photophase and 22°C show an increase in follicle size over the first 8 days after emergence. Females reared at 10 hr and 22°C do not show an increase in follicle size. Follicle size does not gradually increase as photophase is lengthened. Rather, at photophases between 9 and 12 hr the follicles remain small and at photophases of 13 hr or more, the increase is seen. An increase in temperature tends to increase follicle size regardless of the photophase. However, a strong interaction between photophase and temperature is evident. No evidence exists for a single ‘critical stage’. Instead, the final follicle size is dependent, in a complex manner, upon the photophase experienced by all the stages. The final size is not a result of a cumulative effect. Photoperiod, independent of temperature, shows a marked effect on blood feeding. Females reared at 15 hr feed much more readily than those reared at 10 hr. Those 10 hr females that feed show no signs of gonotrophic dissociation.

Fine structure of antennal sensilla of the adult mealworm beetle, Tenebrio molitor L. (Coleoptera : Tenebrionidae)

Abstract The types, numbers and distributions of the antennal sensilla of the adult mealworm beetle, Tenebrio molitor, were studied with the scanning and transmission electron microscopes. The types of sensilla include a sexually dimorphic bristle (sensillum chaeticum), a hair organ (sensillum trichodeum), and thin-walled, thick-walled, grooved, flat-tipped, and smooth-surfaced peg organs (sensilla basiconica). Hair organs and smooth-surfaced pegs are common on all 11 antennal segments. The other sensilla are, generally, most numerous on the distal segment, and progressively decrease in numbers on the distal inner and outer sensory fields of segments 10 through 4. Thick-, thin-walled and grooved pegs have pore systems typical of olfactory sensilla. Sensilla chaetica and thick-walled, grooved, flat-tipped, and smooth-surfaced pegs bear an apical pore suggestive of a gustatory function. Smooth-surfaced pegs, hairs, and bristles have a tubular body normally associated with mechanoreception.

Ultrastructure of sensilla on the distal antennal segment of adult Oncopeltus fasciatus (Dallas) (Hemiftera : Lygaeidae)

Abstract The sensilla on the distal antennal segment of adult Oncopeltus fasciatus were studied with the scanning and transmission electron microscopes. The result has been an elucidation of the ultrastructure of 7 morphologically distinct sensory organs. These include smooth, grooved, and two-chambered pegs, symmetrical and asymmetrical hairs, a pit-peg, and a tactile bristle. Pore tubules are described in the tactile bristle and the uninnervated channel of the two-chambered peg. Dendritic protrusions which extend into the fluid channels of the symmetrical hair have also been identified. A more complete knowledge of insect sensory organs has resulted from the morphological considerations presented in this paper. Heretofore pore tubules have only been described in olfactory sensilla, and few olfactory organs have been shown to possess pores containing dendrites.

Debraining and diapause development in Manduca sexta pupae

Debraining experiments with wounded and normal controls were done at three different ages on diapausing Manduca sexta pupae of Kentucky and Illinois stocks. With early ages of both stocks debrained pupae escaped from diapause over an extended period of time, but wounded insects developed much earlier and at the same time as the normals. With later ages of Kentucky insects there was an immediate developmental response to wounding, and debrained insects showed initiation of pharate adult development over an extended period of time. With later ages of Illinois pupae both wounded and debrained animals showed an immediate developmental response. The responses of Illinois insects to debraining were shown to occur in insects overwintering under natural conditions. The results indicate that at least four endocrine states are possible for diapausing Lepidoptera pupae.

Glutamic acid decarboxylase and the GABA shunt in the supraoesophageal ganglion of the honey-bee, Apis mellifera☆

Abstract The presence of l -glutamic acid decarboxylase in homogenates of the honey-bee brain has been confirmed. The enzyme is most active between pH 6·0 to 9·0. At pH 6·8 K m and V max were 0·06 M and 91 μ moles/hr per g tissue respectively. The honey-bee enzyme is inhibited by high concentrations of GABA and some evidence for substrate inhibition by l -glutamic acid was found. No absolute requirement for the cofactor, pyridoxal-5-phosphate, could be detected. Inhibition by hydroxylamine and p -hydroxymercuribenzoate were competitive and non-competitive respectively. The major portion of the enzyme was bound to cellular particulate fractions sedimenting in a wide range of centrifugal forces. Results of sucrose gradient centrifugations indicated that the enzyme was not bound to subcellular particles of ‘synaptosome’ size. Enzymes capable of metabolizing GABA to succinic acid were also found in honey-bee brain homogenates. The results of this study are discussed in relation to the role of l -glutamic acid and GABA as possible neurotransmitter agents.

Gustatory mechanisms and sugar‐feeding in the mosquito, Culiseta inornata

ABSTRACT. Gustatory hairs on the legs and mouthparts of the mosquito, Culiseta inornata, were stimulated with sucrose solutions to determine their role in the finding and consuming of nectar by females. Stimulation of tarsi initiated probing, which continued without subsequent stimulation of tarsal hairs. Turning in response to tarsal stimulation depended on which leg was stimulated. Once gustatory hairs on the labella were stimulated, turning and probing were discontinued. Stimulation of the hairs on the external surface of the labella apparently initiates the labellar opening response, while stimulation of hairs on the oral surface of the labella maintains the labellar response. Electrophysiologically recorded activity of cibarial and pharyngeal pumps was used to assess the influence of the five relevant sets of gustatory hairs on initiation of sucking. None of the sets alone were capable of initiating sucking. Sucking was initiated when the hairs on the oral surface of the labella were stimulated simultaneously with sensory hairs on the tip of the labrum. The gustatory hairs on the oral surface of the labella exerted considerable influence in determining the amount of sugar or water imbibed.

d-Tubocurarine Chloride: Effect on Insects

Injection of d-tubocurarine chloride into certain insects produces complete flaccid paralysis. The site of injection is closely related to the region of primary paralysis. The effect depends on concentration, with distinct differences in the optimum concentrations for various species so far tested. A dose-response curve has been prepared for Calliphora erythrocephala.

A comparative study of the effects of selective inhibitors on esterase isozymes from the mosquito Anopheles punctipennis

1. 1. Five esterase isozymes were found from soluble extracts of Anopheles punctipennis. 2. 2. Each of the isozymes exhibited a differential specificity depending on the type of inhibitor used. 3. 3. The A and B loci were characterized as specific cholinesterases based on the response to treatment with a variety of organophosphates and carbamates. 4. 4. The other loci did not respond as uniformly to the various pesticides used in this study, but were characterized as either carboxylesterases or aromatic esterases for discussion purposes. 5. 5. The importance of having pure isozyme preparations is considered in conjunction with additional knowledge of the kinetic and stereospecific properties of the inhibitors. 6. 6. The techniques described in this work showed that mosquito isozymes may be clearly separated with a high degree of resolution.