Primitive Insect Research Articles

The Sociogenesis of Insect Colonies

Studies on the social insects (ants, bees, wasps, and termites) have focused increasingly on sociogenesis, the process by which colony members undergo changes in caste, behavior, and physical location incident to colonial development. Caste is determined in individuals largely by environmental cues that trigger a sequence of progressive physiological restrictions. Individual determination, which is socially mediated, yields an age-size frequency distribution of the worker population that enhances survival and reproduction of the colony as a whole, typically at the expense of individuals. This "adaptive demography" varies in a predictable manner according to the species and size of the colony. The demography is richly augmented by behavioral pacemaking on the part of certain castes and programmed changes in the physical position of colony members according to age and size. Much of what has been observed in these three colony-level traits (adaptive demography, pacemaking, and positional effects) can be interpreted as the product of ritualization of dominance and other forms of selfish behavior that is still found in the more primitive insect societies. Some of the processes can also be usefully compared with morphogenesis at the levels of cells and tissues.

Neuromuscular transmission in a primitive insect: Modulation by octopamine, and catch-like tension

1. 1. The third pair of legs of the primitive New Zealand orthopteran insect, the “weta”, has an innervation and muscle cell distribution exactly similar to that of locusts, but wetas do not jump. 2. 2. Neuromuscular transmission to the slow excitatory axon (SETi) is potentiated more than 10-fold by the natural modulator octopamine (OCT). 3. 3. A brief burst of SETi impulses following infusion of as little as 10 −8 M OCT is followed by a very long-lasting plateau of catch-like tension (CT). 4. 4. The plateau is abruptly relaxed by a single inhibitory impulse, or even by a single SETi impulse if this arrives no sooner than about 30 sec following excitation. 5. 5. CT is used by wetas in a defense posture. 6. 6. Locusts and grasshoppers have a different type of modulation by OCT.

Paired spermatozoa in Thermobia (Insecta, Thysanura)

Spermatozoa from the primitive apterygote insect Thermobia domestica have been examined in the living state, in ultrathin sections, and in freeze-fracture replicas. The sperm cells contain an axoneme, two mitochondrial derivatives, and a nucleus as four parallel strands that run along most of the length of the cell. Most of them pair along the anterior region after a release from the testis to form what has been called joined (paired, double, or twin) spermatozoa. The cell junction appears in sectioned material as an attenuation of the otherwise prominent glycocalyx and as globules in the two opposing plasma membranes. These globules are in register. The distance between the opposing plasma membranes of two spermatozoa is 14 nm, which is substantially greater than the distance in a gap junction. In the freeze-fracture replicas the cell junction is seen as a straight row of prominent particles (9–10 nm), that usually are associated with the P face of the plasma membrane. In most sperm pairs the junction is located at the “ventral side” thus near the nucleus but pairing may also occur laterally. The mitochondria seem to be attached to a strand surrounding the flagellar axoneme by a set of specialized thin ribbons which in the freeze-fracture replicas are seen as prominent rows of membrane particles that are associated with the E face of the mitochondrial membrane. We could confirm that spermatozoa are motile only when appearing in pairs and that the posterior free portion can beat independently although in synchrony. The pairing may somehow be a regulating device for sperm motility.

Modifications volumetriques et ultrastructurales des corpora allata du lepisme Thermobia domestica (Pacard) (Thysanura : Lepismatidae) au cours des cycles biologiques

During the moulting and reproductive cycles, which coexist in adult females of the primitive insect Thermobia domestica, the corpora allata (CA) undergo periodical changes: their volumes and numbers of cells are lower at the beginning and at the end of each moulting cycle, and higher about the middle. However, the nucleo-cytoplasmic ratio does not undergo significant variations. An ultrastructural description of the CA cells is given for the first time in a lepismatid. The glandular cells, which are all similar, undergo 2 different stages: the so-called “clear cells” present at the beginning and the end of the moulting cycle, and the “dense cells” in the middle of the cycle. If there is no insemination at the beginning of each intermoulting period, the terminal oocytes are totally resorbed and most of the CA cells are in an intermediate stage between clear and dense cells. These data are discussed in relation to the probable variations in the physiological activity of the CA during normal adult cycles.

Elicitation and abrupt termination of behaviorally significant catchlike tension in a primitive insect.

Sustained steady contractural or catchlike tension (CT) occurs in the metathoracic extensor tibiae muscle of the primitive insect the weta (Orthoptera: Stenopelmatidae) during its characteristic leg-extension defense behavior or following leg-position conditioning. Similar action occurs occasionally in semi-intact preparations and is abruptly turned off by a single peripheral inhibitory impulse. These phenomena were reproduced routinely by first infusing saline containing 10(-8) M (or stronger) octopamine into the muscle for 12 min, and then stimulating the slow excitatory motor neuron SETi with a brief burst. Direct stimulation of the dorsal unpaired median neuron, innervating the extensor tibiae (DUMETi) prior to SETi stimulation, also led to CT. Both octopamine and DUMETi markedly enhanced the tension developed in response to a burst of impulses in SETi.

Defense posture and leg-position learning in a primitive insect utilize catchlike tension.

The capability for conditioning of leg position, using loud sound as an aversive natural reinforcement, was examined in a primitive New Zealand insect, the weta (Orthoptera: Stenopelmatidae). Electromyographic recordings were made during the conditioning. A majority of wetas tested came to occupy stably a metathoracic tibial position window, coupled to turning off the sound, set in either flexion or extension away from the preferred rest position. Steady tensions of up to 7 g in extension and 5 g in flexion were produced. However, no electromyographic activity accompanied the tension. It is concluded that the insects are using a peripheral catchlike mechanism to adjust posture.

Identification of a Juvenile Hormone of a Primitive Insect, the Firebrat,Thermobia domestica(Thysanura)

SYNOPSIS. Juvenile hormone, JH-I was identified as the major juvenile hormone of a primitive insect, the firebrat, Thermobia domestica (Thysanura, Lepismatoidea). Since the same molecule is also present in Orthoptera, Lepidoptera and Diptera, its presence in Thysanura indicates that the juvenile hormones are ancient molecules and have undergone little variation during the evolution of the class Insecta.

Ultrastructure des ovocytes et vitellogenese chez Lepismachilis targionii (grassi) (thysanura: Machilidae)

The present paper describes the ultrastructural transformations of the germinal cells in the panoistic ovarioles of Lepismachilis. Nuclear transformations, i.e. gonial mitoses and the beginning of the meiotic prophase, take place in the germarium; important nuclear modifications inside the vitellarium are connected with numerous ribonucleoprotein emissions into the cytoplasm. Three distinct stages can be distinguished during oocyte growth: (1) Previtellogenesis, corresponding to a euplasmic growth; (2) Primary or endogenous vitellogenesis, characterized by the formation of protein granules inside the vesicles of the rough endoplasmic reticulum; afterwards the granules undergo partial mineralization; (3) Secondary vitellogenesis, which involves extensive growth of the oocyte microvilli and the incorporation of exogenous proteins by micropinocytosis. At the same time, numerous lipid globules are formed; a little glycogen is formed in late vitellogenesis. Then the chorion, secreted by the follicle cells. is deposited around the oocyte. The importance of the endogenous vitellogenesis in different orders of Apterygota is a characteristic feature, which, among other biological data, brings these primitive insects nearer to the Crustacea.

On the Original Feeding Habits of the Hemiptera (Insecta)

The argument is presented that prohemipterans were originally phytophagous and terrestrial rather than carnivorous and hygrophilous as proposed by Cobben. The association of plesiomorphic Heteroptera with aquatic habitats is paralleled by other primitive insect taxa, such as the Ephemeroptera, Odonata, Plecoptera, Megaloptera, Trichoptera, and primitive Diptera and Coleoptera. The frequent restriction of old lineages to such special habitats and habits is a natural consequence of the competitive displacement of old lineages by advanced lineages. The protohemipteran mouthparts are seen as evolving through phytophagy. In this scenario, the protohomopteran lineages exploited sap-feeding and retained an opisthorrhynchous head. The protoheteropteran lineage evolved a prognathous head and gula as an adaptation to searching out and feeding on plant tissues high in nitrogen, buds, seeds, fruits, meristems, etc. The heteropterous feeding strategy then readily evolved carnivorous lineages which variously preserved plesiomorphic character conditions, such as seen in Dipsosocoridae, Saldidae, Enicocephalidae, and the Gerromorpha. The ancestral phytophagous stemgroup was eliminated through competition with advanced phytophagous Heteroptera. This would explain the common presence of the salivary sheath fluid in both Homoptera and pentatomomorphan Heteroptera as a single evolutionary event occurring before the divergence of the suborders.

The carbohydrate levels of insect haemolymph

1. 1. Several species of insects and terrestrial arthropods were analysed for levels of carbohydrates in their haemolymph. 2. 2. Trehalose in all terrestrial arthropods and primitive insects analysed was either absent or present in very small amounts. 3. 3. Glucose showed a similar pattern to trehalose, but in the more primitive animals was generally present in moderate amounts. 4. 4. In the higher insects, high levels of trehalose and moderate amounts of glucose were detected in the haemolymph.

EXTRARETINAL PHOTORECEFTION IN INSECTS

Abstract— Extraretinal photoreceptors are widespread among insects and function in the photoperiodic control of development and in the entrainment of circadian rhythms. The effects of light on the daily and seasonal regulation of brain neuroendocrine activity are mediated solely through extraretinal photoreceptors. In primitive insects, the eyes participate in the entrainment of nonendocrine circadian rhythms such as the locomotor rhythm. In more advanced forms, however, extraretinal pathways appear to be the only pathway for the entrainment of all rhythms thus far examined. But even in this latter case, the eyes sometimes effect a masking of the expression of the overt rhythm. An exact localization of the extraretinal receptors has not been accomplished, but in all studies to date they appear to be associated with the cerebral lobe region of the brain. Action spectra for photoperiodic responses have been determined for a number of insects. In general the responses are maximally sensitive in the blue with a marked decline in the red although exceptions do exist. Complete action spectra for circadian responses have been determined only for two insects. In both cases a plateau of sensitivity extends through the blue with a steep drop at longer wavelengths. From the action spectra data, the extraretinal receptors appear to have a threshold sensitivity less than 3 times 10‐2 J/m2. The pigment nature of the receptor is unknown although it appears not to be a carotenoid derivative.

Ecdysone and the super tick.

TICKS and insects develop and grow through intermittent replacement of their integument. This moulting does not occur beyond the adult stage, with the exception of primitive apterygote insects such as silverfish, which continue to moult and grow after they become sexually mature. Moulting ceases to occur in the pterygote adult insect because the glands secreting ecdysone, the hormone required to induce moulting, break down and disappear soon after the insect (and presumably also the tick) becomes adult1. The adult tissues of both hemimetabolous insects and those with complete metamorphosis continue to respond to ecdysone if exposed to it. There are, however, differences in the responsiveness of different segments of the insects and the resulting ‘super-moulted’ adult insects are usually defective2–5. We have found that ticks also retain the full potential to moult, grow and reproduce normally as adults if they receive ecdysone. Through successive adult moults ‘super ticks’ are obtained (Fig. 1) which consume very large volumes of blood and produce many more viable eggs than normal ticks.

The occurrence of trehalose in an earwig, Forficula auricularia L. (Dermaptera)

1. 1. Forficula auricularia contains low concentrations of trehalose in its blood. 2. 2. There is little good evidence to support the suggestion that primitive insects lack trehalose.

Apparent absence of trehalose in the blood of an insect, Anisolabis littorea (white) (Dermaptera)

1. 1. The blood of the primitive insect, Anisolabis littorea, was analysed for total carbohydrate, reducing sugars, glucose and trehalose. 2. 2. The total amount of carbohydrate was very low when compared with known values for other insects; there was apparently no trehalose present and only moderate amounts of glucose.

Aquatic insects

Insects include the greatest number of species of any class of animals. They have been divided into thirty Orders. However only four Orders of insects consist of species whose larval forms are always aquatic, while another nine Orders contain some species with either aquatic larvae or which are aquatic throughout larval and adult stages. Insects are characteried by a hard, segmented, exoskeleton and by a three segmented thorax, each bearing a pair of legs and usually with two pairs of wings attached to the second and third thoracic segments. In the Diptera and some mayflies (Ephemeroptera) the wings are reduced to a single pair, while in primitive insects such as springtails and silver fish, wings are absent. They have also been lost from some species of more advanced orders of insects.

The compound eye of Archichauliodes (Megaloptera)

The ommatidial structure of Archichauliodes , as shown by electron microscopy, agrees with its systematic position as a primitive endopterygote insect. The eight retinula cells form a long column with distally placed nuclei and proximally located rhabdomeres. In the dark-adapted eye four of the retinula cell bodies reach the cone tip but in the light-adapted eye there is a crystalline tract up to 100 µ m long formed by extensions of the cone. Microtubules are abundant in the cells which move on adaptation, i.e. the cone cell cytoplasm and the primary pigment cells which surround the crystalline tract. This paper forms the first of a group on the neuropteran type of compound eye, found also in some Coleoptera and Lepidoptera.

Effects of juvenile hormone and molting hormone on rectal pad development in Hyalophora cecropia (L.).

AbstractThe histology of the rectal pads was examined in H. cecropia that had been injected as pupae with juvenile hormone or molting hormone. The appearance of the rectal tissues was related to the degree of imaginal differentiation which in turn depended on the dose of juvenile hormone applied. Juvenile hormone inhibits the division of the small hindgut cells that normally form the general rectal wall of the adult. High doses totally suppress the differentiation of the cortical cells. The medullary cells are very sensitive to juvenile hormone even in animals in which the external morphology is only slightly affected. Relatively high doses of molting hormone result in the formation of large, elongate complexes of cortex cells. These are more typical of primitive insects than of Lepidoptera.

Antarctica under Sail

Antarctica under Sail

Electrical responses of muscle fibres of dragonfly larvae in relation to those of other insects and of crustaceans

The membrane constants of the skeletal muscle fibres of Aeschna sp. larvae are of a generally similar magnitude to those reported in other arthropods, except for a very short length constant (ca. 0·4 mm). Resting potentials of the fibres vary between 60 and 90 mV. Fast action potentials are between 20 and 55 mV depolarization, and slow action potentials between 0·5 and 25 mV. The fast responses are pure junctional potentials, there being no active membrane response; the slow junctional potentials do not summate to any great extent, and there is no facilitation in unfatigued preparations. A model system is proposed to explain the apparent variability of the magnitude of the slow response, involving the observed short length constant and end-plate regions which are small compared to the area of post-synaptic membrane which they influence. The evolutionary significance of the responses of this primitive insect is discussed.

Electrical and mechanical responses of the skeletal muscle of a primitive insect.

INNERVATION of arthropod excitatory muscle is of two types, distinguished by mechanical effect; these are “fast” (twitch) and “slow” (tonic), and only in the fast type is there a significant mechanical response to a single nerve impulse. The classes Insecta and Crustacea are the only arthropods the neuromuscular mechanisms of which have been studied in any depth, and considerable differences have been found between them, both in the anatomy and in the form of electrical events which accompany the fast and slow mechanical responses. Nearly all insect muscle fibres are fast-innervated and the electrical response is large, with a non-propagated spike component (active membrane response). Some fibres are also slow-innervated, and in these the electrical response is much smaller, but summates and facilitates greatly to repetitive stimulation, producing large depolarizations1–5. In crustaceans there are relatively fewer fast-innervated fibres, but all are slow-innervated. The two types of response are often difficult to distinguish electrically, and the fast response has no spike component; summation is incomplete although facilitation can be significant, and large depolarizations to either fast or slow stimulation are very rare6,7. Investigations of some of the more primitive insects could possibly show some responses which do not have the large spike activity of the higher insects, and some interesting neuromuscular patterns have been discovered in dragonfly larvae (species of Aeschna) which are thought to be primitive for several other reasons.