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Life Cycle of Spodoptera Litura

Insects have been around for more than 400 million years and it could be argued that they are the most successful and enduring life form that has ever arisen on this planet. Insects are abundant and ubiquitous. From the poles to the equator, from the surface of the sea to the highest peaks and from deserts to rain forests it is estimated that there are somewhere in the range of 1X1018­ individuals on earth at any given time.
The described species of insects are distributed unevenly amongst the higher taxonomic groupings called orders. Five major orders stand out for their high species richness, the beetles (Coleoptera), flies (Diptera), wasps, ants and bees (Hymenoptera), butter flies and moths (Lepidoptera), and the true bugs (Hemiptera). The Hymenoptera have more than 115,000 described species, with the Diptera and Lepidoptera having at least 150,000 described species each, and Hemiptera, almost 100,000. Of the remaining orders of living insects, none exceed the approximately 20,000 described species of the Orthoptera.
Insects are so important to the continued working of the global ecosystem that, as long as the well-being of insects is safeguarded, the earth should remain habitable for humans (Berenbaum, 1995). On the other hand insects are also known for the damage they can cause to the agricultural crops. On average, one fifth of all crops grown around the world are eaten by insects.
Several approaches to pest management have yielded good results, however, with associated problems. Chemical control programs though gave good results initially, are posing problems in the form of environmental pollution, biomagnification, soil infertility and so on, in addition to development of resistance by insects to these chemicals, which has worsen the problem. Resistance by insects led the farmers to increased application of chemicals or switch to another chemical which will also end up with the same fate.
Alternative to chemicals such as pheromone trapping, transgenic plants, and several biopesticides are doing rounds in farming sector. However, are not enough to control some of the pests which are notorious by being polyphagous. An alternative thinking, of the late, conceived by scientists is to use the insects own products, on the lines of pheromones, such as proteins/peptides especially the behaviour modifying peptides and or neuropeptides to control the pest insects. Use of naturally occurring behavior modifying peptides/proteins involved in the regulation of biological processes to interfere with the pest’s own mechanisms resulting in its failure to successfully reproduce could be a novel approach. The advantages of the likelihood of being specific, eco-friendly and sustainable, provided, an effective method is evolved for employment of these proteins; it could turn out to be an effective, if not total replacement, an alternative for chemical pesticides. It would also be possible to artificially manipulate the physiology of the pest by designing synthetic analogs of the behavior modulators as well as cloning the responsible genes and application of genetic engineering to over-express such genes to interfere with the regulatory mechanisms of the insect pests. For the development of specific and safe insect control strategies utilizing peptides/proteins, a clear knowledge of the underlying molecular mechanisms involved is essential.
Several studies have shown the presence of such peptides in the reproductive system of male that are transferred to female at the time of mating and take a control over her post mated reproductive behaviour (Kingan et. al., 1993). To identify such proteins it is important to understand the reproductive behaviour of insects so that one can track the behaviour to biomolecule.
Successful reproduction results from a succession of interdependent steps which are often completely different in nature and take place at various times in the insect’s biological cycle. Both nervous and hormonal mechanisms are important in coordinating these interdependent steps in addition to complex coordination of sensory input and motor responses. Synchronization of copulation with a number of factors is the hallmark of a successful reproduction that has been evolved by many insects over a period of time through several generations. Presence of mature or nearly mature male and female gametes, ability to produce the secretions necessary for sperm transfer in male and availability of nutrients for egg maturation in female synchronizing with copulation ensures the success of reproduction. The underlying neuronal and hormonal machinery ensures this requirement and the neuroendocrine system forms the essential link connecting the two coordinating systems.
The occurrence of a number of peptides/proteins that regulate reproduction have been studied in several insects ( review/ many ref Holman et al., 1990) which are shown to be synthesized, activated or released at appropriate periods. Insects have evolved a simple mechanism to synchronize the occurrence of peptides/proteins in female with its reproductive phase by introducing them at the time of mating. Majority of such peptides originate in the Accessory glands associated with male reproductive system though some of them originate in ejaculatory duct and some times in testis.
In spite of their morphological diversity, the male accessory glands exhibit several commonalities, as for as basic features are concerned, between several insect groups (Chen, 1984). The accessory glands arise as discreet out pockets of the vas deferens, seminal vesicle or Ejaculatory duct which themselves originate from the coelomic cavities of the ninth or tenth abdominal segment. These glands are considered as functional homolog of the human prostate (Bertram et al., 1992). They originate from a special set of cells in the male primordium of the genital disc (Nöthiger et al., 1977) whose developmental fate is determined by the male sex determination pathway during larval period. A single layer of secretary cells set on a basement membrane forms the gland wall, outside which is a muscle layer of varied composition. The glandular cells generally have an ultra-structure similar to cells concerned with the production of proteinaceous material and export. Rough endoplasmic reticulum and well developed Golgi complex is prominent throughout the cells. The nucleus is large and may contain a number of nucleoli. The apical plasma membrane is folded into microvilli of variable density, and the basal plasma membrane may be deeply indented into the cell (Gillott and Gaines, 1992).
The role of male accessory glands in reproduction is undoubtedly proved, by several studies, to be not just essential but critical in insect reproduction. Elicitation of two major responses in the female: elevation of oviposition and repression of sexual receptivity have been attributed to male accessory gland secretions which enter the hemolymph following mating and affect the nervous and/or endocrine system. The main function of male accessory glands is the production of spermatophore for sperm transfer from male to female. Even in some species that do not use a spermatophore, the glands may fulfil a variety of functions (Hinton, 1974).
Male accessory glands contents generally includes carbohydrates (both free and complexed with protein), some lipid (normally bound to protein), and small amounts of amino acids and amines (Gillott, 1988). In some species, for example, cockroaches uric acid is present in the accessory gland secretions (Roth, 1967), in several of others, prostaglandins (Lepidoptera), juvenile hormones (Lepidoptera and mosquitoes) (Borovsky et al., 1994; Park et al., 1998) and various toxic materials that serve as egg protectants following their transfer to the female (Blum and Hilker, 2002; Eisner et al., 2002) are present. However the major components of male accessory gland secretions, in both quantity and importance as modulators of female reproductive activity, are proteins (Gillott, 2003). Once they are delivered to female along with sperms, they virtually regulate almost all the post mated behaviour of that female such as calling, mating, egg maturation, egglaying and so on.
The role of peptides/proteins of male accessory glands on the female reproductive behaviour, though, has been demonstrated in a number of insects, similar information available on Spodoptera litura a polyphagous pest insect is very scanty.
Spodoptera litura Fabricius (Lepidoptera: Noctuidae), though, commonly known as tobacco cutworm, is not restricted to tobacco alone, but, feeds on more than 120 host plants belonging to 44 families(Qin et al., 2001). It is a serious polyphagous pest in Asia and Oceania, from the borders of North Africa to Japan and New Zealand (Armes et. al., 1997). It has a large host range of crop species such as cotton, groundnuts, jute, maize, rice, soybean, tea, tobacco, capsicum, cucurbit, potatoes and so on. Not just that, it feeds on weeds and ornamental plants too (Ramana et al., 1988). Hence, Spodoptera litura is an appropriate choice to explore and unravel the mechanism underlying the regulation of reproduction.
This background formed a basis for selection of the topic Isolation and characterization of male derived factors modifying the physiology of oviposition in lepidopteran pest Spodoptera litura. The study was planned with following objectives.
To study the life cycle of Spodoptera litura.
Localization of proteinacious factors from the male reproductive system of S. litura which are responsible for modifying the physiology of egg production and egg laying.
Purification and Characterization of the protein
Determination of the amino acid sequence of the protein.
As a prelude, for effective implementation of the above objectives, following investigations were carried out.
Standardization of an efficient rearing method to establish insect colonies since mass rearing was necessary for studying the physiology of the insect and also for pooling of accessory gland tissue from the male moths.
Study of life history characteristics of Spodoptera litura, as the literature available revealed that development varied when reared in different conditions.
Identification of parameters for quantification of the reproductive behaviour in female moth.
Development of an efficient bioassay technique for elucidating the influence of various male derived components on the reproductive behaviour of the female moth.
To understand the status of research at both national and international level, on accessory glands secretion and their role in reproduction and pest status of Spodoptera litura, an extensive literature survey was carried out which helped in identifying the objectives and also to design the experiments. An effort was also made to understand similar work carried out on other insects which may help in appreciating the present work.
Secondly, as with any other phenomenon, the diversity of insects does not permit us to extrapolate the understanding of these mechanisms in one insect to even a closely related insect. In most insects, juvenile hormone regulates the secretory activity of the male accessory glands, but in some species allatectomy appears to have no effect on the glandular function (Chen, 1984). While the sensory system, receiving stimuli both from the environment and insect’s own body, plays an important role in the initiation, mediation and termination of behaviour, endogenous factors which reflect the physiological state of the insect modulate the expression of behaviour and ensure its biological appropriateness (Bali, 1998). There are several essential points that await future experiments for clarification. (a) The male accessory secretions elicit two major responses in the female: elevation of oviposition and repression of sexual receptivity. The secretory substances enter the hemolymph following mating and affect the nervous and/or endocrine system. The precise targets, however, are unknown.
Identification of the target sites will be an initial step towards understanding the problem is exacerbated by the difficulties of rearing insects on defined diets.

Classifications of Snakes and Reptiles

Reptiles are some of the oldest living creatures on the planet and made their first appearance some 300 million years ago. It is believed that the first species of snakes contained limbs which became more and more reduced through great periods of time, this phenomenon can be seen as a clear indicator just how evolution took place within a group of organisms. Today vestigial structures occur in certain serpent families such as Pythonidae and Boidae, and are remnants of structures they once possessed. Spurs which occur in the posterior position opposite the cloacae in Boas and Pythons is a clear example of vestigial structures that formed through time.
Snakes are carnivorous reptiles that belong to the order Squamata (Lepidosuaria), which is regarded the most important assemblage, as far as snakes are concerned. Squamates is a very diverse group of ectothermic (organisms that rely on their external environment to obtain the energy needed to facilitate metabolic and other processes crucial for life), amniote vertebrates which contain the distinct characteristic of being elongated and covered in overlapping scales. Squamata is subdivided into three distinct suborders: Ophidia or Serpentes, containing snakes, Sauria containing lizards and Amphisbaenia containing worm- lizards.
The suborder Ophidia contains 15 families which are subdivided into 456 genera that consist of more than 2900 species. Snakes have one of the widest distributional ranges in the animal kingdom, covering the whole planet except Antarctica (Figure 1.1). In South Africa alone there occurs 166 species and subspecies of snakes, 101 of these species have enlarged fangs to deliver venom of which only 15 are regarded as very dangerous and potentially fatal to man. This means that of all our snake species only 8.5% are classified as dangerous, where administration of antivenin is deemed necessary. The remainder of venomous species is of no medical importance to man, in fact in some species the toxicity of their venom is less than that found in bees and wasps.
There are a few morphological characteristics of Ophidia which distinguishes them from the other two suborders e.g. the lack of eyelids, external ears, the lack of limbs and the occurrence of a single row of ventral scales, whereas lizards and amphisbaenas differ in the sense that they have various patterns of scales that do not occur in specific rows. Amphisbaenians scale formation is atypical in the sense that scales are arranged in rows around the body of the animal thus supposedly mimicking the resemblance of an earthworm. The skulls of Serpents are very unique in the sense that their upper jaw bones aren’t united/interconnected at snout of the animal, this enables the two jaw bones to act separate form one another and enables the snake to swallow large prey items. In contrary to popular belief snakes can however not dislocate or unhinge their jaws to swallow large prey items, the two upper jaws are simply connected to each other through connective tissue which is highly elastic and serves as the binding factor between the jaws.
Snakes fulfill a crucial role/function in nature and can be seen as an integral aspect of our environment both as key predators and as prey. They assist in regulating rodent numbers and are good indicators of the natural balance of the environment (bio-indicators). In addition to this, research and development is being done on the properties of venom in the medical field. Research is being conducted on the applications of venom in fields such as high blood pressure, mental disorders and diseases of the central nervous system to mention but a few. Such is the complexity of venom that further studies, beneficial to man, are essential. It is there for imperative that we conserve our snakes not only for the preservation of our environment, but also for the wellbeing of mankind.
Evolution that took place within the Class Reptilia Reptiles evolved from prehistoric amphibians called Labrynthodonts (Flank, 1997), and according to paleontologists made their first appearance in the Pennsylvanian era some 300 million years ago. They were also the first vertebrates to escape dependency on water. The earliest forms of reptiles suggested a mixture of both amphibian and reptilian characteristics, and diversified greatly over the next 200 million years. Reptiles were the dominant animal group on earth during the Mesozoic period, and were represented by 15 major groups. Only 4 of these orders survive today. Extinct are the fishlike Ichtyosaurus, sail-backed Pelycosaurs, flying Pterosaurs, Mosasaurs, plesiosaurs, well-known dinosaurs like Brachiosaurs and many others. The dinosaurs included the largest animals ever to walk on earth-the Sauropods, some of them reaching lengths of nearly 27 meters long. Many of the less familiar dinosaurs were no longer than chickens. (Carr,1963)
Several basic advances made possible the rise and wide distribution of reptiles on land. Most important was the amniote egg, with its tough outer covering and protective membranes, and a cornified skin that protected the animals from drying out. The positioning of the limbs also made it possible for reptiles to move more easily on land, and an improved circulatory system ensured that oxygen rich blood reached the animals.
In their Mesozoic heyday, Reptiles dominated the land, seas and air, and the reason for their dramatic decline during this period is still not clear, although there are some speculation by biologists that the decline was probably caused by a meteor shower which altered a dramatic change in climate and giving rise to the so called Ice Age. Warm blooded vertebrates (Birds and Mammals) began to expand by the end of the Mesozoic period. By the time the Cenozoic period arose only 4 orders of reptiles still existed, and these same four have persisted to this day. The order Rhynchocephalia is represented by only one species, the lizzardlike, granular scaled Tuatara (Sphenodon punctatus) confined to New Zealand where its survival is now threatened. The remaining 3 orders have representatives throughout the world. The order Testudines (turtles) is the most ancient, appearing about 250 million years ago and remaining virtually unchanged for the past 200 million years. The order Crocodylia (crocodilians) is slightly less ancient and is traceable to the Permian thecodonts. The order Squamata refers to scaled reptiles that include lizards, amphisbaenids and snakes. This is the most recent order and was not common until the late Cretaceous times about 65 million years ago.
In order to classify snakes or other organisms it is necessary to understand the origin and evolution of the species and place them into specific genera and families (Figure 1.2)
Scientists believe that modern day snakes evolved from the family Varanidae, a group of lizards that belong to the genus Veranus. The fossils of Lapparentophis defrennei (Figure 1.3) was found in North Africa as we know it today, and it represents the earliest member of the suborder Ophidia. This species however shows no direct link between earlier snake like reptiles, and its origin continues to boggle biologists. Lapparentophis defrennei appeared on the earth around 100 million years ago during the Cretaceous period and were around for about 35 million years, were after it got extinct by the end of the Cretaceous period. Boidae was one of the seven families of snakes that arose after the Cretaceous period and was at its peak of speciation during this time. Colubridae in modern day times is the family that contains the largest amount of different snake species, and first emerged some 36 million years ago during the late Eocene, and the beginning of the Oligocene period. During this time Colubrids started to diversify at an immense rate and eventually gave rise to more new species during the Miocene period. This diversification led to the disappearance of some of the more primitive lineages of snakes because they could no longer compete with the better adapted species that was starting to evolve. Viperidae (vipers, rattle snakes and adders) and Elapidae (front fixed fang snakes generally cobras and mambas and their relatives) originated during the Miocene period and belongs to the infraorder Alethinophidia. The family Viperidae is by far the most advanced evolved species of snake in the world and contains highly specialized structures that enable them to be a very successful hunters e.g. heat- sensitive pits that developed on the upper labial and a brightly colored tail tip that occur in Agkistrodon sp. This is just one example of how specialized this family of serpents is to survive.
Distinguising features of the suborder Ophidia All snakes are elongated, lack eyelids, external ears and osteoderms.
Snakes poses a forked tongue which can be retracted into a sheath (Figure 2.1)
All have along backbone. (Some have in excess of 400 vertebrae), with many articulated ribs used predominantly for locomotion and maintaining body shape.
The lower jaw is not fused, which allows the snake to engulf large items. They do however not dislocate their jaw.
Prey is subdued either by constriction or by the injection of venom. In the case of venomous snakes small prey items are bitten and held in the mouth until paralysis or death occurs, whereas large prey items are bitten and released to ensure that damage do not occur to the snake.
The majority of species have only the right lung but more primitive species such as Pythonidae and Boidae also contains a rudimentary left lung.
Unlike lizards the tail cannot be regenerated.
All snakes shed their skin.
All snakes hatch from eggs, some are Oviparous (eggs hatch outside the females body), and some are ovoviviparous (eggs hatch inside the mothers body thus giving birth to live young).
Classification of snakes Kingdom: Animalia
Phylum: Chordata
Subphylum: Vertebrata
Class: Reptilia
Order: Squamata
Suborder: Ophidia (Serpentes)
Infraorders: -Alethinophidia
The classification of snakes are based on different morphological structures The general morphology of snakes is a crucial factor used in their Taxonomy. Factors such as the arrangement of bones in the skull and other parts of the skeleton, especially the presence or absence of a pelvic girdle are used to distinguish between separate and subspecies of snakes. The hypapohyses (vertebrae with downward pointing spike like projections), the coronoid bone (a small bone that occur in the lower jaw), structures of the hemipenes (Figure 2.2, Jadin, 2000) and microscopic and biochemical material such as chromosome arrangement and protein analyses are also used in classification of snakes.
The presence or absence hypapohyses, especially in the lumbar region of the spine, is used as one of many diagnostic characters when classifying snakes. The hypapohyses is very prominent in the genus Dasypeltis which use them too saw trough egg shells. There occurs much variation in the shape and size of the coronoid bone. It is particularly large in primitive snakes such as Typhlopidae, Leptotyphlopidae and Anomalepididae. The coronoid bone is very small or absent altogether in advanced snake species. A hemipenis is the sex organ of male Squamates. Male snakes has two hemipenes probably for the reason that when one is damaged or injured, it still left with a spare one which can remain to work and carry out its normal function during copulation. This ensures that the male’s genes don’t get lost and can still be carried over through copulation with females. Hemipenes, under normal conditions are used in an alternating fashion when copulation occurs with female individuals. Sperm is carried through the sulcus spermaticus (which is the line running through the middle of a male’s hmipenis) to the female during copulation. By examining the tail of an individual we are able to distinguish its sex. Males usually have a long tail which contains prominent bulges of where the hemipenes are situated and females usually have very short tails without the occurrence of any prominent bulges. The shapes of hemipenes differ greatly from species to species and contain different cranial structures thus forming a very important method for taxonomists to classify snakes into different species and subspecies. Relationships that occur between different species of Squamates as a result of evolution is best explained through the examination hemipenal characteristics of the different species. The function of the spines and ridges that occurs on hemipenes of different species of male snakes, serves as an adaption to ensure that copulation lasts long enough for egg fertilization to occur.
Biology Hearing and Vision
Snakes cannot hear airborne sounds due to the fact that they do not posses external ears. Snakes do however have an auditory nerve enabling them to hear sounds travelling through a dense medium. They are extremely sensitive to vibrations and can thus detect someone or something approaching them. For this reason people seldom see snakes whilst walking in the bush, the snake senses the vibrations created by footsteps and beats a hasty retreat for cover. There is however snakes that do not retreat when approached and this is a direct result of the morphological attributes they contain. Bitis arietans, Bitis atropos and, Bitis gabonica, are species of snakes that rather rely on their camouflage to conceal them from potential predators and dangers than to move away, and it is not surprising to find out that Bitis arietans is responsible for 60% of all snake bites in Southern Africa. Contrary to popular believe snakes do have good vision. How else would they safely navigate through the bush except of course via smell? Their vision however is used mainly for detecting movement. Most snakes have monocular vision (unable to distinguish depth of field) whilst some snakes have binocular vision (able to distinguish depth of field) e.g. Thelotornis capensis and Dispholidus typus. Snakes do not have movable eyelids, instead they possess a fixed transparent shield which covers the eye and is shed during sloughing.
Sense of smell
For this function the snake uses its tongue. The tongue is flickered; picking up minute airborne particles which when retracted back into the mouth is deposited onto organs situated in the roof of the mouth. These organs are known as the organs of Jacobson. Studies have shown that snakes enjoys a similar sense of smell as we do, the epithelium of the organs of Jacobson works in exactly the same way as the olfactory epithelium we as humans possess. The tongue is forked so that the snake can detect the differences in strength of smell and thus enabling it to locate its prey very accurately. Snakes diet consists of quite a few prey items such as: rats, mice, small mammals, birds, frogs, toads, insects, lizards, fish, small antelope, eggs and other snakes, which is swallowed whole usually head first.
Shedding of skin depends primarily on the growth rate. Juveniles for example shed their skin more often than adults for the simple reason that they are growing faster. Juveniles may shed their skin as often as twelve times a year whereas an adult may only shed its skin three to four times a year. During this process the entire skin is shed from the tip of the snout through to the tail including the eye shields. During this time the snakes eyes become opaque, restricting the snake’s vision and therefore making the snake not only more vulnerable, but also more aggressive. A snake may often go into hiding during this period. You may also find snakes basking for longer periods prior to shedding, the reason being higher temperature speeds up the development of new skin, thus reducing the vulnerability period.
Cold Blooded – (Ectothermic) and Hibernation
All members of the order Squamata are so called cold blooded (exothermic) organisms. This simply means that unlike mammals and birds which generate heat internally (endothermic), reptiles obtain their heat externally, usually from the sun. All reptiles will bask in the sun absorbing heat from their environment until their bodies reach the correct optimal temperature (± 30°C) which allows them to function at their maximum potential. The advantage of ectothermy is that it is fuel efficient. Mammals on the other hand convert 90% of what they eat into heat in order to maintain biochemical and muscle efficiency which allows mammals the opportunity to function at colder temperatures. This method demands a constant intake of food. Reptiles however become temporarily dormant at colder temperatures and thus waste no energy. A snake can survive and grow on ten to fifteen meals a year. Reptiles will go into hibernation when their optimal body temperature cannot be achieved from the environment. In areas where there is a significant fluctuation in temperature snakes will go into hibernation. The correct term used is topor. Areas such as the lowveld where there is no significant temperature variations will see reptiles not going into true hibernation but rather into a state of burmation. During hibernation snakes live off the body fat accumulated during the warm periods of the summer, and will exhibit very little signs of activity, thus becoming sluggish. A snake will use anything that will offer it protection against the elements and predation. Sites which are used by Squamates during the winter or cold times of the year for hibernation include deserted termite mounds, hollow logs and rock crevices.
Sexually active males will approach any snake they come across. The reaction of the approached snake will determine how the encounter develops. If the approached snake is a male and reacts aggressively it may give rise to a battle between the two parties. Battles vary according to species, Vipers and Elapids generally engage in a form of ritualistic wrestling, but refrain themselves from biting each other. Colubrids however react violently and bite each other severely. In some species of snakes several males group together amicably and follow a receptive female. Should there be no reaction from the approached snake the sexually active male uses its Vermonasal organ to chemically determine the species and sex of the snake it has approached. It does so with the use of its tongue interpreting the pheromones emitting from the other snake. Should it be of a different species, the male then seeks out a new mate.
All reptiles have internal fertilization. The male places his head on the back of the female and winds his tail around the females and attempts to join their cloacas together. This is seldom achieved at the first attempt. It sometimes takes hours, even days, for successful copulation to take place. The sexual organs of the male consist of two penises, referred to as the hemipenes. Each hemipene is equipped with flexible spines which inflate once penetration has occurred making it difficult for the male and female snakes to become dislodged. Sperm is transferred to the female via a single penis in Crocodilians and Chelonians, and paired penises in lizards and snakes (although only one penis is used at a time). Once mating has taken place the male will often stay with the female for a few days to mate again.
Fertilization of the ovule and spermatozoid takes place high in the oviduct, then the egg gradually moves down into the oviduct where the uterine glands secrete a substance which surrounds the egg. The length of the embryonic development depends on the species and also within the species depending on climate (temperature), and ranges from 2-5 months.
As stated before all snakes hatch from eggs. The method of incubation however does differ between some species. The majority of snakes lay eggs andleave them to be incubated externally (oviviparous) with no parental care whatsoever. Species such as Python natalensis coils around their eggs throughout incubation. This not only protects the eggs but also regulates the temperature to help assist with incubation. In other species such as Hemachatus haemachatus the female retains the eggs inside her body to produce fully developed live young (viviparous).
Between four to eight weeks after mating the female selects a suitable site to deposit her eggs. The site chosen is usually a suitably protected place in the form of rotting vegetation, hollow tree trunks or any other suitable location. The number of eggs deposited depends on a variety of circumstances for example, species, size of the female, habitat (availability of food), age and climate. Eggs laid vary between one and two to as many as 60, sometimes more, depending on factors mentioned above. Eggs usually have soft leathery shells which require a specific amount of heat and humidity in order to ensure that hatch. Once the eggs have been laid there is often no parental care with the exception of a few species. In South Africa the young of Python natalensis may stay with the female for several days after hatching, leaving the burrow by day and returning to the female at night.
In most reptiles the sex of hatchlings is determined by temperature, for example outer eggs (cooler) will be female while the inner eggs (warmer) within the nest will be male. The eggs usually hatch between one to three months after the female has deposited them. In the case of some species of chameleons eggs might take up to a year to hatch. The young are equipped with an egg tooth consisting of a sharp ridge on the tip of the snout which allows the young to slit open the eggshell thus freeing itself. The young that emerges are exact replicas of the adults, and the hatchlings of venomous snakes are equipped with fully functional venom glands and fangs, and are thus venomous directly from birth.
Egg mortality is quite high. Reasons for egg mortality range from predation to unsuitable nest sites chosen. Giving birth to live young may be an evolutionary process to assure the success of a species, reducing the risk of egg mortality in particularly cold areas where the temperatures won’t be adequate enough for incubation.
Movement (Locomotion