Sperm transfer occurs in many ways and insects. Some insects pass on free-swimming sperm in ejaculatory fluids. While others package sperm together with protein-rich accessory gland secretions. Remember, these sperm packets are referred to as spermatophores. An extreme example of sperm transfer occurs in bed bugs. In which males inseminate their mates not by entering the reproductive tract through the genital opening but by pushing their sharp through the females exoskeleton to create a new opening. The male then deposit his sperm directly into the females hemolymph. Unfortunately, this creates an open wound leaving the female vulnerable to infection. This form of sperm transfer is appropriately referred to as traumatic insemination. Beyond bed bugs and their violent mating encounters you may be surprised to learn that this type of antagonistic interaction between sexes is not uncommon in the animal world. Sexual conflict, whereby two sexes have conflicting reproductive strategies is actually quite common in insects. Water striders just like bed bugs are well known examples of insects that experience conflict between the sexes. As with many insects, mating and water striders involves the male mounting the female from above. Because of this position the female has no choice but to support the weight of the male on the water surface for as long as copulation occurs. This is energetically costly to the female. And males tend to stay attached to the females for as long as possible to ensure offspring paternity. Depending on the species mating in water striders can range from four minutes to over seven hours. Although their record for the longest water Strider mating encounter belongs to a species known as Aquarius najas or the river skater. This extremely patient insect has been reported to remain coupled for up to three months. Because of this high energetic cost, females typically accept fewer matings than males initiate and tend to prefer to mate for shorter periods. Females may even physically shake off a male that attempts to initiate mating. As a result, males of many species of water Strider have evolved clasping mechanisms to help them hold on. Evolutionary conflict doesn't stop there, females of the red-backed water Strider have evolved what is essentially a genital shield. Almost like a chastity belt, which blocks males access to the females reproductive system. In addition to the clasping structures seen on most water striders, the male's of this species use a behavioral mechanism called intimidating courtship. Once in copulatory position, the male taps the surface of the water creating ripples that could attract predators. Because the male rests on top of the female she is more likely to be eaten by an underwater predator than the males. Given the choice between death by predator or an energetically costly mating encounter. The females tend to quickly accept the mating so the male stop signaling to potential predators. Just as there is lots of variation in insect mate finding courtship and mating behavior. There are also many different modes of insect reproduction. Most insects reproduce sexually and eggs produced by females are fertilized by sperm from males. Most insects also have direct fertilization that involves coupling of the sexes. The vast majority of insects exhibit OVA parity, which means that the females deposit eggs externally on to something like a leaf. And embryos in these eggs complete their development outside of the female's body. This process of the egg passing from the genital opening to the outside environment is called Oviposition. Oviposition is often the result of a complex suite of behaviors that ends with the female positioning her offspring in a habitat where they are protected and have access to resources required for development and survival. As such many female insects have evolved sophisticated sensory receptors to detect optimal over position sites. We will discuss more about oviposition site selection in a future module when we learn about host location in herbivorous insects. Oviparity requires the female to produce eggs that contain a nutrient-rich yolk, which provides the developing embryo with essential proteins carbohydrates lipids and salts. This mode of reproduction allows females to produce large numbers of offspring. The lack of parental care associated with oviparity reduces the likelihood of offspring survival. The outer layer of insect eggs that functions to prevent water loss called the chorion is sometimes thickened to help protect against predation. That being said, a few insect species do care for their eggs. In most cases females carry out this costly practice. Although occasionally, the role is reversed. An example of this occurs in the male giant water bug which exhibits an unusual form of egg care. After mating, female giant water bugs lay fertilized eggs on the dorsal surface of the male's for wings. The male protects the eggs until they hatch and ensures that the eggs obtain enough oxygen through some impressive underwater acrobatics. By sweeping and circulating water over the eggs on his four wings and remaining close to the air-water interface he can maximize the eggs exposure to oxygen. The females of some insect species protect their offspring by retaining the eggs inside their body throughout embryonic development. This reproductive strategy is referred to as ovoviviparity. The developing embryo remains within the female's body where it receives nourishment from the egg yolk until it hatches. In some instances, hatching may even occur within the female before the free-living juvenile is deposited into the environment. This mode of reproduction not only provides extra protection for the young but is also an important strategy for insects that rely on resources that are only available for short periods of time. By reducing the external development time of the offspring, the juveniles can be highly competitive as they are ready to eat soon after leaving their mother. This allows them to take advantage of temporary food sources recently located by their mothers. And feeding insects are often ovoviviparity because of the temporary nature of their food sources. Although the vast majority of insects lay eggs, some exhibit viviparity or live birth. In viviparity, the embryos develop within the female. It is different from ovoviviparity, as the female provides the developing offspring with nutrients not from yoke, but from accessory gland secretions hemolymph supplements or even placental type tissues. This type of development provides a lot of protection for the offspring. However, it restricts the number of young the female can produce it once and over her lifetime. In extreme cases, such as tsetse flies. The female will carry only a single offspring at a time. The larvae will complete most of its life cycle within the female and is deposited just prior to pupation. While sexual reproduction is the most orders contain at least some species that exhibit asexual reproduction by parthenogenesis. Parthenogenesis occurs when unfertilized eggs develop into embryos without male involvement. Many members of the phasma tatia, the stick insects can reproduce using parthenogenesis. Sometimes a complex insect life cycle can involve stages of both parthenogenesis and oviparous sexual reproduction. A good example of this can be seen in some species of aphids in which females reproduce asexually under optimal environmental conditions. They produce daughters that are genetic clones of themselves with two sets of chromosomes both from the mother. This allows the population size to grow extremely quickly. To make things more complicated, newborn aphid daughters can be ready to reproduce at birth. Making the mother aphid and expectant grandmother as well. These females usually reproduce over several generations by viviparous parthenogenesis. Asexual reproduction in these aphids will continue across multiple generations until conditions deteriorate as the colder seasons approach. Females then produce male offspring because genetic variation from sexual reproduction becomes more important than simply increasing population numbers. This type of reproduction is referred to as holocyclic, meaning that the periods of asexual reproduction are interspersed with sexual reproduction. This means that male aphids may be almost completely absent most of the time and are produced only during certain times of the year. Parthenogenesis also occurs in hymenopteran insects such as ants, bees, and wasps. They produce males through parthenogenesis development from unfertilized eggs. These males are haploid with only a single set of chromosomes. Meanwhile, fertilized eggs produced diploid females with two sets of chromosomes. This type of sex determination system is known as haploidiploidy, and will be discussed in a later module. Other types of reproduction can be found in a small number of insects. For example, some species of insects can abbreviate their life cycles by skipping the pupil and adults ages all together. These insects reproduce by paedogenesis, where by offspring are produced by reproductively mature juveniles. Like parthenogenesis in aphids, paedogenesis can be part of a complex life cycle. Adult females may only be produced during certain conditions, while most of the time reproduction occurs in female larvae. Some species of gall midges reproduced by paedogenesis, the reproductive system within the larvae matures faster than the rest of the individual. So eggs are ready to be laid during the larval stage. Paedogenesis can involve either sexual or asexual reproduction. Another odd mode of reproduction and insects is polyembryony, in which a single egg splits into multiple embryos. This mode of reproduction is rare and restricted predominantly to endow parasitic insects, like parasitic wasps. It allows the development of multiple offspring within a parasitized host with relatively little energetic expense for the ovipositing wasp. Furthermore, the parasitic female will only have two oviposit once that's reducing her exposure to predation and other threats. In polyembryonyi, the number of embryos produced from a single egg varies between species but can range from as few as ten to over 1,000. These embryos do not receive nutrients from egg yolk but from the host they are parasitizing. The larvae complete their development within the host and as they emerge they spin pupil cases from which the free-living adults later eclose. We will learn more about these insects in a future module when we delve into biological control. The last form of reproduction we will discuss is hermaphroditism. Which occurs when both male and female reproductive systems are present within a single individual. Although hermaphrodites can fertilize themselves, they still tend to reproduce sexually. An example of a hermaphroditic insect is a historically important past of citrus trees, the cottony cushion scale. Which can reproduce through self-fertilization. Now that you are more familiar with insect reproductive systems, in the next video we will examine how humans exploit this knowledge of insect reproduction to control pest populations.
