Insect Reproduction AGRI 318 PDF

AGRI 318 GENERAL PHYSIOLOGY AND TOXICOLOGY LESSON 2: INSECT REPRODUCTION Photo courtesy: sciencepartner.info. Taken from https://cutt.ly/BfuePDx  2 Module No. and Module 1: Basi...

AGRI 318 GENERAL PHYSIOLOGY AND TOXICOLOGY LESSON 2: INSECT REPRODUCTION Photo courtesy: sciencepartner.info. Taken from https://cutt.ly/BfuePDx  2 Module No. and Module 1: Basic of insect physiology and anatomy Title Lesson No. and Lesson 2: Insect Reproduction Title Learning After learning the lesson, you will be able to: Outcomes 1. Describe the parts and functions of the male and female reproductive systems of insects 2. Discuss the different modes of reproduction among insects 3. Discuss the insect reproductive behavior Time Frame Week 4 Introduction Welcome to Lesson 2 of Module 1. You will be exposed to the reproductive systems of insects. Here, you will understand the basics and types of reproduction among insects and explain why insects are numerous despite their small size. Isn't it amazing? You will also uncover the different modes of reproduction, notably the unusual reproduction without fertilization (parthenogenesis and paedogenesis). Finally, you will also learn the reproductive behavior, that is, from pair location to oviposition. I hope you find this topic exciting but challenging. Good luck. Draw and label the parts and provide their roles of both the male and female reproductive systems of a typical insect. Record all these to your activity Activity notebook. 1. What reproductive part/s that is/are unique to insects that cannot be found to other groups of animals? Analysis 2. What are oviparity, viviparity, and ovoviviparity? Which of these three modes of giving birth is the most advantageous, and why? 3. What is the series of events in the insect reproductive behavior? Provide some strategies used by insects to find mates. INSECT REPRODUCTIVE STRUCTURES AND FUNCTIONS Abstraction A. Female Reproductive System The functions of female reproductive systems are producing egg cells and receiving sperm cells and storing them for a long time! The female system is composed of a pair of the ovary, with one or more ovarioles where the egg cell is produced (figure 18). The process of egg production is called oogenesis. During egg production, the germ cells, also known as oogonia divide by mitosis to form oocytes (eggs). The oocytes undergo meiosis and continue to increase in size by absorbing yolk produced by adjacent cells. As the oocytes grow, they are pushed downward by the  3 continual cell division in the germarium (referring to the first region of the ovariole). Thus, the oocytes form chains, with the youngest/smallest cells at the top and mature/large cells at the bottom. There are two types of ovariole depending on the source of yolk to nourish the developing oocyte: the meriostic and the panoistic type. Panoistic ovariole is when the source of the yolk is from the follicular epithelium, a common type among Orthoptera, while meroistic ovariole is when the source of the yolk is from the nurse cells, which is the type of ovariole among Hymenoptera as shown in Figure 18. Figure 18. Types of ovariole (A) Panoistic type; (B) Meroistic type (Adapted from Imms, Richards and Davies, 1957, In Elzinga, R. J. (1978). Fundamental of Entomology, Prentice Hall, Inc. Englewood Cliffs, New Jersey 07632 You may ask what structure is found in the female organ that stores sperm cells and makes it viable until lifetime by the female insect? If your answer is spermatheca, you are correct. Yes, most female insects are only mated once, but that millions of sperm cells received are stored in the spermatheca. For eusocial insects like ants, the virgin queen ant will mate once by several drones to establish its colony. The sperms are stored in her spermatheca and will produce millions of progenies for 20 long years! Isn't it amazing? What makes the sperm cells viable for the longest time? The answer is because of the structure known as the spermathecal gland, which provides proteins and essential nutrients to keep the sperm cells active and  4 viable. Once the egg cell is produced from the ovarioles, they will pass through the lateral oviduct and then move down to the median or common oviduct and to the genital chamber where fertilization takes place. Once the eggs are fertilized, the eggs were coated with lubricants, and glue materials originated from the accessory gland; hence this organ is also known as the glue gland. The importance of this material is that once the eggs are oviposited, they will stick to any substrates, particularly on leaves or parts of plants. Figure 19. Female reproductive system. Adapted from Snodgrass, In Faculty of Science (2015). Bugs-101 Insect-Human Interactions, University of Alberta. Parts of insect egg The parts of an insect egg (Figure 20) are as follows: a. Eggs are covered with a tough outer shell called the chorion, and a thinner membranous inner covering called the vitelline membrane. c. A minute opening located at the chorion called the micropyle. This opening is for the sperm cell gateway to the egg. d. Two membranes that surround the nucleus and cytoplasm. e. The egg cytoplasm is consists of a large central area of yolk and an outerthe periplasm, which is located beneath the vitelline membrane.  5 f. The egg nucleus located at the center of the cell is embedded in the cytoplasm. Figure 20. Parts of an insect egg (Adapted from Dr. R. Ali) MALE REPRODUCTIVE SYSTEM The male reproductive system's primary functions are to produce, store, and inseminate sperm cells to the female reproductive organs and be deposited in the spermatheca. The system is composed of the following parts and is shown in Figure 21: (a) pair of testes – houses the sperm tube or follicles (b) sperm tube or follicles – produces the sperm cells. The number varies from one in Coleopterans to over 100 in grasshoppers. Figure _ reveals the close-up view of the sperm tube/follicle. (c) vas efferens – a structure that holds the individual sperm tube (d) vas deferens – structure holding the whole testes at the base (e) Seminal vesicles – a swollen structure bellow the vas deferens where sperm cells are temporarily stored before mating. The cellular lining of the seminal vesicle is glandular, providing nutrients for the sperms. (f) accessory gland – provides additional fluid and nutrients to the sperm cells for lubrication and active movement to successfully enter the female reproductive tract. Figure _ depicts the male reproductive system.  6 Figure 21. (A) Male reproductive structures; (B) close-up view of the sperm tube/follicles showing vas efferens and vas deferens. Adapted from Elzinga (1978). Figure 22. Structure of the sperm tube/follicles showing the various zones and the developing sperm cells. Adapted from Elzinga (1978).  7 MODES OF REPRODUCTION 1. Sexual reproduction - is the type of reproduction wherein both male and female gametes (sperm and egg cells) are needed for fertilization. This type of reproduction is a common method of most insects. 2. Asexual reproduction - this type of reproduction happens even without fertilization or without the union of male and female gametes. Types of Asexual Reproduction (A) PARTHENOGENESIS – is the production of offspring from unfertilized eggs. Under parthenogenesis, there are two types: a.1. Obligatory: eggs always develop through parthenogenesis. Example: Aphids in the tropics. Here, the egg cell develops into a live young even without fertilization coming from sperm cells. a.2. Facultative: eggs may develop without fertilization or after fertilization depending on conditions. A typical example of this type is the aphids in the temperate regions during the summer season. The insects develop parthenogenetically, but during autumn, they develop sexually of what is called alternation of generation, as shown in Figure 23. Eggs are produced in preparation for the winter season as a form of surviving the hostile environment. Figure 23. Alternation of the generation of pea aphid in the temperate region. Photo courtesy: Wordpress.com. Date accessed: August 12, 2020. Taken from https://cutt.ly/dd0vk6w Also, under parthenogenesis, there are 3 classes, these were: 1. Arrhenotoky: males are produced without fertilization, haploid-diploid situation (common in Hymenoptera-Honey bee, here, unfertilized eggs (haploids) are males who become drones, and fertilized eggs (diploids) are female who becomes workers).  8 Figure 24. A honeybee. Photo courtesy: Wikipedia. Date accessed: August 12, 2020. Taken from https://cutt.ly/kd0bssV 2. Thelytoky: only females are produced. 3. Deuterotoky: eggs may be of either sex. B. PAEDOGENESIS – is the reproduction by the juvenile (immature) form. This type of reproduction occurs in a particular family of the fungus gnats (Cecidomyiidae) and a common flower fly (Syrphidae). Here, the ovaries become functional in females with larval body form, and eggs develop parthenogenetically. Eventually, mother larvae become filled with developing daughter larvae and emerge from the mother and, under certain conditions, produce winged males and females and reproduce sexually. Figure 25. A male fungus gnat. Photo courtesy: University of Wisconsin Milwaukee. Date accessed: August 12, 2020. Taken from https://cutt.ly/Jd0v747  9 Figure 26. A syrphid fly. Photo courtesy: Wikipedia. Date accesed: August 12, 2020. Taken from https://cutt.ly/ad0beZ5 C. POLYEMBRYONY – a condition wherein a single egg instead of cleaving together, separate during mitosis, and give rise to different individuals with identical genetic makeup. An example of this type is the parasitic wasp. Types of Reproductive system of insects based on manner of giving birth 1. Oviparous type – eggs are produced, fertilized, and oviposited by the female insect. The mother insect deposits eggs in precise microhabitat where hosts are located. For this purpose, when the egg hatches, the newly hatched young are already given sufficient food for growth and development. However, during the egg stage, they are exposed to the environment's natural forces, such as the action of parasitoids and predators. Most common insects have this type of giving birth. Figure 27. An eggmass of a Vapourer Moth. Photo courtesy: Beentree licensed under Creative Commons. Date accessed: August 12, 2020. Taken from https://cutt.ly/jd0bvVj 2. Ovoviviparous type – eggs are typically developed and fertilized, but are retained and hatched within the body of the mother insect, usually in the ovipositor. This is of more significant advantage because the laid live young are already feeding and are less exposed to the action of predators and parasitoids. An example of this type is the flesh flies deposited directly on  10 fresh carcass without competition from another larva. Figure 28. A tsetse fly laying live larva. Photo courtesy: Ray Wilson. Date accessed: August 12, 2020. Taken from: https://cutt.ly/id0bSvt 3. Viviparous type – development occurs within the female body but is nourished continuously by the mother even after being laid. An example of this type is aphids and tsetse flies in Africa. Figure 29. An aphid giving birth via ovoviviparous reproduction of giving birth. Photo courtesy: Wikipedia. Date accessed: August 12, 2020. Taken from: https://cutt.ly/Ld0bm6i INSECT REPRODUCTIVE BEHAVIOR It is broadly defined to include all of the events surrounding the insemination of the female by the male and the production of offspring. To an extent, all behavior is molded by its influence on an animal's ability to transfer its genepool to the next generation. The success of the species is dependent on its reproductive potential. Six chronological steps in insect reproductive behavior: 1. Mate Location and Pair Formation Systems which have evolved to bring the sexes together, such as: Use of specific cues – pheromones (most common among insects such as moths and weevils), acoustic signals (common among cicadas, orthopetrans such as grasshoppers, crickets), bioluminescence (fireflies)  11 Use of visual cues (common among butterflies) Swarming behaviors (mayflies) 2. Courtship – common by offering a nuptial gift such as in hanging flies and seed bugs where food is provided by the male insect to court or attract female counterparts. Figure 30. Hanging flies while mating. Note the nuptial gift given by the male fly (left) to the female fly (right, black swollen abdomen) to allow male to mate with her. Photo Courtesy: Thornhil and Gwynee, 1986. Date accessed: August 12, 2020. Taken from https://cutt.ly/Qd0cTtZ 3. Copulation – the union of male and female copulatory organs. Copulatory organ in males is called aedeagus while for females is known as bursa. Figure 31. Copulating dragonflies. Photo courtesy: Wikipedia. Date accessed: August 12, 2020. Taken from: https://cutt.ly/kd0bk2E 4. Insemination – is the transfer of sperm cell from male to female reproductive tract particularly stored in the spermatheca. 5. Fertilization – is the union of male and female gametes to produce a diploid chromosome number 6. Oviposition – is the act of laying eggs in insects. Concerning your exercise in insect rearing from Module 1, lesson 1 (Insect growth and development), continue to observe your tortoise beetle until they Application oviposit or lay eggs. Try to find any courtship behavior before mating. Also, see the mating behavior and record the time that mating lasted. This is for the sexual mode of reproduction activity. For the asexual method of reproduction, collect adult bean aphid, Aphis craccivora, banana aphid, and Pentalonia nigronervosa. Provide fresh food and observe for their viviparous  12 behavior, a method of delivery wherein live young are laid by the female insect. Make documentation of all activities conducted. Good luck. Congratulations! You've finally made it! You now have a full understanding of the structures and functions of the reproductive systems of insects. You Closure know that there is an asexual mode of reproduction occurring among insects, which explains their success for the struggle for existence. You have also determined the insect reproductive behavior and uncovered how they locate mates until they oviposit. The activity you have performed and completed in this lesson prepared you for the succeeding lessons. Keep going!  13 Let’s do the bioefficacy trial Application Conduct a simple bioefficacy trial in your garden or farm. Make three treatments to be replicated four times. Choose a short-lived vegetable crop, such as pechay. Make 12 micro plots (3 treatments x 4 replications = 12 plots, measuring 1-meter x 1.5 meters per micro plot) arranged in Completely Randomized Design. Using the procedure from the bio-efficacy trial, collect data such as the number of pests and natural enemies before and after applying your treatments (your treatments are 2 different kinds of pesticides that are intended to be used for pechay insect pests, while the third is untreated). Your application of treatment will start when there is enough population of the pests (e.g., aphids, cutworms, flea beetle) in the plant. Raise your crop following the recommended cultural practices of planting pechay, considering the distance of planting, weeding, fertilizing, harvesting, etc. Use the Philippines recommend for pechay production as your reference using this link https://cutt.ly/ssFHSA8. Please take note that only fungicide/bactericide shall be applied throughout the micro plots to manage diseases of pechay since our treatments are insecticides, which shall only be applied when necessary, as indicated in the above treatments. Start collecting data one day before application and 3 days after applying treatments to count insect pests, pollinators, and natural enemy populations (spiders, ladybird beetle larva and adult, wasps, lacewing larvae, syrphid larvae, etc.). Collect your data through visual counting of the insect population to start at 6:00 AM. Repeat procedure of application when pests reappear in the later stage of the crops' growth. Analyze your data statistically following the CRD ANOVA and comparison of means using Honest Significant Difference. Make a scientific report of your findings. Place your result in your activity notebook. Good luck. Congratulations! You are now introduced to insect toxicology on how Closure poisonous pesticides into living organisms. You have also understood the various ways of classifying pesticides and the regulations of pesticides in the country. Moreover, you have also informed on how pesticides are developed and named. Finally, you have known how to measure pesticide toxicity to living organisms. The next lesson that you will hurdle is the classification of pesticide based on mechanism of action and explain the basics of how pesticide poisoned the target organisms. Further, about the next topic, you will also inform how pests can resist insecticides through the development of resistance to the treatment and how to delay or manage resistance development. I hope that you will have a beautiful day ahead of you as you proceed to the next lesson. Good luck.