प्रारम्भिक कीट विज्ञान/१३
TYPES OF REPRODUCTION IN INSECTS PHYSIOLOGY OF REPRODUCTION 1. Spermatogenesis: (occurs inside sperm tube) mitosis Spermatogonia --------> Primary spermatocytes (2n) Meiosis mitosis Spermatids (n) <------- Secondary spermatocytes (n) Spermiogenesis--------------> Sperms (n)
2. Oogenesis : (occurs inside egg tube) Mitosis Meiosis Oogonia ---------> Primaryoocytes(2n) -------> Secondary oocytes (n) Oogenesis Mitosis Ovum (n) <----------- Oocytes (n) <--------- 3. Sperm transfer (i) Intragenital: Common method, through, aedeagus via vaginal orifice into female genital passage. (ii) Haemocoelous: Sperms transfered into the body cavity e.g. Bed bug. (iii)External: Spermatophores are ejected out into open place by male, while female walk over it and gets inseminated e.g. Silver fish. 4. Fertilization: Sperm entre into egg to produce morphogenesis. Egg nucleous divides meiotically into female gamete nucleus and polar body. Then the fertilization occurs by the fusion of male and female gamete nuclei.
TYPES OF REPRODUCTION[सम्पादन]
Majority of female insects are oviparous that is, they lay eggs. Embryonic development occurs after oviposition by utilizing the yolk, e.g. Head louse moths.
Unlike oviparous, here initiation of egg development take place within the mother. The life cycle is shortened by retention of eggs and even developing young within the mother. Four main types of viviparity are observed in different insect groups.
i. OVOVIVIPARITY Fertilized eggs containing yolk are incubated inside the reproductive tract of the female and hatching of egg occur just prior to or soon after oviposition e.g. Thysanoptera, some cockroaches, few beetles, and some flies-(fleshfly). Fecundity of this group is low. ii. PESEUDOPLACENTAL VIVIPARITY This occurs when a yolk-deficient egg develops in the genital tract of the female. The mother provides a special placenta-like tissue, through which nutrients are transferred to developing embryos. There is no oral feeding and larvae are laid upon hatching. e.g. aphids, some earwigs, psocids and polytenid bugs. ii. HAEMOCOELOUS VIVIPARITY This involves embryos developing free in the female's haemolymph with nutrients taken up by osmosis. This form of internal parasitism occurs only in sterpsiptera and some gall midges. v. ADENOTROPHIC VIVIPARITY This occurs when a poorly developed larva hatches and feeds orally from accessory (milk) gland secretion within the uterus of the mother's reproductive system. The full grown larva is deposited and pupariates immediately (eg) tsetse flies, louse or wallaby flies, bat flies.
Reproduction without fertilization is called parthenogenesis. Different types of parthenogenesis are as follows I. BASED ON OCCURRENCE i. Facultative (not compulsory) - e.g. bee. ii. Obligatory or constant (compulsory) - e.g. stick insect iii. Cyclic or spordic : alternation of gamic and agamic population, e.g. aphid. II. BASED ON SEX PRODUCED i. Arrhenotoky: Produce male e.g. bee ii. Thelytoky: produce female e.g. aphids iii. Amphitoky or deuterotoky: produce both male and female e.g. cynipid wasp. III. BASED ON MEIOSIS i. Apodictic : no meiosis occurs ii. Automictic: meiosis occurs, but diploidy is maintained
This form of asexual reproduction involves the production of two or more embryos from one egg by subdivision. Mostly observed in parasitic insects (e.g. platygaster). Nutrition for a large number of developing embryo cannot be supplied by the original egg and is acquired from the host's haemolmph through a specialized enveloping membrane called trophamnion.
Some insect cut short their life cycles by loss of adult and pupal stages. In this precocious stage gonads develop and give birth to young one by parthenogenesis. i. Larval paedogenesis - e.g. gall midges ii. Pupal paedogenesis - eg Miaster sp.