THE DESERT LOCUST

Mating. 

          The male locust mounts the back of the female, applies the tip of his abdomen to hers and passes sperms into her reproductive tract. The sperms are stored in a sperm sac in the female's abdomen, and as the eggs pass down the oviduct during laying, the sperms are released and so fertilize the eggs.

Eggs. 

          After mating, the female lays her eggs in warm, moist sand following a rainy spell. She pushes her abdomen down into the sand, extending the membranes between the segments, and burrowing to a depth of 50 or 60 mm. In this burrow, 50 to 100 eggs are laid and mixed with a frothy fluid, which hardens slightly and may help to maintain an air supply round the eggs. In 10 to 20 days depending on temperature and moisture, the eggs hatch and the nymphs make their way to the surface and emerge as ‘hoppers’ (like miniature adults but wingless at this stage).

Swarming. 

          If food is in adequate supply and the hoppers are not forced to crowd together when they emerge from the eggs, the locusts live their lives separately as do other grasshoppers. If, however, the hoppers are crowded together for one reason or another, they enter a gregarious phase of activity. The hoppers tend to keep together in a band and move forward together. The crowding effect also results in a change of colour from the normal green, buff or brown to a striking black and yellow (or orange) coloration. There are also structural differences from the solitary form. The bands of hoppers vary in size from hundreds to millions, covering a few square metres or several square kilometres, depending partly on the age of the hoppers and how many bands have combined. As hoppers, they migrate only a few kilometres each day, basking in the early morning sun until their body temperature rises to a level which allows them to move off and eat all the vegetation in their path. When the temperature drops at night they climb bushes and plant stems and remain immobile.

          After the final ecdysis, the adult locusts take to the wing and after a few days of short flights set off on extensive migrations, settling at night and in the middle of the day when it is hottest. A medium-sized swarm may contain a thousand million locusts and cover an area of 20 square kilometres. Such a swarm will consume some 3000 tonnes of vegetation per day; and so if a swarm lands on agricultural crops, the locusts will strip them of every vestige of leaf and edible stem.

The swarms may travel many hundreds of kilometres from their place of origin, e.g. from Africa to India, and the females will lay eggs during their journey, so leaving the nucleus of successive swarms within a few weeks.

Methods of control. 

           The range of the adult locusts is so great that international cooperation is essential for effective control. A swarm may originate in India but cause devastating damage to crops in Africa. Sixty countries in Asia and Africa are threatened by swarms of the desert locust.

          The main method of control is by spreading poisoned bait, for example bran containing insecticide, in the path of the migrating bands of hoppers. The insecticide kills them by being eaten and by its contact with their bodies. Poisoned bait can be used only when the locality of the hoppers is known, and a careful watch must be kept over wide areas so that swarms are discovered as soon as possible after they emerge. The information is then sent to anti-locust centres, e.g. in Nairobi or London, and trucks and personnel are mobilized to take the bait to the appropriate location.

         Other methods employed are to spray insecticides over swarms of hoppers or settled adults using aircraft or motor vehicles, or to spray the vegetation in the path of the hoppers. If the region of egg-laying is known, the vegetation in the area can be sprayed with an insecticide which kills the hoppers at their first meal. The danger with all spraying techniques is that the chemicals used may be poisonous to humans and other animals, particularly if used on food crops.

         Two other species, the red locust and the migratory locust, have been held in check for many years by effective control measures, but the desert locust still constitutes a major threat. Constant vigilance and international cooperation are needed if crops are to be protected against this insect.

Currently it is being discussed whether the hazardous nature of the insecticides and the expense of spreading them is a cost effective way of controlling the desert locust. However, new and safer insecticides are being produced all the time and there is little doubt that farmers whose crops are threatened by locust plagues will want control measures to continue.

Paramecium

               Paramecium is a ciliate protozoan. Ciliates’ bodies are covered with fine cytoplasmic hair-like structures called cilia. Flickering movements of the cilia propel the organism through the water and also create feeding currents. Paramecium is a ciliate. In describing its structure, comparisons will be made with amoeba. It is suggested, therefore, that amoeba is studied first.

Unlike amoeba, paramecium has a distinct and permanent shape and certain areas of cytoplasm, (cell organelles), are specialised to carry out specific functions.

              Locomotion. Individual cilia bend and straighten rapidly in such a way that the recovery stroke offers minimal resistance and the bending stroke helps propel paramecium through the water. The whole complement of cilia beat in a rhythmic pattern, (metachronal rhythm), so that the waves of contraction pass over the cell body like wind blowing through ripe corn.

If paramecium encounters an obstacle, it reverses the ciliary beat and moves back. It then changes direction slightly and moves forward. It will do this repeatedly until it gets past the obstruction. This reaction also shows that paramecium is sensitive to stimuli (in this case, the stimulus of touch).

              Feeding. Paramecium and amoeba both live in fresh water pools or ponds and feed on microscopic organisms such as bacteria and single-celled algae. Amoeba is able to take in food at almost any point on its surface. Paramecium, on the other hand, can take in food only at the cytostome. The cilia in the oral groove create a current of water which wafts the food organisms up to the cytostome where they are ingested in a food vacuole. This food vacuole then follows a specific route through the cytoplasm. On its travels, enzymes are secreted into the vacuole and the food is digested. The digested substances are then absorbed into the cytoplasm.

Any undigested matter is expelled through the anal pore. This contrasts with amoeba which can expel the undigested remains from almost any point.

              Reproduction. Paramecium reproduces, like amoeba, by binary fission. The ciliate stops moving and both mega- and micronucleus divide and move to opposite ends of the organism. The cytoplasm then divides at right angles to the long axis and the daughter paramecia separate. Binary fission may take place 2 or 3 times each day.

There is also a complex sexual process in which two paramecia join by their oral surfaces. The meganucleus breaks down and the micronucleus divides. One of the micronuclei of each individual crosses to the partner and fuses with the remaining micronucleus there. The partners then separate and reproduce by binary fission.

             Osmoregulation. Paramecium and amoeba live in fresh water. Their cytoplasm contains a greater concentration of solutes than their surroundings and so they absorb water by osmosis. The excess water is collected into a contractile vacuole which swells and finally expels water through an opening in the cell membrane.

In amoeba, the vacuole forms near the posterior end but is not associated with a particular structure. Although it empties its contents through an opening in the cell membrane, this also does not appear to be a permanent pore.

             Paramecium has two contractile vacuoles, one at each end, which fill and contract alternately. They are permanent structures and the surplus water is conducted to the vacuoles by a series of radiating channels.

            Other ciliates. There are many other species of ciliate. Vorticella has a stalk which attaches it to pondweed or pond debris and which can retract if the protozoan is disturbed. The cilia do not cover the body but are restricted to a double row on the upper margin. The cilia create a feeding current which wafts food particles into the oral groove.

Characteristics of fish

             Ikan merupakan vertebrata, yaitu mereka memiliki tulang punggung. Dalam kebanyakan kasus tubuh mereka ditutupi dengan sisik yang tumpang tindih. Meskipun mereka sering disebut 'berdarah dingin' suhu mereka bervariasi dengan lingkungan mereka. Ikan tropis akan memiliki darah yang lebih hangat daripada ikan di Laut Utara. Mereka berkembang biak dengan bertelur yang biasanya dibuahi eksternal, yaitu sperma laki-laki atas mereka rilis sebagai mereka melarikan diri dari tubuh perempuan. Beberapa spesies memiliki fertilisasi internal di mana sperma diperkenalkan ke dalam tubuh betina. Ikan bernapas dengan melewatkan arus air ke insang mereka. Banyak ikan memiliki 'ramping' bentuk yang memungkinkan gerakan yang relatif cepat melalui air. Kebanyakan ikan yang berenang dengan gerakan bergelombang tubuh mereka.

Pernapasan
Air diambil dalam melalui mulut, melewati insang dan dikeluarkan melalui operkulum tersebut. Gerakan lantai mulut dan operkulum menciptakan saat ini dan 'katup' (flap kulit) mempertahankan aliran satu arah

sistem peredaran darah
Jantung memompa darah ke depan di pembuluh ventral dan melalui filamen insang di mana oksigen dan karbon dioksida diserap diusir. Kapal punggung membawa darah beroksigen ke seluruh bagian tubuh.

Ikan berenang dengan kontraktor otot-otot di setiap sisi tubuh pada gilirannya. Otot-otot tarik pada tulang punggung dan menghasilkan seperti gelombang undulations yang perjalanan di sepanjang ikan mendorong ke samping dan mundur terhadap air. Komponen samping membatalkan satu sama lain tetapi ketahanan air ke komponen mundur menyebabkan ikan untuk bergerak maju.

Sirip membantu menjaga stabilitas ikan. Sirip dorsal dan ventral mengurangi kecenderungan untuk roll dan yaw. mereka juga membantu dalam mengubah gerakan. Sirip dada dan panggul bertindak sebagai hydroplanes dan kontrol lapangan. Sirip ekor memberikan kontribusi untuk dorongan ke depan.