Locust Life Cycle



Introduction

Locusts are pests that belong to

  • Phylum- Arthropoda

  • Class - Insecta

  • Order - Orthoptera

  • Family - Acrididae.

They are both short-horned and long-horned insects including crickets and grasshoppers. Locusts species vary depending on their characteristics. Example: Schistocerca gregaria (desert locust) found in North Africa, the Middle East, and the Indian subcontinent, iLocusta migratoria (migratory locust) swarms in Africa, Asia, Australia, and New Zealand. They can be both gregarious and solitary. Many agricultural crops are destroyed due to swarms of locusts. They look very similar to grasshoppers and are often confused with them.

Behavioral Traits of Locusts

Locusts exhibit two interconvertible behavioral phases i.e. solitary and gregarious. With the change in population density the behavior of locusts changes. At low population density, these individuals behave as solitary and when the population density is high they behave as gregarious pests and form swarms destroying crops.

Growth Stages of Locust Nymphs

The locust's nymph growth stages (instar), based on characteristics of developing wings are as follows −

1st Instar

  • Newborn locust’s nymphs are white and within 1-2 hours they turn black.

  • No obvious wing buds are present.

  • The growth occurs in a downward direction.

  • The 1st segment is narrower than the 2nd.

2nd Instar

  • Exhibits large head and pale body color and a conspicuous pattern is seen.

  • The breadth of both wings is equal.

  • Two segments are present, from which the first segment is larger than the second.

  • The base of each segment contains a rudimentary wing bud.

3rd Instar

  • On either side of the thorax are two pairs of wing buds.

  • Wing buds are angled backward and distinctly spade-shaped.

4th Instar

  • The color is conspicuously black and yellow.

  • The inner surface becomes the outer surface when the wing buds are flipped.

  • The first wing bud is covered by the second wing bud; it is approximately onethird the length of the abdomen.

5th Instar

  • The color is bright yellow with a black pattern.

  • The second wing bud obscures the first and about half the length of the abdomen.

  • The tympanic organ is covered by the wing.

Identification of Male and Female Locust

  • Mature male and female locusts can be identified on the bases of the tip and shape of the abdomen. In males, the tip of the abdomen is smooth and round in shape due to the presence of a subgenital plate covering the reproductive organs. In females, the tip of the abdomen is serrated because of the presence of the ovipositor which contains upper and lower jaws.

  • Depending on the quality and availability of the food at the nymph stage, the size of the locusts is determined. Size is not the appropriate character to differentiate sex. Male locusts are smaller than their female counterparts.

Life cycle of Locusts

Locust undergoes an incomplete or direct metamorphosis. There are four stages in the life cycle of locusts.

Stage 1- The Egg

  • After fertilization, the female locust usually deposits her eggs inside holes made in warm, damp pods.

  • To ensure hydration and protection from predators, a frothed liquid is produced by female locusts.

  • After this egg undergoes further development and enters the nymph stage.

Stage 2- The Nymph

  • After 10- 14 days of laying eggs, they hatch and nymphs or hoppers come out.

  • Gradually as the nymph grows, they mold 5 times called instar stages.

Stage 3 - The Fledglings

  • After the 5th instar, even though nymphs have fully grown wings they are still soft and fragile so they are not able to fly yet.

  • During this stage, the exoskeleton becomes harder.

  • They consume large amounts of plants in order to conserve energy for wing development and reproduction.

Stage 4 - The Adult

  • The fledglings become sexually mature after about 2 weeks.

  • Locusts are constantly migrating and feeding during this stage.

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Natural Enemies of Locusts

There are many natural enemies which reduce the population of locusts. They are −

  • Egg Parasites − Locusts and grasshopper eggs are attacked by small wasps of genus Scelio which are parasitic in nature.

  • Flies (Diptera) − These can kill and reduce the fertility of locusts thus acting as parasites to them.

  • Mites − Tarsonemid mites (tracheal mites) live inside the locust tracheae. When the locusts spread their wings, the eggs are visible on the dorsal surface of the locust. Attached to the wings and body of predominantly old locusts, is Leptus sp. (body mites) which are red mite larvae. The host remains unaffected here.

  • Nematodes − One of the important parasites of locusts and grasshoppers are Roundworms. They are commonly found in areas of heavy rainfall. And are seldom in dry areas.

  • Protozoans, fungi, bacteria, viruses, and predators are also proved to be harmful to locusts.

Conclusion

Locusts are pests that belong to Phylum Arthropoda, Class Insecta, Order Orthoptera, and Family Acrididae. They look very similar to grasshoppers and are often confused with them. Locusts exhibit two interconvertible behavioral phases i.e. solitary and gregarious. With the change in population density the behavior of locusts changes. Locust undergoes an incomplete or direct metamorphosis. There are four stages in the life cycle of locusts- egg, nymph, fledglings, and adult. They are pests and destroy agricultural crops.

FAQs

Q1. What is the life expectancy of locusts?

Ans. The life expectancy of locusts is about 10 weeks after reaching the adult stage in the life cycle.

Q2. What are the differences between grasshoppers and locusts?

Ans. Locusts look very similar to grasshoppers and are often confused with them. But there are differences that can be looked at so as to differentiate between the two. Some of them are -

  • Locusts show the following two behavioral states: solitary and gregarious, Grasshoppers do not show such behavioral states.

  • With low population density, locusts and grasshoppers both exist as individuals. But with high population density, phase polyphenism (physiological and behavioral changes) takes place, forming gregarious behaving swarms of adult locusts.

Q3. What is the period of sexual maturity in locusts?

Ans. The time period for achieving sexual maturity varies; under favorable conditions, adults may mature in 3 weeks, and under unfavorable conditions, they can mature in 8 months.

Q4. How do protozoans act as natural enemies of locusts?

Ans. Inside the midgut of locusts there are protozoans living in the form of cysts, which are attached to the lining of the gut. When the gut of the host is heavily parasitized it appears yellow in color. Many such parasites disturb the process of digestion, cause a reduction in female fecundity, or can even kill the host.

Q5. What type of back legs are present in locusts and what is their function?

Ans. Large back legs are present in locusts. They help them to hop or jump.


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