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In this article we will discuss about the collection and structure of arthropods.
Arthropods are collected in different ways. Those living in open are sensitive to light and collected by light trap. Those living in soil are extracted by application of heat.
I. Light Trap:
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Some insects are attracted by light. Light trap is used to collect them. The light traps attract and destroy the adult moths.
Types of Light Trap:
A. Simple light source:
In villages Hurricane lamp or Hasack is used as the light source.
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Components of Light Trap:
1. Two wooden stools—(a) one fairly large square/rectangular, of about 60 cm height, (b) one small, round, of a low height.
2. A large round pot.
3. A hurricane lantern/hasack (light source).
The round pot is partially filled with kerosene oil-water mixture and placed on the large table. The small stool is placed on the pot; the light source is put on it and strapped with the large table (Fig. 46.1). The set is placed on the side or middle of paddy field at night. The insects attracted by the light assemble around the lantern and fall in the kerosene-water mixture.
B. Electric bulb type:
An electric bulb is fitted on a frame fixed above a galvanized iron funnel. A cyanide bottle is fitted at the lower end of the funnel (Fig. 46.2). The attracted insects rush to the light source, fall in the funnel, slip into the cyanide bottle and die.
The dead insects are collected from:
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(a) Kerosene-water mixture,
(b) Cyanide bottle and processed following standard technique for preservation and identification.
The common insects are:
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i. Tryporyza incertulus, a stem borer of paddy.
ii. Chilo suppressalis — paddy pest.
iii. Leptocorisa varicornis — paddy pest.
In addition, other moths may be collected in the process. Identify up to order Lepidoptera.
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II. Extraction of Soil Micro Arthropods by Heat:
Soil micro-arthropods are extracted with Tullgren funnel by application of heat.
Components of Tullgren Funnel:
(Fig. 46.3)
1. A large metallic funnel with a fine wire gauge sieve, soldered at the junction of the body and the stem.
2. The funnel is held in position with a clamp.
3. A clean beaker containing 70% alcohol is placed below the funnel. The stem of the funnel stands above alcohol level.
4. A 40-watt electric bulb is fitted above the funnel, close to it. Several such sets (Fig. 46.3) may be fixed in a frame for increased efficiency.
Procedure:
1. Collect known amount of soil from different localities.
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2. Break the clods and spread the soil uniformly on the sieve of the funnel.
3. Switch on the bulb and record soil temperature.
4. Leave it overnight.
The soil temperature can be regulated by adjusting the distance between the soil and the lamp. With the rise of temperature the arthropods move away from the soil surface and at about 50°C all of them drop into alcohol in the beaker.
The arthropods are collected, identified and separated. The number of each species is counted for each soil sample and recorded. A comprehensive account of arthropod population in different soil samples is obtained by the method.
Soil Micro Arthropods:
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1. Springtail (Orchesella sp.):
(Fig. 46.4)
a. Body divisible into head, thorax and abdomen.
b. Abdomen 6-segmented.
c. Mouth parts biting.
d. Thoracic legs three pairs.
e. A retaining hook in the 3rd segment acts with a springing organ on the 4th abdominal segment.
Systematic position:
Phylum — Arthropoda
Class — Insecta
Subclass — Apterygota
Order — Colembola
2. Termite (Termes sp.):
(Fig. 46.5)
a. Soft-bodied, white or light yellow colour.
b. Antennae moniliform.
c. Mouth parts biting and chewing.
d. Tarsi four segmented.
e. Wings when present, long, slender and membranous.
f. 4 casts: Winged males and females. Wing less workers and soldiers.
Systematic position:
Phylum — Arthropoda
Class — Insecta
Subclass — Pterygota
Order — Isoptera
3. Beetle:
(Fig. 46.6)
a. Integument horny or leathery.
b. Fore-wings or elytra horny.
c. Hind-wings thin and membranous.
d. Mouth parts biting and chewing.
Systematic position:
Phylum — Arthropoda
Class — Insecta
Subclass — Pterygota
Order — Coleoptera
4. Beetle larva:
(Fig. 46.7)
a. Body elongated and segmented.
b. Head distinct, black and sclerotised.
c. Pro-legs short and inactive.
5. Ant:
(Fig. 46.8)
a. Body with distinct head, thorax and abdomen.
b. Junction between thorax and abdomen much constricted.
c. Mouth parts biting or licking type.
d. Tarsi 3 to 5 segmented.
e. Wings when present, fore-wings or elytra horny or leathery; hind-wings membranous.
f. 4 casts : Winged males and females. Wing less workers and soldiers.
Systematic position:
Phylum — Arthropoda
Class — Insecta
Subclass — Pterygota
Order — Hymenoptera
6. Mite:
(Fig. 46.9)
a. Body ovoid, flattened and un-segmented.
b. Thoracic appendages 4 pairs.
c. Chelicerae small; pedipalpi long, 5-jointed and leg-like.
d. Mouth parts biting and sucking.
Systematic position:
Phylum — Arthropoda
Class — Arachnida
Order — Acarina
7. Pauropod:
(Fig. 46.10)
a. Body with twelve segments.
b. Nine pairs of legs.
c. Antennae branched and delicate.
Systematic position:
Phylum — Arthropoda
Subphylum — Mandibulate
Class — Pauropoda
8. Symphyla sp. (Garden centipede):
(Fig. 46.11)
a. Body divided into head and trunk.
b. Legs 7-12 pairs.
c. Antennae un-branched and beaded.
d. A pair of cerci and sensory hairs present.
Systematic position:
Phylum — Arthropoda
Subphylum — Mandibulata
Class — Symphyla
