SEC-1-P_TOPIC_2
Methods of Collection, Preservation & Identification of Economically important insects
Environmental conservation, pesticide reduction, agricultural productivity, food affordability, and global trade are all challenges faced by human society. The study of economically important insects is becoming increasingly significant. Substantial economic losses are caused by pest species each year, while vital services like pollination and pest control are contributed by beneficial species. For effective research and management, it is imperative that specimens are properly identified and preserved.
- Objectives:
To know the pest occurrence of the locality.
To study the taxonomic character of insects.
To keep the different insects in museum.
To study the bionomics of pests.
- Equipment required for insect collection:
1) Insect Collecting Net : Length is nearly 2 ft. with handle, having circular iron of ring of 1 ft. diameter attached to it. Ordinary mosquito net attached to the iron ring looks like a bag like collecting net structure, which is used to catch the flying insects.
Collecting nets are of three types:
- Aerial nets- Very light weight, designed especially for collecting flying insects including butterfly.
- Aquatic nets - Helpful for gathering insects from water.
- Sweeping Nets: It is moved quickly through foliage, shrubbery and other vegetation to dislodge insects feeding or resting on foliage.
2) Insect Storage Box : Insect storage boxes are made from seasoned wood with intact, dust-proof joints. The bottom and top are covered with cork sheets, which makes it easy to mount pinned insects. After drying, insect specimens are transferred to these boxes, which are then used to store the specimens.
3) Insect Killing Bottle (Ethyl acetate; used for terrestrial insects): For terrestrial insects, a glass bottle with a metal lid and a thin layer of plaster-of-Paris at the bottom is used. The plaster layer is saturated with ethyl acetate, which then kills the insects placed inside by asphyxiation. The most important chemicals used to kill insects are sodium or potassium cyanide, chloroform, and ethyl acetate.
4) Insect Setting/Spreading/Stretching Board : A groove runs down the middle of this board to hold the insect's body, while its two flat pieces support the wings. The specimen (for example, a butterfly) should be pinned through the thorax using a pinning block. Next, place it on the mounting board so that its legs and body are in the central groove with the dorsal surface facing up. Carefully pull the wings into the desired position. A strip of paper should be placed across them and held down with pins to keep the wings in place. This process should be repeated for each wing.
5) Small Hair Brush
6) Entomological Pins of different sizes.
7) Insect Rearing Cages
8) Insect Killing/Preserving Media
9) Aspirator : A glass tube, which is fitted with a rubber cock, is used for collecting small insects. The rubber cock has two holes, into which two small tubes are fitted. One of these two tubes is longer and is used for sucking collected insects so that they cannot escape. The other tube is further fitted with a rubber tube which is used to collect smaller insects. After the insects have been collected, 70% alcohol may be added to the specimen tube to preserve them.
10) Hand Lens
11) Forceps/Needles of different sizes
12) Specimen tubes and Glass Vials [Used for aquatic/soft bodied insects]. Insect specimen may be preserved in 70% Ethyl alcohol.
13) Sweep net
14) Aerial net
15) Aquatic net.
- Collection:
Locating insects:
1. On plants
2. In/On decaying matter
3. Under rocks, leaf litter
4. In/On water with nets
5. On animal/birds body
6. In crevices.
7. Camp lights, mercury vapor lighted around stores & gas stations.
Method of Preservation of Hard bodied insects:
Materials required: Killing bottle, Entomological pins, Setting board, insect store box, drying chamber etc.
a) Preparation of killing bottle-
A wide-mouthed bottle with a capacity of 500g and a tight metal screw cap/lid should be washed and dried. At the bottom of the bottle, one or two spoon of potassium cyanide or sodium cyanide are placed. This poison is then covered with a layer of plaster of Paris that is 2-3 cm high. Two drops of water are added, and the plaster of Paris layer is allowed to harden. After a couple of days, a circular blotting paper is placed over it, and the bottle is ready to be used.
Precaution:
i) Killing bottle should never be kept open as it gives out hydrocyanic acid gas
which is poisonous.
ii) The bottle must be labelled as “POISON”
iii) Broken pieces of the bottle should be disposed-off by burying.
iv)Do not keep the lepidopterans insects simultaneously with other insects.
b) Mounting the insect specimen: If collected specimens are not mounted immediately, they become very hard and brittle. Before mounting, such insects are relaxed. Relaxation is performed in a wide-mouthed, airtight jar that is filled with moist sand and covered with blotting paper. To prevent mold formation, a few drops of carbolic acid are added to the jar. The insects are then placed in this container for a day or two.
c) Pinning: This is the best method for preserving hard-bodied insects. Pinning facilitates convenient handling and safe storage of the specimens for study purposes. Special rust-proof entomological pins, which are made from a mixture of brass and nickel, should be used. The pin should be inserted vertically through the thorax.
As a rule, one-third of the pin must be above the insect's body, and two-thirds must be below. Once pinned, the insects are carefully placed on a setting board and then kept in a drying chamber.
For Lepidopterans, the wings must be spread before they are placed in the drying chamber. The hind margin of the first pair of wings should be at a right angle to the body. Finally, the specimens should be labeled with their scientific classification, locality, host plant, date of collection, and the name of the collector.
d) Drying: Insect specimens after pinning should be kept in drying chamber to avoid rotting. After drying, the specimens are transferred to insect stored box.
e) Storing: Pinned insects are to be stored in the insect stored boxes for preserving them in safety for longer period. Dried specimens become very brittle and extreme care is to be taken while handling the specimens. The specimens without legs or antennae are considered are useless. Only best specimens are to be preserved. The proper time of insect collection is early morning or at night with the help of light traps. Mercury light is always attractive to the insects than any other light.
f) Protecting insect collection: It is often difficult to avoid mould developing on newly caught and imperfectly dried specimens, especially in damp climate. Before keeping specimens, it is desirable to treat the boxes with saturated solution of naphthalene in benzene. Few drops of carbolic acids on cotton balls are also kept in these boxes at regular intervals to avoid fungus attack on specimens.
If collected insects in store boxes are attacked by dermastid larvae, ants and other pests and repellent action of naphthalene is in sufficient, it is necessary to fumigate the boxes by fumigants viz; ED, CT, CS2 etc.
Method of Preservation of soft bodies insects:
Soft-bodied insects such as aphids, jassids, thrips, midges, scales, bugs, and the immature life stages of insect pests are preserved in 70-75% ethyl alcohol with a small amount of glycerin. This is done in small specimen tubes or glass vials, which are then properly labeled. These insects are also preserved in a 5% formalin solution.
Permanent Mounting: Very small insects can also be preserved by mounting them on permanent slides. This method is also used to study their various structures and stages. The insects to be preserved are boiled in a 10% KOH solution for a few minutes before being passed through 20-100% alcohol for dehydration. They are then mounted on cavity slides in Canada balsam.
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