Pulse Beetles and Its Types | Insects | Invertebrates | Zoology

In this article we will discuss about the pules beetles and the pests which belong to their family affecting the stored foods.

The pulse beetles belong to one rather small family named Burchidae, just as all the pulses belong to one family of plants called Leguminosae. The Bruchids, as these pests are commonly referred to, are small beetles rarely exceeding half of a centimeter in size and with very characteristic facies which clearly distinguish them from other pests of storage.

Their characteristic appearance is mainly due to their small head with a blunt snout, the femur of the hind leg specially thickened, truncated elytra which do not cover the posterior portion of the abdomen, the abdomen also peculiarly thickest and serrate or pectinate antennae. The majority of the Bruchids attack the leguminous pods in the field where from they are carried to storage godowns.

However, they do really serious and spectacular damage under storage conditions. Pulse-seeds are often brought out from the storage godowns in a miserably damaged conditions, each grain being studied with a number of whitish scale-like eggs or egg-shells and a number of prominent circular exit-holes from which the adult Bruchids have already emerged.

In the field, the eggs are laid on developing leguminous pods either on the outside or inside of the pod and the larvae hatching out from these eggs bore their way up to and into the soft, developing grain inside the pod. Since the larvae are very tiny at the time of boring, the entry hole is generally not only too small to attract notice but it also soon get healed up.

Also the pulse-grain matures earlier than the insect inside and the result is that the grain is harvested and stored in an apparently healthy condition even though the internal infestation may be quite high. That is the reason why the farmer gets a shocking surprise on finding his grain completely spoiled although he has taken reasonably good precautions not to allow insects to get into his stored grain.

The beetles often lay a number of eggs on each grain, depending on its size, and these eggs look like yellowish white round scales very prominent against the contrasting background of the grain surface. The eggs hatch within a few days and the larvae bore into the inner wall of the egg-shell, which is in direct contact with the grain surface and then bore into the grain.

Thus unlike other eggs those of Bruchids do not show up the exit holes even though the larvae have already hatched Inside the grain. The pupal period lasts only a few days after which the beetle emerges by further cutting out the circular disc into an emergence hole. As regards the specific requirements for Bruchids, the species, which has been, studied shows that it can breed in pulse grain with even less than 6 per cent moisture content.

Hence keeping the grain dry does not constitute a dependable insurance against damage by this pest. It is, however, becoming clear that some stages are quite susceptible to reduction in oxygen tension. Thus, from the viewpoint of control, it is more like khapra than like Sitophilus.

1. Rice Moth (Corcyra Cephalanica):

It is widely distributed in Asian, European and African countries as well as in America. It is a serious pest of stored grain in India, Pakistan and other countries of Indian sub-continent. It damages the stored grains of other variety like gram, sorghum, maize groundnut and other food materials as well as rice. The larva is the destructive from which causes the damage to the cereals.

Quite active during night hours the moth is reported from March to November. The winter season is passed out in the larval form and next generation comes some times in February or March. The moth is very active, small buff coloured structure. The males are smaller than the female. The abdomen of female is swollen rounded and smooth where as that of the male is cylindrical and tip is pointed.

The wings are with fringed margin. Conspicuously large eyes are the characteristic feature. The male and female both are the non-feeding stages. The female lives for 4-6 days under normal suitable conditions and mates only once within 24 hours after her emergence and lays eggs.

The eggs are shiny white, small, rounded about 200-250 in number. They are laid singly or in group of two and three on the grains, bags, walls of godown in the cracks crevices or any other such places where conditions are favourable. They hatch in 6-8 days.

The larvae are small pale yellow or dull coloured with yellowish brown head; they soon migrate to a short distance and attack on the grains. They web a silky net and spoil the grains. Full grown larvae are about 2 cm. and dirty white in colour. It takes about 25-30 days for a larva to complete its all the give instar stages then it pupate. Pupae are brownish yellow coloured, within die cocoon with attached grains. The pupal period varied from 6-10 days. The insect over winter in the larval stage and sometimes in pupal stages.

They cause damage to the grains and render them unfit for human consumption.

2. Indian Meal Moth (Plodia Iterpunctella):

It is a worldwide pest infesting grains, food, meals and breakfast products of soybean, herbs dried plants, dead insects and other small animals. Extensive damage is caused by the caterpillars, which web and contaminate the cereals and render them unfit of human consumption. They crawl a short distance only.

The larva is small 1.5 to 2.00 cm. in length, dull coloured, brownish yellow head oval thorneic plate on the back and with white or pink tinge. The total larval span varies from 30-35 days and the pupal from 4-35 days. It passes the unfavourable time as pupal stage. The pupa is safe inside the silken cacoon.

The moth measures about 1.5-2 cm. across the wings. It is a small, active and non-feeding form. The dorsal portion is with coppery lusture and the rest with whitish grey in colour. Female lives a short duration and lays eggs on cereals and bags in groups, about 300-350 eggs are laid which are oval, creamy white with an incubation period of 2-4 days which can be extended up to two weeks depending upon the condition of the weather. These are highly active during mild summer and humid conditions. The winter is passed in larval stage.

The damage can be checked by applying suitable control measures in the godown as spreading of DDT powder or BHC on the floor or spraying of godown with 10% BHC or DDT. Proper storage and hygiene at the time of the storage helps in minimising the loss. The larvae can be killed by using chemicals or by exposing grains to the sun.

3. Almond Moth (Ephestia Cantella):

A common pest of stored dry fruits. This moth is little bigger than the rice moth and is active in evening hours. It attacks on the dried fruits like walnut, fig, apples, almond, tamarind seeds, dates and barriers besides this it has a wide range of attack on the milk products dried fruit pulps and figs. It is known as fig moth, grey in colour the moth measure about 1.5 cm. across the wing buff coloured with greyish wings provided with transverse strips on the outer region.

The eggs are small about 50-60 in number, shiny white, oval in shape and are laid particularly on the hairy surface or in the grooves of the fruit.

The larvae are about 1.2 cm. large, pinkish coloured and with white tinge. It causes the great damage and makes tunnel in the fruit. Spines silken thread spoils the food and the tunnel is filled with excreta. The larval period stands for 40-50 days. They have a tendency to migrate from one to another fruit so damage is done up to great extent.

The pupal period varies from 10-12 days. Pupa is protected inside a pupal cacoon. Generally 5-6 generation in a year.

4. Khapra Beetle (Trogoderma Khapra Arrow/T. Granarium):

The beetle is reported from all parts of the world but it is a serious pest in Indian sub-continent, Asian countries and some of the European nations. It attacks on the stored grains on the superficial layer only but in acute cases may enter the whole lot. Generally it is unable to penetrate deep. In India it very common in warm climatic parts with humid atmosphere. It attacks the dry region of Punjab, Haryana and Rajasthan too.

Besides wheat it attacks on gram, barley, rice, maize and other stored grains. It attacks the dried fruits and pulses also.

The larval stage is the most harmful stage. The grub feeds upon the grains and spoils the lot.

The small, dark brown, shiny adult is about .25 cm. in length. Female and the male can be distinguished on the basis of their external colour and the shape the males are smaller and darker in colour than the female. The antenna in male is more pointed; otherwise they possess club shaped antennae and setractile proboscis. They are incapable of flying.

They copulate 2-3 days after emergence and lays white, small, cylindrical eggs, which are rounded at one end and pointed at other end. There are translucent and laid in cluster of 1-5. In total 80-85 eggs are laid within a span of 7 days. The eggs hatch in 3-6 days. Maximum numbers of eggs are laid on the first day. Temperature and humidity play important role in the hatching. The newly emerged grub is small about 1.5 mm. in length yellowish, white in colour with dark shining black head.

A full-grown larva is brown in colour and about 4 mm. with long hairy brittle and yellow brown bands on the body. The integument between the segments is of different colour. Male and female larvae have different span of life. The male feed for 20-30 days while those developing into female continue for 20-40 days, but in adverse conditions may extend its larval phase. They possess a bunch of long brittle at the end of the body.

They pupate in the grains and in the larval skin. The pupal period stands for 4-6 days or up to 18 days. Generally 4-5 generations are completed in a year.

5. Rice Weevil (Sitophilus Oryzae) Linnaeus:

Most widely distributed pest of store grain S. oryzae is common in almost all parts of the world particularly in warm climates. India is considered its native land and on the account of its breeding in the field and stores of rice it is known as rice weevil. But it causes damage to almost all the cereals like, wheat, gram, bajra, jwar and maize. The attack is sudden and more severe in moist and humid conditions.

Previously known as Calendra oryzae. This pest is known for its habit of attacking the standing crop if available in nearby areas in ripens stage. Adult as well as the larvae both damage the grains. Mansoon is supposed to be the worst season when the attack is maximum. They not only damage the grain and make unfit for human consumption but they destroy their germinating capacity also rendering the grain useless for germination.

The adult is small cylindrical about 4 mm. with a long snout projecting downwards. The colour range varies from red brown to dark brown or black. Thorax is provided with round depressions and yellowish marks are found on elytra. The males are smaller and look weak than the female and bear a shorter rostrum.

The female mates the first day after the emergence and starts laying eggs. The eggs are laid singly or in-group of 2-3 in the excavations made in the kernel of the seed. The excavations are made by the strong mandible and the whole in later on blocked by the gelatinous glue. 150-400 eggs are laid by the female depending upon the climate and condition of the grainary. The eggs are oval, translucent, white and about .6-. 7 mm. in length. The hatching takes place within 4-9 days.

The newly emerged grub is a dirty white or yellow coloured minute structure with a dark brown head. It starts feeding upon the kernel of the seed and develops inside. Generally one larva per seed is seen but the number may vary depending upon the size of the grain. The larva eats voraciously and grows in size up to 5 mm. in length. 19-34 days are required for full larval growth.

The full-grown larva pupates inside the grain and before pupation it undergoes 1 -2 days as prepupal stage when the movement is slow and larva stops feeding. The pupae are small and dirty white which later on turn black or brown. Pupal stage lasts for 3-6 days but under unfavourable conditions it can be extended upto 20 days also. The adult may live for 4-5 months and 4-5 generation in year is reported. They take about 25-30 days for a complete life cycle.

There are few natural enemies which parasitize the grub e.g. Aplestomorpha calandrae. How. (Hymanoptera: Pterometidae) Larrophagus distenguendus Forst (Hymenoptera: Chaleidiae).

6. Tribolium Castaneum Herbs Rust Red Flour Beetle:

Cosmopolitan in distribution, this beetle is a serious pest of stored grains like wheat, rice, jawar, bajra, maize or any other grain available in the store. They generally attack the broken and ruptured grains but in case of bajra they have been reported to attack on the complete grain also. The beetle as well as the larva both is injurious for the godown. They not only destroy the grain but also change them into powder form.

In severely infested stages the colour of the grain is also changed. Because the insect produces a gelatinous product which adheres the grain side by side secondary infection of the mould also attacks the store which makes the food unhygienic for human consumption.

The beetle previously known as “Bran bug” is supposed to be predator also. It not only attack the grains but inhibit the flour also where the development is more rapid and pests are healthier. These are very particular about wheat godowns.

The adult beetle is bright red to almost black insect. These are very active and vary from 3-4 mm. Cephalic capsule is prognathous, the eyes large the antennae elevate, prothorax freely movable. Elytra and second pair of wings well developed but they cannot fly for long. Male is smaller than female.

The adult breeds in April October and over winter in adult stage. They copulate one -two days after the emergence and lays about 350- 1000 eggs depending upon atmospheric conditions. The eggs are transparent and cylindrical and sticky. Incubation period ranges from 4-12 days. The larvae are small thin slender and cylindrical with a large number of fine bristles on the body and a terminal appendage. Larval period varies from 27-90 days and moults from 5-6. It is 6-7 mm. in length when fully grown and cream coloured with black head.

Fully grown larva passes one or two days prepupal period as dormant days and then changes into pupal conditions which are white tending towards brown. Entire body is covered with small bristle. Sexual dimorphism is clear at this state. The last segment in case of ♀ possess a flat disc like depression, ventrally and two conical appendage in case of female. The pupal period stands for 1-2 weeks. One complete life cycle takes about 6 weeks and 2-3 brood in a year.

7. Lesser Grain Borer (Rhizopertha Dominica):

It is a pest of Indian origin now distributed almost all parts of the world: It is a known pest of Japan, China and most of the Asian and American countries. Besides wheat it has a variety of choice for food as maize, sorghum, barley, to dried potatoes, biscuits, corn-flour, beams and tamarind and millet seeds.

Both adult and grub damage the crop. Adults are more destructive than the larvae they not only consume the food but tender them useless for human consumption. Both the larvae and the adult feed on the starchy portion of the grain leave the outer shell. The powder is left useless. The full-grown larvae are found outside whereas the first instar is always inside the grain.

The adult is 3 mm. in length, black in colour with deflexed head covered with a hood shaped pronotum. The antennae are club shaped. The pest is active in summer and monsoon seasons and over winter either as adult or larva.

The insect is active during March to November and by first week of April oviposition starts. 300-400 eggs are laid either singly or in batches and are glued together. They are .6 mm. in length, oval, white and ornamental structure. Incubation period varies from 5-9 days.

The tiny grub, straight in built, grey or white or cream coloured in colour emerges and feeds upon the starch and makes tunnel in the seed. It is about 3 mm. longer and hairy with dark brown head and elongate body. The average larval period is about 36-40 days and moults 4-5 times.

Prepupal period is of one day and pupal for 7 days. The total life cycle is completed in 30-32 days. There are 5-6 generations in a year.

Biological control can be done by the mite pediculoides spp., which attacks the larvae and eggs. The chalcid parasite Lariophagus spp. attacks the larva and pupa.

8. Gram Dhora (Callosobruchus Chinensis):

Previously known as Pachymerus (Bruchus) chinensis Fab. Popularly known as pulse beetle, it is native of China but is a serious pest of all type of pulses in all parts of India. Pest is reported on almost all kind of pulses like mung, arhar, peas, cow pea and gram.

It is the larvae, which cause the damage, but the adult is also harmful up to certain level. The larva is cream coloured, small slender with light brown head and hairy body. It is a voracious feeder which makes tunnel and enters the pulse feeds upon and grown in size. A full grown larvae is about 1 cm., white fleshy cylindrical and heavily wrinkled grub. The total larval span is of 17-18 days.

The pupae are small and white coloured which later on turns brown. Pupae period is from 4-20 days depending upon temperature and humidity.

The adult lays eggs in groups of two or three but mostly singly in the cracks and crevices of the seed and grainary, on the upper surface of the seed and other associated parts, eggs are small oval shining and white tiny bodies with an incubation period of 6-18 days.

The moth comes out of the grain by cutting the outer covering of the opening of the tunnel and mates within 24 hours. The life span of adult is 5-20 days and life cycle is completed in 35-40 days, generally 7-8 generation are reported in a year, overlapping each other.

9. Mung Dhora (Collosobruchus Analis):

The minor pest of peas and corn peas, the Mung Dhora is a notorious pest of mung, mash, moth and other leguminous crops pulses. The damage is caused by both larval and adult, maximum damage is done during April to August when almost all the stages are present. The larvae feed and adult breed on the grains and consume almost all the grains. The rest of the grain is left useless either for consumption for sowing.

The life cycle and the mode of development is almost same as in case of pulse beetle.