The C-shaped larvae, called grubs, are pale yellow or white. Most adult beetles are nocturnal, although the flower chafers (Cetoniinae) and many leaf chafers (Rutelinae) are active during the day. The grubs mostly live underground or under debris, so are not exposed to sunlight. Many scarabs are scavengers that recycle dung, carrion, or decaying plant material.[4] Others, such as the Japanese beetle, are plant-eaters.
Some of the well-known beetles from the Scarabaeidae are Japanese beetles, dung beetles, June beetles, rose chafers (Australian, European, and North American), rhinoceros beetles, Hercules beetles and Goliath beetles.
In Ancient Egypt, the dung beetle now known as Scarabaeus sacer (formerly Ateuchus sacer) was revered as sacred. Egyptian amulets representing the sacred scarab beetles were traded throughout the Mediterranean world.[2]
The various scarab beetles occupy different habitats. Some are nocturnal; others are active during daytime. Many are good fliers and are attracted to lights at night. Scarabs that feed on decomposing materials, such as dung beetles and green June beetles, are seen on rank and rotting materials. Plant feeders are found on their favorite species of plants: rose chafers on members of the rose family, the delta flower scarab on members of the carrot family, etc. Others eat underground plant parts.
Complex traits like limbs, brains, or eyes form through coordinated integration of diverse cell fates across developmental space and time, yet understanding how complexity and integration emerge from uniform, undifferentiated precursor tissues remains limited. Here, we use ectopic eye formation as a paradigm to investigate the emergence and integration of novel complex structures following massive ontogenetic perturbation. We show that down-regulation via RNAi of a single head patterning gene-orthodenticle-induces ectopic structures externally resembling compound eyes at the middorsal adult head of both basal and derived scarabaeid beetle species (Onthophagini and Oniticellini). Scanning electron microscopy documents ommatidial organization of these induced structures, while immunohistochemistry reveals the presence of rudimentary ommatidial lenses, crystalline cones, and associated neural-like tissue within them. Further, RNA-sequencing experiments show that after orthodenticle down-regulation, the transcriptional signature of the middorsal head-the location of ectopic eye induction-converges onto that of regular compound eyes, including up-regulation of several retina-specific genes. Finally, a light-aversion behavioral assay to assess functionality reveals that ectopic compound eyes can rescue the ability to respond to visual stimuli when wild-type eyes are surgically removed. Combined, our results show that knockdown of a single gene is sufficient for the middorsal head to acquire the competence to ectopically generate a functional compound eye-like structure. These findings highlight the buffering capacity of developmental systems, allowing massive genetic perturbations to be channeled toward orderly and functional developmental outcomes, and render ectopic eye formation a widely accessible paradigm to study the evolution of complex systems.
Beetle common name for insects of the order Coleoptera, which with over 2,80,000 described species, constitutes the largest of the insect orders. The major diagnostic characteristic of the beetle is the modification of the forewings into hardened wing covers, or elytra. These may be rigid, thickened or leathery, and lie over the back, meeting in a middorsal line. The membranous hindwings are used for flight in most species. The elytra serve to support the body during flight and protect the hindwings when at rest.
The body of the beetle is hard but built on the general insect plan consisting of head, thorax and abdomen; in beetles, however, the last two thoracic segments are joined to the abdomen, and the prothorax lies under a protective plate called pronotum.
As members of the largest order, there is a great diversity of form and adaptations in beetles. In many, the elytra are brightly coloured or patterned. The ground beetles (Carabidae) have an oval, flattened body; in water beetles (Hydrophilidae) the underside is very smooth and there are long hairs on the hindlegs that give greater surface when swimming. The ladybeetles (Coccinellidae) are round in contour and flat below; stag beetles (Lucanidae) have enormously enlarged mandibles; a long and backwardly directed antennae and slender body. The fireflies (Lampyridae) have soft elytra and can produce light; weevils (Curculionidae) have their mouthparts at the tip of the snout.
Beetles live on plants, underground, in water, as commensals in the nests of various social insects, in rotten logs and in other habitats. Many beetles are predaceous. Adult ground beetles are nocturnal and feed on various insects and also snails. Both larval and adult diving beetles (Dytiscidae) eat insects and small fish. Ladybeetles eat aphids and scale insects, while soldier beetles (Cantharidae) prefer worms and various insect larvae. Fireflies mostly eat snails. On the other hand, a large number of beetle species eat plants. Certain beetles (Scolytidae) share their arboreal habitat with particular fungi.
Among the beetles, some are subject to a fair amount of predation. Frog, birds and certain mammals are insectivorous and feed on beetles among other insects. Tachinid flies parasitise adult beetles and various wasps parasitise beetle larvae.
Most beetles are bisexual and the females are oviparous although there are a few parthenogenetic species. They undergo a complete metamorphosis. Beetles under the following families are found in Bangladesh.
Carabidae (ground beetles) - Largely ground living forms found under stones, bark, rotten wood and other similar situations. They are carnivorous both as larvae and adults. Calosoma is predaceous on caterpillars.
Cicindellidae (tiger beetles) - Elytra often brilliantly coloured; mandibles sharp. Predatory as larvae and adults. Cicindella sexpunctata is a predator on the rice bug. Hydrophilidae (water scavengers)- mostly aquatic, adults feed on decomposing vegetable matter. Hydrophilus is a common genus.
Histeridae (hister beetles) - Mostly predaceous or saprophagous. The species of Hister is found in dung and decomposing substances. Lampryidae (glow worms, fireflies)- soft-bodied, nocturnal beetles with photogenic organs on abdominal segments 6 and 7. Buprestidae (metallic wood boring beetles)- colour metallic green, golden, bronze, or blue. Larval prothorax large and expanded. Charysochroa sp., an irrideseent green beetle, is common. Sphenoptera gossypii is the cotton stem borer.
Dermestidae (skin beetles) - Both larvae and adults feed on leather, hair, wool, dry meat, etc. Dermestes species, are pests of dried fish. Trogoderma granarium feeds on stored rice and wheat. Coccinellidae (Ladybeetles)- the great majority of the species feed on aphids, coccids, etc; others are phytophagous. Coccinella, Adatia, Chilomenes, Scymnus are the common predaceous genera occurring in Bangladesh; Epilachna species are phytophagous.
Tenebrionidae (darkling beetles) - Red flour beetle, Trilobium species, are pests of flour. Tenebrio molitor is the well-known mealworm, a pest of cereal products. Bostrychidae- species of Sinoxylon and Dinodems are extremely destructive to bamboo and felled trees. Rhyzopertha dominica is a pest of stored grains.
Anobiidae (deathwatch beetles) - Anobium striatum is destructive to furniture. Lasioderma sericorne is the cigarette beetle. Scarabaeidae (scarabs, dung beetles)- most species are ornamented, with lamellate antennae, and horns. Larvae are called white grubs. Onthophagus, Copris, Heliocopris, Onitis, Oxycetonia are common genera. Oryctes rhinoceros is destructive to the coconut tree. Bruchidae (pulse beetles)- species of Bruchus and Callosobruchus are pests of pulses.
Chrysomelidae (leaf beetles) and the allied families Galerucidae, Hispidae and Cassididae have nearly similar habits, and were originally treated as subfamilies of the Chrysomelidae. Both adults and their larvae feed exclusively on the leaves of a variety of plants; some of them are serious pests of cultivated crops and vegetables. Aulacophora species, Altica, Galemcella, Monotepta species. Dicladispa armigera, Aspidomorpha spp. are among the common leaf beetles. [Monawar Ahmad]
Dung Beetle Name for a group of highly specialised coprophilous beetles of the subfamily Scarabaeinae. Although the members of the family Scarabaeidae are commonly known as dung beetles or lamellicorn beetles, the name dung beetle is usually restricted to the dung inhabiting species. On the basis of food habit the scarabaeids are categorized into two types as, phytophagous, where adults feed on plant materials and pre-adult stages pass either in animal excreta or decaying organic matter; and scavenger beetles subsisting primarily on dung/decaying organic matters. They are usually found in association with dung pads, carrion, biological refuges of all kinds, humus, rotting wood and fungi. It is reported that in India during May and June as much as 40-50 thousand m tons of exposed excrement are carried by scarabs each day into the soil. Dung beetles habitually dig tunnels in the soil under dung pads and carry a fragment of dung at the bottom for consumption or breeding purposes. This habit increases soil fertility and porosity. The scarab dung beetles also play a role in reducing populations of parasitic organisms living in various types of dung.
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