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Insects

Insects are considered as the largest and remarkably-diverse group of organisms in the world. Moreover, they play numerous roles in different ecosystems around the globe because of their enormous diversity in form, function, and life style, as well as their interactions with other organisms. Some insect species particularly those involved in pollination, honey production, silk production, predation, and parasitism are brought about great benefits to human beings. On the other hand, some insect species can negatively affect human activities by transmission of diseases and phytophagy which cause considerable damages to agricultural production.

Insects are the most prominent successful group among animals in terms of number of species. The largest orders are: Coleoptera (beetle), Lepidoptera (butterflies and moths), Hymenoptera (ant, bee, and wasp) and Diptera (true flies).

Coleoptera consisting of beetles and weevils are considered to be the largest insect order representing over 360,000 species or 40 % of the known insect species in the world. Members of this order play different roles in various ecosystems, from agricultural pest such as Colorado potato beetle (Leptinotarsa decemlineata) and the boll weevil (Anthonomus grandis), to natural enemies of the insect pests such as ladybirds (Coccinellidae).

The order lepidoptera comprises more than 160,000 species of butterflies and moths, characterized by their complete metamorphosis, during which they go through four distinct stages namely, egg, larva (caterpillar), pupa, and adult. During the larva stage of growth, they largely feed on plant materials by chewing or biting green or non-green plant tissues. On the other hand, adult insects of this order are largely anthophilous, meaning that they develop a specific mouthpart, proboscis, for imbibing nectar and other liquid substances from flowers. The role of lepidopteran as pollinators in the ecosystem has been well established. The most important pest of this order including, Tomato leafminer (tuta absoluta), codling moth (Cydia pomonella), The cotton bollworm (Helicoverpa armigera), rice stem borer (Chilo suppressalis) and etc.

Hemipteran, which are also referred to as the true bugs, are an order of insects including cicadas, aphids, plant hoppers, leafhoppers, and shield bugs. Most of the hemipteran pests feed on plants through piercing and sucking plant phloem sap. Some insects of this order are considered as important agricultural pests, damaging crops through direct feeding or indirectly by being vectors of serious viral and phytoplasma diseases. Among the insects of the order hemiptera, aphids constitute more than 4700 species, out of which 250 are considered as agricultural pests both through direct phloem feeding or indirect virus transmission. Like other types of plant-insect interactions, phloem feeding is also associated with plant defense responses that are thought to be mediated by particular molecules known as elicitors. In phloem-feeding insects, the injected saliva proteins may play a critical role in preventing the plant’s wound response and may contribute to plant-insect interaction.

Insects, mites, and ticks are the main arthropods involved in the transmission of many plant and animal-disease caused by viruses.

 The application of chemical insecticides is the main approach used for insect pest control. However, pesticide application has raised concerns regarding the risks posed to the ecosystem by perturbing natural and/or environmental balance and due to the high persistence of these compounds as well as their toxicity to non-target organisms. Public and academic concerns over the use of pesticides with respect to food safety, especially about their residual toxicity in contaminated crops on one hand and the induction of resistance in insects on the other hand have motivated researcher around the world to find novel chemical molecules.

Insecticides

General trends in the history of pesticide production, trends have changed from organophosphates, carbamates, and synthetic pyrethroids to nicotine and diamide insecticides.  There are also new different group other the two mentioned group that recently introduced to market. Need for specific molecules which have a short phi and without effect on natural enemies arises.

Insect growth regulators (IGRs) are insecticides that mimic hormones in young insects. Generally IGRs are low in toxicity to humans. IGRs affect certain hormones in insects, hormones that humans don’t have. They disrupt how insects grow and reproduce. Many IGR products are mixed with other insecticides that are more effective against insects.

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