Insecticide
Insecticides are pesticides used to kill insects. They include ovicides and larvicides used against insect eggs and larvae, respectively. The major use of insecticides is in agriculture, but they are also used in home and garden settings, industrial buildings, for vector control, and control of insect parasites of animals and humans.
Acaricides, which kill mites and ticks, are not strictly insecticides, but are usually classified together with insecticides. Some insecticides are effective against other non-insect arthropods as well, such as scorpions, spiders, etc. Insecticides are distinct from insect repellents, which repel but do not kill.
Sales
In 2016 insecticides were estimated to account for 18% of worldwide pesticide sales. Worldwide sales of insecticides in 2018 were estimated as $ 18.4 billion, of which 25% were neonicotinoids, 17% were pyrethroids, 13% were diamides, and the rest were many other classes which sold for less than 10% each of the market.Synthetic insecticides
Insecticides are most usefully categorised according to their modes of action. The insecticide resistance action committee lists 30 modes of action plus unknowns. There can be several chemical classes of insecticide with the same mode or action. IRAC lists 56 chemical classes plus unknowns.The mode of action describes how the insecticide kills or inactivates a pest.
Development
Insecticides with systemic activity against sucking pests, which are safe to pollinators, are sought after, particularly in view of the partial bans on neonicotinoids. Revised 2023 guidance by registration authorities describes the bee testing that is required for new insecticides to be approved for commercial use.Systemicity and translocation
Insecticides may be systemic or non-systemic. Systemic insecticides penetrate into the plant and move inside the plant. Translocation may be upward in the xylem, or downward in the phloem or both. Systemicity is a prerequisite for the pesticide to be used as a seed-treatment. Contact insecticides remain on the leaf surface and act through direct contact with the insect.Insects feed from various compartments in the plant. Most of the major pests are either chewing insects or sucking insects. Chewing insects, such as caterpillars, eat whole pieces of leaf. Sucking insects use feeding tubes to feed from phloem, or to suck cell contents. An insecticide is more effective if it is in the compartment the insect feeds from. The physicochemical properties of the insecticide determine how it is distributed throughout the plant.
Organochlorides
The first and best known organochloride, DDT, was first synthesised by Othmar Zeidler. Swiss scientist Paul Müller found DDTs insecticide properties. For this discovery, he was awarded the 1948 Nobel Prize for Physiology or Medicine. DDT was introduced in 1944. It functions by opening sodium channels in the insect's nerve cells. The contemporaneous rise of the chemical industry facilitated large-scale production of chlorinated hydrocarbons including various cyclodiene and hexachlorocyclohexane compounds. Although commonly used in the past, many older chemicals have been removed from the market due to their health and environmental effects.Organophosphates
s are another large class of contact insecticides. These also target the insect's nervous system. Organophosphates interfere with the enzymes acetylcholinesterase and other cholinesterases, causing an increase in synaptic acetylcholine and overstimulation of the parasympathetic nervous system, killing or disabling the insect. Organophosphate insecticides and chemical warfare nerve agents have the same mechanism of action. Organophosphates have a cumulative toxic effect to wildlife, so multiple exposures to the chemicals amplifies the toxicity. In the US, organophosphate use declined with the rise of substitutes. Many of these insecticides, first developed in the mid 20th century, are very poisonous. Many organophosphates do not persist in the environment.Pyrethroids
insecticides mimic the insecticidal activity of the natural compound pyrethrin, the biopesticide found in Pyrethrum species. They have been modified to increase their stability in the environment. These compounds are nonpersistent sodium channel modulators and are less toxic than organophosphates and carbamates. Compounds in this group are often applied against household pests. Some synthetic pyrethroids are toxic to the nervous system.Neonicotinoids
are a class of neuro-active insecticides chemically similar to nicotine, with much lower acute mammalian toxicity and greater field persistence. These chemicals are acetylcholine receptor agonists. They are broad-spectrum systemic insecticides, with rapid action. They are applied as sprays, drenches, seed and soil treatments. Treated insects exhibit leg tremors, rapid wing motion, stylet withdrawal, disoriented movement, paralysis and death.Imidacloprid, of the neonicotinoid family, is the most widely used insecticide in the world. In the late 1990s neonicotinoids came under increasing scrutiny over their environmental impact and were linked in a range of studies to adverse ecological effects, including honey-bee colony collapse disorder and loss of birds due to a reduction in insect populations. In 2013, the European Union and a few non EU countries restricted the use of certain neonicotinoids. and its potential to increase the susceptibility of rice to planthopper attacks.Diamides
selectively activate insect ryanodine receptors, which are large calcium release channels present in cardiac and skeletal muscle, leading to the loss of calcium crucial for biological processes. This causes insects to act lethargic, stop feeding, and eventually die. The first insecticide from this class to be registered was flubendiamide.Biological pesticides
Definition
The EU defines biopesticides as "a form of pesticide based on micro-organisms or natural products". The US EPA defines biopesticides as “certain types of pesticides derived from such natural materials as animals, plants, bacteria, and certain minerals”. Microorganisms that control pests may also be categorised as biological pest control agents together with larger organisms such as parasitic insects, entomopathic nematodes etc. Natural products may also be categorised as chemical insecticides.The US EPA describes three types of biopesticide. Biochemical pesticides, which are naturally occurring substances that control pests by non-toxic mechanisms. Microbial pesticides consisting of a microorganism as the active ingredient. Plant-Incorporated-Protectants are pesticidal substances that plants produce from genetic material that has been added to the plant.
Market
The global bio-insecticide market was estimated to be less than 10% of the total insecticide market. The bio-insecticide market is dominated by microbials. The bio-insecticide market is growing more that 10% yearly, which is a higher growth than the total insecticide market, mainly due to the increase in organic farming and IPM, and also due to benevolent government policies.Biopesticides are regarded by the US and European authorities as posing fewer risks of environmental and mammalian toxicity. Biopesticides are more than 10 x cheaper and 3 x faster to register than synthetic pesticides.
Advantages and disadvantages
There is a wide variety of biological insecticides with differing attributes, but in general the following has been described.They are easier, faster and cheaper to register, usually with lower mammalian toxicity. They are more specific, and thus preserve beneficial insects and biodiversity in general. This makes them compatible with IPM regimes. They degrade rapidly cause less impact on the environment. They have a shorter withholding period.
The spectrum of control is narrow. They are less effective and prone to adverse ambient conditions. They degrade rapidly and are thus less persistent. They are slower to act. They are more expensive, have a shorter shelf-life, and are more difficult to source. They require more specialised knowledge to use.