1. Chemical Control: Insecticides
Insect Pest Management by David Dent  -   CABI Publishing

2. Insecticides are one of the four building blocks of IPM
Chemical
Biological
Cultural
Plant resistance
IPM is made up of 4 building blocks: chemical control, biological control, cultural control and plant resistance. We have already seen biological control. Now we will study chemical control.
Insecticides are one of the four building blocks of IPM

3. Component of pest control since the 1950s
The guy in the picture (right) is Paul Muller the chemist that gave us DDT. DDT was very popular when it just came out. People thought it was the solution to all our insect pest problems. Later we realized that chemical control was far from being perfect. Problems involving human and environmental health were detected and alternatives to chemical control have been explored ever since.

4. Not a perfect solution At least 3 million workers poisoned each year
deaths per year
Teratogenic, carcinogenic and mutagenic effects
Part of the problem with insecticides is the risk they pose for human health.

5. Public concern about Insecticide use
~100% of us have some insecticide residue in our bodies

6. Insecticides represent an $ 8 billion industry
There are a lot of economic and political interests associated with the insecticide industry though.

7. For the Correct use of insecticides, we need to consider:
Ease of use
Insecticide resistance
Economics
Safety
Insect behavior
Way of delivery
Ecotoxicological impact
When applied correctly insecticides are extremely effective in controlling pests. In many instances when applied incorrectly, they seem to kill pests the same though. Thus, the perceived benefits to the farmer are always good (this is where the danger of incorrect insecticide use resides). However, not using insecticides properly have dangerous consequences. The consequences of incorrect insecticide application are long lasting.
Toxicology

8. When to apply? Thresholds Calendar applications
One important question in chemical control is when to apply it. Threshold applications are only done when needed. Scouting the field at regular intervals will provide the signal or threshold level that will prompt into insecticide applications. Calendar applications are done on specified dates independently of the population numbers of the pest in the field. What is the problem you see with the calendar application approach? (the answer in next slide, but try to answer it yourself first).

9. Problems with calendar application approach
Resistance
Secondary pests
Destruction of natural enemies
Health hazards
Environmental hazards
These are some of the problems with calendar applications. Since you are exposing pests to the insecticides constantly the potential for the development of insect resistance is high. Also, natural enemies (e.g. insect predators and parasitoids) get also killed when insecticides are used. The decrease in natural enemy populations (the ones attacking the pest and other natural enemy populations that normally attack other insects) creates a situation in which herbivorous insects which were normally being controlled by those natural enemies get loose and can become secondary pest species once their natural enemies are killed by the insecticides. Needless to say that the health hazard for humans and the environment increase when insecticides are applied more than when it is necessary.

10. Going towards better insecticide use
There is a trend for a reduction in the amount of certain insecticides used in agriculture. This is a healthy trend. The more we understand the organisms involve in a pest problem the more we will rely on other pillars of IPM and the less we will rely on chemical control.
(Dent 2000)

11. Insecticide Composition
Insecticide = Active Ingredient + Additives
Every insecticide out there in the market is composed of the active ingredient (the actual insecticide) and some additives. Additives facilitate insecticide application.

12. Classes of Insecticides
Botanical Insecticides
Sabadilla
Nicotine
Quassia
Unsaturated isobutylamides
Ryanodine
Naphtoquinones
Rotenone
Sweet flag
Marigolds
Pyrethrum
Azadirachtin
Essential oils
Botanical insecticides
Synthetic Insecticides
Organochlorines
Organophosphates
Carbamates
Pyrethroids
Neonicotinoids
Lets start studying the active ingredients of insecticides.
Biorational Formulations
Growth regulators
Pheromones
Microbial formulations

13. Botanical Insecticides
Secondary compounds
Alkaloids
Terpenoids
Phenolics
Glucosinolates
Etc.
Chemicals used by plants to protect themselves against insects are called secondary compounds.

14. The use of plant extracts as insecticides can be dated back at least 4000 years. The earliest documented examples of plants being used as pesticides occured in China, Egypt, Asia and Europe. None of this involved mass production though. It is in the sixteenth century than European explorers began to discover the plants that native cultures were using for pest control. After those observations widespread commercial use of botanical insecticides in Western Europe and North America continued from the sixteenth century up until the second World War. However, with the widespread use of synthetic insecticides in the 40s, the use of botanical insecticides has declined.

15. Some large-scale plant screening programs took place during the 1940s 1950s and 1960s, particularly in the USA and in China. However, although several potentially useful extracts were identified these efforts could not be sustained due to lack of proper funding. There has been a revival of interest in botanical insecticides. In part due to the high costs of synthetic insecticide development, the small proportion of plants that have been assayed for toxicological activity, and the fact that some synthetic insecticides such as carbamates and pyrethroids were developed from studies on plant-based chemicals. With the exception of neem most botanical insecticides are only used by native communities (mostly on developing countries).
Conservative estimates place the number of plant species in our planet in a number between and species. Around 2400 plants have been recorded as being useful for pest control. Of these, only a tiny proportion (less than 10) have been developed commercially. It is very likely that novel and potent molecules that can be used for pest control remain to be discovered

16. Reasons for lack of Commercial Development
Perceived as old fashioned
Lack of representation on official lists
Not as dramatic effects as synthetic insecticides
Inactivation by exposure to air and light
Problems due to seasonal availability
Lack of quantitative information regarding dosages
Lack of quantitative information regarding toxicity
This slide mentioned some reasons that explain why the use of botanical insecticides is not as widespread as the use of synthetic ones

17. Synthetic Insecticides
Organochlorines
Organophosphates
Carbamates
Pyrethroids
Neonicotinoids
These are the different classes of synthetic insecticides available. They vary in their spectrum or range of action, persistence in the environment, toxicity to non-target organisms including vertebrates. Each of them is available in a variety of formulations destined to be used in very diverse situations. As diverse as they are though, they all share a very similar target and mode of action.
Organochlorines were the first synthetic insecticides to be mass produced. DDT is an organochlorine. Organophosphates were developed as a by product of World War II when trying to produce nerve gas.
Carbamates are mostly used to control insect pests from agricultural and horticultural crops.
Pirethroids’ chemical composition was derived from a flower in the chrysanthemum family (Pyrethrum cinearaefolium) and their synthetic analogs. This kind of insecticide is very good against Lepidoptera but it is used for other groups as well. Used in households and in grain storages. 5g of deltamethrin (a pyrethroid) can protect the same area of cereals from aphid damage as 0.5-1Kg of an organophosphates and 15 Kg can treat as many households as one ton of DDT. Thus, it is an efficient insecticide.
Neonicotenoids are based on the chemical structure of Nicotine. They are contact and Systemic activity. Their mode of action involve the inhibition of the nervous signal by binding to postsynaptic receptors

18. Affect synaptic transmission
All the classes of synthetic insecticides target the insect nervous system. Little variations in specific target areas exist among the different classes of synthetic insecticides we know today. But in the end they are all affecting the nervous system.
Organochlorines for example, affect synaptic transmission. The synaptic transmission is responsible for transmitting the nervous chemo-electric signals from one nerve cell (neuron) to the next. Thus, insects exposed to organochlorines experience serious problems at the nervous system level. If you affect the synaptic transmission you are creating some sort of short circuit in the bug and you can tell by they way they react after being exposed to this kind of insecticide. They have all sort of uncontrolled movements when exposed to organochlorines.
Like the organochlorines, organophosphates, also affects the insect nervous system. They inhibit the enzyme cholinesterase. Cholinesterase is involved in the transmission of the chemo-electrical signal in the synapses.
The carbamates mode of action is basically the same as the organophosphates. The carbamates affect the enzyme acetylcholinesterase (the organophosphates affect the enzyme cholinesterase). Both of these enzymes (i.e., cholinesterase and acetylcholinesterase) are involved in the synaptic transmission of the neural electro-chemical signal in the insects’ nervous system.
The pyrethroids are axonic poisons. They bind to the protein called voltage-gated sodium channel in the axon preventing the transmission of the neural signal. Thus, it messes up with the insect nervous system again but this time at a place removed form the synapses.
Affect synaptic transmission

19. Concerns Some are highly persistent in the environment
They accumulate in the food chain
If release from fats, poisoning or death
Some are banned in developed countries
Unfortunately, still used in some developing countries
Due to their solubility and stability Organochlorines are highly persistent in the environment. These insecticides accumulate in food webs. Particularly in tissues of predatory and parasitic insects and even more in vertebrates. Since Organochlorines accumulate in animal fat they are not excreted. Thus, predatory animals feeding on many individuals that have organochlorines in their fat tissues, accumulate these compounds in their own fat multiplying the accumulation effect. Vertebrates that feed on insects that have fed on prey contaminated by organochlorines will concentrate this compounds at even higher concentrations.
Organophosphates are non persistent in the environment so they are less of a thread than the Organoclhorines. Insects treated with carbamates can recuperate if the carbamate dosage is low because the enzyme inhibition is more easily reversed than in the other insecticide groups we have discussed.

20. Examples -Tefluthrin Carbamates Organochlorines Pyrethroids
- Aldicarb -Carbofuran
- DDT Endosulfan
- Aldrin Gamma HCH
- Dieldrin Gamma BHC
Pyrethroids
-Tefluthrin
- Deltamethrin
- Lambda
-cyhalothrin
- Permethrin
- Cypermethrin
Organophosphates
-Diazinon
-Fenitrothion
-Dichlorvos
-Dimethoate
- Malathion
Keep in mind that organochlorines, or organophosphates, or carbamates are all chemical generic names. The names in these examples (in red) are the specific names or specific synthetic insecticides. These names are different from the brand names (the ones in the bottle or can, in the first example Kybosh is the brand, DDT the specific chemical name and Organochlorine the generic chemical name). Next time you are sharing a room with an insecticide take a look. You will see that the brand name is accompanied somewhere in the label by the name of the specific compound and sometimes even the generic name.
-imidacloprid
-nitempyram
- acetamiprid
- thiamethoxam
Neonicotenoids

21. Biorational Formulations
Growth regulators
Pheromones
Microbial formulations

22. Growth Regulators Interfere with development
Disrupt metamorphosis and reproduction
Specific for arthropods

23. Hormones involved Moulting hormones or ecdysones
- Re-absorption of old cuticle
- Deposition, hardening and tanning of new cuticle
Juvenile hormones
- Prevent insect from going to next instar.
Ecdysones are steroid-like molecules. Ecdysones are too expensive to be synthesized and used as control agents. However, some relatively new insect growth regulators which are not based on steroids have proven effective against Lepidoptera. Juvenile hormones keep insects at specific instars when present and allow maturation when absent. A number of juvenile hormones have been identified and their structures established. Derivatives of juvenile hormones have been synthesized and used for chemical control of insects. They are referred as juvenile hormones analogues or juvenile hormones mimics, or juvenoids.

24. The used of these hormones produce monster individuals or intermediate stages between larva and pupa or pupa and adult that are unable to reproduce or even move sometimes.

25. Concerns Take longer to act than conventional insecticides
Ecdysones are expensive
Not ideal when larval stages are the pest
Even though insect growth regulators are no the way to go when the pests consist of larval stages, these substances are still used when pests consist of adult individuals (e.g. ants, mosquitoes, fleas, etc) or when you want to prevent the build up of populations by preventing their reproduction.

26. Examples - Methoprene - Tebufenozide - Diflubenzuron - Fenoxycarb
Juvenile Hormones
Chitin Synthesis Inhibitors
- Methoprene
- Tebufenozide
- Fenoxycarb
- Pyriproxifen
- Diflubenzuron
- Hexaflumuron
- Triflumuron
Triazine Derivatives
Methoprene is the oldest insect regulator. It is used to control flies (particularly of livestock), fleas, mosquitoes stored food and tobacco pests and pharaoh ants.
Fenoxicarb can be used to control moths that attack trees (e.g. Cydia pomonella, Epiphyas postvittana) and termites.
Pyriproxifen is active against fleas in very small dosages. It has recently being approved for release in dog and cat collards, sprays and wash formulations.
If you affect chitin production you affect insect development substantially.
Triazine derivatives attack mostly Diptera larvae. Triazine compounds do not act directly on chitin synthesis but they produce integumental lesions.
- Melamine
- Cryomazine

27. Pheromones Mediate intraspecific interactions
Around 50 available for IPM
Mostly use in association with traps
Pheromones belong to a group of chemicals refer as semiochemicals. We will talk about this chemicals later in the course. For now just remember that pheromones are chemicals that transmit intraspecific (i.e., within the same species) messages. Pheromones can be defined as externally released chemicals that cause a specific reaction in a receiving organism of the same species. The word pheromone is derived from the greek words “Pherein”= to carry and “hormon”= to excite.

28. Pheromones Uses in IPM Monitor pest populations Mass trapping
Mating Disruption
Lure and Kill

29. Microbial Formulations
Uses bacteria, fungi, nematodes, protozoa and viruses
Mostly used as inundative releases
Specific for arthropods
Although theoretically several agents can be employed for microbial formulations (e.g., bacteria, fungi, nematodes, etc) only one species, Bacillus thuringensis, is involved in 80-90% of the sales in this market.

30. Increase interest in Microbial Pest Control
Resistance to synthetic insecticides
Decrease in discovery of new synthetic insecticides and increase of discovery of microbial novel agents
Increase in the perception of risk posed by synthetic insecticides
The high host-specificity of microbial pesticides
Improvements in the production and formulation of microbial pesticides
Relaxation of the regulations governing registration of microbial pesticides
Remember they are living organisms so there are differences between them and synthetic insecticides in terms of shelf live, mass rearing and virulence, as we discussed when we looked at augmentative biological control. Although we are mentioning microbial control in this section, I think it is more appropriate to consider microbial pest control as part of biological control than as part of chemical control. Some people makes the distinction between using living organisms versus using their products (like in the case of BT toxins). They refer to the latter as biorational pest control. As you can see classifying control practices can get complicated.

31. The Pesticide Treadmill
Pest resurgence
Secondary pest outbreaks
Pesticide resistance
These three phenomena together have been termed the pesticide treadmill. They lead to increasing dependence on pesticides, seemingly an addiction for use of this type of control.

32. Going towards better insecticide use
Notice how the use of organoclorines (OC) has diminished and the amount of pyrethroids has increased over the years.
(Dent 2000)

33. Insecticide Composition
Insecticide = Active Ingredient + Additives
Every insecticide out there in the market is composed of the active ingredient (the actual insecticide) and some additives. Additives facilitate insecticide application. We will explore this in more detail in our next class.