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Let’s face it, the majority of people hate bugs, especially the pesky ones that take over your household. And while bugs make up a massive part of the ecosystem, outnumbering humans 1 to 200 million, most of us would prefer to appreciate them from afar…

 

Image Credit: iStock Photo

Now that summer is here, we are more likely to spend time outdoors, and the increase in temperature also correlates with an increase in insect activity—in which case, we will need bug spray. Without it, a camping trip or even a short walk to the park becomes an itchy experience! It is important to note that under the general term ‘bug spray’ there are two subgroups: repellent that deters bugs and insecticides that kill bugs. Let’s have a closer look at these subtypes and focus specifically on how insecticides kills these poor buggers!

Insect repellent

Repellents are mostly products that you put on your skin, meaning that they don’t kill bugs but, rather, keep them away from you. The way they do this is quite clever, they mask your scent. Your scent is made up of the chemicals, products and perfumes you use as well as the naturally occurring carbon dioxide you make, released when you exhale, via pores and sweat. Mosquitos and other insects are able to track that CO2 to find ‘food’ (that’s you). So, by putting on insect repellent you are disguising your scent to essentially become ‘invisible’ to hunting insects. Some repellents go even further to make you smell repulsive to bugs which will help keep them away from you!

Ingredients

Insect repellent is made up of a pressurised and concentrated dose of their active ingredient, which can either be synthetic or natural. Most of these have to be tested and deemed safe by TGA and other regulating committees as we use them on our skin. Here are a few of them:

  • DEET: a synthetic chemical that is colourless and water resistant
  • Oil from the ‘catnip’ plant
  • Citronella oil
  • Oil derived from lemon eucalyptus trees

You can read more about these here.

Insecticides

Picture this scenario: you’re getting ready for bed and turn the light on in your room. As you make your way to your bed you notice something scurrying across the wall. You get closer to take a look and realise it is a massive cockroach. Just when you thought things couldn’t get worse, it starts to fly across the room! You quickly grab a can of bug spray and spray half a can in your panic which quickly soaks the cockroach—the chemicals quickly enter its nervous system and cause its legs and body to twitch, spasm and eventually it lays motionless. Dead. You stand above its lifeless body—you, the triumphant hero.

I am sure you are no stranger to the situation above. But, first of all, what is the difference between pesticides and insecticides? These are the sprays you grab when a flying cockroach appears on the wall. And every time I see bugs I can’t help but think that they are not alone… and that if you see one, there’s bound to be more lurking. Now that’s a one sentence horror story you didn’t need to read! Pesticides are chemicals used to kill fungus, bacteria, plant diseases, weeds, insects, snails or slugs. Insecticides are a type of pesticide used to kill insects specifically, including ant/wasp killer and snail pellets. Here, we will focus on insecticides which, unlike repellents, are made to kill bugs. The way they work can be compared to the way nerve agents are used in warfare.

It is important to note that these insecticides are not only harmful to insects but can also be toxic to birds, bees and even fish. Factors such as the surface you are spraying on, the chemicals in the spray, the weather, and time can affect the efficiency and duration of action of the insecticide.

The active ingredients of insecticide sprays will cause death differently:

  • Pyrethroids are synthetic copies of pyrethrins which are natural compounds found in chrysanthemum flowers. Pyrethroids are neurotoxic, so once it enters the insect’s body it targets neurons. Specifically, they target proteins that transport sodium and potassium across the neuron’s membrane. Neurons are in charge of transmitting messages to and from the brain, and they do this by controlling the entry and exit of sodium and potassium, so the insecticide affecting the transport proteins for these ions essentially stops the signals and paralyses the insect.
  • Organochlorides work by opening sodium ion channels in neurons causing them to spontaneously fire, and resulting in the insect going into spasms and eventually dying.
  • Organophosphates and carbamates target an insect’s nervous system, specifically the enzymes cholinesterase and other cholinesterases. It disrupts nerve impulses and stops neurons from communicating with each other, thus disabling or killing the insect.
  • Neonicotinoids are a synthetic version of nicotine, a natural insecticide. They are acetylcholine receptor agonists that compete with acetylcholine for the same receptor and stops the binding of acetylcholine to the receptor. This causes leg tremors, rapid wing motion, disoriented movement, paralysis and eventual death of the insect
  • Butennolides are a similar mode of action to neonicotinoid.
  • Ryanoids are synthetic versions of ryanodine. It binds to calcium channels in cardiac and skeletal muscle blocking nerve transmission, so the muscle cells lose function and slow or stop beating.

Image Credit: iStock Photo

Do bugs feel pain?

We often don’t think twice about swatting flies, stepping on ants and soaking cockroaches in bug spray. But whether insects have the same or similar subjective experience of pain is not easy to answer. First, we must agree on a definition of pain. Is it pain if it does not hurt you? Human and insect nervous systems/pain receptors are built differently. Do insects have emotions?

A deep dive on Google will unearth a plethora of evidence and opinions. Researchers have known since 2003 that insects experience some sort of sensation related to pain. However, new research published from the University of Sydney has found that insects experience chronic pain that lasts long after the initial injury has healed. For this study, researchers damaged one leg on a fruit fly, then allowed it to heal. They found that even after the fruit flies have recovered, their uninjured leg grew more sensitive—a reaction similar to chronic pain in humans. After an animal has been hurt badly it becomes hypersensitive to try and protect itself for the rest of its life. The fruit fly is essentially receiving ‘pain’ messages from its body to the ventral nerve cord (a fly’s version of our spinal cord).

It also raises ethical issues such as, if insects can feel pain and suffer should they be used in pesticide research—a specialty devoted to creating chemicals capable of killing them and other types of research. There is much debate to this fascinating discussion, however no single scientist has the answer.

So, will you think twice before buying Mortein next time you’re at Coles…?