Immediate effect of insecticides

The effect of insecticides can be immediate and seen as soon as we use them. Whether we use a natural substance or a synthetic one, there are immediate effects. Read my blog called ‘How insecticides work’ for an overview of their modes of action on insects.

We may use an insecticide with the intention of killing a target insect such as aphids or caterpillars. However, sometimes (perhaps more often than not) we also kill other non-target insects that we didn’t intend to. For sure, soapy water, horticultural oil and Neem oil are all less toxic than synthetic insecticides, but they can kill non-target species.

Therefore, one common immediate effect of insecticides is that they can kill beneficial and predatory insects as well as the target insects. For more information read my blog on how insecticides work.

If we know for example that horticultural oil works primarily by suffocation we understand that we must use horticultural oil mindfully and carefully. Otherwise, we may harm other insects even when we’re trying to use non-toxic remedies.

Soapy water can kill by disrupting cells, suffocation and dehydration. Some household soaps can harm microbes and plants. However, even horticultural soaps will kill predatory mites. So even with the best of intentions, we can cause harmful effects.

The natural and least toxic remedies mostly have short to medium term effects. Synthetic insecticides such as carbamates, neonicotinoids, pyrethroids and a whole host of others have short, medium and long terms effects.


Medium term effect of insecticides

We can effect the lives of other insects in the medium term when we use natural or synthetic insecticides. How?

When we kill an insects food source, we reduce their numbers. Populations decline as food becomes scarce. That’s why many of us check for predator insects first – before resorting to a chemical remedy.

The photo below shows young lady beetles hunting mealy bugs on leaves. Any insecticide would take their dinner away!

lady beetles hunting mealy bugs

When we use insecticides and pesticides generally, we “select for the pest”Most contemporary research shows us this fact: when we kill “pest” insects with insecticides we increase the numbers of those pests in the medium and long term. We do this by eliminating predator insects (by unintentional killing or by reducing their available food resources) when we use the insecticide.

So even if we use our fingers to crush the scale insects or the caterpillars, we are taking away a food source for others. I’m not saying “don’t do it”. I’m simply pointing out a fact.

When we kill or reduce predators the ‘pests’ prevail.  This is despite short term indications to the contrary. Predator insects (and microbes and animals) reproduce at a much slower rate than our pest insects. We only need one herbivore (pest) insect to escape our insecticide application or fingers for thousands to born. Without the predators the problem escalates.

That keeps us on a pesticide treadmill where we need to keep using pesticides. The only reason is that we’ve helped to create the conditions for their survival. One of those conditions is the elimination of their natural predators.

There’s another serious effect of insecticides and pesticides generally. This is a long term issue affecting each and every one us on this planet. This is mostly due to synthetic insecticides and pesticides rather than natural ones.

Read my blog called Insect adaptation and resistance to synthetic chemicals for an understanding of the long term impacts of synthetic insecticides.


The Pesticide treadmill

The resistance effect of insecticides is enhanced when we continue to use insecticides.

Here’s how it works: Because organisms like plants and insects get exposed to repeated doses of a chemical, they form a resistance. As a result, we tend to use more of that chemical and we do so more often to try to create the same control effect. If we use the same or similar chemical with the same mode of action this only increases the organism’s ability to adapt to it. The pesticide treadmill.


Off label use of insecticides – it’s also unlawful

Licensed agricultural chemical operators undergo training and therefore become aware that using an agricultural chemical in a way that is inconsistent with the label is unlawful, unless there’s a permit stating otherwise. However, non-licensed operators tend to not know this. And it might be that even licensed operators ignore this.

Organisations such as IRAC and Croplife suggest the labelling regime is based on reducing or delaying resistance. That may be the case.

If we use a pesticide solution that is too weak resistance builds up quickly. That’s a key effect of insecticides where we didn’t’ follow the label. A solution that is too strong (and not consistent with the label) affects other species and may cause other detrimental effects. Is collateral damage a reasonable effect of insecticides?

The same thing can occur if a chemical is used at the wrong time in the life cycle of a target species or under sub-optimal environmental conditions.

For example: I’ve seen people use an insecticide on leaves covered in stippled dots. Typically, stippled leaves indicate mites. However, unless we look at the leaf through a microscope, we won’t know if the mites are still there or not. Where are they in their lifecycle?

Often they’ve moved on and all we see under the microscope is a bunch of empty egg shells. So spraying a stippled leaf may not be effective and may not be consistent with the label. In doing so we’re breaking the law. That’s the law in most countries including Australia and the USA.

However, I’ve seen two insecticidal products with exactly the same active ingredient: one was registered for use in certain ways the other wasn’t registered at all. They were Neem oil products. The registered one had a label that said what insects the Neem oil was to be used on. It was twice the price of the unregistered one.

That made me wonder: is the system based on control and money rather than health? What a stupid question!

Of course corporations pay for registering their products for use on certain organisms. The Neem oil was a classic example of this double standard. It isn’t about the active ingredient alone. It isn’t necessarily about delaying resistance.

When a company registers their product under this system, their product becomes lawful to use in particular ways. All other products (with the same active ingredient) that aren’t registered are unlawful to use in those same ways. Hmmm…


Let’s not engage in the machine gun approach, it’s overkill

This is so common I could write a thesis on it. Instead of using the remedy that causes the least harm, we go for the big guns! There’s a few aphids on my plant! Quick get the systemic killer with the Imidacloprid in it! A hose would suffice. Less… Leave the aphids and let the lady beetles and hoverflies have them.

I was on a gardening forum this morning and someone had a bunch of bugs on her nasturtium leaves. Everyone identified them as aphids and a whole host of people suggested remedies. There were remedies including soaps, systemic sprays you name it. Apparently I was the only one who saw the two parasitic wasps in the photo. Moreover, most of the aphids had already been parasitised! Doing anything (except marvel at nature)  in that situation is overkill!

I see the same thing with diseases like fungal infections. A leaf has spots, it’s identified as a fungus and so people use a fungicide. Most fungicides kill all fungi and so all the fungi in the soil are also killed. That throws out the soil microbiology and causes more plant health issues. A simple remedy might be root zone watering and thinning the leaves.

We bring out the big guns rather than employ a simple remedy. Often a simple remedy for fungal infections is to reduce humidity. Stop watering the leaves, or take the plant out of the greenhouse. That’ll usually work too! Easy. No big guns required. No destroying soil ecology. Go for the cause… not the mere symptom. Often we can’t even diagnose the cause without the use of microscopes or a laboratory.

The machine gun approach is overkill. It’s when we go for the big guns rather than leaving the big guns as the last resort. Another issue connected with insecticide use is a lack of correct identification.


Misidentification and the use of the wrong chemical

I’ve seen this one over and again too. I had a client who showed me her passionfruit vine. I saw it had chomp marks in it and immediately recognised these as the marks left by the leaf cutter bee. It’s a bee that chews circular bits out of leaves to build her nest to raise her young.

My client saw me looking at those and informed me that she had used a systemic insecticide to kill the grasshoppers ‘that made those marks’… but of course grasshoppers didn’t make those marks. The chemical she used didn’t kill any grasshoppers, it killed bees.

She incorrectly identified a ‘pest insect’ and used a chemical to kill a key pollinating insect. No passionfruit for her!


Tyranny of small decisions

Bit by bit we’re wreaking havoc on nature. When we each individually misuse these toxins we create a system of misuse. Our habit of seeing certain insects as pests and enemies is our downfall.

Our lack of compassion and our ignorance leads us to do things that we wouldn’t otherwise do. We would never use a neurotoxin on our dogs or on another human but on an insect it’s somehow ok. Is it?

Where do ethics stand in this issue? Where is our respect for creation and nature and the creatures of this world? Where does God really stand here? Can our beliefs and notions be wrong? Is it possible?

Is it possible that we’re growing our food and plants in a way that causes these problems? Isn’t that how everything on this planet works? If we continue to do things that cause suffering, suffering persists. If we do things in a way that doesn’t cause suffering, suffering dissipates.

Whether we use big guns rather than small tweezers, or the wrong chemical for the wrong insect or the right chemical too often we are creating havoc and destroying nature.

When I studied environmental law we called this the ‘tyranny of small decisions’. Seemingly small decisions made locally here and there create a fabric, a blanket, a system of abuse that causes monster nemeses, extinction events and global, environmental change. We are living in those times now.

Are we learning anything? Are we adapting? Or is our denial and pride so strong that we are resistant to the truth?

Categories: insecticides


Beverley H. · July 17, 2018 at 11:10 am

That’s a very extensive and thought-provoking article, Amber. We must always remember that we share this World with many other creatures, both ‘good’ and ‘not-so-good’! Good one!

    Amber Hall · July 20, 2018 at 1:43 pm

    Thanks Beverley, yes we aren’t alone on this planet and if we were, we wouldn’t survive here 🙂

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