Percentage of all insects on the planet that are pests #433414

Asked November 01, 2017, 7:26 AM EDT

I see on the attached chart that only a sliver of all arthropods are considered pests to agriculture. Breaking this down. Do you know what percentage of all insects (not arthropods) are considered pests? And, what percentage are considered beneficial? Thank you

Frederick County Maryland

Expert Response

I doubt there is a really good guesstimate of how many species of all arthropods are considered 'agricultural pests' for people living in all corners of the world. I also doubt there is a good guesstimate of how many arthropods are considered 'beneficial' to agriculture or people. "Good' and 'bad' are in the eyes of the beholders. What might be considered beneficial in one country could be considered a pest in another or vice versa. And it always seems that agriculturists are stumbling across species new to science or new to different countries that are damaging pests.

On your chart, I don't see any figures (numbers) for numbers of species that fit into each category---blue or yellow. There are also some very thin sections of something that's purple. But that might not matter a whole lot.

If you try to look up how many species of insects there are---or are now---or that could be 'out there' somewhere, you'll get a variety of numbers. 'One million insect species' has been considered one reasonable, conservative guess.

However, for systematists studying the fauna of particular countries or regions or biomes, the more they look (especially in the tropics), the more varieties of creatures they discover. Some of these may be previously undescribed (new) species---at least from their anatomy or appearance.

This leads some of the more 'liberal' guessers to suggest a worldwide inventory of just insect species to be in the neighborhood of 30 million.

So, we have 2 possible---and reasonable for different situations---denominators for our fractions---1 million and 30 million.

I don't believe I've seen any listings or counts of how many pest species or beneficial species are known from our various continents. For under-developed areas, especially tropical ones, these are the areas being surveyed---where possible---for new species. These 'newly recognized' species may not be pests in their home countries, but they certainly could be when presented with 'new opportunities.' That might be agricultural development---maybe planting new areas or planting new crops in a new area. The unrecognized species might find that new crop in an easily accessed area 'right up its alley.'

Further, if this newly recognized species happens to be introduced---accidentally---to another country, it might establish itself without the usual predators and parasitoids that were in its homeland. That happens all too often---and another 'new pest problem' hits the news. Some of these become targets for identifying natural enemies from the homeland with potential for introduction into the area where the 'new pest' is running rampant. Sometimes, that might be a possibility---with very strenuous vetting of these candidate 'beneficials' for introduction.

So---let's take a wild guess of two (or more). We have 7 continents, but can probably drop Antarctica right away since no one that I know of is trying to grow any agricultural crops outdoors. That leaves 6 continents. 

Let's guess that each of these continents has 1,000 pest species and 1,000 beneficial arthropod species. That may be super conservative.

So our fractions would look like this:     ________6,000 species___
                        1,000,000 species

or   _6,000 species__
  30,000,000 species    and you can simplify the fractions from there. 

Six thousand looks pretty paltry for both pests and beneficials, huh? Considering that a guesstimate is for a whole continent x 6, guesstimate higher and recalculate. You can easily 'fudge' on both higher guesstimates by saying that some beneficials and some pests are not as effective or serious as others---it's just a guesstimate anyway.

You can always 'come back to earth' with statements like---even though these %ages are guesstimates, some of the most serious pests of agriculture (s.l.) are devastating to local economies and to local populations, creating considerable hardship, sometimes on top of serious diseases, other disasters (e.g. weather, earthquakes, volcanos) and warfare.

Consider the very recent plight of people in Puerto Rico. Maria wiped out a lot of their agriculture and set back pest and beneficial populations---except for mosquitoes, fleas, flies, etc. etc. that prey upon survivors and their health and well-being.

I hope some of this makes sense.......

Carol Sutherland Replied November 01, 2017, 5:26 PM EDT

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