Insects don't need native plants?

[DCTropics]

“Insects are not dependent on native plants. They are just as likely to use related non-native plants in the same genus or even plant family with similar chemical properties and nutritional value.”

This claim was made in a recent gardening-related blog post, and I got in a bit of trouble for objecting to it. The authors were trying to rebut a Washington Post column about growing native plants that made some rather hyperbolic statements, but I think they made a few sweeping generalizations and outright false statements of their own.

So here’s my question: are there any projects on iNaturalist dedicated to matching herbivorous insects to the plants they’re feeding on, and/or identifying whether the respective insects and plants are native or non-native to the area where they were observed? It seems like this would be an excellent project, whether on a local, regional, or global level, and could make good use of observations of even the commonest of species on iNaturalist.

Here’s a link to the Washington Post opinion piece: https://www.washingtonpost.com/opinions/2023/04/07/suburban-lawn-climate-change-biodiversity/

And here’s a link to the blog post “rebuttal” I’m objecting to: https://gardenrant.com/2023/08/wapo-columnist-says-nonnative-plants-are-killing-the-earth-experts-respond.html

[bernhard_hiller]

Hm. Depends. Buddleja davidii is not native to Germany, but a good plant to look for adult butterflies. In the tropics, Celosia argentea is a common non-native weed, and attracts many kinds of insects.
But when it comes to larvae, butterflies are often extreme specialists.

[dianastuder]

The clue is in the name.
Garden RANT has always set out provoke a reaction. Going back a decade or more.

Gardeners want to greenwash eye candy, since ‘insects’ feed on it anyway. Especially the nursery plants that come pre-treated with neonic pesticides. Feed the bees, kill the bees?

I haven’t read Garden Rant for years. But I do read

https://www.clayandlimestone.com/ Tennessee and her Wildflower Wednesdays
https://www.monarchgard.com/thedeepmiddle/on-rabbits-and-salad-bars-in-suburbia Prairie

[dianastuder]

• When the climate changes, vegetation must also change. Many non-native plants are better adapted to current climate and environmental conditions in disturbed ecosystems.

So I can just forget my Cape fynbos and enjoy horticultural horrors from wherever. No more fynbos endemics and the insects and birds they support. And, you know, such a good excuse not to change our behaviour because of climate change. The Anthropocene rules.

[sedgequeen]

The only accurate thing to say is, it depends.

Most pollinators have a relatively loose relationship with plants, and the plants with them. Plants want lots of visits, so most provide nectar or pollen in forms that can be used by many kinds of insects, though many use flower structure to somewhat limit potential pollinators and to prevent nectar theft (taking nectar without pollinating). Pollinating insects will usually go to any source of nectar or pollen that they can access. (I can almost hear you screaming “But! No!” – Yes, some pollinator/plant relationships are very strict, but that’s unusual.)

Many (most?) insects that eat plants have a much tighter relationship with plants, though others are generalists (e.g. locusts) and we don’t have to worry about food sources of generalists. Plants “want” to prevent being eaten and they have evolved a diverse array of more or less toxic chemicals to repel or kill the animals most likely to eat them. Of course, some insects have evolved methods of coping with those chemicals by avoiding them, destroying them, inactivating them, or storing them. However, those coping mechanisms are expensive, so one kind of insect can’t evolve many of them. They’d have no energy left over to reproduce!

Usually, insects that eat plants actually can eat close relatives of their “favorite” plant. Often they really can eat the other species in the same genus (Monarch butterfly larva), sometimes even others in the same family (Painted Lady larvae). Sometimes they can’t, and we usually don’t know which species will be edible and which won’t. And sometimes there are other complications. For example, the level of toxic chemical that protects Monarch adults depends on which species of milkweed they ate as caterpillars.

So, native plants are important for native insects, though that statement with a little slop in it. I think the more honest statement from a gardener would be, “It’s my garden and I’ll plant what I want to!” I respect that choice. I support it. AND native plants are, in general, better for native insects, in some cases necessary for them.

[egordon88]

We have a project for a native group of plants called “rabbitbrush” - 424 species interacting with the plant in different ways https://www.inaturalist.org/projects/organisms-interacting-with-rabbitbrush (with bees significantly underrepresented)

Oaks are known to support hundreds of Lepidoptera caterpillars and Hymenoptera species (oak gall wasps)

I could go on!

[giannamaria]

What about larvae and their hostplant? things like monarchs and milkweed, swallowtails and carrot family, and spicebush swallowtail larvae in particular love sassafrass.

Some things, like adult butterflies and bees, and then the colorful little flower-loving flies, will drink nectar from many flowers, but I think that Gardenrant is spreading false information that could harm the specialist larvae.

I am wondering what gardenrant’s definition of “expert” is, bc all the experts I know in this field would say that many insects count on native plants, and even if an insect can have a non-native, native plants are better for the area and fill an important niche.

The gardenrant author says: “I was disheartened to read this anti-gardening screed” I think she is being ridiculous, the WP piece is not “anti-gardening” it is giving gardeners info on how to do better and how to work WITH pollinators.

The WP author literally says: “But in a couple of seasons, if all goes well, my yard will be full of pollinators, birds and other visitors in need of an urban oasis. Years from now, those tender oak seedlings, now 6-inch twigs, will stretch as high as 100 feet, feeding and sheltering generations of wild animals struggling to survive climate change and habitat loss.” THAT is pretty much a garden imo, and sounds like a great garden/habitat at that.

Back to the gardenrant person, this quote: “All plants, whether native or non-native, convert carbon dioxide to oxygen and store carbon. Destroying them contributes to greenhouse gases causing climate change.” is ridiculous too, since phytoplankton store so much more carbon than a handful of garden plants. Ripping out invasives and planting something better is NOT going to raise greenhouse gasses at all.

This quote from McAllister is also ridiculous to me: McAllister: This description of Milbank’s ravaged garden is consistent with my 25 years of observing native plant “restorations” on public land. They all begin with destruction, usually accomplished with herbicides. The first stage of these projects is often described as “scorched earth.”
Idk WHAT restorations this person has seen, but generally when converting, say, an old field, it is plowed, burnt w/fire, and/or covered in tarp. after that, they have killed ALL of the plants underneat naturally, and can go on to planting.

McAllister continues saying: “Years later, there is rarely habitat comparable to what was destroyed. Colored flags usually outnumber plants.”
I have no clue where they got this information from. I am helping to plant a field full of natives (plus zinnias, idk why they were in the seed mix but I guess we will see what happens with them, these zinnias might be an example of a nonnative working out well, but they don’t prove that ALL nonnatives are a good idea to just plant wherever.)

Here are two pictures of the same field: the first one was taken in June of 2023, and the second one August of 2023:

June 2023: freshly tilled soil, just planted with seeds, only one sign in sight.

August 2023: LOOK AT THIS! LOOK at what Pheasents Forever and 4-H accomplished. It is beautiful! Little kids helped to plant this field, and they made a beautiful habitat! There was so much wildlife here I still haven’t uploaded it all yet.

I am irratated by GardenRant dumping negativity on restored habitats. They are being ridiculous. And also, as for the many flags McAllister complains about, those are for urban areas and the flags are to keep people from walking/letting their dogs poop there.

[DCTropics]

One of my objections was that that widespread cultivation and naturalization of non-native plants favors generalists at the expense of specialists, but they basically countered that specialists are so few as to be negligible.

[lothlin]

@giannamaria

Back to the gardenrant person, this quote: “All plants, whether native or non-native, convert carbon dioxide to oxygen and store carbon. Destroying them contributes to greenhouse gases causing climate change.” is ridiculous too, since phytoplankton store so much more carbon than a handful of garden plants. Ripping out invasives and planting something better is NOT going to raise greenhouse gasses at all.

I should go take a picture of the metropark near me that used to be a golf course and now is a gorgeous prarie in full bloom full of Joe Pye Weed, Rudbeckia, Liatris, etc etc etc. Restoration projects absolutely work.

I skimmed the rebuttal article but the fact that their expert is saying that Rose of Sharon aren’t really an issue is frustrating and tells me they have a very limited focus. Sure its only listed in four states, but I’m in Ohio and its listed in PA and guess what - they have VERY similar ecologies, especially western pa vs eastern oh. If its not listed in ohio, its merely because the state DNR is lagging, not because they’re not listed.

My neighbor has a rose of sharon hedge and I’m CONSTANTLY having to deal with the seedlings. They are a nightmare. And while I will admit they do attract animals (hummingbirds love them,) I’d still much rather see something that supports natives in all their stages instead of just being a nectar plant.

Also the rebuttal seems to conveniently skip the second half of the WP article that discusses how its okay to leave some non-native ornamentals in your garden, as long as they aren’t actively destructive, but to interplant them with more natives. This is the approach I’m taking with my garden, instead of ripping out what I have and completely starting over, when I buy new plants I try to focus on upping my percentage of native plants instead.

Its purposefully inflammatory to drive traffic.

[giannamaria]

I think that they may just be upset that others aren’t gardening the same way as them.

Rose of sharon sounds like an annoying plant, especially when you can have a hedge made up of Aesculus pavia or honeysuckle instead.

@lothlin

I should go take a picture of the metropark near me that used to be a golf course and now is a gorgeous prarie in full bloom full of Joe Pye Weed, Rudbeckia, Liatris, etc etc etc. Restoration projects absolutely work.

I would love to see that! I will never understand golf or why they need perfect grass. My mom absolutely LOVES rudbeckia. I am so annoyed that this “expert” says that restoration projects never work, but then again, that is probably what they want, a reaction.

[dianastuder]

Gardenrant has rolled out this nativist argument frequently down the years.

Benjamin Vogt, who I linked to up top, battled them a few times. Now he concentrates on helping people to convert lawned suburban gardens to something like prairie. And how to deal with the HOA and their rules about lawns.

[swampster]

Non-native plants reduce abundance, richness, and host specialization in lepidopteran communities:

Non-native plants supported significantly fewer caterpillars of significantly fewer specialist and generalist species even when the non-natives were close relatives of native host plants.

Can invasive species replace native species as a resource for birds under climate change? A case study on bird-fruit interactions:

We found that while invasive shrubs […] comprised a large proportion of the total available fruits in late-autumn, birds primarily consumed the fruits of native species throughout the autumn season. Our results demonstrate that native fruits are an important food resource for birds during the autumn migration season and are unlikely to be replaced by abundant fruits of late-season invasive species

These two studies come to my mind right off the bat, but there are many others. Do some native insects sometimes use non-native plants? Sure! But you can’t extend that to say insects are “not dependent on native plants” and “are just as likely to use related non-native plants.”

Douglas Tallamy, one of the authors of the first study, also has several general-audience books about the importance of gardening with native plants. They are excellent!

[dianastuder]

Back to 2007 https://gardenrant.typepad.com/my_weblog/2007/12/doug-tallamy-an.html

Still at it in 2021 https://gardenrant.com/2021/09/when-gardening-to-save-the-planet-the-argument-isnt-aesthetics-vs-ecosystems.html

I would love the opportunity to hear him live!

[mabuva2021]

As others have said, it depends a lot on the insect. Some species are generalists while others, like gall forming wasps and midges, may only form galls on one native plant and a few close relatives. I believe its important that we preserve native plants and the notion that we should just let non-natives take over is absurd to me. Even for insects with a general diet, native plants are probably better and healthier for them than non native ones. Plus, native plants play other important roles besides feeding insects like soil retention, providing habitat for species and carbon capture.

In my garden, we have native plants such as black eyed susans, as well as non native ones like petunia’s. I have seen dozens of species of insects either pollinating or climbing on the black eyed susans. I have never seen an insect so much as land on my petunias, they just don’t recognize them and want nothing to do with them.

[DCTropics]

I have gardens with a large number of both native and non-native plants. Many of the non-natives attract generalist pollinators like butterflies and bumblebees. But the number one pollinator magnet in my garden is the locally native species Monarda punctata. It swarms all day long with several species of native wasps and bees, most of which I have never seen visit any other flowers in my garden.

[chugbug111]

Some insects species are dependent on native plants. They are called specialists by humans. They evolved to be specialists, if they don’t adapt, they die out. It might also be a habitat thing. Like a forest habitat or a grassland habitat.
Some news articles has a feel of far-rightness. The horticulture and agriculture trade is an industry. A lot of plants in cultivation will be deemed non-native, but I haven’t think too much into it. Like say Oranges, and apples, pears, water melons, potatoes. It is hard to estimate the size of land usage by residential areas planting ornamentals compared to planting large scale monoculture crops. It is true some plants escape cultivation and can be a problem. No human can understand nature thoroughly. Pheasants, horses sounds like non-natives to some area too, as recorded by history, but it has been centuries since it was first imported.
Some local laws are redundant. Temperate regions has 4 seasons, and hash winters make it difficult for some species to thrive in some months of each year. There is some feel of rarity if you don’t get to see them.
Some people are allergic to oaks in some ways. I read that. I don’t know if it is true.

[spiphany]

@DCTropics

One of my objections was that that widespread cultivation and naturalization of non-native plants favors generalists at the expense of specialists, but they basically countered that specialists are so few as to be negligible.

The claim that “only a few” insects are dependent on particular plants is interesting and the person making this claim needs to provide some sources to back it up.

According to Paul Westrich, nearly 1/3 of the bee species recorded for Germany are oligolectic; I imagine numbers for North America are likely to be similar (with some variation depending on how narrowly or broadly one defines oligolecty). In some cases, oligolectic bees will also use closely related non-native plants if their native pollen source is not available. But these non-native varieties may not always be suitable – for example, cultivars with modified flower structures that may provide less pollen/nectar or make it more difficult for bees to access. Or the flowering period may not align with the few weeks a year in which the bee species is active (e.g., an allium that blooms in early spring versus in the summer).

In terms of the total bee population, I imagine the generalists are considerably more numerous – precisely because they are not limited to specific plant genera. But this also means that the specialists are more vulnerable, so if one is trying to promote biodiversity, the needs of the specialists should be given particular attention, and thus native plants are an important element in that equation.

This isn’t even considering insects more closely tied to specific hosts for part of their life cycle (food plants for larvae of butterflies/sawflies, gall-forming insects, etc.). Now I imagine these aren’t necessarily the types of insects one thinks about when trying to attract pollinators to one’s garden, and their presence may not be desirable to the gardener. But non-natives will attract pests, too, and they may have poorer defenses against the local pests or the pests that attack them may not have local predators to keep the population in check.

It seems like this person is setting up a false dichotomy. There is no reason why planting more native species can’t happen alongside the use of non-native ornamentals or vegetable crops.

[deboas]

@DCTropics

they basically countered that specialists are so few as to be negligible

Specialists make up a large proportion or even the majority of species globally, but they tend to be less represented in gardens precisely because it’s the generalists who adapt well to gardens! Generalists by definition are commoner in human-modified environments and are more widespread, so most of the organisms we tend to encounter are of generalist species. But the species who are actually at risk of extinction and need our help are more likely to be specialists.

[dianastuder]

The ‘expert’ rolled out to fend off those tiresome nativists, who won’t go away, even after years.
The ‘expert’ doesn’t say who funds them and their research. Big Hort and the turf-grower’s association?

[cbirds22]

@DCTropics

are there any projects on iNaturalist dedicated to matching herbivorous insects to the plants they’re feeding on, and/or identifying whether the respective insects and plants are native or non-native to the area where they were observed?

In answer to the original question, I recently started a project focused on Native and Introduced Species Interactions. The scope of the project includes more than what you asked about, but I’m guessing that insect/plant interactions will likely comprise the majority of observations in time. One of the recommended observation fields for the project is for the associated species. (I didn’t make the first required because someone may not know the name of the associated species, but I hope that field especially gets filled out.)