Absurd question. Does anyone have extensive knowledge of measuring the UV reflectivity on materials?

Absurd question.... But I gotta ask. Does anyone have extensive knowledge of measuring the UV reflectivity of various materials ?? Anybody?

This is a long shot but I just have to ask. Here's the thing.... I know lots of you have the same problem that I do. Little green caterpillars are eating all your cabbages, broccoli etc. It sounds like most of you are having this problem because of 'cabbage moths' or the 'cabbage looper' moths. They all look the same to me. But I don't have any of those around here. Here, the caterpillars are from the 'White Cabbage Butterfly'. It's a small white butterfly with a couple of black spots on it's wings.

When I started gardening here 11 years ago I saw maybe 5-10 in a day. Not a big problem. But each year there are more. These last 2 years I see about 5-10 every minute. Maybe I'm just seeing the same 50 to 100 and they found my yard and won't leave. I usually spray my crops a few times each summer with Spinosad or Neem oil but this year they are unstoppable. I keep my brassicas in tunnels covered in bird netting when they are small and this has always kept out most of them. But these last 2 years they are all about ½ the size they used to be and they can go right through the bird netting. So I am trying to come up with a better way than putting solid covers over them which seldom works.

I have spent a lot of time researching online looking for real scientific evidence to fix this, not just anecdotal ideas that people keep passing around and never works. And I finally hit PAYDIRT!! Pun totally intended! I found Real science!

NEW ZEALAND HAS ERADICATED THE 'WHITE CABBAGE BUTTERFLY FROM THEIR ENTIRE COUNTRY! New Zealand is awesome! Granted, it only arrived there in 2010 and was only seen in 2 small areas but they used all the tools in their toolbox and eradicated them in just a few years before things got bad. They got the public involved, and sprayed the same organic insecticides that I do. Caught every one of them. Good job!!  However, since they are everywhere here in America that wouldn't work for us. BUT....

It says in their report.....”Research was conducted to develop attractants for P. brassicae adults, but did not produce practicably useful results [45,46]. However in 2014 a DOC staff member, W. Wragg, developed an ultra-violet (UV) reflective lure that was attractive to P. brassicae adults. Its efficacy was optimised by measuring the UV reflectivity of various materials [47] to identify one with similar reflectivity to P. brassicae wings [48,49]. A cloth with suitable UV reflectivity was glued to ornamental butterflies’ wings, which moved by solar power, and the models were used to attract P. brassicae adults towards staff with nets.

The UV lures were first deployed in October 2014 when detection rates had already declined to low levels (Fig 2). Pieris brassicae adults approached the lures in a manner similar to P. rapae [48,62], but never alighted on them. From 10 October 2014 to 3 November 2014, it took 180 person-hours to capture three P. brassicae adults without a lure, whereas it took 44 person-hours to capture seven with a lure.”

Here is the report from New Zealand if anyone wants to read it.... https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0236791  accept the cookies.

So again, my question is 'Does anyone have extensive knowledge of measuring the UV reflectivity of various materials'? If someone can replicate the reflective material, why can't we build a simple trap. The material would lure the butterfly in to.... a bug zapper?, a bowl of water to drown in?, something. Do the wings have to flap by solar power or could it be just as simple as a small piece of paper on a bobby pin moving in the wind?

If we all put our heads together we could create and manufacture these..... and solve my problem..... and we can patent it and agree to give all the proceeds to Permies. Just a crazy idea but I had to try.

Sidenote- I took a stupid anecdotal suggestion off the internet last year and planted lots of catmint all around my yard because they said that it's super-duper at attracting lots of great pollinators. So far they are only attracting the damned 'white cabbage butterfly'! You can't see them all in this picture because they wouldn't leave the bush and fly. They  refused to obey my command! I would send 'Mother Nature' another complaint but I think she's gone off her meds right now!

If you haven't tried it already, Mason bees are the best pollinators, non aggressive and easy to establish a colony with little tube houses. You can also share larva from your colony with friends to help grow bee populations world wide.

Regarding uv reflective value, I know that UPF factor for fabric refers to microscopic space between the threads. So fabric with a UPF of 50 blocks 98% of the sun's rays. I would assume that it is being reflected.

I have only seen UV reflective value used with building materials,   That one is called Solar Reflectance Index (SRI) , so you could potentially paint your decoy with a high SRI coating with a known reflective value listed by the manufacturer.

By the way, I spotted this fancy water in the store today. Are you familiar with this one?

Debbie Ann wrote: However in 2014 a DOC staff member, W. Wragg, developed an ultra-violet (UV) reflective lure that was attractive to P. brassicae adults. Its efficacy was optimised by measuring the UV reflectivity of various materials [47] to identify one with similar reflectivity to P. brassicae wings [48,49]. A cloth with suitable UV reflectivity was glued to ornamental butterflies’ wings, which moved by solar power, and the models were used to attract P. brassicae adults towards staff with nets.

Interesting! I take it they were "looking for love in all the wrong places?"

Measuring is probably easiest with a spectrometer: Laboratory equipment that is far from easy to operate and expensive.
But I don't think you actually have to measure it yourself.

White paper should be quite good already. And if it is not good enough, search for UV reflective paint like this:
http://www.birdstoppers.com/flock-off-uv-paint

Aluminium foil seems to be a somewhat usable reflector as well.

Um, don't want to rain on anyone's campfire, but we have not eradicated the white cabbage butterfly here. They are an extreme pest, to the point where I've given up trying to grow brassicas for 4-6 months out of the year. My horseradish always gets skeleton leaves. Any stray mustard plants out in the paddocks are destroyed. Seedlings sown in autumn for winter and the following spring have to be netted and watched daily.

The article is referring to a second species, the "large" white cabbage butterfly, that was successfully contained around Nelson and is now probably gone. But the small ones are everywhere, thanks to the common planting of fodder brassicas and turnips as animal feed crops. If the farmers in each district would agree not to plant any about one in five years, we could get a handle on it using a combo of neem, Bt, and the UV tricks. But they won't have a bar of it.

Not an absurb question at all. I seem to remember a post on Permies about hunting for caterpillars under uv light - yes here it is!
 Fun can be had!

I found a bit more on UV photography here


Some lovely pictures of flowers there too, but if you dive in there may be some tips of how to "see" like an insect. I seem to remember that foxgloves have uv visible spots that lead the bees to the nectar...

On the subject of protecting your brassica, have you tried mixing them with other plants? I've heard that some insects just see leaves as "green" and can't differentiate their food plant before they land on it. I gather that companion planting underneath or amongst them with a non food source plant like clover means they land on one or two leaves, find they're not food and go away.
It looks to me like the catmint is doing it's job great. If they're landing on that, they're not on your cabbages! I think it's super that your insect population is soaring, hopefully the predator population will soon too and nature will rebalance. As long as they leave you a few cabbages in the meantime!

Hi Everyone,

Hi Phil Stevens... Your news leaves me soooooo disappointed. Why did your Department of Conservation make such a big deal about eradicating the 'large cabbage butterfly' if you already have the small ones? I had my hopes way up. This was science, real science! I am really, really bummed. I hoped I was on to something.

Hi William Kellogg... I have a long list of upcoming projects and building some mason bee habitat is on it. I do have lots of honey bees all summer and I am trying to find new ways to lure in more of the predator bugs. I always have lots of ladybugs but not nearly enough to eat all the aphids.
And yes, that's our water. The mountain ranges around us are full of springs that feed the aquifer below us. Sedona has 5 wells tapped into it to supply us which is so lucky since they are now seriously restricting all the water from the Colorado river  to the folks down south and in California. It's 'hard' water with a ph of 8 but it's very good. I read our water quality reports every year and so far so good. And most other people here buy bottled water from other places! Go figure!!

Hi Nancy Reading... Not all caterpillars are reflective under UV light but the tomato hornworm is. Hornworms are usually pretty easy to find in daylight but every once in awhile one will be very good at hiding and I do go out at night with a black-light flashlight to get it. Works well.
And yes, For the last few years I have been planting my brassicas next to other plants to hopefully repel the bugs and butterflies but it just doesn't seem to help. The catmint is also supposed to 'repel' aphids, the 'cabbage looper moths' and 'Colorado potato beetles' and bring in good pollinators. This year I am focusing a lot on more companion planting for this reason but it turns out it's very difficult to get the plants to all grow at the same time. I guess 'Mother Nature' just doesn't roll like that.

Just one plant has been a huge success for me. In the picture it is the dark purple plant  just behind the catmint.  Here is another picture of it. It is 'Mystic Spires Sage' It dies to the ground every year and begins to grow again in February/March. It easily handles full screaming hot sun and 110* all summer and only needs a little water. And deer and rabbits won't touch it! By May it is about 3 feet tall and wide and each one will be covered with hundreds of honey bees all day, every day until late October. I have about 30 of them all around the yard and my gardens hum with many thousands of bees all summer.

Thank you all so very much for your feedback. I'm going to have a good cry now and then get back to my garden. Happy gardening everyone.

That's a beautiful garden, you are really greening the desert!

I think over time these caterpillars will complete their their natural cycle. I hope you can find a way to live with them in the meantime.

Meanwhile focus your energy on improving bird habitat and other natural predators for the next invasive species that shows up. I know you mentioned ladybugs, which is great (make sure they have a good source of water) What about mantis?

Grant me the Serenity to accept the things I cannot change, Courage to change the things I can; and the Wisdom to know the difference. Living one day at a time; enjoying one moment at a time; accepting hardship as the pathway to peace.

Kia ora Debbie -

The reason DOC got involved was because the large white apparently has a taste for some of our native brassicas, while the small white mostly goes for cultivated plants. If it were just another pest of arable or horticultural crops, the task would have been the job of the Ministry for Primary Industries. The fortunate bit was that the butterflies were noticed early, before they had a chance to really start breeding and spreading beyond the small area that they had colonised, and that was a big part of the the operation's success.

I'm with William on the suggestion to increase your predator habitat and try to bring in reinforcements to help control the butterflies. I grew stuff in Tucson for many years and my best assistants were things like lacewings, ladybugs, thrashers, and lizards.