Durian Worms, Organic Solutions, And Lots and Lots Of Frass | Growing Durian

One of the very first durians I ever bought had something wrong with it.

I was in our tiny kitchen in our tiny cottage on a dreary, midwinter day in Oregon. It was so miserably drizzly we’d bought a durian just to cheer ourselves up.

I remember standing tip-toe at the counter in my thick socks, hacking and pushing and generally mangling the half-frozen durian, willing it to open. 

When at last it gave way I let out a little shriek. And not of joy.

Nestled in the soft, gooey folds of my favorite fruit was a giant, voluptuous purple grub. It glowed a deathly magenta, locked in a frozen, arching flail.

Strangely, it was finding that creepy crawler in my durian that got me thinking about actually going to Thailand.

I mean, how cool is a plump, purple worm?

Of course, it wasn’t actually a worm. It was a caterpillar. And it was 100% dead, having made the transatlantic sea voyage all the way from Thailand while
frozen at -18 C.

Not many arthropods can
boast such extensive and hazardous travel.

And in fact, getting such a critter in our durian all the way in the US was a great stroke of luck. Most Thai durian growers expend a vast amount of effort and toxic chemicals just making sure that we don’t find stowaways in our fruit.

But for me, that bug fueled my imagination.  This was before I’d ever visited a tropical country, and finding a huge, brightly colored insect inside my weirdo, spiky fruit made me feel like I was holding a remnant of another planet in my hands. As I stood in my thick socks staring out the kitchen window at a barren, misty winter world, I began dreaming of the jungle.

So in honor of that first inspirational grub (and all the others I’ve sent scurrying since), here’s a look at the two invertebrate durian fanatics you’re most likely going to be fighting with over durian and some ideas how you can win that battle without poisoning yourself, your friends and customers, and the planet.

The Very Hungry Caterpillar

The poor little fellow I found in my durian was a baby of one of the Mudaria moths.  There are three separate species of them, but to anybody who doesn’t study insects (like me) they look nearly identical.

Like all twins can’t tell apart, they are often lumped together under one group name: Durian Seed Borers, a boring if apt description for the plump purple caterpillars with black spots. 

Durian Seed Borers are durian specialists. They literally only eat durian for the entirety of their lives (got you beat there, Mads).  

But in a defiance of logic and reasoning, this caterpillar doesn’t give two hoots
about the creamy, chocolatey-caramel fudge that drives us wild. The only thing the caterpillar wants is the semi-poisonous durian seed. Explain that
one. 

So it’s all good, right? A sort of symbiotic relationship where the caterpillar eats the seed and we eat the fruit?

In a blatant contempt for durian lovers everywhere, the caterpillar throws its poo all over, riddling the scrumptious cream with orangey-brown balls of sh** called in more polite circles frass. 

The frass renders the durian inedible, the durian eater disgusted, and the durian farmer possibly broke with unsellable durians.

All because of a moth with picky taste buds. 

Mature Durian Seed Borer, photo gratefully borrowed/stolen from thailand.ipm-info.org

Dangerous in yellow 
  
But we can’t blame all the frass-mess on the Mudaria triplets. There’s another, more devious caterpillar at work, although you’re unlikely to catch a glimpse of this trouble-maker.

Conogethes punctiferalis begins its life in much the same way as the Durian Seed Borer. Mama Moth abandons a single tiny, practically microscopic egg on the shell of a baby durian. Within a day or two, the tiny white caterpillar emerges, realizes its quite alone on a cold, lonely, thorny planet, and in fright begins chewing its way into the shelter of the durian fruit.

Except unlike the large, bumbling, selective  Durian Seed Borer,  the Yellow Peach Moth eats everything. It eats the shell, or the seed, or the fruit, or whatever is closest. It’s been discovered on over 35 crops. One durian agriculturalist noted it that it is “likely to attack whatever it comes across.” Spooky.

So don’t be fooled by the cheery color and polka dots of the adult moth. These guys are dangerous.

Yellow peach moths making more of themselves. Photo from hkwildlife.com

The reason you’re unlikely to actually catch a glimpse of these skinny, white, maggot-like critters with dark heads is because they’re
practiced escape artists. While Durian Seed Borer need about 40-50 days to begin chewing its clumsy way out of the durian, the Yellow Peach Moths pupate after only 2-3 weeks and are long
gone by the time we durian-entranced humans get a hold of the fruit. 

How
do we know they were ever there? Frass. Lots and lots of frass.

And get this: when they’ve had their fill, they actually climb back out
of the durian, wrap themselves in their poo, and metamorphose right
there on the durian hull. Awesome.

But here’s a tip for consumers: they’re so tiny when they enter the durian that the growing durian seals up the entrance hole. This means there’s no way to tell if there’s a caterpillar inside the durian, just if it’s already left. If you see a hole in your durian, you can expect to find a lot of frass, but the perpetrator has already flown the coop.

The incriminating evidence – frass

Chemical Warfare 

The combined damage of these miniature durian fanatics can be pretty fatal to a durian farmer’s income. Some resources estimate that if an orchard is left untreated as much as 50% of the crop can so filled with frass its unfit for sale.

Now, I know every creature deserves a fair share of durian, but half of the crop seems mighty greedy for critters only 4 cm long at max.

So most farmers spray. Starting when the fruits are tiny green spike balls, farmers spray up to every two weeks throughout the season (this is worst case scenario), including  two weeks before the harvest, with chemicals like Carbaryl, Deltamethrin, Dimethoate, Endosulfan, Fenthion, Metahamidophos, and Phosalone.

Look, I put the list in alphabetical order just to make them seem more friendly.

These little guys are the number one reason durian farmers tell us they can’t possibly stop spraying and take up more organic practices. They’d have to deal with too much frass. That word is too much fun.

But nobody really wants to spray chemicals on durian trees. For one, lugging gallons of pesticides up and down and around in the hot tropical sun is way too much work. Plus, studies on durian farmers suggest many develop neurological disorders due to over exposure and improper use. No fun.

Keeping Durian For Ourselves, Organically

Luckily, researchers and practical people have already figured out how to discourage durian-munching caterpillars without relying on probably toxic chemicals.

There are a lot of ideas out there. One organic durian farmer we spoke to uses smoke and special fertilizers to keep the caterpillars at bay, while another swears by sunlight.

One is to encourage parasitic wasps like Trichogrammas or Cotesias to hang out in the orchards. These guys lay their eggs inside the caterpillar’s egg, either killing it before it’s even had the chance to realize it likes durian.

Another is to prevent the moths from mating by putting lady-moth pheromones all over the orchard, driving the horny male moths crazy as they try to get it on with everything that smells good yet doesn’t actually have an egg or whatever substitutes for a moth vagina.

Even stranger, a company in Canada called OK SIR (I do not lie) has been specializing in the sterilization of up to 2 million male moths each day. The eunuchs are then released into the orchards to distract lady moths from guys with real balls (Didn’t think it could get better? Oh it does. Somebody wrote a poem about sterilized male moths)

There are other measures farmers can take to protect their crops from winged bandits as well, like moth traps or using poisoned sugar bait to reduce the population in your area but the most effective solution might be far easier than we think.

Put A Bag On It

Probably, the easiest way to prevent caterpillars from eating all your durians is to cover the durian with a bag.

One of the secrets to the most expensive durian in the world is that
they are wrapped in sheets of plastic, said to slightly sweeten the
durian in addition to protecting it from nibbling insects.

Covering ripening fruits is a common practice with other fruits, like bananas or longans, or cempedak. We’ve seen them hanging from trees wrapped in newspaper cones, woven reed baskets, or paper bags.

And studies have found that bagging is at least as effective as spraying with chemicals. This 2003 study compared the effect of bagging durians at six weeks or eight weeks to common chemical treatments. They found that all methods of protection had a 100% effectiveness. Yet except for our trip to Nonthaburi and the BPI research station in the Philippines, I’ve never seen bagged durians.

It’s of course easier to put a bag around a durian when the trees are kept relatively small and low to the ground, like in Thailand, but in Malaysia and Indonesia it’s common to see durians a hundred feet in the air physically tied onto the tree with twine to prevent fruits from smashing on the ground. If someone is talented enough to do that, why not add a protective bag at the same time?

Learning To Share

But ultimately, even the best system isn’t perfect. We still find the purple critters in the most sprayed of durians, like that Thai durian I opened in Oregon. The little guys are a persistent. And who wouldn’t be, if you’re entire existence depended on durian?

I mean, the little guys only eat durian. That’s it. If we humans refuse to share, they might go the way of the dodo bird.

And while it’s great to think that there are some pesky insects that we could happily live without (seriously, what was Noah thinking when he let mosquitoes on board?) moths are actually kind of important in the whole interconnected ecosystem thing.

In fact, along with bats, moths are the major pollinator for durians. It’s in part thanks to them that we get to eat durian in the first place.

So just maybe, we should be a little more willing to share, and just a little more accepting when we find these cutsey, magenta and polka dot caterpillars in our durians. Even with all their disgusting frass. 

Do you agree? How do you feel when you find an insect in your durian?

If you have experience with growing durian,  please don’t hesitate to share your own thoughts and wisdom in the comment box below!

Further Reading:

• Tropical Fruit Pests and Pollinators – Available on Google Books
• Thailand Integrated Pest Management Seed Borer
• The Agronomy and Economy of Turmeric and Ginger Available on Google Books
•  Ultrasonic courtship song of the yellow peach moth, Conogethes punctiferalis (Lepidoptera: Crambidae) Applied Entomology and Zoology,
  Volume 47, Issue 2 (May 2012), pp. 87-93. 
• Appropriate Bagging Time To Prevent Durian Fruit Borers 
• Seasonal Occurrence of the Durian Fruit Borer