Category Archives: Nature

Bti honeypot traps for killing mosquito larvae

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An easy way to kill thousands of mosquitoes each summer is to drop some Bacillus thuringiensis israelensis (abbreviated to “Bti”) into containers filled with stagnant water. The photograph below shows one fashioned out of a litter box, but any large container will work. Then just lob in a Mosquito Dunk (made by Summit) or any equivalent product that contains live Bti spores, and repeat every three weeks so that there is a fresh supply of bacteria. Over the summer months, hundreds or thousands of females will find the container and oviposit onto the water surface as well as any objects such as wood and terracotta pots placed inside. When the larvae begin to feed they’ll be killed by the toxins produced by the bacteria.

Tips

As you can see from the photograph, I’ve covered the container with chicken wire. This prevents birds from drowning but also serves to prevent dogs, foxes, deer, and raccoons from draining the water, which they do quickly in my yard.

To increase the attractiveness of the water, add a handful of leaves or grass, which decompose but emit distinctive volatiles (not CO2, fyi) that attract gravid females.

I’ve also added a board that is partially submerged so that Asian tiger mosquitoes have something wet and rough to oviposit onto (they don’t oviposit onto the water’s surface like many other species). I set the board at an angle so innocent insects might be able to climb up out of the water when they fall in. Terracotta pots are another excellent option because the entire surface stays hydrated, something that mosquitoes love. Even some dry leaves floating on the surface will do the trick.

Finally, I recommend adding some sort of white object (like a yoghurt lid weighted down with a rock) that allows you to easily view larvae wriggling around; if you see them you need to add a fresh Mosquito Dunk or equivalent.

When siting your honeypots (the more the better) opt for locations that don’t get direct sunlight, are near vegetation, and are at the bases of larger trees. And it’s totally OK and even preferable to have each of your honeypots set up in a different way. E.g., if you live in an area with yellow-fever mosquitoes (Aedes aegypti), add some salt (0.25%) to increase oviposition rates. And other species of mosquitoes like large amounts of rotting vegetation. Your yard has dozens of different mosquito species so the trick is to identify your problem species and then design a honeypot that attracts them best.

PRO-TIP: If you don’t mind eye-sores in your yard, use tires. Asian tiger mosquitoes go bonkers for them. For slightly prettier traps you can cut tires apart and make ovillantas (“egg tires”). Smithsonian Magazine has a nice overview of these traps (just swap in Bti instead of the pesticide). You’ll need a Sawzall-type tool to cut through tires with metal reinforcements.

Purge your yard of standing water

Bti honeypot traps won’t do a thing if mosquitoes have plenty of other sites where they can dump their eggs. So get rid of all the objects that are accumulating water: kid toys, plastic tarps, saucers under plant pots, etc. And make especially sure that your gutters are free of clogs. If you’d like a visual guide to the places that accumulate water, see this page. The success of Bti honeypot traps will also be improved if you can somehow get your neighbors invested in removing their stagnant water, too. One trick for getting neighbors on board is to make sure one of yours is highly visible when you have people over for dinner. When they ask what that is, have one ready to gift them. The more neighbors participating, the better.

Are they working?

To determine whether mosquitoes are ovipositing, just look for egg rafts on the surface of the water. Eggs from Asian tiger mosquitoes (Aedes albopictus) are oviposited singly or in small groupings on the edges of the container or on pieces of wood. If there are eggs and no larvae, the Bti is doing its thing.

Raft of mosquito eggs (Culex sp.) next to a dead female mosquito.

Warning

After a few weeks the bacteria will die off, so you have to keep adding new Bti throughout the summer, approximately every three weeks. But as mentioned above I think it is a good habit to glance at your containers every several days to confirm that the Bti is doing its thing. If you are not vigilant about refreshing the Bti all those containers will start pumping thousands of mosquitoes into your yard every week and your neighbors with loathe you if they don’t already. So if you like to start projects but not maintain them, Bti honeypots are not for you. Here’s what mosquito larvae look like:

Are they safe?

Bti toxins are completely nontoxic to mammals, birds, and all insects except mosquitoes, black flies, and fungus gnats. For an excellent overview of the mode of action and safety, please see this report (PDF).

Sources of Bti

Other sites with similar information

Killing adult mosquitoes

If you also want to kill adult mosquitoes, please see my post on autocidal gravid ovitraps. Several companies sell them but you can make your own. I own a half-dozen of these traps AND a similar number of Bti honeytraps.

Autocidal gravid ovitraps made by Biogents and Springstar.

Birds are eating my pea plants

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This spring I decided to figure out which bird species are decimating my peas, with the hope that an ID might help me better protect my crop next year. Sneaking up on my allotment so as not to spook the birds, it didn’t take me long to figure out that the culprits were mainly house sparrows. Usually a large flock of them. As proof, here’s Exhibit A, a female house sparrow with a big chunk of a leaf in her mouth.

But I’ve also observed northern cardinals and American goldfinches doing the same, so I can’t blame everything on the sparrows. Indeed, I suspect I’d see additional species helping themselves if I camped out under cover of a bird blind for a day. Pea shoots are just that good.

Naturally, I immediately ran out and purchased bird netting and fully enclosed my trellises in a large box, complete with multiple doors made from overlapped netting, all pegged at the ground with rocks. The netting is delicate and black so it’s hard to see in the photograph below but trust me, it’s there and it covers everything rather tightly.

But after I set it all up the damage to the pea plants continued at pretty much the same level as before. Please refer to Exhibit A, above, and note how the background of the photograph shows the bird netting — the birds just found tiny gaps in the netting, ate their fill, then let themselves out. The cardinals and finches weren’t deterred much, either, and at one point I saw all three species inside, happily munching away.

Below are photographs of the damage in case you’re interested why I’m so worked up about this situation: growth on primary meristems are nibbled off, leaves covered in tiny beak-shaped compression wounds, shoots bent when fat birds perch on the stem while foraging, severed branches left on the ground. When I surprised the birds I could see them flying off with pieces still in their beaks.

I should point out that my allotment is just one of many, and other people have completely unprotected pea plants (gasp!). So I’m wondering, why bother navigating my cage system when there is plenty to eat elsewhere?? Although other people’s plants certainly show damage, whenever I spy on the gardens from afar the birds seem to be on mine plot, on my peas. I’m thinking they must prefer the varieties I’ve planted, all heirloom varieties that climb (‘First 13’, ‘Magnolia Blossom’, ‘Tall Telephone’, and ‘Purple Podded’).

Perhaps the dwarf, self-supporting varieties that most people grow have more lignin and such in the stems and leaves, rendering them less palatable to birds. In support, I’d note that of the varieties I have the birds seem to prefer ‘Magnolia Blossom’, a sugar snap pea (Pisum sativum var. macrocarpon, I think) which Burpee says has “edible tendrils” (tendrils = shoots to pea folks, I think). The Ottawa Gardener, writing about peas with edible shoots and tendrils, says something similar: “I’ve noticed that most recommended varieties are those with edible pods which may be [sic] because the shoots are less fiborous [sic] or sugary.” Andrew Barney says something similar about peas with edible leaves: “any variety with both p / v genes for low fiber in the pod would be a good candidate for this. Plants with lower fiber in the pods also have lower fiber in the leaves,” adding that leafcutting bees (Megachile spp.) also seem to have a preference for tender-leafed types.

So, what to do? I think for this season I’m just going to keep fussing with the netting to minimize the damage. But next year I’ll replace it all with stiffer netting that can be better fastened together with twist ties and such. It will be a lot of work but man I love fresh peas and I don’t like to share.

Anyone have suggestions? I’ve tried a fake owl (birds don’t care at all) but I haven’t yet experimented with holographic tape, threatening mylar balloons, or CDs suspended from monofilament. I’m think none of these will work. What I’d really like to do is leave a hungry cat inside the trellis cage. But I know that would be frowned upon by the locals. Same for the laser defense systems that some vineyards use.