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Many of my small almond trees are invaded by tree borers, and it is impossible to locate them since they make serpentine tunnels inside the tree, near the ground level. I am willing to risk one or two trees (but not my safety :) ) and will try to kill the borers with an electrical shock, hopefully without damaging the tree itself. I may experiment with the proper parameters to find the best solution. However, I know very little about electricity, and even less about high voltage, low current. I am not asking a full solution (but would be happy to receive one), all I am asking is to guide me into the general path to start my research.

For example: can I use a cordless drill charger as the source, should I use a transformer, and how does the tree resistance come into play?

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    \$\begingroup\$ You are more likely to kill the tree or yourself doing this. You will not be able to make any kind of meaningful potential gradient across the very thin larvae without either A: a direct electrical connection to the larva (in which case you can just stab it), or B: an amount of power that will damage the tree (perhaps explosively). \$\endgroup\$
    – vir
    Commented Oct 31, 2022 at 21:11
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    \$\begingroup\$ you seem really desperate, willing to try a things you know little about. it's unlikely that you are the only person with borers in their almond trees, you should consult a tree expert. \$\endgroup\$
    – Jasen Слава Україні
    Commented Oct 31, 2022 at 22:00

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The big problem with this idea is the huge difference in cross-sectional area between the larvae and the tree.

Wood is a wonderful electrical insulator. Even damp wood only has a specific conductivity of around 10^-4 S/m (Siemens per meter).

Let's assume that you have a 10kV voltage source, which is already way more than enough to kill cattle if the current capability is high enough. Let's also assume a cylindrical tree with 20cm diameter and 2m length. The cross-sectional area of the tree is 1257cm² (0.1257m²). To get the tree's conductance, we multiply the specific conductivity with the tree's cross-sectional area and divide by its length: G = 10^-4 S/m * 0.1257m² / 2m = 6.285µS (microsiemens).

To get the total current flowing through the tree, we can multiply the voltage and conductance: Itree = 10kV * 6.285µS = 62.85mA.

Let's also assume that you have some very large larvae in the tree with a cross-sectional area of 4cm². Given that the larvae are small compared to the size of the tree, the current will divide between the larva and the surrounding wood roughly in proportion to their area: The larva will get a current share of p = 4cm² / 1257cm² = 0.0032 = 0.32%.

This means the larva will experience an electrical current Ilarva = Itree * p = 62.85mA * 0.0032 = 0.2mA = 200µA.

The larva isn't even going to notice this. The tree's wood is very effective at protecting the larvae within it from electricity.

On the other hand, the tree is already experiencing P = Itree * U = 62.85mA * 10kV = 628.5W of power being dissipated within it, which will kill it quite quickly.

TL;DR: Tree dies, larvae live.

You could of course increase the voltage even further, but...

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    \$\begingroup\$ Agree. But the problem is probably worse, the cambium layer is probably more conductive, so the current will flow around the perimeter. \$\endgroup\$
    – Mattman944
    Commented Oct 31, 2022 at 21:53
  • \$\begingroup\$ What about half a minute of 1 kW focused micro wave power? If eggs exlode.. \$\endgroup\$
    – Jens
    Commented Oct 31, 2022 at 23:15
  • \$\begingroup\$ @Jens That might work better, but anything around (especially behind) the tree is not going to be happy either - including law enforcement... \$\endgroup\$
    – Jonathan S.
    Commented Oct 31, 2022 at 23:16
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    \$\begingroup\$ Well, I just remembered killing a rat in the wall with an old magnetron \$\endgroup\$
    – Jens
    Commented Oct 31, 2022 at 23:28
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I think a quick try would be to use an electric fence system. These systems send periodic HV pulses to charge the fence wire. They’re intentionally limited in energy as so not to harm the animal (or human) that comes into contact with them, yet they will deliver a painful shock.

Here, you’d take the charger ground to a grounding rod near the tree roots, then take the ‘fence wire’ side and connect it to the tree trunk above where you suspect the pests will be. With luck, the low-resistance path will be the insects in the wood. If it doesn’t kill them outright it will at least annoy them.

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