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locusts - disease outbreaks?

edited January 18 in Bug Farming Questions

Hi,

During my farming of Locusta Migratoria I had several “outbreaks” of some kind - when suddenly, without any change in conditions, my locusts start dying.

I’ve since changed my methods to be more sanitary and isolated from any outside environment, it seemed to work for some time, but now it seems to be back.

I am having a really hard time trying to identify the source of these problems or coming up with a solution.

It usually presents like this:

  • after of period of zero noticed deaths, locusts start dying, not all at once but rather slowly (say 1-4% of the population daily)

  • in all cases so far the die-off first occurs in later instars (subadults / adults) and then spread to younger ones

  • it starts in one cage and spreads to other cages within up to a week

  • nothing visually wrong with the locusts, only in one case (so probably irrelevant) I’ve noticed a spot on a dead one’s face, see here: https://pasteboard.co/HX3V0rO.jpg

  • if nothing is done, they keep dying until there is only a few of them, at which point it seems to stop

  • if I let locusts from a "dying" cage breed and lay eggs, the successive generation is fine until subadult/adult again (or I haven't noticed any dead small hoppers)

  • I used to have Schistocerca Gregaria in the same boxes, same problems for them

Outside of these outbreaks, they seem to be thriving under the same conditions (permanent 32-35 °C, 12 H light, 30-40% RH, dry food + water)

Has anyone experienced this? Are there any known locust pathogens that would cause this? I am assuming it is a pathogen due to the way it presents itself, but of course I might be totally wrong.

Also, is there any "normal" or "expected" level of die-offs in locust farming? Or does any death always imply a problem?

Thank you

Comments

  • edited January 18

    Locusta migratoria are plagued by at least 2 kinds of fungi that are pathogenic to this kind of locust. I don't recall these fungi exact names & can't find those in my notes to relay specifics. My assumption is the contamination came into your bins with some food items.

  • @gringojay Thank you. I did find mentions of nosema locustae, is that what you meant? There's even a guide to treating it with sulfa drugs here https://www.jstor.org/stable/3503403 , however I have tried that and it doesn't seem to help (of course I might have jumbled the dosage etc.).

    Would keeping humidity low destroy fungi contamination? What would be a way to confirm it is the fungi?

  • If you did not treat the habitat bin surfaces then re-contamination likely resurged from those surfaces. I'll assume you changed out their bins in such a way they could be sanitized?

    Nosema locustae is now called Paranosema locustae. It is a micro-sporidian (protozoa). It has been commercialized for field spraying. The selling point is that it can transfer from one locust to another & even between generations.

    Another micro-sporidian attacking locusts is Antonospora locustae. I assume it is also being commercialized for spraying on grass land.

    A naturally occuring soil fungus also used commercially to kill locusts is Metarhizium anisopliae var. acridum (previously called Metarhizium flavoviridae). At lethal doses this fungus is faster killing than the micro-sporidian(s).

    I've seen reference to an Aspergillus variety that is also fatal to locusts. From memory this too is faster acting at lethal dose than micro-sporidians.

    If it is micro-sporian pathogen then will need to isolate progeny from several breeding lines. You'd be trying to find breeding stock that transmitted less (& then again less) micro-sporidia to progeny.

  • Again slupik, - For micro-sporidia maybe the information about honey bee Nosema apis problem will give you some ideas. The isolated microbial compound called "fumagillin" has been used for bees; but it has to be used at a high enough dose to control spore levels (plus for wax moths fumigillin depresses their immunological system).

    Two other honey bee tactics for controlling micro-sporidia were oxalic acid & also formic acid. I haven't followed their applications, but you might get some leads from bee keeping websites with veterinarian orientation.

    I did see other "natural" bee keeping controls, like essential oil & pri/pre-biotics, that have been touted. But these have apparently not really worked well in practise.

    Human's with AIDS are prone to get micro-sporidia & are given anti-fungal medication(s). I don't recall which & can't say if any are suitable for insects, but am sure those can be tracked down on the internet.

  • edited January 19

    Thank you @gringojay, breathtaking knowledge as usual.

    1. When I had the last outbreak I actually got rid of all the diseased stock as well as the cages, vacuumed and disinfected the room

    2. I purchased fresh stock

    3. What might have been a fatal mistake I see now is that I kept a batch of eggs from the “diseased” stock, as the small hoppers from them seemed to be unaffected and no death occurred until they started molting into adults. There is no direct path from one cage to another, the spores would have to be air-borne, which I don’t know if they are.

    4. I’ve heard about spraying with Nosema Locustae, I was hoping that since I’m in central Europe, this pathogen wouldn’t be present here. Even less so, since I talked to other breeders here and none reported similar issues.

    5. Metarhizium anisopliae var. acridum - from what I’ve found, this presents visually on the locust, so likely my problem is with another pathogen

    So from all this my guess is that it points to a very unlucky contamination with Paranosema locustae (as it is slow acting and works “inside” the locust).

    I have very little experience in solving something like this.

    My thinking right now is:

    1. I have to find a way to confirm it is Paranosema - I’m guessing finding a lab that would be able to do this?

    2. Either try getting rid of everything and disinfecting again (gets expensive and not a good precedent as I want to scale up in the future), or keep treating with the sulfa drugs for a long time (maybe the full cycle?), to increase the chance of getting rid of the disease in all individuals.

    Will read up on beekeeper's methods, thank you for that tip.

  • Yes, sounds like the eggs either when laid got micro-sporidia P. locustae on them or the spores were actually inside the eggs. Fisheries have lots of attempts to deal with their micro-sporidia outbreaks & link below Fig. 2 has good set of clear pictures of spores inside eggs; the report (2011) discusses how transmission from parent to progeny is less virulent "vertical trasmission" & breakdown egg transfer "intra-ovum" ( inside egg) or "extra-ovum" (surface contact).

    Authors cite reference #30 as example of how lab colonies infected with a fish micro-sporidia were handled, but you can get new founder locust cheaper than that. Am typing on small tablet so let me know if this link doesn't work & I'll try again: https://journals.plos.one/plosone/article?id=10.1371/journal.pone.0076064

    As for why the colony is not 100% killed by this pathogen: it can only live (as something other than suspended animation spores) inside it's host. Micro-organisms produce volatile compounds that the group uses for "quorum sensing".

    Quorum sensing lets the pathogen cohort know when their hosts are not abundant enough to keep supporting their microbial load. Your survivors were probably infected, but the level was held down to non-fatal numbers.

    A signalling molecule used for quorum sensing by some insect symbionts is N-(3-oxohexanoyl) homoserine lactone. By ramping up levels of a signalling molecule the individual microbes' response regulators to what the group (quorum) is telling them will then be to repress a suite of genes in the microbe.

    Given the micro-sporidia P. locustae mode of behavior inside it's host I believe some of it's genes ablated (extrapolating from other insects) will be involved in getting a hold by spores on the internal locust surfaces. In one aspect N-(3-oxohexanoyl ) homoserine lactone results in lower levels of chitin-ase enzymes being called into production (gene expression) in a member parasite.

    Since the interior chitin of host locust needs to be breached (attacked by parasite's chitin degrading enzyme chitin-ase) more spores will be passed out (low chitin degrading enzyme under quorum sending orders).Since less spores adhered inside some locusts (the quorum needs hosts) the infection load is not fatal; which is why when there were only a few locust left alive that is "the point at which it seems to stop."

  • 50 ml of 0.25 Mole oxalic acid (sourced from Ecoxal product name) in a syrup was trickled to honey bees for micro-sporidia control. As described in section 2.2 " field trial" of study (2015) titled "Effect of oxalic acid on nosema ceranae infection"; free full pdf text available on-line.

  • Thank you again.

    Currently treating the locusts with sulfa drugs. However from I've researched it still isn't ideal, as it can take up to 6 months to eradicate, due to the spore leftovers everywhere. Even then some breeders use is as an ongoing precaution (a bad idea when intended for human consumption).

    Interestingly wikipedia mentions Nosema Apis spores can be destroyed when left at 49°C for 24 hours. Wondering if something similar works for P. Locustae - as locusts should be able to withstand 40-45°C without much harm, 50 °C for only short periods. However, I've found no research so far into heat resistance of P. Locustae.

  • I see that microsporidia have been re-classified from protozoa to fungi. Which makes me think you might try bee hive propolis, since it is anti-fungal; being non-toxic to bees it concievably would be benign to locusts.

    Propolis is ~30% wax, 5% pollen, 10% aromatic compounds, 50% resin & balsam, plus 5% other things (including debris). You'd want to get rid of it's wax for practical usage.

    A quick way to do this is using 95% alcohol at a ratio of 3 gr. bee propolis in 10 ml alcohol on a magnetic stirrer; run a stir bar in the mixture for 24 hours. Then filter out solids & put the fluid portion into a freezer; when the wax layer forms remove it & then, at very cold temperature, filter the de-waxed solution again. (You can always re-freeze after a wax layer removal & subsequently again remove residual wax until get it all off).

    A slower method is to let 30 to 35 gr. propolis sit in 100 ml of 95% alcohol for 7 days in a container. It's sort of like a tincture extraction; you agitate the mixture 1-2 times a day to get propolis surfaces exposed to solvent.

    If high % alcohol is hard to obtain a readily available solvent is propylene glycol (human pharmaceutical products use it safely in sensible amounts). Put the propolis in propylene glycol at 36°C & stir/shake/agitate for 48 hours. You then de-wax it by double filtering.

    After wax removal the propolis extracts' volume (of carrier solvent) can be reduced. Alcohol does evaporate fairly easily; however, propylene glycol's boiling point is quite high so concentrating it more complicated.

    As for dosing: consider this experimental & use only on a test population until verify safety. In theory you could apply propolis to the locust food & let it dry (set) on that before offering as feed. Propolis is expensive so (extrapolating from controlling fungii that produce the myco-toxin patulin) I'd initially aim to be feeding the equivalent of 2mg propolis (not counting the solution solvent) per 1 ml of insect's water weight daily.

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