Even if you tried to avoid collecting unhealthy seeds, it can happen that you return from a field collecting trip and you realize some of your seed collections are infested by insects. Perhaps you see flies, worms, or other insects, or you see holes in the seed coats or other signs of infestation. Or possibly you decided to collect seeds even if you were aware of the issue, because there were not other healthy populations available or because the species is endangered or otherwise a priority to be collected.
No worries! It is possible to save the seeds that are still intact, but you need to act quickly. If the insects are still alive and active, they will keep eating the seeds, and eventually the whole seed collection could be ruined. That’s why it is important to prioritize these seed lots for processing once they arrive at the seed bank.
First of all, use an appropriate location in the seed bank or outside where you can work safely with the infested material to avoid an infestation spreading to other seed lots. Always keep the infested seed collection in a closed but breathable bag, possibly using a double layer (e.g., use two paper or cloth bags, one into the other), and be careful when you open it. Luckily, insects are usually specific to certain plant species, but there is always the risk that they find other target species in your seed bank.
When you are ready to process these seed lots, you can follow the recommendations below:
- Perform a visual inspection using a hand lens, a headband magnifier, or a stereo microscope. This method reveals insects, eggs, or mites that move freely, as well as proliferation of fungi such as sclerotia, galls, blight balls, or bacterial masses.
- As the human eye cannot fully identify all the seeds infested by insects, dry the inspected seed collection as soon as possible, and then freeze it (if orthodox) or refrigerate it (with special monitoring if recalcitrant) as soon as the target relative humidity (40% ± 3%; 30% ± 3% respectively) is reached. This will kill the insects, instead of using chemical treatments, which could harm the seeds or staff. Avoid storing seeds with possible infestation in thin plastic bags, as insects can penetrate them. Instead, use thick sealed plastic bags or plastic boxes. Any small holes in the bag or box will allow the insects to go out and potentially affect other seed lots. Additionally, the holes through which airflow can pass may result in seed water content increase.
- Leave the seeds in storage for at least seven days and then withdraw them following the recommended procedure (according to the storage method — freezer or refrigerator) to finish processing (see Foundations of Seed Banking textbook, Section 6.4). Check the samples again visually for purity and damaged seeds.
- Carefully destroy the waste material to prevent the spread of insects and diseases to other material.
For some species with already low water content, you may be able to skip the drying step and store your inspected seeds for seven days to kill insects following the storage instructions mentioned above. Do not forget to fill the thick sealed bags or containers completely, with as little air as possible. Consequently, the developing beetles will consume available oxygen in a short time and thus suffocate before their development can cause serious damage.
If you know or suspect the seeds might be recalcitrant or intermediate, freezing should be avoided, and you’ll need to visually check the seeds and then propagate them immediately in an isolated area of the nursery, to avoid insect colonization.
If you are dealing with fleshy fruits, you’ll need to clean them before drying and storing them. Otherwise, if your infested collection is made of dry fruits or seeds alone, you can dry and store them before cleaning to speed the process and avoid spreading the insects.
However, if you decide to clean the seeds before storage, and it seems that all infested seeds are removed, be aware that some insects might remain inside the seeds without being visible at that time. That’s why it is important to follow the steps above anyway.