Organic and Biological Pest Control: Predatory Mites
Fungus gnats used to be one of the most common pests on the interior landscape. With the now standard practice of using beneficial nematodes (Steinernema feltiae) they are no longer an issue.
Interiorscapers love the nematodes because it is a natural way to manage a pest without dealing with the hassles of spraying a pesticide indoors. Luckily, there are also other natural ways of controlling some of the other major interior pests on tropical foliage. Twospotted spider mite is a good one for starters.
When encountering mites on tropical foliage in the interiorscape, you are most commonly dealing with the twospotted spider mite, Tetranychus urticae. This species is found all over the world and can thrive in the dry indoor climates. They are about 0.4mm in length. Mites have four pairs of legs and no antenna. The plant feeders are typically found on the undersides of leaves. They feed by inserting their mouthparts into plant cells. They will suck up the contents of the cell and then move onto the next cell. This leaves behind damaged plant tissue that reduces photosynthesis causing yellow speckling, graying or bronzing of the leaves. The stress from heavy plant feeding can cause defoliation.
These mites get their name because as the population grows, a fine webbing can be found on the plants. This webbing traps dust and can be unsightly. If you find plants in this condition they will need to be wiped down or washed to remove this webbing, along with many of the spider mites. Once the plants are “cleaned” up it would be advisable to start a predatory mite program.
There are a few different predatory mite species on the market, so picking the right one important. So how do you know which mite to use? The two most commonly used predatory mites are Phytoseiulus persimilis (aka P mite) and Neoseiulus californicus (aka Cali mite). Both of these mites are being commercially reared in California. Domestic production allows for fresh mites to be delivered by next day air. This is great because these beneficial predatory mites will only be in their shipping bottles less than a day, providing a very fresh effective product.
Phytoseiulus persimilis, approximately 0.5 mm long, are red to orange in color with a glossy pear-shaped body. Once P. persimilis mites are released onto a plant they search the leaf surfaces for the webbing of the twospotted mites. Once they find webbing, they will refine their search looking for the mite’s eggs to feed on (as well as the other life stages). The persimilis will also deposit her oval eggs near pest mites, so when they hatch there will be a ready food source close by for them. P. persimilis will consume up to 7 adult spider mites or 20 eggs per day. Their life cycle is shorter than that of spider mites, allowing them to reproduce more quickly and overtake the pest mite. Once the mites have been eliminated, the P. persimilis will die of starvation.
The other main predatory mite for the control of spider mites is N. californicus. This mite has a wider dietary range. It feeds not only on spider mites but also broad mites, first instar thrips, as well as pollen. They have a biology very similar to P. persimilis.
Where do you get these mites? It is best to work with a professional horticultural supply company like Southern Ag or CPS and not to order off internet resale sites. Another option is to order direct from companies like BioBest, Beneficial Insectary, or Koppert. Often when ordering over the internet, the age and the origin of these biological products can be a mystery. They should always be drop-shipped directly from the production insectary.
When releasing predatory mites, always keep in mind they are living creatures! The bottles or vials of mites should come packed in a cooler with a cold pack. When they arrive, they should be applied as soon as possible. Some companies like Syngenta Bioline have a package design that is great for interior use. Their vials of P. persimilis have pointy tops making it easy to get the mites on the plants, without making a mess by spilling the carrier media on the floor.
Using organic biological control on the interior landscape today is a great way to deal with pest issues. They have no odor, no REI, and they will keep working after hours. For more information on how to identify, manage, and prevent indoor landscape pests, check out my Free Professional’s Field Guide to Plant Pest Control.