Insects That Will Help Cannabis Grow Better

Adam Parsons

Cannabis Journalist & Staff Writer at Zamnesia

Adam Parsons

June 13, 2019

The trick is to know your enemies from your friends, and to keep allies nearby. Friendly forces like ladybugs and assassin bugs are generalist predators. Recruit them to feed on some of the most common invasive pests like aphids, thrips, and whiteflies.

Assassin bug

An Assassin bug is small and flat with a long, moveable snout that can be folded up underneath its body. Its most characteristic feature is its red eyes. The most commonly found type is brown-black with light flecks on the cases of the wings. The females are about 3 mm in size and the males are a little smaller.

There are many species of bug, but the one most interesting to us is the assassin bug. Assassin bugs are in turn also dividable into a great many species, the one most interesting to us being the one called Orius.

When thinking of applying Orius you have to bear in mind that the assassin bug is sensitive to various chemical plant protection agents. So for example, you should not apply Nomolt (teflubenzuron) or Admire (imidacloprid) if you don’t want to devastate your Orius population.

Lacewing

The body of the lacewing is slender and elongated, and its colour is green to yellow-green. Lacewings look a little like mosquitoes, but the wings are much larger, rounder and show their fine veins clearly. In rest, the wings are folded away on its back like a canopy, while in flight they glisten with a pearly sheen. It is certainly not a quick or agile flyer and it can easily be snatched out of the air. All four of its wings have the same shape and can move independently of each other. Lacewings are vulnerable; the wings are easily damaged, whereupon it will no longer be able to fly to the plants it feeds on.

Prevention and feeding

Lacewings come in many species and sizes, the other well-known one being the Brown lacewing (Micromus variegatus), which is less common. The Green lacewing is found all over the world, with the exception of Australia and Antarctica.

It is handy that this lacewing eats enormous quantities of aphids, especially when they are larvae. The imago (adult) mainly feeds on the secretions of aphids (honeydew) and pollen. Females also eat the odd aphid, especially when they are pregnant with eggs. Aphids are the exclusive food of the larvae, which are veritable eating machines and look a little like the larvae of ladybirds.

The aphids are not actually eaten but sucked dry, as are red spider mites and whitefly, two other plant pests. In greenhouse horticulture especially, lacewings are used en masse to clean up aphid infestations. A single larva can gobble up to 50 aphids a day.

Development

The eggs are laid in between aphid colonies, and are on long stalks. These stalks are designed to keep the eggs clear of ants, which enjoy the honeydew secreted by the aphids, which they protect. The larva is broad and caterpillar-like and has a brown, irregular colour, three pairs of little legs and long, pincer-like mandibles (jaws).

Some species of lacewing larvae camouflage themselves with bits of plant or dead aphid in order to hide from ants. When after some time the larvae pupates a web is spun amongst the vegetation. There are two generations a year, and in the winter the imago hibernates, often in houses. During this resting period the lacewing turns brown, but in the spring it turns green again.

Ladybirds

The ladybird is a brightly coloured beetle, usually red or yellow with black spots. They have an oval, almost round shape. A large part of the head and thorax are covered by the neck shield, and its back end is covered by two wing cases (the hard main wings). Ladybirds congregate with other ladybirds. If they are endangered, they usually fall stock-still and refuse to move at all. They can also excrete a yellow fluid that tastes and smells very bitter. This fluid is not poisonous, but gives a good impression of being so.

Usefulness for cannabis

The ladybird is a welcome partner in the agricultural world. The reason for this is evident: they’re aphid guzzlers. A ladybird can eat up to 500 aphids in a day. What’s more, they are in no hurry to move on so long as there are still aphids to be eaten (unless you chase them away). If you see a ladybird, just leave it in peace! Take note, however, that the ‘Lemon ladybird’ is not looked on so positively. This is a yellow variant with black spots. This doesn’t eat aphids but mildew. Even though mildew is a cannabis pest, the lemon ladybird is not much help; in fact, it’s a carrier and spreader of the disease.

Protected

Although they’re very desirable, it should be noted that the ladybird is a protected species in Belgium. People are therefore not allowed to catch them, kill them, collect them, sell them, transport them, imprison or disturb them. In other words, you can’t do anything with or to them. The above information, therefore, is only to be acted upon in countries where the ladybird is not a protected species.

Predator mite

Red spider mite is a pest that causes severe damage - mercilessly - indoors and outside. Especially when the weather is hot and dry, a population of spider mites can explode in numbers. For many years now, it has been tackled with success by the predatory mite Phytoseiulus persimilis.

Biology

The predator mite Phytoseiulus persimilis is originally from Chile, but has subsequently been spread by humans (consciously or unconsciously) all over the planet. A Phytoseiulus predator mite is about the same size as a glasshouse red spider mite, but has a red-brown colour, stands a little higher on its legs and is much more mobile.  There are usually four times as many females as males in a population.

The female lays her eggs in or near to a red spider mite colony. They can be distinguished from the spider mite eggs by their oval shape, their light orange colour and by the fact that they’re around twice as big. The six-legged larvae do not eat anything. Just as in greenhouse mites, the larval stage is followed by the protonymph, which molts into the deutonymph, and finally the adult stage.

There’s no real rest between the developmental stages. After becoming an adult, it takes at 20°C around 2 days for the predator mite to lay eggs. The development lasts under normal circumstances for a shorter time than the greenhouse mite and takes about 5 days at 30°C, 9 days at 20°C and 25 days at 15°C. The female cannot lay eggs without being fertilized. At 20°C she lays over the course of 22 days around 54 eggs, but this can be as many as 75.

Under normal conditions, a predator mite population, therefore, grows faster than a spider mite population. At higher temperatures (above 30°C) or in drier weather (when the air moisture level is below 60%) the spider mite is favoured and its control will be harder. With too low an air moisture, the predator mite’s eggs crumple up.

The diet of Phytoseiulus consists almost exclusively of red spider mites. In the absence of these, the predator mite will cannibalise its own species. An adult predator mite devours spider mites at any stage of their lifecycle, whilst the nymphs stick to their eggs and protonymph stages. In a single day an adult Phytoseiulus can eat around 20 spider mite eggs or larvae, 13 protonymphs, or five adult spider mites.

Thanks to their faster development and bigger appetite, the predator mite can fully eradicate a spider mite population. Although Phytoseiulus nymphs usually tend to stay in one place, the adults do go off in search of other hunting grounds. If your plants are touching each other the predator mites can quickly spread out throughout the crop.

Application

Phytoseiulus can be used on all sorts of vegetable and decorative plants grown in greenhouses, such as peppers, cucumbers, melons, aubergines, strawberries, green beans, gerbera, roses and all kinds of pot plant. For a successful biological treatment against red spider mite, it is important to catch the infestation early on to be able to get it under control. Given that a red spider mite population multiplies more quickly in the summer, when it will be harder to bring under control biologically, it is best to start your biological control immediately from the first warm days of spring in order to catch the spider mites as they emerge from hibernation.

After detecting the first spider mite colonies, release Phytoseiulus as soon as possible. Depending on what’s being grown and the environmental circumstances you should bank on releasing 4 to 6 Phytoseiulus/m² into the full field. On and around the infected plants you should release around 20 predator mites/m². In normal conditions Phytoseiulus is capable of keeping the spider mite numbers under control for the rest of the growing season. In dry, warm weather they can still create major problems though. Experience has shown that control with Phytoseiulus can be boosted by keeping the air moisture percentage level by misting from a high-pressure hose with a fine nozzle.

Instructions for use

• After taking delivery of them, the predator mites should be released as soon as possible. They can be kept for a short while; store the small bottle lying down in a cool (6-10°C), dark place.

• Let the bottle with the predator mites in reach ambient / room temperature before using them. Twist and gently shake the bottle, so that the predator mites are spread evenly between the vermiculite blocks.

• Avoid allowing the bottle of Phytoseiulus to become too hot (hand temperature is best).

• Remove the sticker from the distribution opening. Spread the material on the leaves. Never sprinkle by removing the cap (otherwise you’ll get too many predator mites in too few places).

• A single bottle can be shaken about 190 times. Per shaken out pile, there will be on average six to seven predator mites. Release Phytoseiulus from the moment that the first red spider mites rear their heads.

• It’s best to aim for a minimum of 2-3 predator mites per m². If necessary you can release a second batch a couple of weeks later. In extreme cases, you can release up to 20 Phytoseiulus/m².

• For a good predator mite development the relative air moisture needs to be kept fairly high (65% or more) and the environmental temperature should be regularly above 20°C.