Naturally occurring beneficials in the greenhouse
August 21, 2023 By Larissa Schinkel, Cara McCreary, and Dr. Roselyne Labbé
Every year, we see a diversity of beneficial insects and mites that appear in greenhouses from surrounding natural landscapes (like little Santas bearing mini pest management gifts). While some of these species may not be commercially available, they may still reduce pest pressure, sometimes in economically important ways.
This article focuses on helping with recognition of some of the species we routinely see in southwestern Ontario greenhouses but may also be present in greenhouse production sites across Canada.
Natural enemies of loopers or other caterpillar pests
Multiple species of parasitic wasps attack loopers and other caterpillars in agricultural systems, including in the greenhouse. Adult wasps may be observed on sticky cards or during parasitism attempts. However, it is most likely that greenhouse staff would observe the pupal stage (the cocoons) as they are developing on or near host larvae. Depending on the species, cocoons come in a variety of shapes and colours. The following are descriptions of some of the species that may be observed in Ontario.
Cotesia species. There are several species of endoparasitic braconid wasps in the genus Cotesia that attack caterpillars by laying multiple eggs inside their larval hosts, consuming, and developing first within, then outside of these hosts. Adults are small dark wasps that range from three to seven millimetres in length (Fig. 1). Females have a curved, narrow ovipositor used for laying eggs. Once the larvae exit the host, they build cocoons either directly on their host or on the foliage nearby.
Cotesia glomerata was introduced into North America in 1883. This species builds yellow cocoons either directly on their host or on nearby foliage. Cotesia vanessae is relatively new to North America (collected in 2009), is thought to have a relatively broad host range, and has successfully developed on common agricultural pests including cabbage and tomato loopers, Trichoplusia ni and Chrysodeixis chalcites, respectively. Larvae of this species work together to form a single protective cocoon that looks surprisingly like a cotton ball (Fig. 2).
Campoletis sonorensis. The native parasitoid, Campoletis sonorensis, is a medium sized (12.7-millimetres long) ichneumonid that has been reported attacking looper larvae. The adult wasps, like other species of ichneumonids, have distinctly thin abdomens, with long antennae and legs (Fig. 3A). Differentiating between species of Campoletis wasps can be difficult, often requiring advanced taxonomic expertise. Eggs are laid inside the host larvae, which exit their host, and spin a white cocoon with two distinct dark stripes on either long end of the cocoon (Fig. 3B)
Euplectrus spp. Euplectrus species are ectoparasites of many caterpillars, including loopers. Adult female wasps lay between five and several hundreds of eggs per caterpillar. Cocoons are formed typically on the undersides of caterpillars (Fig. 4).
Figure 4. Euplectrus sp. cocoons on looper larva. Photo credit: Agriculture and Agri-Food Canada, Harrow Research and Development Centre, 2018.
Natural enemies of aphids
Syrphid flies. Syrphids are an important family of flies commonly known as hover flies or flower flies. They are the hummingbirds of the insect world. Don’t be fooled by their appearance as many species bear yellow and black or brown bands making them easily misidentified as bees or yellow jackets. As flies, they only have one pair of translucent wings whereas bees or yellowjackets have two pairs. Their body lengths range between eight to 15 millimetres varying by species. Adults are important pollinators feeding on nectar and pollen, and also consume aphid honeydew. The predaceous larvae are avid consumers of aphids, with a single larva eating as many as 400 throughout its development. The larvae resemble slightly flattened maggots that narrow slightly towards the head (Fig. 5). The larvae can be seen “swinging” their heads back and forth in the air in search for aphids. The eggs are laid within aphid colonies to ensure a bountiful food source. Syrphids are frequently observed in greenhouse pepper crops in Ontario and are now available for purchase through some insectaries or distributors.
Hundreds of species in the Syrphid family are reported in Canada. Although the species diversity has not been documented in greenhouses in Ontario, to demonstrate variation in external characteristics, there are a few examples below of species known to feed on aphid pests of greenhouse crops.
Adult Eupeodes americanus are approximately seven to 11 millimetres in length, stout, and black to metallic green with three broad yellow crossbands (Fig. 6A). The larvae are pale gray. Their natural habitat is meadows and fields with an abundance of flowers. Banker plant systems have been used to facilitate their establishment when used as biological control agents and some studies have demonstrated that plant species can influence the aphid species preferences of E. americanus. Adult Sphaerophoria contigua are small to medium sized (between six and nine millimetres in length) and slender with bright yellow markings on the head, thorax, and abdomen (Fig. 6B). Some species in this genus have an abdomen that is almost entirely black. The larvae have been observed feeding on many different aphid species.
Adult Syrphus ribesii are approximately eight to 13 millimetres in length and their larvae have been documented feeding on several species of aphids. This species shows a lot of variation in colour and markings (Fig. 6C).
Natural enemies of shoreflies
Hexacola sp. are small parasitic wasps (three to four millimetres in length) with black, nearly spherical abdomens, and transparent wings. They lay their eggs inside shorefly larvae and have been observed decimating local populations of this pest in Ontario greenhouses (Fig. 7).
Natural enemies of thrips and whiteflies
There are several important hemipteran (“true bug”) predators of thrips, whiteflies and other greenhouse pests including at least two anthocorid species from the genus Orius, and several mirids. As mirids require a lengthier discussion for future articles, here we focus on two Orius species.
Orius spp. Commonly known as minute pirate bugs, Orius species they are tiny, voracious predators as both adults and nymphs. Adults also feed on pollen and nectar. Orius insidiosus, commonly known as the insidious flower bug, is a commercially available species that also visits greenhouses from the surrounding landscape. They are small (between 1.7-1.9 millimetres), oval bugs, with black bodies, and see-through white to yellowish-brown hindwings with black at the ends (Fig. 8A). Adult females lay eggs directly into plant tissue. Once hatched, small yellow to orange tear-drop shaped nymphs gradually darken to brown before adult emergence (Fig. 8B). Another native species, Orius tristicolor, is visually similar. One distinction is the hindwings of O. tristicolor are clear (no colour), with black at the ends.
Predatory thrips. This group of predators might throw some people for a loop: beneficial thrips! Predatory thrips such as Aeolothrips spp. can be found hunting in greenhouse crops and are often mistaken for Echinothrips americanus, an increasingly sighted pest in greenhouse crops. They pack a punch as they can be observed feeding on mites, whiteflies, and even other thrips. Aeolothrips spp. are dark thrips with three distinct white bands on their wings (Fig. 9A) but can be distinguished from the similarly dark-coloured Echinothrips which have orange pigmentation between segments and their wings are dark with white at the base (Fig. 9B).
Welcoming the invaders
There are some simple ways to create and support an ecosystem in or around the greenhouse that serves to attract and retain naturally occurring beneficials. Applying these tactics could even help thwart future pest infestations and support existing inoculative or inundative biocontrol programs by creating a diverse and resilient natural enemy food web. Importantly, if you see a new insect or mite species you don’t recognize on your crop, don’t immediately assume they are going to cause damage.
To lure in these beneficials, they need food and reproductive host resources to complete their development and sometimes, crop plants are not adequate at providing these. To boost natural enemy populations, consider including outdoor wildflower hedgerows for predators and parasitoids to establish on and overwinter in near or around the greenhouse. This may not only attract natural enemies to the greenhouse, but it also gives them a place of refuge when crops are removed. Inside the greenhouse, some species may need alternative food sources to sustain all life stages, not just the predatory stage. This could be accomplished by distributing/spraying pollen onto plants, providing alternate protein sources like sterilized eggs of flower moths, Ephestia, or decapsulated brine shrimp, Artemia cysts. The provision of banker plants can also provide optimal oviposition sites for natural enemies or a source of nectar and pollen that support adult parasitoids and other omnivorous beneficials. One note of caution when aiding in the establishment of natural enemies is that some strategies could also be beneficial to specific pests such as thrips. As well, banker plants may require different nutrient and watering regimes than what is provided to the crop. When planning these new strategies, it is helpful to consider existing pest pressure and to test a particular strategy in a small area first before applying it at a larger scale. Either way, ready or not, here they come!
Larissa Schinkel, Research Assistant, Ontario Ministry of Agriculture, Food and Rural Affairs
Cara McCreary, Greenhouse Vegetable IPM Specialist, Ontario Ministry of Agriculture, Food and Rural Affairs
Dr. Roselyne Labbé, Research Scientist – Greenhouse Entomology, Agriculture and Agri-Food Canada
Print this page
- Roadmap to resiliency in greenhouse soils
- New study finds vertical farms can use 98 per cent less water than traditional ag