Cannabis plant damage caused by aphids
Photo by Mel Frank

Quality assessment of biological control agents (aka natural enemies) is important in a successful biological control program implementation. The success of any biological control program is contingent on receiving functional natural enemies capable of locating and killing a target host (prey). Natural enemy quality is dependent on numerous factors, including: rearing conditions, packaging, transit survival and handling by the end-user (the cultivator).

The Biologicals Supply Chain

In general, natural enemies are reared in large quantities as colonies (populations of individuals) under laboratory conditions where they feed on a food source, such as a sugar-water solution (honey-water), prey that are feeding on plants or both. Natural enemies are collected from established rearing colonies and then shipped to the end-user. Biological control companies generally produce, supply and distribute natural enemies. These may be producers/suppliers, distributors or both. Distributors typically do not rear their own natural enemies; they order natural enemies from a producer/supplier. Producers maintain facilities where they rear one or multiple types of natural enemies, which are sent to distributors upon request.

Differences between laboratory and cultivation environments may cause substantial natural enemy variability. Rearing natural enemies under laboratory conditions is ideal in terms of space, ability and consistency, due to the capacity to control environmental conditions, such as temperature, relative humidity and photoperiod. However, problems with natural enemy effectiveness may arise when they’re released in cultivation environments, due to the wide variability in conditions compared to the constant laboratory environment. For example, natural enemy-searching efficiency and dispersal may be negatively affected from rearing under laboratory conditions.

The Inspection Process

Even though natural enemies may leave a producer/supplier (or insectary) in “good” condition, inappropriate shipping and/or handling procedures by distributors or cultivators may result in a decrease in natural-enemy quality, based on the number of functional individuals (capable of flying and/or searching for a host or prey) prior to release. For instance, improper handling or exposure to extremes in hot (>90ºF or 32ºC) or cold (<40ºF or 4ºC) temperatures can negatively impact the natural enemies’ effectiveness when they are released into a cultivation environment. Poor shipping conditions can kill natural enemies or render them nonfunctional, thus impacting a biological control program’s success. Shipping containers must provide favorable environmental conditions, such as temperature and relative humidity, and allow for sufficient air exchange, which ensures natural enemies’ survival during transit.

Natural enemies should be delivered in a sturdy container packed with either Styrofoam peanuts or newspaper to minimize movement during transit. In addition, an ice pack should be placed in the container to keep the natural enemies cool.

During shipment, many natural enemies do not have an abundant food source, and some may be shipped with no supplemental food source, which can decrease survival rates. Natural enemies must be shipped by a reliable carrier for delivery within a one- to two-day period. An extended shipping time may cause high mortality rates or a reduced number of functional individuals, reducing the natural enemies’ effectiveness in sufficiently regulating insect or mite pest populations. Any delays during transit can lead to mortality due to cannibalism (eating each other) or desiccation (drying up). For example, when shipped or packed in granular carriers, populations of the predatory mite Phytoseiulus persimilis are susceptible to cannibalism or desiccation when shipping is delayed.

Once received, shipments of parasitoids or predators should be stored for a minimal period (no more than seven days) to avoid negatively affecting their fitness and foraging ability. In general, natural enemies should be released immediately upon delivery.

Close-up of the inside of a sachet of predatory mites. It is important to ensure that the predatory mites are alive prior to release.
Photo by Raymond Cloyd

Before releasing them, always check to make certain they are alive. Various methods can be used to assess the shipment’s quality. For instance, for predatory mites that are shipped in containers consisting of bran or vermiculite carriers, a small carrier sample can be placed on a white sheet of paper—8.5 inches by 11 inches (22 cm by 28 cm)—and checked with a 10X hand lens to determine whether or not the mites are active.

Natural enemies shipped as eggs or pupae can be evaluated differently. For example, the quality of whitefly parasitoids, such as Encarsia formosa or Eretmocerus eremicus, that are shipped on release cards containing “mummified” parasitized whitefly pupae or aphid parasitoids (including: Aphidius colemani and Aphidius ervi (both parasitic wasps)) in plastic containers can be assessed by placing a sample release card or a plastic container of “mummified” aphids inside a glass Mason jar with a lid. Next, affix a yellow sticky card to the bottom of the lid. The jar should be regularly monitored and the yellow sticky card checked to ensure that adults are emerging from the pupae or from “mummified” aphids. The actual number of potential functional parasitoids that emerged from pupae or “mummified” aphids can be determined afterward when all the parasitoids have died in the jar. This experiment will provide an estimate of the quality of the rest of the containers.

Raymond Cloyd is a professor and extension specialist in horticultural entomology/plant protection in the Department of Entomology at Kansas State University.