Why Biological Control Fails: Encapsulation May be the Culprit

Brown soft scale
Brown soft scale attacks a wide range of ornamental and greenhouse crops, as well as citrus.

Mealybugs and scales are insect pests of many horticultural plants grown in greenhouses, nurseries, and interior plantscapes. One option associated with plant protection is the use of biological control by releasing parasitoids. A number of parasitoids are commercially available currently to address problems with specific mealybug and scale species. For example, Leptomastix dactylopii and Anagyrus pseudococci are available for use against specific mealybug species. Aphytis melinus and Metaphycus helvolus are sold for use against specific scales. However, there may be instances when parasitoids are not providing sufficient regulation of mealybugs or scales because some mealybug and scale species are able to encapsulate the eggs of certain parasitoids.

Encapsulation is the main defensive response affiliated with the cellular immune system of insects such as mealybugs and scales to prevent attack by parasitoids or prevent parasitism, and may be responsible for determining the suitability of a host (prey) in supporting the development of parasitoids.

What is Encapsulation?

Encapsulation is a process by which the immune system of an insect responds to a foreign body (parasitoid egg) by surrounding the egg, resulting in death by means of asphyxiation or suffocation. Encapsulation may occur within 24 hours. Consequently, parasitoid development can be hindered by encapsulation, thus reducing the ability of parasitoids to provide sufficient regulation of mealybug or scale populations. The host blood cells are responsible for encapsulation of eggs, a process mediated by hemocytes. Hemocytes are free-floating blood cells that circulate within the hemolymph (blood) of an insect and are involved in insect immune system responses.

Once an egg enters the body cavity of the host by means of the parasitoid female laying an egg, hemocytes form a capsule composed of melanin (a dark-brown to black pigment) that surrounds and adheres to the surface of a parasitoid egg (this process is called melanization); consequently killing the egg and preventing development of the parasitoid. Encapsulation may substantially reduce the efficacy of parasitoids released against mealybugs or scales. This diminishes the numbers of parasitoids (offspring) in the next generation, thus decreasing regulation/suppression of mealybug populations. Encapsulation is effective primarily against endo-parasitoids, which are parasitoids that lay eggs within the host body and have to contend with the host immune system, whereas ecto-parasitoids lay eggs on the outside of the host body.

Leptomastix dactylopii is a parasitoid of the citrus mealybug (Planococcus citri) and the eggs inserted into citrus mealybug crawlers by females are susceptible to encapsulation.

How Encapsulation Affects Parasitoid Efficacy

Encapsulation by an insect host is an important parameter affiliated with host suitability and influences the efficacy of mealybug or scale parasitoids. High encapsulation rates may occur with mealybugs. For instance, the parasitoid Leptomastix dactylopii can suffer encapsulation rates of 100% when attempting to parasitize the citrus mealybug (Planococcus citri). High encapsulation rates may result in outbreaks of mealybugs or scales due to insufficient regulation by parasitoids.

Factors that can affect encapsulation include: parasitoid species, host plant, and host age. Host and parasitoid-type may differ in regard to the incidence of egg encapsulation. Host plant or plant type may affect encapsulation by mealybugs. In addition, the host plant may influence the ability of insects such as mealybugs or scales to encapsulate eggs due to nutritional quality (nitrogen content). This can either enhance or lessen immune system responses based on the nutrient value of the plant to mealybugs or scales.

Older, or larger hosts (later instar larvae), contain higher numbers of hemocytes responsible for encapsulation of parasitoid eggs, whereas younger, or smaller hosts (early instar larvae) have fewer hemocytes available for encapsulating eggs. Therefore, parasitoids that parasitize young or smaller hosts (early instars) may be more successful biological control agents or natural enemies because they parasitize hosts before the host has developed the ability to encapsulate eggs.

Parasitoids have evolved mechanisms that allow them to avoid or overcome encapsulation by a host. For example, some parasitoids inject a virus into a host along with an egg, which interferes with the immune system and protects the egg from encapsulation. Furthermore, certain parasitoids are not affected by encapsulation in any host.

Be sure to consider the possibility of encapsulation when biological control does not seem to be working for you.

Topics: ,

Leave a Reply

More From Insect Control...
Aphids

July 7, 2017

New Tools for Your Crop Protection Arsenal in the Greenhouse

Over the past few months, crop protection companies have developed several new products designed to help you manage a wide range of insect and disease pests. Here’s a look at some of them.

Read More
Yellow Stick Card for thrips

July 5, 2017

Tips From a Top 100 Grower for Effective Thrips Control

A combination of conventional materials and biologicals can help provide season-long management of thrips in hanging baskets.

Read More
Magnesium deficiency on poinsettia

July 4, 2017

How to Manage the 3 M’s of Poinsettias: Manganese, Molybdenum, and Magnesium

Proper nutrition is a critical part of successful greenhouse production. Managing these three key elements properly will keep your poinsettia crops healthy and strong.

Read More
Latest Stories
Aphids

July 7, 2017

New Tools for Your Crop Protection Arsenal in the Green…

Over the past few months, crop protection companies have developed several new products designed to help you manage a wide range of insect and disease pests. Here’s a look at some of them.

Read More
Yellow Stick Card for thrips

July 5, 2017

Tips From a Top 100 Grower for Effective Thrips Control

A combination of conventional materials and biologicals can help provide season-long management of thrips in hanging baskets.

Read More
Scale on leaf nodes

July 2, 2017

Why Biological Control Fails: Encapsulation May be the …

If your biological control isn’t working for you, encapsulation could be to blame. Learn how this defensive response can cripple a biological control program.

Read More
Koppert Ulti-Mite Swirski sachet

June 21, 2017

New Tool from Koppert Provides More Effective Thrips Ma…

A newly patented sachet for the predatory mite Amblyseius swirskii is resistant to both low and high levels of humidity, helping growers combat thrips infestations.

Read More
Cannabis Seedling

May 20, 2017

Biocontrols: A Practical Option for Cannabis

With limited options for chemical pest control, cannabis growers are incorporating biocontrols into their integrated pest management programs. More education will cement this solution as a viable option in this emerging market.

Read More
Four Lined Plant Bug

May 8, 2017

Four-Lined Plant Bug Emerges as Troublesome Pest in Pen…

Four-lined plant bug damage is very characteristic: circular brown to black spots about one-sixteenth of an inch in diameter. The spots are easily mistaken for disease or frost damage.

Read More

May 4, 2017

Bayer Altus Update: Neonic Insect Control Alternative N…

Altus, a butenolide class insecticide with the active ingredient flupyradifurone, will be available beginning May 1, and is labeled for greenhouse and nursery use on ornamental plants, vegetable transplants, and indoor vegetable production.

Read More
Ambrosia Beetle

April 7, 2017

Tips On How to ID Ambrosia Beetle Damage, And How to Co…

Ambrosia beetles are often overlooked as being a primary cause of plant loss, but research and experience are proving otherwise.

Read More

February 28, 2017

OHP Launches New Ovicide/Miticide, Announces Partnershi…

Applause is a new miticide that targets eggs and immature stages of several mite species. Through the Vestaron partnership, OHP will market Spear-O, a toxin-derived bioinsecticide.

Read More
Remote Sensing Feature

February 12, 2017

Using Remote Sensing to Optimize IPM in Greenhouses

Researchers at the University of California Davis are developing advanced remote sensing technologies to automate detection of insect pest infestations in greenhouses, which could revolutionize integrated pest management practices.

Read More
Adult Thrips feature

January 25, 2017

Tips to Stay Ahead of Aphids, Mites, and Thrips

Control these persistent pests with innovative chemistries that will expand your rotation options with new modes of action.

Read More
Effective pest control

January 12, 2017

Prevention and Early Intervention: The Keys to Biocont…

Advance preparation and starting out right helps you implement an effective biocontrol program that reduces pest pressure.

Read More
Two-spotted spider mites, adults and eggs

January 10, 2017

Pest Management Workshop to Take Place in Virginia on J…

Battlefield Farms will host the workshop, which is being coordinated by Virginia Cooperative Extension and will focus on new techniques in disease and insect control.

Read More
foxglove-aphid

November 29, 2016

How Greenhouse Growers Can Manage The Foxglove Aphid

Recent research is shedding new light on the foxglove aphid. Understanding host plants, identification, and biology will help growers deal with this pest.

Read More

October 25, 2016

Why Logic May Be The Best Defense Against Q-Biotype Whi…

Greenhouse Grower Editor Laura Drotleff says while you may feel you're in a lose-lose situation with pest control, there are some solutions that can help.

Read More
Downy mildew lesions on light coleus cultivars feature

October 4, 2016

Crop Protection Manufacturers Detail 2017 Early Order D…

Greenhouse Grower asked crop protection product manufacturers to send us the details for their 2017 Early Order Discount Programs and ongoing rebate programs, to provide you with a compiled knowledge resource of all discount offers at a time when you're making decisions for 2017.

Read More

September 28, 2016

Floriculture Industry Working To Solve The Whitefly Pro…

This summer, the floriculture industry has been faced with a dangerous new development — the detection of the Q-Biotype whitefly (Bemisia tabaci) in outdoor landscapes. It’s the first time that the Q-Biotype has been found in the U.S., outside of a greenhouse or wholesale nursery, since the pest was first detected on an ornamental plant in an Arizona greenhouse in December 2004. This year in Florida, there have been 47 detections of the Q since April, in retail nurseries and residential landscapes in 10 counties in Florida, from Miami-Dade to Duval County, primarily on hibiscus. Other hosts involved are crossandra, eggplant transplants, lantana, ficus, and porter weed. The detections have been in 17 retail nurseries, eight wholesale nurseries, 10 residential landscapes, and two agricultural fields. Other states have reported Q-Biotype detections this year, as well. The discovery of Q-Biotype whitefly in the landscape is troubling for the entire ornamentals industry, […]

Read More
Chrysanthemum Aphid

August 22, 2016

How To ID And Manage Black Aphids In Chrysanthemums

Growers in Michigan have recently been reporting a higher presence of this pest. Here are some tips on how to control it.

Read More