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T-STAR, Tropical & Subtropical Agric. Research

Sustainable Pineapple Mealybug Managment via Augmentative Biological Control

Marshall W. Johnson,
Department of Entomology, University of Hawaii at Manoa, 3050 Maile Way, Honolulu, Hawaii  96822



mealyroots.jpg (34031 bytes)

The pink pineapple mealybug feeding near the soil surface on the roots of Rhodes grass.

Pineapple crops worldwide are infested by tiny insects called mealybugs which feed on the pineapple plant sap. Mealybugs may cause pineapple growers problems because they may impact the size of pineapple fruit due to withdrawn of plant nutrients; they produce large volumes of the sweet liquid called "honeydew" that makes the pineapple fruit sticky and black colored from an associated fungus called sooty mold; and they transmit and interact with plant pathogens, thought to be closteroviruses, that often kill the pineapple plants if the plants are stressed via mealybug feeding. In Hawaii, the most common mealybug infesting pineapple is the pink pineapple mealybug, Dysmicoccus brevipes (Cockerell), (Homoptera: Pseudococcidae). A close cousin called the gray pineapple mealybug, Dysmicoccus neobrevipes Beardsley, may also be found in fields.



Big-headed ants

The Big-headed ant tends mealybugs on pineapple.

  Like aphids, mealybugs are often found in association with ants (e.g., the big-headed ant) that carefully oversee the mealybugs, providing protection in exchange for the sweet honeydew liquid. The ants protect the mealybugs from their natural enemies such as small wasps that act as parasites on the mealybugs and from predators such as ladybugs. They also aid in the elimination of excess honeydew that can reduce the growth of mealybug colonies because the mealybugs become entangled in the accumulated honeydew. The presence of the ants is very important to the mealybugs’ survival, and elimination of the ants using poisonous ant baits, will usually mean the destruction of the mealybug colonies. Thereby, farmers routinely use ant baits in their pineapple fields to eliminate the mealybugs’ guardians. Although this is an efficient and evidently safe management system, farmers have no "backup" control systems if the ant baits suddenly become unavailable or less effective.

  The research goals of this project are to determine the potential of using periodic releases of one of the pink pineapple mealybugs’ most effective natural enemies, the encyrtid parasitoid Anagyrus ananatis Gahan. Field data indicate that this natural enemy can be found attacking mealybugs in the presence of ants, although its impact on mealybug mortality is low. Laboratory studies indicate that the parasitoid is only scared away from mealybugs when ants are present, but are rarely killed like predators such as the ladybugs. When ants are absent, the parasitoid is highly effective in lowering the mealybug populations in pineapple plantings.


Anagyrus ananatis

The encyrtid parasitoid Anagyrus ananatis is a highly effective natural enemy of the pink pineapple mealybug in the absence of ants.

  Before one can conduct periodic releases of millions of Anagyrus ananatis, they first must be reared. This requires the rearing of larger numbers of the mealybugs in the laboratory to feed the parasitoids so they can reproduce. Until recently, it was difficult to efficiently rear large numbers of the pink pineapple mealybug in the laboratory because individuals often fell off of the squash fruit used as a food source and they often got stuck in their own honeydew because the ants were not present to eliminate the honeydew. Solving these problems turned out to be very simple, but contrary to logical thinking. Mealybug-infested squash were actually buried in a substrate called vermiculite which consists of light and absorbent particles that flow like sand or fine soil. It is commonly used around agricultural laboratories in growing plants. An average sized squash (12–16 cm long & about 0.5–1.0 kg) produced about 4,000 large 3rd instar and adult (> 0.85 mm in size) and 2,500 2nd instar and small 3rd instar (0.5–0.85 mm in size) mealybugs 5 – 7 weeks after initial infestation with 1,000 – 2,000 adults. This does not include the numerous crawlers that would be produced by the mealybug adults. To increase mealybug production efficiency, studies to enhance crawler settlement on the squash are in progress. Additionally, we are evaluating the use of growth units that can hold several squash (3 to 6), thereby reducing personnel hours required to process squash.

  Initial monthly production (only 300 individuals) of the parasitoid A. ananatis was very low given the unlimited supply of mealybugs that we could provide to mated female parasitoids. The challenge appears to be the manner in which the mealybugs are exposed to the searching parasitoids. Various methods of exposing the 3rd instar and adult mealybugs to the parasitoid were tried, and one of the best appears to be the use of cheesecloth to cover the mealybugs. Use of cheesecloth increased our production by about 6-fold. We are still refining this technique.



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