Entomological HYDROCAPSULE^® Encapsulation Research

Insect Photography by Dr. Patrick D Greany, Entomologist

        ARS, Inc. under previous USDA SBIR Phase I & Phase II funding (1996 & 1997) recently developed patent-pending methods to encapsulate various insect diets (Greany and Carpenter, 1999) using proprietary Hydrocapsule^® technology.  In this form, the encapsulated artificial diet (a suspension of nutrients containing proteins, carbohydrates, and lipids) remains stable and sterile despite its high water content (50-75%).   The size range of Hydrocapsules^® currently produced by ARS, Inc's. encapsulation technology is from 100 microns up to 2 cm diameter, with a typically size of approximately 2 to 3 mm.  Wall thicknesses generally range between 10 to 100 microns as measured by scanning electron microscopy (SEM).  The mechanical properties of ARS Hydrocapsules^® can range from hard and plastic-like, to soft and flexible, like silicone rubber.  Membranes thin and soft enough to be punctured by a human hair have been produced.  These softer membranes were developed to feed insects with piercing-sucking mouth parts (such as the spined soldier bug, Podisus maculiventris), and have shown the ability to penetrate through the capsule wall under laboratory conditions.  It has also been observed that many species of insects with chewing mouth parts are capable of eating through the harder/thicker shell formulations of ARS's capsules (ants, mites, cockroaches, and lady beetles).   Observations indicate that roaches and lady beetles actually consume the entire non-toxic ARS Hydrocapsule^® shell along with the contents. This is an unexpected benefit which has favorable environmental consequences.

      These same capsules which have been successfully used to feed beneficial insects may be converted into lethal snacks for pest insects, simply by incorporating the entomopathogenic agents into the aqueous or oil-based solution core.  For applications such as cockroach and fire ant baits, it would not be necessary that the shell be soft to allow the entrapped organisms to escape on their own, since the shells are easily breached by the feeding insect.  In fact, the capsule can serve as a convenient package which allows the target insect to carry the infective agent directly into its nest.  This feeding behavior has been observed in studies involving wild fire ants feeding on encapsulated artificial diet at the USDA-ARS Center for Medical, Agricultural and Veterinary Entomology and the University of Florida (both located in Gainesville, Florida).  Incentive to feed on the capsules could also be provided by incorporation of essential nutrients, or by the addition feeding stimulants or kairomones.  For more passive delivery approaches, it is possible to adjust the shell formulation to the needs of a particular system, so that the entomopathogenic agent can emerge without direct contact between the insect and the capsule.  In fact, a combination of the two release mechanisms may serve to be the most effective approach.

     The Technology as applied in the field-of-use of beneficial insect food production is currently being used by ARS, the USDA, and two additional commercial customers.  This technology has shown success in feeding several different insect species, to include: Orius, Geocris, C.mac ladybird beetles, cockroaches, and imported red fire ants.  All insect feeding data is reported to ARS, Inc. by third party scientists and entomologists, to include: the USDA-ARS, U.S. Forest Service, the Univ. of Florida, ENTOMOS, LLC., KOPPERT Biological Systems, Inc., and several other private beneficial-insect producing companies.  ARS does not develop or test insect diets, nor mass rear any insects or mites.  All entomological data provided by ARS, inc. using this technology has been supplied to ARS, Inc. by third party collaborators, customers and governmental agencies.

       The Hydrocapsules^® used to feed the insects listed above, are routinely produced in a size range from 2 to 5 mm.  The wall thickness of the polymer shell (coating) vary from 10 micron to 100 microns in thickness, and are typically running around 25 microns.  Wall thickness as thin as 5 microns have been produced.  The wall thickness of the coating is user / operator controlled, and is dependent upon several operational parameters to include: capsule size, properties and chemistry of contents, speed of production, and cleanliness of system and nozzles. 

       The Hydrocapsule^® shell formulation that ARS, Inc. has developed specifically for beneficial insect feeding is a proprietary mixture of six (6) different chemical compounds that is available in a pre-mixed formulation from ARS, Inc. or can be purchased individually from many chemical suppliers and can be mixed by the user.  ARS, Inc. can only guarantee the performance of the formulation with chemicals purchased either from an ARS authorized supplier (this is to insure compatibility & quality) or ARS directly.  ARS has tested chemicals from each of its authorized suppliers for compatibility. The cost of the chemicals used to make any formulation vary with the quantity purchased at a single time, the chemical company supplier, and the distance the chemicals have to be transported.  Pricing generally decreases as more bulk weight of each chemical is purchased from a supplier and the closeness of the supplier.  Chemicals can typically be purchased in 1 Gallon, 5 Gallon and 55 Gallon drum containers 

        ARS has produced several different coating formulations for various other applications, that include time release, pH-activated release, and gas permeable shells.