Controlled release system for insect attractant

A controlled release system for volatile liquid insect attractant compositions can be formed from a container having an aperture closed by a membrane, wherein the dimensions of the container, the dimensions of the aperture, the nature of the membrane, the liquid level, and vapor space within the container are conformed to produce an effective attractant release rate.

FIELD OF THE INVENTION 
The invention relates to a system for the controlled release of a volatile 
liquid attractant for insect pests. More particularly, the invention 
relates to a release device for a volatile liquid ethanolic attractant for 
common flies, typically Musca domestica, wherein the liquid attractant is 
released as a vapor at a controlled rate for the purpose of attracting the 
insect pests. While the release rate of the attractant slowly declines, it 
remains at a highly effective level until the attractant is consumed. 
BACKGROUND OF THE INVENTION 
A great number of attractants for insect pests have been disclosed in the 
art. Such attractants comprise typically fermented materials or hydrolyzed 
proteinaceous materials which release volatile ingredients into the 
atmosphere, which tend to attract pests including flying insect pests. The 
released volatile materials include a vast array of volatile compositions 
including alcohols, aldehydes, amines, hydrocarbons, etc. Ethanol has been 
identified as one component of such natural attractant compositions. These 
compositions have been used without significant control over release 
rates. Many volatile compositions having some risk of flammability have 
been avoided as attractants because of safety considerations. To the best 
of our knowledge, no effective commercially successful control release 
system for neat, volatile attractants, such as ethanol, has been developed 
in the prior art. 
Further, our review of the literature in this area indicates that volatile 
attractants, such as ethanol alone or in combination with other volatile 
components, have attracted no effective commercial attention, and the 
prior art provides no teaching with respect to the effective release rate 
for ethanolic attractants. 
In large part, the use of controlled release systems for insect attractants 
has been directed to dispensing a variety of pheromones from a composition 
that can release the pheromone at their inherently low effective 
concentration. Pheromones are most commonly impregnated into porous 
plastic or onto natural materials such as corncob grits. Therefore, a 
great need exists for a controlled release device for a volatile 
attractant composition in which the device exhibits an effective release 
rate of attractant that continues to maintain a useful attracting 
concentration of the attractant in the environment during the useful life 
of the device. While the rate may slowly decline, the components of the 
controlled release device cooperate to maintain an effective release rate 
for the volatile attractant that can continue to attract pests, including 
flying insect pests, until the attractant is consumed. 
SUMMARY OF THE INVENTION 
The invention relates to a container having an aperture closed by a 
membrane wherein the geometry of the container, the semi-permeable 
membrane, and the size of the aperture cooperate to release an effective 
concentration of the volatile attractant vapor into the environment at a 
rate that maintains attractancy until the attractant is fully dispersed or 
consumed. We have found that the distance between the membrane and the 
surface of the volatile liquid held within the container affects the 
release rate of the vapor. We have designed the container to insure the 
vapor space remains saturated by attractant vapor and to minimize the 
change in height of the vapor space over time to dispense the attractant. 
The membrane materials and the orifice size, taken in conjunction with the 
container dimensions, permit vapor diffusion at a controlled rate such 
that the device continues to attract flying insects until the volatile 
liquid is entirely dispensed from the container. The preferred membrane 
materials additionally prevent liquid penetration through the membrane to 
enhance the safety of the controlled release system. The container can be 
configured to provide an effective amount of attractant vapor for up to 6 
months. 
In greater detail, we have further found that a volatile ethanolic 
attractant for flying insect pests, particularly flies of the order 
Diptera including Musca domestica, the common household fly, can be 
effectively controlled using the controlled release system of the 
invention to provide improved attractancy. For the purposes of this 
invention, semi-permeable means that attractant vapor can penetrate the 
membrane while attractant liquid is retained within the container.

DETAILED DISCUSSION OF THE INVENTION 
Containers for the fly attractant useful in the invention can take any 
convenient shape. The containers can be spheroidal, cylindrical, in the 
form of a cube, a rectangular prism, an oval prism, pyramidal, etc. The 
preferred shape for the container of the invention is cylindrical, an 
oval-shaped prism, or a rectangular-shaped prism. The overall dimensions 
of the container are important in preventing a large change in the 
distance between the surface of the volatile liquid/vapor interface and 
the semi-permeable membrane. We have found that the rate of vapor transfer 
through the membrane decreases as the height of the vapor space increases. 
Accordingly, the diameter or length and width of the container is greater 
than the depth. 
For a container holding 50 to 2000 gms of volatile liquid attractant, 
preferably holding 100 to 500 gms of fly attractant, the cylindrical 
container should have a radius of 3 to 15 cm, preferably 5 to 12 cm, and a 
depth of 2 to 15 cm, preferably 3 to 8 cm. A container having the form of 
a rectangular prism can have a length of about 5 to 10 cm, the width being 
less than the length, and a depth of from about 3 to 5 cm. 
The container can be prepared from any barrier material capable of 
preventing any significant molecular diffusion or permeation of the 
attractant through the material. Typical barrier materials for the fly 
attractants of this invention include metals such as aluminum or steel 
sheet, thermoplastic materials such as polyethylene, polypropylene, 
polyester (polyethylene terephthalate, polybutylene terephthalate), etc. 
The choice of materials is not critical except that the barrier material 
should be inert to insect attractants, be moldable or shapeable into the 
container of the invention, and can be easily assembled. 
The controlled release device for a volatile attractant of the invention is 
designed to have a service life of at least 1 week at a temperature of 
about 60.degree. to 100.degree. F. at a release rate of at least about 
0.02 gm/hr. Preferably, the service life of the device is greater than 2 
weeks, and can be as much as 6 months or more. More preferably, the 
service life of the device is from about 4 weeks to 8 weeks. Accordingly, 
at ambient temperatures, generally about 70.degree.-85.degree. F., the 
device should contain at least about 8.5 to 17 grams of the attractant to 
release about 0.05 to 0.1 grams of the attractant per hour to provide the 
minimum 1-week service life. For longer service life, for example, 2 
weeks, the container should hold about 17 to 35 grams of the attractant to 
provide a service life at a release life of about 0.05 to 0.1 grams per 
hour. For a device having a service life of from 4 to 6 weeks, the 
container can hold about 35 to 100 grams of the attractant material to 
operate at a release rate of about 0.05 to 0.1 grams per hour for the 
service life. A controlled release system having a service life of 6 
months can require about 250 to 500 gms of attractant to last for 6 months 
at a release rate of 0.05 to 0.1 gm/hr. If higher temperatures are 
expected, the rate of release will increase in proportion to the vapor 
pressure increase of the liquid attractant. 
In order to provide additional guidance for design of the release system, a 
mathematical model was developed for describing ethanol evaporation 
through semi-permeable membranes. This model will allow one to predict the 
evaporation rate as a function of time, temperature, and membrane/liquid 
area ratio. The rate is shown to vary with the inverse of the distance 
between the liquid/vapor interface and the porous membrane. The rate also 
varies with temperature in a manner proportional to the vapor pressure of 
ethanol at that temperature. Finally, the rate decreases as the ratio of 
membrane area to liquid surface area (Am/Ao) raised to some power n which 
is less than 1. The general equation of the model is as follows: 
##EQU1## 
dw/dt=evaporation rate (g/hr) k=rate constant (cm.sup.2 /hr) 
S=grams of attractant liquid per unit height in cms of reservoir 
L=vapor space distance (cm) 
n=constant between 0.5 and 1.0 
Am=membrane area (cm.sup.2) 
Ao=liquid surface area (cm.sup.2) 
a=constant between 0.5 and 0.9 
The rate constant k varies with temperature by: 
##EQU2## 
where ko=rate constant in cm.sup.2 /hr (usually between 0.01 and 0.10 
cm.sup.2 /hr) measured at some reference temperature To (temperature is in 
degrees Kelvin). EXP indicates a power of 10. 
If the above differential equation is substituted with dw/dt=S dL/dt and 
solved by separation of variables, we obtain: 
EQU L=(Lo.sup.(1/a) +2(Am/Ao).sup.n kt).sup.a 
where Lo=beginning vapor space distance at t=0 and the rest of the 
variables are defined above. This model was tested against actual data and 
found to accurately predict the rate of evaporation once the parameters k, 
a, and n were determined for a particular container geometry. 
The container has an aperture covered by a release membrane through which 
the attractant vapor is released into the environment. The aperture is 
conveniently of any shape. However, we have found that the circular or 
oval aperture is most easily manufactured. The aperture can be about 0.1 
to 5 cm in diameter, preferably 0.2 to 2 cm. We have found that the size 
of the aperture and the vapor space distance between the liquid surface 
and the membrane are important in controlling the release rates. A desired 
ratio between the area of the aperture and the area of the liquid surface 
is about 0.01 to 0.1, preferably about 0.01 to 0.025, and, most 
preferably, about 0.01 to 0.02 to ensure the optimal release rate of the 
attractant from a liquid surface area ranging from about 50 to 80 
cm.sup.2. We have found that as the vapor space between the liquid surface 
and the aperture increases, the release rates are reduced. Accordingly, 
the distance between the liquid/vapor interface (liquid surface) and the 
semipermeable membrane should not change more than about 5 cm, preferably 
less than 4 cm, most preferably less than 3 cm during the useful service 
life. As the dimension from the membrane to the surface of the liquid 
attractant increases, the attractant vapor molecules must traverse an 
increased average distance, thus reducing the rate of release through the 
membrane. The design of the container is overall adjusted to minimize the 
change in distance from the liquid to the membrane and to maximize the 
surface area of the liquid. All these modifications ensure the consistent 
release of an effective concentration of the attractant into the 
atmosphere. 
Polymeric materials useful in preparing the membrane covering the aperture 
in this invention may be selected from a wide range of substances. A 
variety of materials can provide a semi-permeable membrane that, due to 
its internal structure or to the formation of microporous structure in the 
membrane, can release the attractant at a significant rate. The preferred 
membrane is a semipermeable membrane having a pore size of about 0.001 to 
0.05 microns in diameter. Such membranes are typically formed by modifying 
a film of the material using known techniques to provide the desired pore 
size and then laminating the material in a woven or nonwoven fabric to 
provide mechanical strength. The membranes can be manufactured from a 
variety of polymers, copolymers and terpolymers derived from the 
polymerization of one or more ethylenically unsaturated monomeric 
materials. Such polymer materials include polyethylene, polypropylene, 
polyvinyl chloride, polyurethanes, polysiloxane, thermoplastic elastomers, 
rubbers, polyesters, nylons, polyamides, polytetrafluroethylene, 
polychlorotrifluroethylene, etc. The thickness of the polymer layer will 
generally range between about 25 to 100 microns. 
The membrane is typically sealed to the container at the aperture such that 
the vapor can only exit the container through the membrane. The membrane 
can be attached to the aperture using adhesive means, heat sealed means, 
mechanical seals, etc. 
There are a variety of known attractants that can be used in the device of 
the invention. The device of this invention is primarily designed for use 
with volatile attractant compositions having a vapor pressure (at ambient 
conditions) of at least 30 mm Hg, preferably about 40 to 70 mm Hg. 
A variety of volatile liquid compositions can be found having a vapor 
pressure within this useful range. One volatile attractant we have found 
that is useful in the controlled release system of the invention comprises 
absolute ethanol or denatured absolute ethanol. Such material can be 
dispensed by the controlled release device of the invention at a rate of 
about 0.02 to about 0.2 grams per hour for the purpose of attracting 
typically flying insect pests. Once attracted, they can be trapped, large 
populations can be sprayed, the change in the density of the flying insect 
populations can be monitored, etc. 
A preferred attractant for use in the device of the invention comprises a 
major portion of an ethanol attractant and an effective amount (preferably 
0.05 to 5 v/v-%) of a volatile C.sub.1-5 alcohol ester of a C.sub.1-3 
carboxylic acid (most preferably 0.1 to 1 v/v-% by amyl acetate). We have 
found that the combination of these materials is a significantly better 
attractant than either ethanol or the volatile ester alone, and throughout 
the useful release ranges tested for this attractant, the material remains 
an attractant to flying pests. The liquid material has a very pleasant 
mild odor. At concentrations in the air typically used in attracting 
flying pests, the material provides a barely detectable low level of a 
background mild, somewhat fruity odor. Preferably, this preferred 
attractant matreial is dispensed into the environment at a rate of about 
0.05 to 0.2 grams per hour to draw flying insects to the insect trap. 
The device of this invention can be conformed to lure household flying 
insect pests. The typical flying insect pest attracted by the device of 
this invention are flies belonging to the order Diptera, including flies 
of such families of Phoridae, Psychodidae, Fungivoridae, Chloropidae, 
Calliphoridae, Sacrophagidae, Anthomyiidae, Muscidae and Drosophilidae. 
The primary flying insect pest attractant of the preferred device of the 
invention are flies of the Muscidae family and, in particular, Musca 
domestica, the common household fly. 
The device of the invention can be used in conjunction with any trap, which 
can kill or entrap a significant portion of the fly population, thus 
removing that proportion of the fly population from the human environment. 
Such traps can simply be a mechanical trap or a reservoir in which the 
flies cannot exit once they have entered. The trap can comprise a layer of 
highly tacky pressure sensitive adhesive whereon the flies are trapped by 
the tacky surface layer. The trap can comprise charged mesh screens 
causing the immediate electrocution of the flies upon entry. Any means for 
trapping, stunning or killing the flies in conjunction with the device can 
be used. 
DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to the drawings, wherein like numbers represent like parts 
throughout the several views, there is generally disclosed in FIG. 1 the 
controlled release system 10 for a liquid insect attractant 24. The system 
10 includes a reservoir 12 having a base 14 and a lid 16. The lid 16 is 
sized and configured to form a vapor-proof seal with the reservoir 12. In 
the preferred embodiment, the reservoir 12 is generally cylindrical in 
shape. While it should be understood that many configurations, sizes and 
shapes of the reservoir 12 can be envisioned within the scope of this 
invention, the dimensions of the reservoir 12, as illustrated in FIGS. 1 
and 2 of the preferred embodiment, are 8.2 cm in diameter by 5 cm in 
height. The reservoir 12 is made of a nonporous impermeable material. In 
the preferred embodiment, polyethylene and polypropylene have been found 
to perform satisfactorily. 
The lid 16 includes an aperture 18. The aperture 18 is generally circular 
in the preferred embodiment. The aperture 18 is closed by a membrane 20. 
The membrane 20 is sized and configured to fit within or over the aperture 
18 to seal the liquid 24 within the system 10. The membrane 20 is of the 
type which allows vapor to escape the reservoir while retaining liquid. 
Therefore, a semipermeable membrane may be utilized as well as a stretched 
material where the stretching introduces pores for release of vapor. The 
pores are preferably small enough to prevent passage of liquid while 
permitting permeation of attractant vapor. A chemically treated material 
may also be utilized where the treatment introduces holes into the 
material for escape of vapor. A stretched or expanded polypropylene 
membrane (Celgard) can be used in the present invention. 
A cover 22 can be utilized with the present invention to seal the reservoir 
12 until a user desires the vapor to escape the reservoir 12 through 
aperture 18. In the preferred embodiment, a nonporous impermeable or 
barrier material is adhered to lid 16 and covers aperture 18. The cover 22 
may be heat sealed or adhered to the reservoir. The cover 22 may also be 
sized and configured to be press fit within aperture 18. The user will 
remove the cover 22 to use the present invention. In another preferred 
embodiment, an empty container 12 can be filled at the use site. In such 
an embodiment, the cover 22 is optional, and serves only to protect the 
membrane during shipment and storage. 
The bulk of the liquid flying insect attractant 24 is contained within 
reservoir 12 for attracting the insects. Above the liquid is a vapor space 
or head space 26. A preferred liquid attractant 24 is an ethanol/amyl 
acetate mixture discussed above. 
In FIGS. 2 and 3, an insect holding or retaining means 28 is shown mounted 
on the lid 16 of the present invention. It should be understood that the 
retaining means 28 need not be mounted on lid 16 but must be associated 
with reservoir 12 and aperture 18 in a manner which attracts insects 
within range of any retaining means. 
In the preferred embodiment, the retaining means 28 includes a generally 
tubular shaped member 27 and a layer of tacky adhesive 29 to retain the 
insects. It should be understood that any configuration of member 27 may 
be utilized which is within the scope of this invention. 
Although an adhesive surface trap 29 is shown in FIGS. 2 and 3, a 
mechanical or electrical trap may also be used to retain the insects, 
whereby the insect enters the trap but is unable to crawl or fly out. 
As illustrated in FIGS. 2 and 3, a shield 30 is utilized in the preferred 
embodiment to hide the insects which have been caught from view of the 
user. The shield 30 includes a wall 31 having first and second flanges 33, 
35 proximate each end. The shield 30 can be formed as an integral unit and 
can be constructed of plastic in the preferred embodiment. The wall 31 is 
of a semi-circular shape. The shield 30 is connected to reservoir 12 by an 
adhesive in a manner which does not block or cover aperture 18. Tubular 
member 27 fits within the flanges 33, 35 of shield 27 in the preferred 
embodiment 
In operation, the user will remove cover 22, if present, from aperture 18. 
The removal of cover 22 allows a vapor from the attractant 24 in the vapor 
space 26 to escape through membrane 20 of aperture 18. When the attractant 
is released, flying insects are drawn to the device where the insects are 
retained by insect-retaining means 28, thus, eliminating pests. 
The rate of release of the flying insect attractant 24 is at least about 
0.02, preferably 0.03 to 0.2 grams of attractant per hour in the preferred 
embodiment. This effective rate of release is achieved by means of 
combining the preferred area of the aperture/membrane 18 which is about 
0.7 to 1.0 cm.sup.2 ; the area of the liquid/vapor interface about 50 to 
80 cm.sup.2 ; the initial distance between the membrane and the attractant 
liquid vapor interface about 1 to 2 cm; and the temperature of the 
attractant 24. With the proper combination of these factors, significant 
volumes of attractant 24 may be released at a controlled rate over a 
period of 1 to 2 months. The result is a device with a consistent 
attractant vapor output over a prolonged service period resulting in 
effective insect attractancy during the service period. 
As discussed above, the particular configuration, shape and combination of 
materials for the system can be varied to suit the particular results 
desired. For example, the reservoir dimensions affect the release rate of 
attractant. It has been found that a relatively wide, flat reservoir is 
optimal because the vapor space distance between the membrane and the 
liquid surface does not change significantly over time. With an optimal 
attractant, the level of attractant decreases without substantially 
affecting the release rate of the vapor. 
TABLE I 
__________________________________________________________________________ 
RELEASE RATES FOR 
VARIOUS ATTRACTANTS 
RELEASE RELEASE RELEASE 
RATE FOR RATE FOR RATE FOR 
ELAPSED 
ATTRACTANT 
ATTRACTANT 
ATTRACTANT 
TIME #1* #2** #3*** TEMP 
t (hrs) 
(g/hr) (g/hr) (g/hr) .degree.F. 
__________________________________________________________________________ 
0.00 82.4 
17.65 
0.116 0.123 0.097 83.8 
48.38 
0.116 0.120 0.103 86.0 
65.67 
0.119 0.128 0.116 84.2 
89.80 
0.124 0.126 0.109 86.0 
161.60 
0.122 0.127 0.110 87.8 
185.33 
0.123 0.126 0.113 87.8 
209.17 
0.127 0.129 0.117 87.8 
233.78 
0.111 0.108 0.097 78.8 
257.92 
0.115 0.116 0.102 84.2 
330.18 
0.113 0.115 0.102 88.7 
354.00 
0.104 0.104 0.095 85.1 
377.68 
0.103 0.102 0.093 82.4 
401.40 
0.108 0.105 0.094 85.1 
425.25 
0.107 0.104 0.094 84.2 
497.32 
0.109 0.107 0.096 86.0 
529.77 
0.107 0.106 0.098 84.2 
553.55 
0.109 0.105 0.097 84.2 
570.25 
0.113 0.106 0.099 86.0 
593.93 
0.114 0.107 0.096 86.0 
665.70 
0.107 0.102 0.097 85.1 
689.78 
0.110 0.104 0.093 86.9 
742.92 
0.103 0.100 0.092 87.8 
833.50 
0.097 0.090 0.082 87.8 
857.53 
0.099 0.089 0.087 85.1 
880.45 
0.107 0.096 0.092 86.0 
905.83 
0.101 0.098 0.092 86.0 
932.00 
0.101 0.094 0.088 86.0 
__________________________________________________________________________ 
*Attractant #1 is: Absolute Ethanol with 5% water added. 
**Attractant #2 is: Absolute Reagent Ethanol (contains about 5% isopropyl 
alcohol and about 5% methanol). 
***Attractant #3 is: Absolute Reagent Ethanol with 5% water (contains 
about 5% isopropyl alcohol, 5% methanol and about 5% water). 
The data shown in Table I establishes that the controlled release means 
shown in FIG. 1 is effective to release a variety of attractants at a 
significant rate over an extended period. Over a 39-day period, the 
release rates varied somewhat, but showed a minimal continuing decline in 
rates of release. During the testing, the release rates remained well 
above the 0.02 gms/hr threshold required for attractants. The data shows 
that rates tend to increase with temperature. Overall, the controlled 
release system proved to be effective in release of a variety of 
attractants for an extended period. 
While particular embodiments of the invention have been described, 
modifications of the invention will be apparent to those skilled in the 
art in light of the foregoing description. This description is intended to 
provide specific examples of certain embodiments which clearly and fully 
disclose the present invention. Accordingly, the invention is not limited 
to the described embodiments or to the use of the specific elements 
therein. All alternative modifications and variations of the present 
invention which follows in the spirit and broad scope of the appended 
claims are covered.