Device for controlling stored food insects
This invention relates to a device for controlling certain common insect pests of stored food products in human residences, food storages and the like. 
     DESCRIPTION OF PRIOR ART 
     Certain insects are pernicious pests of stored food products such as cereals, nuts, seeds, dried fruits, cake and confection products etc. stored in human residences, food storages or similar areas. Common insect pests are the confused flour beetle, Tribolium confusum Duv. and the merchant grain beetle, Oryzaephilus mercator Fauvel. The latter is widespread as a household pest, particularly in multiple dwelling buildings where the insect can migrate between units via pipe chases, ducts, crevices etc. 
     Several insect control methods and devices have been used and known thus far. Fumigation, or gassing of infected areas is still widely used. It is commonly known to attract and trap insects on a sticky surface of a bait dispenser, such as a fly trap. 
     Various insecticides, usually adopted to control a particular strain or species, are often employed, sometimes mixed with attractants. U.S. Pat. No. 4,227,333 granted Oct. 14, 1980 to H. Levinson et al. discloses a device comprising fibrous fabric or paper strips forming a trap provided with living agents and insecticides. Accumulation of larvae and adult insects, viz. Khapra beetles, is also promoted, beside the attractants, by the thigmotactic stimuli provided by the fibrous substance of the trap. 
     For use in residential areas, fumigation or gassing with pesticides has many environmental drawbacks. It is also known that insects can develop resistance to the insecticide used and this phenomenon can cause serious rebound problems. 
     Silica gel, particularly amorphous fine silica gel, is known for its insecticidal properties. It is effective to control various insects such as some beetles, cockroaches, mites, termites. It may be applied in a dust form, e.g. by spraying in relatively low concentrations. Its insecticidal effect is due to biochemical action (selective adsorption of cuticular lipid) and mechanical action (death by desiccation) depending on which part of the insect body comes in contact with silica gel particles. Owing to the above-described mechanism, there is virtually no danger of insects developing resistance to silica gel. 
     However, the physical properties of silica gel, especially the small size of its particle aggregates (about 3 microns) make its use troublesome in residential areas. The particles float in the slightest air currents and thus may easily be inhaled by humans or domestic animals. Thus, the use of silica aerogel (silica gel in powder form) should be discouraged based on the present knowledge of related health hazards. 
     Another objection to dust formulations is that in still air, silica gel aggregates would settle on furniture, floors, counter tops etc. leaving an objectionable grey haze or film. 
     In view of the above, this invention is aimed at utilizing the advantageous properties of silica gel in its powder, or dust form while eliminating the associated drawbacks and inconveniences. 
     STATEMENT OF INVENTION 
     According to the invention, there is provided a device for controlling crawling household or stored product insects, particularly in residential areas. The device comprises, in general, a substrate and a deposit of fine silica gel particles releasably secured to the substrate. A binding means may be provided to ensure a releasable bond between the substrate layer and the deposit. Preferably, the binding means is an adhesive, particularly a substantially permanent adhesive. The deposit of silica gel particles may be applied on a variety of substrates, preferably paper, burlap, cardboard or porous plastic. 
    
    
     BRIEF DESCRIPTION OF DRAWING 
     The invention is illustrated in a single drawing showing in cross-section an embodiment of the device for controlling insects. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     In the drawing, a strip of paper 10 forms a layer to which is secured a double-coated tape 12 consisting of a plastic film 14 and two layers of non-drying adhesive 16 and 17. As clearly seen in the drawing, the tape 12 is secured to the paper strip 10 with one adhesive layer 16. A deposit of silica aerogel particles 18 is applied onto the other adhesive layer 17. 
     In this embodiment, the silica aerogel is amorphous silica gel known as Dri-Die ™, or SG-67, a product of Fairfield American Corporation. According to the specification, the aerogel contains amorphous silica gel--95%, ammonium silicofluoride--2% and inert ingredients--3%. The aggregates of silica gel particles have an average size of about 3 microns while the particles in the aggregates are 0.01 to 0.05 microns in diameter. 
     In another embodiment of the invention, not illustrated in the drawing, a single layer of adhesive is applied onto the substrate by spraying and a deposit of silica aerogel particles in one or more layers is applied onto the single adhesive layer. 
     EXPERIMENTAL 
     In the experiments, paper, burlap, corrugated cardboard strips or porous plastic sheets were used as substrates and were found equally suitable. 
     Two types of binding means were used, all of them products of 3M Canada Inc. (a subsidiary of the U.S. parent company). The first type comprised 415 and 666 double-coated film tapes (Table 1). 
     The second type of binding means comprises three aerosol-type spray adhesives as described in Table 2. 
     
                       TABLE 1                                                     
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CHARACTERISTICS OF                                                        
THE DOUBLE-COATED TAPES USED                                              
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Product symbol                                                            
            415              666                                          
Adhesive type                                                             
            A-40 medium-firm acrylic                                      
Adhesive carrier                                                          
            Polyester film   UPVC film                                    
Release liner                                                             
            Tan paper        PE film                                      
Temperature                                                               
operating range                                                           
long term (days)                                                          
            65° C.    52° C.                                
short term  82° C.    52° C.                                
(minutes, hours)                                                          
Approximate                                                               
thickness                                                                 
film        0.025 mm         0.025 mm                                     
adhesive    0.10 mm          0.09 mm                                      
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                       TABLE 2                                                     
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CHARACTERISTICS OF THE SPRAY ADHESIVES USED                               
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Product symbol                                                            
           74         75         77                                       
Base       synthetic  synthetic  SBR                                      
           elastomer  elastomer  (styrene                                 
                                 butadiene                                
                                 rubber)                                  
Solvent    chlorinated                                                    
                      chlorinated                                         
                                 hexane and                               
           &amp; aliphatic           cyclohexane                              
Solids     10          9         25 ± 2                                
content wt. %                                                             
Bond type  strong     temporary  strong                                   
           flexible   flexible   flexible                                 
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     In this specification, tests conducted on two species of beetles commonly found in residences, the merchant grain beetle (Oryzaephilus mercator) and the confused flour beetle (Tribolium confusum) are reported. In the tests reported herein, results obtained using the spray adhesives (Table 2) are indicated. 
     Oryzaephilus mercator. Groups of insects were exposed for 3 hours and for 24 hours respectively to fresh or &#34;old&#34; deposits of silica aerogel (Dri-Die) on paper coated with 74, 75 and 77 adhesives respectively (see Table 2). The mortality results for these insects are indicated in Table 3. 
     
                       TABLE 3                                                     
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MORTALITY OF O. MERCATOR EXPOSED TO                                       
LIGHT DEPOSITS (0.15-0.18 MG/CM.sup.2) OF DRI-DIE                         
Mean number dead* out of 20                                               
3-hour exposure      24-hour exposure                                     
Age of deposit, days                                                      
0         7      14     21  35   0   7    14  21   35                     
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74 adhes-                                                                 
       20     20     19   18  7    20  20   20  20   20                   
ive (0.17                                                                 
mg/cm.sup.2)                                                              
75 adhes-                                                                 
       20     20     11    9  2    20  20   20  20   20                   
ive (0.17                                                                 
mg/cm.sup.2)                                                              
77 adhes-                                                                 
        7      6      2    2  1    20  20   20  20    7                   
ive (0.15                                                                 
mg/cm.sup.2)                                                              
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 *Figures rounded to nearest unity                                        
 
    
     Additional tests were conducted with heavier deposits of Dri-Die (0.55 to 0.59 mg/cm 2 ) on all adhesives. The results are shown in Table 3A. 
     
                       TABLE 3A                                                    
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MORTALITY (%) OF O. MERCATOR                                              
EXPOSED FOR 3 HOURS OR 24                                                 
HOURS TO HEAVY (0.55-0.59                                                 
MG/CM.sup.2) DEPOSITS OF DRI-DIE                                          
42 DAYS OLD ON PAPER                                                      
COATED WITH 74.75 OR 77 ADHESIVES                                         
              Time of     Mortality                                       
Adhesive      exposure, hours                                             
                          %                                               
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74            3           100                                             
75            3           100                                             
77            3           100                                             
77            24          100                                             
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     Groups of adult O. mercator beetles were immersed in Dri-Die for about 5 seconds, then cleaned in water or air stream and placed in containers with and without food. The mortality results are presented in Table 4. 
     A series of tests was conducted to determine the effect of food after a 30-second exposure of O. mercator to a surface layer of Dri-Die applied on a filter paper coated with a spray adhesive. The mortality results are presented in Table 5. 
     
                       TABLE 4                                                     
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MORTALITY OF ADULT MERCHANT                                               
GRAIN BEETLES 24 HOURS AFTER                                              
THEY WERE IMMERSED IN SG-67,                                              
CLEANED IN AN AIR STREAM                                                  
OR WATER, AND THEN PLACED IN                                              
CONTAINERS WITH AND WITHOUT FOOD                                          
       Time of Mean.sup.1                                                 
       exposure,                                                          
                (±SE) within 24 h after exposure                       
Treatment                                                                 
         sec       Without food With food                                 
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SG-67     5        100     (0)    29.7  (0.88)                            
         15        100     (0)    24.3  (2.33)                            
SG-67 + air                                                               
          5        100     (0)    9.0   (3.06)                            
         15        100     (0)    11.0  (1.00)                            
SG-67 +   5        8.0     (0.58) 0.3   (0.33)                            
water rinse                                                               
         15        11.0    (2.33) 1.3   (0.33)                            
Air      15        2.0     (1.00) 0     (0)                               
Water rinse                                                               
         15        0.7     (0.33) 0     (0)                               
No treatment                                                              
         15        0.3     (0.33) 0     (0)                               
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 .sup.1 100 adults in each of 3 replicates. Twoway ANOVA and ttests done o
 transformed data. Difference due to treatment F = 1115.45; difference due
 to foods F = 2720.33; difference due to time of exposure F&lt;3.31; tvalues 
 for differences due to foods ranged from 6.17 to 103.06.                 
 
    
     
                       TABLE 5                                                     
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MORTALITY OF ADULT MERCHANT                                               
GRAIN BEETLES EXPOSED FOR                                                 
30 SEC TO A SURFACE LAYER                                                 
OF SG-67 ADHERING TO                                                      
FILTER PAPER COATED                                                       
WITH AN ELASTOMER ADHESIVE                                                
Mean no.      Mortality                                                   
Treat-  (±SE)  24 h         48 h                                       
ment   on surface Mean.sup.1                                              
                         (±SE)                                         
                               %   Mean.sup.1                             
                                        (±SE)                          
                                              %                           
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No food provided after treatment                                          
SG-67  63.3.sup.2                                                         
              (3.28)  50.0 (5.023)                                        
                                 78  10.3 (1.2) 100                       
Control                                                                   
       99.0   (1.00)  0    (0)    0  1.0  (0.58)                          
                                                 1                        
Food provided after treatment                                             
SG-67  88.3.sup.2                                                         
              (3.28)  10.3 (0.33)                                         
                                 11  4.7  (0.67)                          
                                                17                        
Control                                                                   
       99.7   (0.33)  0    (0)    0  0    (0)    0                        
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 .sup.1 100 adults in each of 3 replicates. Twoway ANOVA and ttests done o
 transformed data. For comparison of mortality between beetles given food 
 or deprived of food after treatment F = 81.00 and 357.00 at 24 and 48 h, 
 respectively; t = 9.00 and 18.89 at 24 and 48 h, respectively.           
 .sup. 2 No. of beetles on treated surface for 30 sec.                    
 
    
     CONCLUSIONS 
     Deposits of Dri-Die on 74 and 75 adhesive are highly effective and long lasting against adults of the merchant grain beetle (Oryzaephilus mercator) exposed for 24 hours. Even at relatively short exposures of 3 hours, 100% mortality will occur on deposits not older than 7 days. 
     Light deposits (Table 3) on 77 provide 100% mortality only at exposures of 24 hours and only on deposits 0 to 21 days old. However, heavier deposits on all adhesives provide 100% mortality even when the deposits are 6 weeks old (Table 3A). 
     O. mercator is highly susceptible to the Dri-Die in dust form. Exposure to the dust for as little as 5 seconds caused 100% mortality. However, if food is provided after the exposure, mortality is drastically reduced, probably due to removal of dust particles on body and ability to restore water lost due to selective adsorption of lipids from the epicuticle (Table 4). 
     Dri-Die on an elastomer adhesive causes 100% mortality within 48 hours after a 30-second exposure of adult O. mercator. If food is provided after treatment, mortality is only 17%. 
     Tribolium confusum. Groups of insects were exposed for 3 hours and 24 hours respectively to fresh and old deposits of silica aerogel (Dri-Die) on paper coated with 74, 75 and 77 spray adhesives specified in Table 2. The mortality of the insects is indicated in Table 6. 
     At three-hour exposures at light concentrations (0.15-0.18 mg/cm 2 ) of Dri-Die, maximum mortality was 28%. On deposits 14 to 35 days old, it was 4% or less. At heavier concentrations (0.55-0.59 mg/cm 2 ), 100% mortality occurred on deposits up to 14 days old on 74 adhesive. At 24-hour exposures at light concentrations, 100% mortality occurred on deposits up to 35 days old on 74 adhesive. 
     Thus, heavy concentrations of Dri-Die on 74 adhesive provide the best control for Tribolium confusum. 
     
                       TABLE 6                                                     
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MORTALITY OF TRIBOLIUM CONFUSUM                                           
EXPOSED TO LIGHT (0.15-0.18 MG/CM.sup.2)                                  
AND HEAVY (0.55-0.59 MG/CM.sup.2)                                         
DEPOSITS OF DRI-DIE                                                       
       Mean No. Dead* out of 20                                           
       3 hour exposure                                                    
                    24 hour exposure                                      
       Age of deposit (days)                                              
       0   7     14     21  35  0    7    14   21  35                     
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(light dep)                                                               
         6     1.5   1    0.3 0   20.1 19.5 10   10  8                    
74                                                                        
(heavy dep)                                                               
         20    20    20   17  11  20   20   20   20  20                   
(light dep)                                                               
         5.5   1     0.5  0   0   20   9    4.5  4   4                    
75                                                                        
(heavy dep)                                                               
         20    18    11.5 10  7   20   20   16.5 18  8.5                  
(light dep)                                                               
         1     0     0    0   0   5    1.5  0    1.5 0.5                  
77                                                                        
(heavy dep)                                                               
         20    5     3    4   2   18.5 20   17   3   2                    
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 *Figures rounded to nearest 0.5.                                         
 
    
     It is to be appreciated that the invention is not aimed at controlling all insects known as stored food product pests. Its applications are limited, understandably, to those species that are affected by the insecticidal action of silica gel, specifically silica aerogel, consisting of very fine particles of amorphous silica gel such as described hereinabove. 
     A most important aspect of the invention is the provision of a suitable substrate/binding means combination ensuring that the release of silica aerogel particles from the substrate does not take place in normal conditions (drafts, natural air convections) until specific forces are applied onto the silica gel particles anchored to the substrate. The bond between the silica gel deposit and the substrate should be of such magnitude, however, that the particles would be released from the substrate, generally, when contacted by insects such as merchant grain beetles (Oryzaephilus mercator) or confused flour beetle (Tribolium confusum). When the bond is of a suitable strength, the silica gel particles are not detached from the substrate by currents of ambient air, but are released and picked up by the insects. The particles can adhere to mouth, feet or other parts of the insect body, eventually causing the insect&#39;s death. 
     While detailed tests were conducted on the two aforementioned species only, merchant grain beetle and confused flour beetle, it is reasonable to assume that the scope of application of the invention is broader, covering other household species affected by silica aerogel. Other household insects susceptible to the action of silica aerogel are, e.g. cockroaches, silverfish and wood termites. It is the provision of suitable binding means, or adhesive in particular, that ensures the advantageous features of the invention. 
     While an adhesive is used in the above-described embodiment of the invention, it is also conceivable to provide a suitable bond between the silica gel particles and a substrate using other binding means. An example thereof might be controlled passing of silica gel particles into the surface of a fibrous or porous material, e.g. a plastic. 
     In the course of experiments, suitable binding agents were selected to meet the goal of the invention, i.e. to provide a bond between the silica gel particles and the substrate such that the silica gel particles do not get swept away off the substrate by usual air currents but can be released off the substrate by forces concomitant with an insect, such as the merchant grain beetle, contacting the device, particularly touching the silica gel particles. 
     Optionally, but not necessarily, the device may include an insect attractant, e.g. a pheromone or a food attractant or bait. 
     Food attractants may be mixed with the silica gel, added to the adhesive or impregnated into the substrate. 
     The device is designed to allow insects to leave the device and not to trap them. The silica gel particles adhering to the insect&#39;s body bring about its death through mechanical or biochemical action sometimes many hours after the insect leaves the device.