Abstract:
An electrical penetration graph (EPG) system includes a monitoring device with a buffered and stabilized voltage source assembly and a buffered internal amplifier with switched gain control. The system also includes a head stage amplifier. During the EPG process, the voltage source assembly directs an electrical current through a feeding insect. As the current passes through the insect, the insect&#39;s feeding process modulates the current and creates voltage waveform data. A head stage amplifier with selectable input resistance receives and amplifies the voltage waveform data. The data is transmitted back to the monitoring device where it is manipulated and further amplified by the monitoring device internal amplifier assembly. The waveform data is then transmitted to a controller and ultimately to an output device where the data is displayed.

Description:
FIELD OF THE INVENTION 
     The current invention relates to an improved electrical penetration graph (EPG) monitoring system. 
     BACKGROUND OF THE INVENTION 
     The current invention was designed to record the feeding processes of aphids and other soft-bodied, piercing-sucking agricultural pests. These insects spread numerous, deleterious plant viruses that cause many millions of dollars in damage to crops worldwide every year. 
     Aphids and other piercing-sucking insects acquire plant pathogens from infected plants and inoculate them to healthy plants. After aphids acquire the pathogens, it remains in the insect&#39;s body throughout its life. Researchers (including the inventors) are attempting to combat these plant diseases by better understanding how aphids and other vectors of plant pathogens carry and spread the pathogen via their feeding processes. 
     One means of studying the transmission of the disease is through an understanding of the way the insects feed. Direct current electrical penetration graph (EPG) technology provides information regarding the way that the insect draws its fluid food from plants. The EPG process is initiated by attaching a gold wire to the body of a sharpshooter and placing the sharpshooter in a feeding position on the leaf of a host plant. A plant electrode is then placed in the soil adjacent to the plant or attached directly to a part of the plant. A lead wire from the plant electrode and the gold wire attached to the insect are then connected to a monitoring device. 
     When the stylets (the probing and penetrating mouth parts of the insect) connect with the host plant, an electrical circuit is completed. As the insect&#39;s stylets probe the host plant, the voltage in the circuit fluctuates. The voltage fluctuations are depicted as waveform data on a computer monitor or on a time-based chart in a similar manner to an electrocardiogram (EKG) chart. Researchers have been able to correlate the waveform data (i.e. voltage fluctuations) with certain feeding activities to better understand the biological mechanisms that facilitate the spread of the  Xylella fastidiosa  bacteria. 
     Although the hardware associated with the direct current EPG monitoring process has been around since the 1970s, no meaningful update of the monitoring system design has apparently been attempted since its inception. The currently available monitor has been marketed under the name “Giga 8” or “Giga8”, although a cursory search of the US Patent and Trademark Office, Trademark Electronic Search System indicates that neither name is trademarked in the US. 
     The Giga 8 is a direct current EPG monitor that was originally designed primarily for aphids and other small piercing-sucking insects. Aphids are very tolerant of direct current excitation signals and consequently direct current EPG monitors continue to be used to study aphids. However, even for these direct current tolerant insects, the Giga 8 is no longer sufficiently suited for scientific inquiry. The direct current EPG system of the current invention eliminates several problems with the Giga 8, and also expands its usefulness for other, direct current-tolerant insects, especially larger insects such as large leafhoppers and heteropterans. 
     Among other things, the excitation voltage source of the Giga 8 is unregulated and uncompensated. The excitation control potentiometer has a negative DC voltage applied to one end of a fixed resistance element and a positive voltage applied to the other. Further, the excitation voltage cannot be precisely and reproducibly set. No means is available to determine the actual excitation voltage selected because the instrument is not capable of calibration. The excitation voltage is fed directly out from the control potentiometer wiper, without compensation to stabilize the voltage at any set level and the instrument has no index or dial settings available for reference and adjustment. 
     Although the Giga8 has a head stage amplifier (i.e. “head amp”), the head amp is limited to a single, fixed input resistance setting. This severely limits the sensitivity of the Giga 8, making it only useful for aphids and closely related insects. The main internal amplifier of the Giga 8 has a very low gain. This is not problematic for the small range of insect species that it was designed to monitor, but the Giga 8 design limits the instrument&#39;s ability to study other species of arthropod. 
     Further, as with other aspects of the Giga 8, the gain control has no scale. An operator simply arbitrarily adjusts the gain control until he/she is satisfied with the result. Consequently there is no means of documenting the exact instrument settings associated with the produced waveform data, therefore the results obtained from an evaluation using the Giga 8 are not precisely reproducible and verifiable by other researchers. 
     As indicated above, most of the electronic components of the Giga 8 are obsolete. For example, the Giga 8 operational amplifier is a μA741, which was designed in the 1970&#39;s. It has a very limited ability to change the output voltage to follow the input signal (i.e. slew rate). At even a moderate gain, the output may not closely resemble the shape of the input waveform, especially when the amplitude changes rapidly. Thus, output signals may be inaccurate and artifactual. 
     Because of the limitations described supra, the Giga 8 is only marginally useful. The need exists for a new EPG monitor that includes updated components as well as a wider range of applicability. 
     The current invention provides an EPG monitoring system that includes the ability to produce more detailed, accurate, and higher-resolution waveforms than the prior art system. The EPG monitoring system of the current invention also provides switchable amplifier sensitivities and expands the utility of the direct current EPG process to essentially all direct current-tolerant piercing-sucking arthropods. 
     SUMMARY OF THE INVENTION 
     The current invention is directed to a system for monitoring the feeding behavior of insects. Current is directed from a regulated and buffered voltage source in a monitoring device to an insect electrode that is attached to an insect feeding on a host plant. The current travels through the insect and is picked up by a head stage amplifier system. The head stage amplifier system is comprised of an operational amplifier assembly and a switched resistor assembly. The switched resistor assembly is comprised of multiple selectable resistors yielding multiple selectable levels of input resistance for the head stage amplifier. A resistance selection means such as a switch or rotary dial enables an operator to select one of the selectable resistors and thereby specify an input resistance for the head stage amplifier. 
     The head stage amplifier transmits a waveform voltage signal back to a buffered internal amplifier within the monitoring device. The internal amplifier is essentially comprised of a chain of operational amplifiers that include input and output buffers and allow an operator to adjust the gain and offset of the of the waveform signal. 
     In operation, an operator initiates an evaluation of an insect by connecting the insect to an insect electrode and placing the insect in a feeding position on a host plant. Current is directed from the voltage source in the monitoring device, through the feeding insect to the head stage amplifier. The feeding insect modulates the current so that a waveform voltage signal is received by the head stage amplifier. The head stage amplifier amplifies the waveform voltage signal and transmits the signal back to an internal amplifier in the monitoring device. The monitoring device ultimately transmits the signal to a display device so that the waveform voltage signal can be examined by researchers. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a leaf hopper with an electrode attached. 
         FIG. 2  depicts a leaf hopper connected to the monitoring system of the current invention. 
         FIG. 3  is a block diagram of the voltage source for the monitoring system. 
         FIG. 4  is a circuit diagram of the voltage source shown in  FIG. 3 . 
         FIG. 5  is a block diagram of the head stage amplifier of the monitoring system. 
         FIG. 6  is the circuit diagram of the of the head stage amplifier shown in  FIG. 5 . 
         FIG. 7  is a block diagram of the internal amplifier of the improved monitoring system. 
         FIG. 8  is a circuit diagram of the internal amplifier shown in  FIG. 7 . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The present invention is directed to an improved direct current electrical penetration graph (EPG) system for studying insect feeding behavior. In the preferred embodiment, the current invention is used to study the feeding behavior of aphids and small leafhoppers, although the system may be used to study a wide range of other insects. 
     As generally shown in  FIG. 1 , a leafhopper  25  feeds on a host plant  27  by inserting its mouthparts (i.e. “stylets”)  26  into the leaf of the host plant  27 . An electrode  28  is attached to the head of the insect  25  and a thin gold wire  29  is attached to the electrode  28 . 
     As generally shown in  FIG. 2 , the thin gold wire  29  attaches the insect  25  and the electrode  28  to a head stage amplifier system (i.e. “head amp” system)  50  through an input terminal  31 . A head amp cable  32  attaches the head amp system  50  to a monitoring device  30 . A plant electrode  34  is attached to the host plant  27  or inserted in the soil adjacent to the host plant  27 . A plant electrode cable  36  attaches the host plant electrode  34  to the monitoring device  30 . 
     In the preferred embodiment, a portion of the signal generated by the monitoring device  30  is directed from the monitoring device  30  to a marking device  22  and then to a controller  20 , and a portion of the signal is sent directly to the controller  20 . The controller  20  transmits the signal to one or more output devices  24 . These output devices  24  may include computer display screens, video monitors, printers, and the like. In alternative embodiments, the signal from the EPG monitoring device  30  may be sent directly to a display or to any other device(s) specified by an operator. The marking device  22  is the subject of a patent application previously filed by the current inventors. 
     Although the EPG process is generally known in the prior art, the current invention includes significant improvements to the prior art system. Specifically, the current invention comprises: (a) an improved EPG voltage source assembly  40  (housed in the monitoring device  30 ) so that the voltage applied to the system is consistent, reproducible, reliable, and accurate; (b) an improved head amp system  50  so that the EPG process is sensitive enough to accurately relay subtle changes in the detected waveforms, and so that a greater range of insects can be evaluated, and (c) an improved internal amplifier assembly  80  (housed in the monitoring device  30 ) to allow for further adjustment as well as clear and accurate transmission of the waveform signal. 
     As shown in  FIGS. 3 and 4 , the voltage source assembly  40  of the current invention allows an operator to selectively specify whether a positive or a negative voltage is applied to the system substrate. In the preferred embodiment, the substrate is comprised of the material between the insect electrode  28  and the plant electrode  34 . Because of the relatively small amounts of current, precise control of the system voltage is critical. 
     The voltage source assembly  40  is powered by a 12 volt direct current (DC) power source  38 . Current flows from the power supply  38  to a reference diode assembly  42  that is connected to an internal level adjustment (i.e. potentiometer)  44 , an input buffer amplifier assembly  46 , and an externally adjustable polarity switch assembly  48 . As shown in  FIG. 4 , within the polarity switch assembly  48 , a polarity switch component  43  (designated SW 100  in  FIG. 4 ) allows an operator to select either a positive or negative voltage. 
     As further shown in  FIG. 4 , the voltage source assembly  40  voltage can be further fine-tuned through manipulation of a variable resistor component  45  (designated R 100  in  FIG. 4 ). In the preferred embodiment, a switch associated with the polarity switch component  43  and a dial associated with variable resistor component  45  are disposed on the outside of the monitoring device  30  shown in  FIG. 2  so that the settings are easily adjustable by an operator. 
     As best shown in  FIG. 4 , the variable resistor component  45  is connected to an output buffer amplifier assembly  49  that buffers the output voltage. The output buffer amplifier assembly  49  is connected to an output terminal  47 . As best shown in  FIG. 2 , the output terminal  47  is connected to the plant electrode cable  36  which delivers power from the voltage source assembly  40  to the plant electrode  34 . 
     As shown in  FIG. 4 , in the preferred embodiment, the reference diode component  37  is comprised of an LT1004-type component. The operational amplifiers  39  in the input buffer assemblies  46  are comprised of OPA2134-type components. The amplifier  41  in the output buffer amplifier assembly  49  is also comprised of an OPA2134-type component. In alternative embodiments, these components  37 ,  39 ,  41  may be comprised of any type of device consistent with the function as described herein. As shown in  FIG. 2 , the current invention also includes an updated and improved head amp system  50 . As best shown in  FIG. 2 , the head amp system  50  is positioned near the insect  25  and host plant  27 . The gold wire tether  29  connects the head amp  50  with the insect electrode  28  through an input terminal  31 . 
     As shown in  FIGS. 5 and 6 , the head amp system  50  comprises two primary assemblies: an operational amplifier assembly (i.e. “op amp assembly”)  52  and a switched resistor assembly  54 . The op amp assembly  52  and the switched resistor assembly  54  are coordinated to produce the best quality and most useful output signal. 
     Different insect species have varying levels of inherent electrical resistance/conductivity that are primarily a function of the size of the insect and the diameter of the insect&#39;s mouth parts. For the purposes of this application, “inherent resistance” is the electrical resistance (measured in ohms) evidenced by an insect placed in a simple direct current circuit. 
     The inventors have found that the clearest and most generally useful EPG waveform results are achieved when the head amp&#39;s selectable input resistance is essentially equal to the resistance level of the subject insect. However, the optimal instrument settings associated with a particular insect are generally derived through an iterative trial and error process. As shown in  FIG. 6 , the head amp design allows an operator to vary the input resistance through the switched resistor configuration to achieve the best possible result for the insect studied. 
     As shown in  FIG. 6 , in the preferred embodiment, the switched resistor assembly  54  is comprised of a circuit with five selectable resistance settings. Specifically, in the preferred embodiment, the switched resistor assembly is comprised of a circuit with R 1  through R 6  resistors having corresponding respective resistance values of 1 MΩ, 10 MΩ, 100 MΩ 1000 MΩ, 5000 MΩ, and 5000 MΩ. A resistance selection means such as a switch/rotary dial  68  (designated SW 1  in  FIG. 6 ) allows an operator to selectively switch between the respective head amp  50  resistance settings. 
     As indicated supra, the inventors have empirically determined that the most useful information can be gathered when the resistance value of the selected head amp input resistance setting is essentially equal to the resistance value of the subject insect  25 . For example, if the studied insect  25  imparts a resistance of 1 MΩ, a switched resistance setting with a 1 MΩ resistance value  56  should be selected. 
     The inventors have also learned that the differing signals transmitted in response to the selection of different input resistance levels indicate information about varying aspects of the studied insect  25 . For example, the signal associated with a high input resistance may indicate information regarding charges generated by the insect&#39;s own internal nervous and muscular system, while the selection of relatively low input resistance indicates information regarding the quality of the connection between the insect electrode  28  and the insect  25 . Essentially, the configuration of the switched resistor assembly  54  allows an operator to tailor the settings of the head amp  50  to the particular insect and the specific behaviors being studied. 
     As shown in  FIGS. 5 and 6  and discussed supra, in addition to the switched resistor assembly  54 , the current invention also comprises an op amp assembly  52 . The op amp assembly  52  receives the electrical signal from the insect  25  through an input terminal  31  and relays it through an output terminal  33  to the head amp cable  32  (see also  FIG. 2 ). The purpose of the op amp assembly  52  is to receive, preserve, and amplify the signal from the insect  25 . In the preferred embodiment, the op amp assembly  52  has again of about 20 so that the outgoing signal is amplified 20 times relative to the incoming signal. However, in alternative embodiments, the op amp assembly  52  may be designed so that the gain may be of any magnitude specified by a designer/operator. 
     As shown in  FIG. 6 , the op amp assembly  52  comprises an op amp component  70  designated Z 1  as well as R 8  and R 9  resistors. In the preferred embodiment, the op amp  70  is an OPA134-type component and the R 8  and R 9  resistors have a resistance of 4.99 KΩ and 100 KΩ respectively. In alternative embodiments, the op amp assembly  52  may be comprised of any components or combination of components consistent with the functions described herein. 
     As generally shown in  FIG. 2 , the waveform voltage signal is transmitted from the head amp  50 , through the output terminal  33  to the head amp cable  32  and through an input terminal  51  to an internal amplifier system (i.e. “internal amp” system)  80  located within the monitoring device  30 . 
     As shown in  FIGS. 7 and 8 , the internal amp system  80  is comprised of a chain of adjustable amplifier assemblies  82 ,  90 ,  100 ,  110  that allow an operator to adjust the gain and polarity of the output waveform signal. The amplified waveform signal is the transmitted through an output terminal  120 . 
     As shown in  FIG. 8 , the waveform signal enters through an input terminal  51  and moves through an input buffer amplifier assembly  82  that includes an adjustable gain control  84 . The Z 1  input buffer amplifier component (i.e. “input buffer amp”)  86  buffers the input signal from the head amp  50 . In the preferred embodiment, the input buffer amp component  86  is comprised of an OPA2134-type component. The signal then proceeds to an adjustable resistor  84  (designated as R 100  in  FIG. 8 ) that functions as an adjustable gain control. In the preferred embodiment, the adjustable resistor  84  comprises an adjustable 20Ω resistor connected with a knob-type adjustment mechanism on the face of the monitoring device  30  that allows an operator to fine tune the internal amp assembly&#39;s  80  gain. 
     As shown in  FIGS. 7 and 8 , first  90  and second  100  switched gain control assemblies are connected to the input buffer amp assembly with adjustable gain control  84 . The first gain control assembly  90  comprises an amplifier component  92  and a switched gain adjustment control component  94  designated SW 100  as well as a series of resistors designated R 1  through R 4 . 
     In the preferred embodiment, the switched gain control component  94  allows an operator to select a gain factor of 10, 25, or 50. In alternative embodiments the circuit may be arranged so that other gain settings are possible. Similarly, as shown in  FIG. 8 , the amplifier component  92  of the preferred embodiment is an OPA2134 amplifier and the resistance values of the R 1  through R 4  resistors are 49.9 KΩ, 1 KΩ, 1 KΩ, and 3.01 KΩ respectively. In alternative embodiments the amplifier component and the resistance values of the respective resistors may be altered to achieve a specific desired result. 
     As shown in  FIGS. 7 and 8 , the second gain control assembly  100  comprises an amplifier component  102  designated Z 1 B and a switched gain adjustment control component  104  designated SW 101  as well as a series of resistors designated R 5  through R 7 . 
     In the preferred embodiment, the switched gain control component  104  allows an operator to further increase the gain by a factor of 10 so that the total maximum amount of gain from the insect signal is a factor of 10,000. In alternative embodiments the circuit may be arranged so that other gain settings are possible. Similarly, as shown in  FIG. 8 , the amplifier component  102  of the preferred embodiment is an OPA2134 amplifier, and the resistance values of the R 5  through R 7  resistors are 20 KΩ, 20 kΩ, and 200 KΩ respectively. In alternative embodiments the amplifier component  102  and the resistance values of the respective resistors may be altered to achieve a specific desired result. 
     As further shown in  FIGS. 7 and 8 , an output buffer amplifier and signal offset control assembly  110  is connected to the first  90  and second  100  gain control assemblies. The output buffer amplifier (i.e. “output buffer amp”) portion of the assembly  110  comprises an amplifier component  112  designated Z 2  and associated resistors R 8  and R 9 . The output buffer amp portion of the assembly  110  ensures that the internal amp assembly  80  is unaffected by changes on the output side of the internal amp assembly  80  that are exterior to the amp assembly  80 . 
     In the preferred embodiment, the output buffer amp component  112  is comprised of an OPA134 amplifier and the R 8  and R 9  resistors both have resistance values of 20 kΩ. In alternative embodiments, the output buffer amp portion of the assembly  110  may be comprised of any alternative components or combination of components consistent with the functions as described herein. 
     The offset control portion of the assembly comprises a variable resistance resistor  114  (designated R 101 ) and a voltage offset switch  115  (designated SW 101 ) selectively connected to either a positive twelve volt power supply  116  and associated resistor R 102 , or a negative twelve volt power supply  118  and an associated resistor R 103 . 
     A switch associated with the voltage offset switch  115  is disposed on the front of the monitoring device  30  to allow an operator do adjust the offset in a positive or negative direction. A fine tune knob associated with the variable resistance resistor  114  is also disposed on the front of the monitoring device  30  (see  FIG. 2 ) to allow an operator to allow an operator to further fine tune the offset. In operation, an operator may use the voltage offset switch  115  and the variable resistor  114  to ensure that the monitoring system waveform data is properly normalized to zero volts output prior to the initiation of an insect evaluation. 
     In the preferred embodiment the variable resistance resistor  114  is comprised of a 10 KΩ resistor and the R 102  and R 103  resistors are both comprised of 10 KΩ resistors. In alternative embodiments, the resistance values of the respective resistors may be varied as required consistent with the function of the current invention. 
     As shown in  FIGS. 2 ,  7 , and  8 , the output buffer amplifier and signal offset control assembly  110  is connected to an output terminal  120 . As shown in  FIG. 2  and discussed supra, in the preferred embodiment, a portion of the output waveform signal is sent to a marking device  22  and then to a controller  20 , and a portion of the signal is sent directly to the controller  20 . In alternative embodiments, the output waveform signal may be sent directly to an output device(s)  24  or processed, recorded, and/or displayed as required. 
     For the foregoing reasons, it is clear that the current invention provides an improved EPG signal generating and processing device. The current invention may be modified and customized as required by a specific operation or application, and the individual components may be modified and defined, as required, to achieve the desired result. For example, although the invention was originally intended to monitor a feeding insect, the invention may be modified to monitor other organisms or phenomena. 
     Although the materials of construction are not described, they may include a variety of compositions consistent with the function of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.