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Colonization of potato fields by postdiapause Colorado potato beetles, Leptinotarsa decemlineata (Say)
East, David Andrew, Ph.D.
The Ohio State University, 1993
UMI 300 N. Zeeb Rd. Ann Arbor, MI 48106
COLONIZATION OF POTATO FIELDS
BY POSTDIAPAUSE COLORADO POTATO BEETLES,
LEPTINOTARSA DECEMLINEATA (SAY)
DISSERTATION
Presented in Partial Fulfillment of the Requirement for
the Degree Doctor of Philosophy in the
Graduate School of The Ohio State University
by
David Andrew East, B.S., M.S.
*****
The Ohio State University
1993
Dissertation Examination Committee: Approved by
C.W. Hoy
P. L. Phelan
J. Cardina
D. J. Horn 'Adviser/ Department of Entomology Copyright by David Andrew East 1993 To my wife Janet and my Parents
ii ACKNOWLEDGMENTS
I would like to thank my advisor Dr. Casey Hoy for his guidance, help and financial support throughout my research.
I thank my committee members Dr. David Horn, Dr. Larry
Phelan, and Dr. John Cardina for their support and assistance. I appreciate the training and use of the Spectronics 20 spectrophototmeter provided by H. W. Ockerman.
I would like to acknowledge the financial support awarded to me by Sigma Xi, the scientific society, for the
CPB orientation to plant models experiment.
Special thanks to Secretaries Maxine and Mabel, whose support, friendship and assistance made working at OARDC a pleasure. And to the noon Volleyball gang, whose butts I enjoyed kicking my first summer at OARDC.
To my Mom and Dad, who I can never thank enough for their endless love, support, encouragement and car tires.
And for my one and only snookie, my wife Jan, whose love means more to me than anything. Thanks for always being there, and for all your help on this dissertation.
iii VITA
June 19, 1959 ...... Born - Ashland, Oregon
1982 ...... B.S., Oregon State University, Corvallis, Oregon
1983-1985 ...... U.S. Peace Corps/Jamaica
1988 ...... M.S., Texas A&M University, College Station, Texas
1989-Present ...... Graduate Research Assistant, Department of Entomology, Ohio State University, Columbus, OH
PUBLICATIONS
East, D.A., J.V. Edelson, E.L. Cox and M.K. Harris. 1992. Evaluation of screening methods and search for resistance in muskmelon, Cucumis melo L. to the twospotted spider mite, Tetranvchus urticae Koch. Crop Protection. 11: 39-44.
Scully, B., D.A. East, J.V. Edelson and E.L. Cox. 1991. Resistance to the twospotted spider mite in muskmelon. Proc. Fla. State Hort. Soc. 104: 276-278.
East, D.A., J.V. Edelson and B. Cartwright. 1989. Relative cabbage consumption by the cabbage looper (Lepidoptera: Noctuidae), beet armyworm (Lepidoptera: Noctuidae) and diamondback moth (Lepidoptera: Plutellidae). J. econ. Entomol. 82: 1367-1369.
FIELDS OF STUDY
Major Field: Entomology Studies in Integrated Pest Management of Insect Pests of Vegetables TABLE OF CONTENTS
ACKNOWLEDGMENTS ...... iii
VITA ...... iv
LIST OF TABLES ...... vi
LIST OF FIGURES ...... ix
INTRODUCTION ...... 1
CHAPTER PAGE
I. Literature Review ...... 3
II. Flight Initiation in the Colorado Potato Beetle
Materials and Methods ...... 17 Results and Discussion ...... 27
III. Potato Field Colonization
Materials and Methods ...... 37 Results and Discussion ...... 45
IV. The Orientation of Postdiapause Adult Colorado Potato Beetles to Potato Plants
Materials and Methods ...... 75 Results and Discussion ...... 84
V. Summary and Conclusions ...... 114
REFERENCES CITED ...... 117
APPENDIX ...... 123
V LIST OF TABLES
TABLE PAGE
1. Effect of artificial light source on CPB flight initiation ...... 27
2. Flight activity of "weak" flying CPB fed three diets ...... 28
3. Flight activity of non-flying CPB fed three diets ...... 28
4. Flight activity of three classes of CPB starved for 48 hours ...... 29
5. Flight activity of three classes of CPB starved for 96 hours ...... 30
6. Percent of flight of CPB due to mating status and sex ...... 32
7. Percent of flight of CPB due to ovipositional status and sex ...... 32
8. Greenhouse flight test on May 11, 1992 ...... 35
9. Greenhouse flight test on May 15, 1992 ...... 35
10. Greenhouse flight test on May 20, 1992 ...... 36
11. Greenhouse flight test on May 28, 1992 ...... 36
12. Greenhouse flight test on June 1, 1992 ...... 36
13. Greenhouse flight test on June 8, 1992 ...... 37
14. ANOVA results for pattern of infestation study of commercial potato fields in 1990 ...... 50
15. ANOVA results for pattern of infestation study of commercial potato fields in 1991 ...... 51
16. Mean numbers (±SEM) of adults and egg masses in unenclosed and flashing-enclosed areas ...... 54
vi 17. Denn 1992. Semi-variograms ...... 67
18. Colonization experiment 1-1991 ...... 85
19. Colonization experiment 11-1991 ...... 87
20. Experiment II, 1991. Orthagonal contrasts for both sample dates pooled ...... 88
21. Colonization experiment III-1991 ...... 89
22. Daily mean catches (±SE) of adult CPB for inside traps (flying beetles) for artificial plant orientation experiment, 1992 ...... 112
23. Daily mean catches (±SE) of adult CPB for outside traps (walking beetles) for artificial plant orientation experiment, 1992 ...... 113
24. CPB densities for sections of commercial field Rho, 1990 ...... 124
25. CPB densities for sections of commercial field Rho II, 1990 ...... 125
26. CPB densities for sections of commercial field Rho III, 1990 ...... 125
27. CPB densities for commercial field Don III, 1990 ...... 126
28. CPB densities for sections of commercial field Mooext, 1990 ...... 126
29. CPB densities for sections of commercial field Moo, 1990 ...... 127
30. CPB densities for commercial field Don, 1990 ...... 127
31. CPB densities for OARDC field Fry 1, 1990 ..... 128
32. CPB densities for OARDC field Fry 3, 1990 ..... 129
33. CPB densities for commercial field Don 3, 1991 ...... 129
34. CPB densities for commercial field Don 1, 1991 ...... 130
vii 35. CPB densities for commercial field Don 2, 1991 ...... 130
36. CPB densities for commercial field Rho 1, 1 9 9 1 ..... 131
37. CPB densities for commercial field Rho 3, 1991 ...... 131
38. CPB densities for commercial field Rho 2, 1990 ...... 132
39. CPB densities for OARDC field Synder, 1991 ..... 133
40. CPB densities for commercial field Denn 4, 1991 ...... 133
41. CPB densities for commercial field Denn 5, 1991 ...... 134
42. CPB densities for commercial field Rho 4, 1991 ...... 134
43. CPB densities for commercial field Rho 5, 1991 ...... 134
44. CPB densities for commercial field Denn 2, 1991 ...... 135
viii LIST OF FIGURES
FIGURE PAGE
1. Experimental design for experiment on colonization of a field by flying C P B ...... 40
2. Pattern of Infestation: Commercial field Rho over four sampling dates in 1990 ...... 42
3. North/south semi-variogram of CPB in Rho field on May 23, 1990 ...... 58
4. East/west semi-variogram of CPB in Rho field on May 23, 1990 ...... 60 5. Omnidirectional semi-variogram of CPB in Rho field on May 23, 1990 ...... 62
6. Plot of raw data from commercial field Rho on May 23, 1990 ...... 64
7. Mean numbers of CPB caught during season in plant colonization experiment, 1992 ...... 90
8. Total infestation by CPB during season in plant colonization experiment, 1992 ...... 93
9. Daily totals of plants infested during plant colonization experiment, 1992 ...... 95
10. Total daily CPB caught in bucket traps for artificial plant experiment ...... 99
11. Combined CPB catch for treatments during season for artificial plant experiment ...... 102
12. Flying CPB catch for treatments during season for artificial plant experiment ...... 104
13. Percent reflectance of model surface for artificial plant experiment ...... 107
14. North/south semi-variogram of adults in Denn field on June 3, 1992 ...... 136
ix 15. East/west semi-variogram of adults in Denn field on June 3, 1992 ...... 138
16. Omnidirectional semi-variogram of adults in Denn field on June 3, 1992 ...... 140
17. North/south semi-variogram of adults in Denn field on June 9, 1992 ...... 142
18. East/west semi-variogram of adults in Denn field on June 9, 1992 ...... 144
19. Omnidirectional semi-variogram of adults in Denn field on June 9, 1992 ...... 146
20. North/south semi-variogram of egg masses in Denn field on June 9, 1992 ...... 148
21. East/west semi-variogram of egg masses in Denn field on June 9, 1992 ...... 150
22. Omnidirectional semi-variogram of egg masses in Denn field on June 9, 1992 ...... 152
23. North/south semi-variogram of adults in Denn field on June 19, 1992 ...... 154
24. East/west semi-variogram of adults in Denn field on June 19, 1992 ...... 156
25. Omnidirectional semi-variogram of adults in Denn field on June 19, 1992 ...... 158
26. North/south semi-variogram of egg masses in Denn field on June 19, 1992 ...... 160
27. East/west semi-variogram of egg masses in Denn field on June 19, 1992 ...... 162
28. Omnidirectional semi-variogram of egg masses in Denn field on June 19, 1992 ...... 164
29. Contour map using kriged estimates of adult populations in Denn 1992 field on June 3 ..... 166
30. Contour of standard deviations of kriged estimates of adult populations in Denn 1992 field on June 3 ...... 168
31. Contour map using kriged estimates of adult populations in Denn 1992 field on June 9 ..... 170
x 32. Contour of standard deviations of kriged estimates of adult populations in Denn 1992 field on June 9 ...... 172
33. Contour map using kriged estimates of egg mass populations in Denn 1992 field on June 9 ...... 174
34. Contour map of standard deviations of kriged estimates of egg mass populations in Denn 1992 field on June 9 ...... 176
35. Contour map using kriged estimates of adult populations in Denn 1992 field on June 19 .... 178
36. Contour of standard deviations of kriged estimates of adult populations in Denn 1992 field on June 19 ...... 180
37. Contour map using kriged estimates of egg mass populations in Denn 1992 field on June 19 ...... 182
38. Contour map of standard deviations of kriged estimates of egg mass populations in Denn 1992 field on June 19 ...... 184
xi INTRODUCTION
The Colorado potato beetle (CPB), Leptinotarsa decemlineata (Say) is a major pest of potatoes, Solanum tuberosum L., in Ohio and in many other potato growing areas in the United States and Europe. Tuber yield in potatoes is susceptible to defoliation by adult and larval CPB up to 60 days from planting (Zehnder and Evanylo 1989), or through the bloom stage (Shields and Wyman 1984). In Ohio, the potato crop bloom period, late June or early July, typically coincides with the first generation of CPB, the offspring of postdiapause adults. CPB management techniques that significantly reduce or delay the initial colonization of a field by postdiapause beetles will reduce population levels of subsequent damaging generations, and potato plants will be in a stage that can better tolerate defoliation.
CPB have demonstrated the capacity to develop resistance to a wide variety of pesticides (Gauthier et al.
1981, Forgash 1985, Casagrande 1987). Applications of broad spectrum pesticides can also be counterproductive by destroying natural enemies of the CPB and other pests.
Chemical management of the CPB is not sustainable for these reasons, and less- ecologically disruptive, more sustainable management techniques must be developed. Developing or improving alternative methods of managing
CPB that rely less on pesticides, such as crop rotation, altered planting date, feeding deterrents, physical colonization barriers, trap crops, edge control, and host plant resistance, require a more detailed knowledge of CPB host orientation, searching behavior, and patterns of field colonization than we currently possess.
In this dissertation, I present the results of research on the factors affecting CPB dispersal, patterns of colonization and dispersal in potato fields by postdiapause
CPB, and the orientation of flying and walking postdiapause
CPB to host plants. I also present research on the application of geostatistical methods as an aid to understanding colonization of potato fields by CPB and the management of CPB. CHAPTER I
Review of Literature
Description and Life History
The adult Colorado potato beetle (CPB), Leptinotarsa decemlineata (Say) is about 1 cm long, oval and convex dorsally. The elytra are yellowish white with ten black stripes running lengthwise, and the pronotum is orange-brown with black dots and markings. The ventral side of the CPB is orange-brown. The adult CPB overwinters in the soil at a depth of 5-
25 cm (Metcalf et al. 1951). CPB adults emerge from the soil in the spring as temperatures begin to warm (Lashomb et al. 1984). After emerging from the soil, CPB may move short or long distances by flight or walking to locate host plants
(Harcourt 1963, Johnson 1969, Voss and Ferro 1990a).
Postdiapause CPB mate, feed, and lay eggs on potato seedlings, potato shoots from volunteer plants, other hosts
(Popenoe 1909, Metcalf et al. 1951, Norman et al. 1981), or feed on potato seed pieces exposed to the air (Popenoe
1909). Adult female CPB deposit groups of 10-40 bright orange, oval eggs on the undersides of leaves (Metcalf et al. 1951, Norman et al. 1981). Each female is capable of
3 4 laying a total of 300 to 500 eggs (Metcalf et al. 1951,
Norman et al. 1981). For CPB fed on potato foliage, however, Brown et al. (1980) reported a mean total of 3348 eggs/female.
Eggs hatch in approximately one week, and foliage- feeding CPB larvae pass through four instars in 2-3 weeks, depending upon temperature (Metcalf et al. 1951, Norman et al. 1981). CPB larvae are capable of dispersing relatively long distances to new host plants if crowding occurs or food becomes scarce (Cass 1957, De Wilde 1958, Harcourt 1963).
The larva has a large reddish, crescent-shaped abdomen with two rows of black spots on each side of the body. Mature larvae drop from the foliage to the ground, burrow into the soil and pupate. The pupal stage lasts 5-10 days depending on the temperature, and the new adult emerges from the soil to mate, feed and oviposit on the host plant (Norman et al.
1981). There are one to three generations of CPB per year, depending on latitude (Davidson and Lyon 1987).
Adult CPB sometimes disperse or migrate in the summer and this movement is not related to diapause or overcrowding
(Jermy 1988, Voss & Ferro 1990b). Males search for females by flight during the spring and summer (Jermy et al. 1988,
Voss and Ferro 1990a). In the fall, CPB move to overwintering areas and burrow into the soil. CPB in
Massachusetts are believed to overwinter in the potato field in which they fed, edges of the field or along the edges of nearby woods (Voss & Ferro 1990b).
The CPB feeds and reproduces on potato, Solanum tuberosum L.; tomato, Lvcopersicon esculentum Mill.; eggplant, Solanum melonaena L.; tobacco, Nicotiana tabacum
L.; and pepper, Capsicum annuum L. Weed hosts include bitter nightshade, Solanum dulcumara L.; horsenettle,
Solanum carolinense L.; and buffalobur, Solanum rostratum
Dunal. A more comprehensive review of the acceptance by and suitability for CPB of 104 plant species belonging to 87 genera and 39 families is provided in Hsiao and Fraenkel
(1968) .
Economic History of the Colorado Potato Beetle
The CPB is believed to have originated in Mexico on a buffalobur (Johnson 1969). From 1845 to 1900, the CPB expanded its range on cultivated potatoes throughout the eastern United States (Johnson 1969). The CPB was first noted as a pest of potato in 1859 in an area 100 miles west of the Missouri river in Nebraska (Davidson and Lyon 1987).
The CPB first gained a foothold in Europe in France in 1922 and spread through most of Europe by 1964 (Johnson 1969).
Migration and Dispersal in Colorado Potato Beetle
Insect dispersal can be divided into two general categories, appetitive movement and migratory movement. 6
Appetitive movement is that movement which is local and includes orientation activities such as food finding, mate finding, escape from enemies, location of oviposition sites, and territorial defense (Mathews and Mathews 1978).
Migratory movement involves the displacement of populations from one habitat to another (Kennedy 1975). Migration always involves females, and is characterized by persistent, enhanced locomotion in a directed manner, and migrating individuals do not typically respond to stimuli for behaviors such as feeding or oviposition (Kennedy 1975).
Usually, a migrating insect must travel a certain distance or be active for a certain period of time before becoming responsive to host related-stimuli (Mathews and Mathews
1978). Migration of females is usually prereproductive or interrepproductive (Johnson 1969). CPB may migrate to new host habitat by moving in a specific direction. This behavior ensures that CPB leaves an area where no patches of potatoes exist. This theory has been proposed with the mechanism being photomenotaxis (light compass orientation,
Jermy et al. 1988). Photomenotaxis is the orientation and movement of an insect at a fixed angle to a light source
(e.g. the sun, Kennedy 1977). Ng and Lashomb (1983) showed that the CPB in unfamiliar habitats walk to the Northwest, but that the sun and wind did not play a major role in the orientation of the CPB. According to Jermy et al. (1988), early emerging CPB adults are neither arrested nor attracted by the host plant, but simply disperse, and some postdiapause beetles will not even feed when placed on plants. However, Voss et al.
(1988) suggest that the first activity of CPB adults emerging from the soil after diapause in Massachusetts is to search for host plants on which to feed and oviposit. Fall and spring migration behavior in the CPB is still poorly understood.
Behavior and physiology of the CPB is highly variable and strongly influenced by regional environmental conditions
(De Wilde and Hsiao 1981, Johnson 1969). Ambient temperature has a strong influence on CPB movement. CPB flight in Michigan occurs in spring at temperatures as low as 15°C., but most unfed CPB fly at 20°C (Caprio and
Grafius, 1990). However, in Virginia, Zehnder and Speese
(1987) caught no flying CPB below 22°C and caught most flying CPB above 25°C. Johnson (1969) reported that CPB could fly at temperatures as low as 17°C, but the maximum frequency of flight was seen at 25°C. Even at 25°C, CPB required 6 hours of insolation before flight (Johnson 1969).
In New Jersey, Lashomb and Ng (1984) reported that CPB began walking at temperatures above 15°C. CPB locomotion is reduced under an overcast sky (Jermy et al. 1988).
Wind dispersed CPB and other insects are often reported to be deposited along landscape contours, such as forests, gullies, field edges (Johnson 1969), hills, ridges, buildings, and hedges (Lewis 1969). In open country, small hills can slow wind speed on the leeward side by 20% (Lewis
1969). Most insects accumulate in these calmer zones (Lewis and Stephenson 1966).
Host Location by Colorado Potato Beetle
The major behavioral stages in successful food location by insects have been listed as: (1) food habitat location,
(2) food finding, (3) food recognition, (4) food acceptance and (5) food suitability, (Mathews and Mathews, 1978;
Prokopy 1983). The process of host plant location has also been described as occurring in four main steps: orientation, arrestment, initiation of feeding, and maintenance of feeding (Jolivet et al. 1988). The chemicals which act in each step are called attractants, arrestants, incitants, and feeding stimulants, respectively (Jolivet et al. 1988). The chemicals eliciting negative responses in each step are termed repellents, locomotor stimulants, suppressants and feeding deterrents, respectively (Jolivet et al. 1988).
The successful colonization of host plants by insects depends on many more factors than direct orientation to or acceptance of the host plant. The spatial and temporal arrangement, and nature of the population, guild, community, ecosystem and landscape surrounding a host plant affect the searching insect. These components of an ecosystem: 1) provide a wide variety of potential visual or olfactory cues; 2) alter, obscure or dilute visual or olfactory cues;
3) provide physical barriers that alter or impede insect movement; and/or 4) make the searching insect more or less vulnerable to predation or other hazards.
Hicks and Tahvanainen (1974) showed that flea beetle feeding preference was affected by whether the plant was growing in a cool shady environment (moist woodlands) or in open, sunny fields. Risch (1981) demonstrated that polycultures of annual plants (bean-squash-corn) containing at least one non-host plant had lower population densities of specialist beetles per unit host plantthan did monocultures. Risch showed that beetles moved more in the polyculture and shading caused beetles to leave host plants.
At the population level, patch size, shape and density can be very important in host location by insects. Patch size can increase the probability of location by randomly searching insects. The probability of an insect immigrating to a host plant area is directly related to the peripheral distance around that patch or to the patch area (Stanton
1983). The concentration of host plant odors downwind is affected by plant density, and patch (field) size (Stanton
1983) ; a bigger field could have a wider odor plume and a more dense field could have a more concentrated odor plume.
Patch shape relative to wind direction could also affect the 10 size and concentration of host volatiles down wind (Stanton
1983) . A large patch of plants may be more visually obvious to insects than a small patch.
Landscape patterns may have a strong influence on host orientation or dispersal by phytophagous insects. Pieris rapae may orient toward treeless areas to find host plants that typically grow in that habitat (Cromartie 1975).
Host plant color, odor, height and shape are used by insects to locate host plants (Stanton 1983). Leaf shape has been shown to be important in host searching patterns of
Battus philenor (Rausher and Papaj 1983). Rhaqoletis flies are attracted to large vertical targets, (Moericke et al.
1975). Herbivorous insects tend to be attracted to yellow- green wavelengths of light (Stanton 1983).
Non-host vegetation in or around potato fields has an important effect on CPB host seeking activity. Mulching potato fields with straw has been shown to reduce CPB populations. The straw acts as a physical barrier to the movement of the CPB (Zehnder and Hough-Goldstein 1989).
Lashomb and Ng (1984) demonstrated that wheat plants are a physical barrier to CPB movement and also lower the temperature around the beetle, thus limiting CPB activity by altering the micro-climate. The increasing density of non host (grass turf) vegetation in or around fields slows CPB movement significantly (Ng and Lashomb 1983), and weeds are 11 believed to reduce colonization in tomato fields by acting as a barrier (Zehnder and Linduska 1987).
Some researchers believe that the CPB has a limited ability to orient to host plants. Bach (1982) suggested a random colonization of potato plants by postdiapause CPB.
Jermy et al. (1988) concluded that host location by CPB is a chance event. Young adults searching for hosts have been observed visiting or probing every small weed they happen to encounter (Jermy et al. 1988). Cain (1985) determined that the CPB has a low radius of host detection. The CPB is not considered to be well endowed with visual or olfactory senses (Jolivet, 1988). Concentrated stands of potato plants (fields) make a random search strategy more effective
(Jolivet 1988). Replacement of forest by large potato monocultures in Maine has been given as a reason for the rise of the CPB as a pest (Tothill 1958).
Laboratory research has shown that adult CPB orient to a specific blend of odors of the potato plant known as green leaf volatiles. However, altering this blend in any way, either artificially or by introducing odors from other plants, drastically reduces the orientation of the CPB to the odor source (Thiery and Visser 1987, Visser and Ave
1978). For this reason, it is unlikely that olfactory cues operate over a long distance, which has been vaugely defined in the literature as greater than 1 meter for insects
(Kennedy 1977, Prokopy 1983). Jermy (1988) showed that non overwintered adults could not discriminate between cabbage and potato at more than 40 cm, which actually demonstrates an ability of CPB to orient to potato at less than 40 cm.
Little research has been conducted on olfactory orientation to other host plants, including the CPB's original host buffalobur, so general statements about the host locating abilities of the CPB are premature. Additionally, little research has been conducted on the orientation of CPB to potato tubers. CPB may be locating potato plants by the odors of potato seed pieces or potato seedlings.
Evidence for visual orientation is also in the literature. Zehnder and Speese (1987) showed that flying
CPB adults are attracted to yellow traps with peak wavelength reflectance between 550 and 580 nm. CPB may avoid red (680 nm) and black traps with low uniform reflectance (Zehnder and Speese 1987). CPB has been shown to move more frequently toward potato plants greater than 8-
15 cm in height than shorter plants (Boiteau 1986).
However, it is unclear whether this response was due to more odor from the larger plants or the increased stimulus size.
The feeding status of host seeking CPB has important effects on behavior. Starved CPB orient directly to host plant odors, while fed adults do not respond to host odor
(Visser 1988), and Jermy et al. (1988) observed that young adults forage for food if deprived of it. Starved postdiapause CPB have a greater tendency to fly, and tend to 13 fly farther (Caprio and Grafius, 1990). Postdiapause CPB that have not yet fed contain enough glycogen reserves to permit flights over a nine day period (Johnson 1969).
Postdiapause adult CPB have a considerable capacity for starvation, but must eat before oogenesis (De Wilde et al.
1969). Hsiao (1969) claims that a food plant is first selected by a female during the process of oviposition, and oviposition is the first step in host selection.
All CPB life stages have been shown to have a clumped distribution in the field (Harcourt 1963). Therefore, CPB might emit an aggregation pheromone after a host plant has been successfully located, and other CPB could cue in on this pheromone and locate those plants, in a manner similar to that for citrus root weevils which aggregate on citrus trees by detecting pheromones in the frass (Jones and
Schroeder 1984) .
Pattern of Infestation and Geostatistical Analysis
A CPB pattern of infestation study of potato fields has shown that the highest populations of the CPB are located nearest the previous year's potato fields irrespective of the direction of wind or position of the field (Wilusz
1958). More research on the pattern of infestation of potato fields by postdiapause CPB should be conducted, so that the patterns of arrival, and post colonization movement 14 over time can be better understood for CPB over a wide variety of conditions.
Geostatistics were first theorized by Georges Matheron in the 1960's and had their first application in geology and mining problems (Clark 1979). Geostatistics can be used wherever a continuous measure is made on a sample at a particular location in space or time (Clark 1979).
Geostatistical methods include a means of interpolation called kriging which utilizes the degree of autocorrelation
(from a semi-variogram) between adjacent samples to estimate values for any coordinate position in a domain (Vieira et al. 1982). A more detailed explanation of geostatistical methods will be provided in Chapter III Materials and
Methods.
Geostatistics have been applied to entomological problems. Kemp et al. (1989) estimated rangeland grasshopper counts with kriging, and produced hazard maps of grasshopper infestation. Schotzko and O'Keeffe (1990) studied the effect of sample placement on geostatistical analysis. Williams et al. (1992) compared geostatistical to conventional measures of dispersion.
Thesis
The little research that has been done on flight in CPB has focused on defining temperature thresholds for flight initiation. Little is known about the flight capability within a population of CPB. In this dissertation, I
demonstrate that, in Ohio, behavioral polymorphism in
postdiapause CPB with regard to flight is unlikely, and many
postdiapause CPB are capable of flying. Flight capability
after diapause is not influenced by flight capability or migratory status in the fall. In agreement with the
literature, I show that previously fed, non-diapause CPB are more likely to fly if starved. However, my experiments
demonstrate that non-diapause, mated CPB are more likely to
fly than unmated CPB. I have found that postdiapause or
non-diapause CPB are capable of flying prior to oviposition.
Previous investigators have observed edge effects,
concentrations of CPB on the edges of potato fields, during the spring. The set of circumstances that result in edge effects and the duration of edge effects have not been well documented. My pattern of infestation studies show that
field planting date and rotation distance are important
factors associated with edge effects in potato fields, and
edge effects can persist for weeks. I will present evidence that distantly-rotated and late-planted fields can be colonized primarily by flying CPB. Contrary to previous reports, I have found that postdiapause CPB disperse to new potato plants after initially colonizing a potato plant.
The application of geostatistical methods to the study of potato field colonization by CPB will be demonstrated, and 16 the direct use of geostatistics in the management of CPB will be discussed.
Little research has been conducted on the orientation of flying CPB to host plants. The literature contains ample labororatory data on the orientation of walking CPB to host odor, but is still inconclusive on the ability of CPB to orient to host odor under natural conditions. Little research on the orientation of walking CPB to visual cues has been reported. My research shows that flying CPB use visual cues to orient to host plants or host plant habitat.
Wavelength and the total surface area of stimuli are important visual cues for CPB, while fine details of plant structure, such as leaf shape are not important. Olfactory and tactile cues are not important in the orientation of flying CPB to potato plants. CHAPTER II
Flight Initiation in the Colorado Potato Beetle
Materials and Methods
Section A - Preliminary Laboratory Flight Tests
Flight Room All preliminary flight tests were conducted in a 3.7 m x 11.6 m room with three 40 cm x 73 cm translucent windows
on one side. Flight platforms were constructed from wood and were 10 cm high with a 10 cm by 10 cm platform. The
standard light source used in all tests, unless specified, was a General Electric 250 Watt clear infrared lamp. This
lighting source was located 80 cm directly above the flight platforms. Temperature at platform height directly under the lamp was 32°C and was 25°C in the rest of room.
Test Group 1
Recently emerged first-generation beetles were
collected in research potato fields at the OARDC in Wooster,
Ohio on June 28, 1991. In preliminary flight tests on July
3, 1991, beetles were rated as either "strong", "weak" or
"non-fliers" under the artificial lighting conditions
described above. Non-fliers did not leave the platform by
17 flight, weak fliers did not fly above an arbitrary level of
7.5 cm vertically above the top of the platform on the first flight attempt, and strong fliers flew higher than 7.5 cm on the first attempt.
Test Group 2
Ninety-five first-generation beetles were collected in research potato fields at the OARDC in Wooster, Ohio on July
5, 1991. In preliminary flight tests on July 9, 1991, beetles were rated as either strong, weak, or non-fliers as described for group 1.
Test 1-3
The test was started at 9:20 a.m. and ended at 11:20 a.m. on July 6, 1991 and was designed to test the effect of the light source on weak and strong fliers. The four strong fliers and 5 weak fliers from test 1 & 2 (group 1) were kept separated and each was placed on a flight platform. The platforms were 7.5 cm apart and the midpoint between the two platforms was located directly underneath the standard light source. All beetles were starved for 72 hours prior to the test. The light was turned off and on for consecutive 30 minute periods. All flights from the stand by use of wings were recorded as flights. All beetles were returned immediately to their originating platform after each flight.
18 19
Test 2-1
On July 9, 1991 from 3:39 p.m. to 4:09 p.m., 33 weak fliers from group 2 were randomly divided into three groups.
One group was fed bitter nightshade, Solanum dulcamara L., foliage for 24 hours prior to testing, another group was fed potato foliage for 24 hours prior to testing and the third group was an unfed control. Each treatment grou£ was confined to a separate flight platform. Flights were scored as in test 1-3, and beetles were returned to the platform immediately after flight.
Test 2-2
This test was conducted from 4:31 p.m. to 5:01 p.m. and was a repeat of test 2-1, except with 48 non-flying beetles from group 2 (16 per treatment).
Test 2-3
This test was conducted from 5:50 p.m. to 6:20 p.m. on
July 9, 1991 to compare the ratio of flight activity among three groups of beetles. Beetles from group 2 were re classified into three groups based on their first flight attempt under the lighting conditions described at the beginning of this text. These three groups were 1) strong fliers, beetles that flew above the platform on the first flight attempt, 2) weak fliers, beetles that flew but did not rise above the top of the platform on the first flight 20 attempt and 3) non-fliers, beetles that did not fly at all.
Nine beetles were randomly selected from each group and confined to a platform and the standard light was turned on for 30 minutes. All beetles were starved for 48 hours prior to the test. Flights were rated as in test 1-3, and beetles were returned to the platform immediately after flight.
Test 2-4
This test was conducted from 11:13 a.m. to 12:27 p.m. on July 11, and was a repeat of test 2-3, except that beetles were starved an additional 48 hours prior to the test and the test consisted of two trials.
Test 3
The test was conducted on Sept. 1, 1991 from 4 p.m. to
4:30 p.m. Twenty-one beetles that were collected on Aug.
30, 1991 flying in the field were placed on a flight platform and flown under the conditions described in previous tests. Any beetle that flew higher than 7.5 cm above the platform was removed and recorded as a strong flier. This test was a check of flight of known field fliers under the conditions described at the beginning of this chapter. 21
Section B - Flight Initiation Factors and Progeny Test.
Flight Room
The flight room is the same as described previously,
except that flights were conducted on 4 platforms placed
directly under the light source and arranged in a square
pattern.
Beetle Colony
CPB eggs were placed on potato foliage of potted plants
on July 28, 1991 and held within screen cages in a greenhouse. If plants became defoliated, all stems were removed at soil level, the pots removed and fresh potted potato plants supplied. The soil in the pots that were removed was sifted for pupae 4 to 5 days after most larvae had burrowed into the soil. All pupae found were removed and transferred to petri dishes (9 cm x 1.5 cm) covered with thick paper to prevent light entry and placed in an environmental control chamber set at 16:8 hr light/dark cycle and 22°C night temperature and 25°C day temperature.
Petri dishes were checked daily for beetle emergence. Based on the date of adult emergence, beetles were divided into three test groups for replication of the experiment. These groups had emergence dates of 1) Aug. 19-21, 2) Aug. 22, and
3) Aug. 23-25. 22
Flight-lnitiation Factors Test
This experiment was a 2 x 2 factorial with the two
factors being food and mating status. For the food
treatment, beetles were either continuously supplied with
fresh potato foliage, or provided water only. For the mating treatment, beetles were allowed access to mates, or were denied access to mates.
The experiment was replicated for each of the three
emergence groups described above. Due to the large number
of beetles available, each group was broken into sub-groups to make flight testing manageable. Each treatment (food x mating status) was replicated twice per sub-group for a total of eight beetles per sub-group. Group 1 beetles had
2.5 sub-groups, group 2 had 5 sub-groups and group 3 had 10
sub-groups. Each sub-group was flown at the same time using the previously described flight room. Two beetles of each treatment per sub-group were placed on a single flight platform. Sub-groups were flown in consecutive 30-minute periods. Flight activity was rated as in test 1-3. All beetles were monitored daily, the dates of all oviposition by individual females were recorded, and the sex of all beetles was determined by dissection after the test.
Progeny Test
Eggs were retained from two females that exhibited
flight activity (flew above the level of the flight 23
platform) and from two females that exhibited no flight
activity (did not open elytra). Since mated females were
group mated, the flight history of the males was unknown.
Eggs from the flying and non-flying females were reared
separately to adult on potted potato plants within screened
cages and held in an environmental chamber set on 16:8
light/dark cycle and 22°C night temperature and 25°C day temperature.
Beetles were grouped as progeny of fliers or non-fliers
and each group was placed on a separate flight platform and
flown in the flight room as described above. All flights were rated as in test 1-1.
Section C - Behavioral Polymorphism
Description
This experiment was designed to test for behavioral polymorphism in postdiapause adults, with regard to flight,
in a local population of the Colorado potato beetle. In the
fall, CPB from two behaviorally distinct groups (flying and not flying) were collected and immediately subjected to a
feeding test to determine the migratory status by measuring the response to food. After this feeding test, both groups
over-wintered at the same location outdoors, and were
allowed to emerge naturally in the spring. After emergence,
a comparative flight test was conducted. The tests were 24 structured on the following hypotheses: 1) H0: percentage flying in each behavioral group will be equal; Hfl: fall migrating CPB group will fly more frequently in spring, and
2) H0: percentage flying between age groups will not differ; H0: most recently emerged CPB will fly less frequently.
Feeding Test On Sept. 5 1991, two groups of CPB, one dispersing by flight and one not, were collected in or around Smithville,
Ohio. One group of beetles flying from a commercial potato field to an adjacent wooded area was collected using an insect net. These beetles were presumably migrating by flight into the woods to diapause, beacuse green potato foliage remained plentiful in this commercial field. On the same day, a second group of beetles that was feeding gregariously on the stems of defoliated potato plants in a research potato field at the Ohio Agricultural Research and
Developmental Center, located near Smithville, Ohio, was collected. This group was hypothesized to be behaviorally different, since they had not left the field by flying or walking despite declining day length and deteriorating food source.
The following feeding test was conducted to determine if either group fit the definition of migratory based on the lack of response by dispersing individuals to food cues 25
(Kennedy 1975). Thirty beetles were randomly selected from each group and placed individually into plastic petri dishes
(9 cm X 1.5 cm). A fresh 2 cm diameter potato leaf disk was placed in each dish. Petri dishes were held under fluorescent lights at 25°C. Beetles were allowed to feed on leaf disks for 12 hours, after which disks were rated as either completely consumed, fed upon, or not fed upon. The percentage of leaf disks in each feeding category for each group was analyzed using a G-test (Costat, 1990).
Flight Test
On Sept. 9 and Sept. 12, 1991, a total of 280 beetles was collected flying into the woods from the previously described commercial field. On the 12th, 200-300 beetles that were clustered and feeding on defoliated potato stems at the OARDC field described above were also collected.
Each group of beetles was divided in half and put into a separate aluminum screen over-wintering cage immediately after capture. The two cages with the flying beetles were marked with yellow flags.
The over-wintering cages were constructed by making a
30 cm diameter by 90 cm long cylinder from fine-mesh aluminum window screen. The long edge of the cylinder was sealed with a glue gun. An open end of each screen cylinder was buried 0.3 m deep into the ground and the other end was crimped over and held tightly shut with clothes pins. These 26 cages were located on the edge of a wooded area at the
OARDC, and ensured that all emerging beetles would be recovered the following spring after winter diapause in the ground.
Starting on April 22, 1992, cages were monitored approximately every two days for beetle emergence. All emerging beetles were removed from the cage and placed in a one liter plastic container with a screen top. All beetles were separated according to the collection date from the cages, and by the original collection locality. All collected beetles were maintained in the laboratory at 27°C under a 15:9 hr light/dark cycle. Beetles were not fed, but received fresh cotton moistened with water each day.
When sufficient numbers of beetles were emerging in the field cages, flight initiation tests were conducted in a greenhouse to compare percentage flying for each locality and date of collection from the emergence cage. Ten randomly selected beetles per experimental group (date X locality) were used.
A flight test was conducted for one hour in a glass greenhouse starting between 2-4 p.m. Beetles in each experimental group were placed separately upon the top of a clear plastic takeoff platform (13 cm high x 13 cm diameter) under petri dishes. Platforms were arranged in two rows on the greenhouse floor with a distance of 15 cm separating platforms both between and within rows. Beetles from the 27 same collection date were located opposite one another in either row 1 or row 2. All beetles were released from the petri dish covers at the same time. Whenever a beetle flew from a platform, it was recorded as a flight initiation and returned safely to a sealed container for use on the next test date. If more than two CPB were lost or injured from any group, then all CPB from that corresponding date were not included in the next test. Tests were conducted once or twice weekly during the spring and summer.
Results and Discussion
Section A - Preliminary Laboratory Flight Tests
Test 1-3
In this and other similar tests, CPB only flew during the lights on period (Table 1). Although the infrared light does provide some heat, CPB typically flew very soon after turning on the light. Most flights were only a few seconds in duration.
Table 1. Effect of artificial light source on CPB flight initiation.
Number Number of 30 minute period of CPB Flights
Lights on 8 14 Light off 8 0 Lights on 8 20 Lights off 8 0 28
Test 2-1
CPB fed nightshade did not fly in the 30 minute test period (Table 2), and those fed potato foliage only flew 6 times. Unfed CPB flew 34 times. Starved CPB are more likely to fly than recently fed CPB.
Table 2. Flight activity of "Weak" flying CPB fed three diets.
Number Number of Diet of CPB Flights1
Unfed 11 34 a Potato 11 6 b Nightshade 11 0 b
1 Rows followed by the same letter have overlapping 95% confidence intervals based on cell percentages.
Test 2-2
The non-flying CPB group showed little flight activity for any diet regime (Table 3).
Table 3. Flight activity of non flying CPB fed three diets.
Number Number of Diet of CPB Flights1
Unfed 16 2 a Potato 16 0 a Nightshade 16 0 a
1 Rows followed by the same letter have overlapping 95% confidence intervals based on cell percentages. Test 2-3
Strong fliers and weak fliers flew more often than non fliers (Table 4). Distinct variability in flight initiation exists in this population; however, it is unclear what causes the variation. The weak flying CPB could be too old, young or sick, or the lack of flight could be due to inherent genetic variation in the population.
Table 4. Flight activity of three classes of CPB starved for 48 hours.
Number Number of Treatment group of CPB Flights1
Fliers 9 30 a Weak Fliers 9 22 a Non-Fliers 9 1 b
Rows followed by the same letter have overlapping 95% confidence intervals based on cell percentages.
Test 2-4
The results of this test were similar to those for test
2-3. Non-fliers flew less than weak or strong fliers (Table 30
Table 5. Flight activity of three classes of CPB starved for 96 hours.
Number Number of Treatment group of CPB Flights1
Fliers 9 34 a Weak Fliers 9 30 a Non-Fliers 9 7 b
1 Rows followed by the same letter have overlapping 95% confidence intervals based on cell percentages.
Test 3
Because only 4 of 21 CPB flew under these artificial conditions, and all 21 were caught flying outdoors earlier in the day, these results suggest that the conditions in the flight room could responsible for the low level of flight activity observed in this test, and also in all other flight room tests. Although handling may have influenced CPB behavior in this test, CPB were handled in a similar manner in greenhouse flight tests (see section c) and high percentages of CPB flew in those tests. The response to the conditions in the flight room probably represent individual variation in flight initiation with regard to light. Some
CPB in the population must require more intense light, or more UV light. Temperatures in the flight room were well above levels where flight initiation has been recorded for
CPB.
The preliminary flight tests were conducted with the goal of understanding flight in the CPB, and developing an apparatus where CPB could be flown in a sustained and 31 consistent manner in the laboratory. I conclude that lighting and space (CPB often hit the walls soon after takeoff) were the limiting factors. A vertical airflow flight chamber (approximately 2mx2mx3m) was tested briefly in an attempt to deal with the space problem, but the few CPB that engaged in flight quickly flew out of the top of the chamber at the maximum airflow setting.
Section B - Flight Initiation Factors and Progeny Test.
Flight Initiation Factors Test
The CPB in this study were not postdiapause, so the results here do not necessarily apply to postdiapause CPB.
No CPB starved from pupal emergence flew in this study, and many died before the experiment was completed. Flight results are only presented for beetles that were fed after emergence, but starved just prior to flight testing.
Mated males flew significantly more than unmated males
(G-test, df=l, G=5.922, P=0.01, Table 6). However, mated females did not fly significantly more times than unmated females (df=l, G=3, P=0.08, Table 6). When results for each sex were pooled, mated CPB flew significantly more (58.0%) than unmated CPB (25.8%), (df=l, G=7.39, P=0.007). 32
Table 6. Percent of flight of CPB due mating status and sex.
Percent Total Flying
Mated Females 19 57.9 Unmated Females 17 29.4
Mated Males 14 64.3 Unmated Males 18 22.2
Males flew as frequently as females (Table 7). Thirty- three percent of females flew before they laid their first egg mass (Table 7). Female CPB will fly before or after oviposition.
Table 7. Percent flight of CPB due to ovipositional status and sex.
Percent Percent Flying Before Percent Sex Total Flying Oviposition Ovipositing
Females 36 44.4 33.3 94.4 Males 32 40.6
Progeny Test
The results of this test showed no difference between the progeny of flying and non-flying females. Twenty-six percent (N = 38) of the progeny of non-flying females flew, while 27% (N = 33) of the progeny of flying females flew.
If the flying status of the males could have also been controlled, then perhaps a difference might have been observed in this generation, or multiple generations of selection and breeding might be required to produce differences. However, any differences observed in flight intiation in the laboratory might not be biologically relevant outdoors and tests must ultimately be conducted under the latter conditions. Conversely, any differences observed in flight initiation might not be directly related to genetic variation, but might result from poor health or nutrition.
Section C - Behavioral Polymorphism
Feeding Test
In the flying CPB group, only 1 of 30 disks was entirely consumed, and 5 of 30 had evidence of feeding. In the non-flying group, 16 of 30 disks were entirely consumed and 19 of 30 had some evidence of feeding. This study supports the hypothesis that the flying beetles were migrating to the woods to diapause, and the non-flying
(resident group) beetles were not yet ready for diapause.
Experimental Results
Results from each test date are presented in Tables 8-
13. Only on May 28 (Table 11) did a significantly higher total percentage of the resident beetles fly than the 34 migratory population (G-test, df=l, G=4.49, P=0.03). On all other test dates, the groups were not different. There is no way of determining, in this study, whether individuals of the resident group would have flown to over-wintering sites after the fall 1991 collection date. Regardless, this study supports the hypothesis that most postdiapause CPB are capable of flight in the spring.
This study also demonstrates that a low percentage of
CPB are flight capable soon after emergence from diapause.
On every date but the last (Table 13), a significantly higher percentage of CPB in the older group flew than did the youngest group. Recently emerged beetles, however, were very active walkers and would be capable of colonizing a nearby potato plant. This study also demonstrated that flight can occur in unfed postdiapause CPB, because no CPB were fed in this study. Many of the flights observed in this test were strong and controlled. Little oviposition was observed by females during the study indicating that postdiapause CPB can fly before oviposition.
CPB that flew immediately after release in this experiment were marked with fingernail polish and observed in subsequent flight trials. Frequently these marked CPB would be the first to fly from the stand trial after trial.
Similar marking and tracking of CPB was done in all flight studies with similar results. Although most CPB are flight 35 capable, wide variation exists among individuals in response to flight stimuli.
Table 8. Greenhouse Flight Test on May 11, 1992.
Migrating Resident
Emergence dates N % Flying N % Flying Total %
Before April 27 5 60.0 3 67.0 62.5* April 27-30 2 100.0 6 33. 0 50. 0* May 4-7 3 67.0 6 50.0 55.6* May 7-11 9 0.0 8 0.0 0.0
Total 19 36.8 23 30.4 33.3
* For total %, significantly greater than last date (G- test, df=l, P < 0.001).
Table 9. Greenhouse Flight Test on May 15, 1992.
Migrating Resident
Emergence dates N % Flying N % Flying Total %
Before April 27 5 80.0 2 100.0 85. 7* April 27-30 2 100.0 4 0.0 33.3 May 4-7 2 50.0 5 100.0 85.7* May 7-11 10 40.0 8 12.5 27.7 May 11-13 10 30.0 10 20.0 25. 0
Total 29 48.3 29 34.5 41.4
For total %, significantly greater than last date ( G- test, df=l, P < 0.01). 36
Table 10. Greenhouse Flight Test on May 20, 1992.
Migrating Resident
Emergence dates N % Flying N % Flying Total %
May 7-11 8 62.5 7 42.8 53.3* May 11-13 10 100.0 10 60.0 80.0* May 13-15 5 100.0 1 100.0 100.0* May 18-20 10 10.0 10 10.0 10.0
Total 23 63.6 28 39.3 52.3
* For total %, significantly greater than last date ( G- test, df==1, P < 0.01) .
Table 11. Greenhouse Flight Test on May 28, 1992 • Migrating Resident
Emergence dates N % Flying N % Flying Total %
May 18-20 10 100.0 10 100.0 100.0* May 20-22 10 90.0 10 100.0 95.0* May 22-26 9 44.4 9 88.8 72.2
Total 29 79.3 29 96.6 87.9
* For total %, significantly greater than last date ( G- test, df=l, P < 0.05).
Table 12. Greenhouse Flight Test on June 1, 1992 • Migrating Resident
Emergence dates N % Flying N % Flying Total %
May 18-20 10 100.0 10 80.0 90.0* May 22-26 7 85.7 9 100.0 93.8* May 28-June 1 8 12.5 8 62.5 37.5
Total 25 68.0 27 81.5 75.0
For total %, significantly greater than last date ( G- test, df=l, P < 0.001). 37
Table 13. Greenhouse Flight Test on June 8, 1992.
Migrating Resident
Emergence dates N % Flying N % Flying Total
May 28-June 1 8 37.5 7 71.4 53.3 June 1-3 10 40.0 10 70.0 55.0 June 3-5 10 40.0 10 50.0 45.0 June 5-8 8 75.0 7 28.6 53.3
Total 36 47.2 34 55.9 51.4 CHAPTER III
Potato Field Colonization
Materials and Methods
Section A; Patterns of Infestation by Postdiapause CPB in
Commercial Potato Fields in Smithville. Ohio for 1990 and
1991.
In 1990, nine commercial potato fields in Smithville,
Ohio were sampled to measure the pattern of CPB density.
Five of these fields were immediately adjacent to fields that were in potatoes during 1989, whereas the other four were rotated various distances away. Each field was divided into four or five sections, depending on the field's size and shape. The sections included the outer four rows of field edges and the field center. Several long and narrow fields were sampled only on one edge and the field center.
Each week, after plants began emerging from the soil, twenty plants were sampled from each section and all adult
CPB on each plant were recorded. Plants were randomly selected along a straight line pattern on field edges, or on a "ZH pattern in the field center. Sampling was continued in each field until large numbers of fourth instar larvae
37 38
were observed, then postdiapause colonization was considered
to have ended.
In 1991, fields in each of four categories were sampled:
1) early planted (potatoes up before June 1) and adjacent to
a 1990 potato field, 2) late planted (potatoes up after June
1) and adjacent to a 1990 potato field, 3) early planted and
not adjacent to a 1990 potato field, and 4) late planted and
not adjacent to a 1990 potato field. The sampling procedure
used in 1990 was also used in 1991 except that 30 plants were sampled per section. Data were analyzed by analysis of variance (ANOVA, Systat, 1991) and field sections were
compared using least significant difference (LSD, Systat,
1991).
Section B: Colonization of a Potato Field by Walking and
Flvina CPB
An experiment was performed to test the hypothesis that
the number of flying CPB colonizing a late-planted (potatoes up after June 1) potato field that was not adjacent to a previous year's (1991) potato field, would be the same or
greater than the number of walking CPB colonizing the field.
On May 22, 1992, a 34 m x 52 row wide potato field (Katadin) was planted 180 m west of a 1.05 ha. field that was in potatoes the previous year and therefore served as a source
of beetles to colonize the experimental field. A corn field
and an alfalfa field were between the experimental field and the CPB source field. When potato plants just started emerging (1 plant per 11 m of row) in the experimental field, on June 12, and few beetles had yet colonized the field, nine 3 m x 3 m areas were surrounded with a 15 cm high aluminum flashing barrier with a Tanglefoot11 band along the top edge. This barrier was designed to prevent walking beetles from reaching the plants emerging inside the barrier. The areas protected by the barriers were spaced uniformly throughout the field. The placement of the barriers in the field is illustrated in Figure 1.
This experiment was sampled four times, on June 15, 18,
22 and 26. The experiment was terminated after June 26 because potato plants were beginning to grow over the barriers. On each sampling date, 10 plants were randomly sampled both inside the barriers and at 12 locations outside the barriers (Figure 1). All adults on each plant sampled were recorded and on the last sampling date all egg masses on each sampled plant were also recorded. No larvae were found on any sample date.
Section C: Post-Colonization Movement Experiments
To study dispersal of postdiapause CPB within a potato field, two mark recapture studies were conducted. In the first study on May 28, 1991 at 5 p.m., all the adult CPB were removed from a 4 row by 5.1 m section in a demonstration Figure 1 Experimental design for experiment on colonization of a field by flying CPB. 41
Experimental Design for Experiment on
Colonization of a Field by Flying CPB Figure
With Flashing f \ without 42 potato field at the OARDC in Wooster, Ohio. Potato plants were 10 to 12 cm tall at the time of the study. Twenty-five
CPB marked with fingernail polish on the pronotum were randomly placed on plants within 2 m around the cleared section. After 24 hours all plants in the cleared section and any plants up to 6.4 m from the cleared section were searched for marked CPB adults, and the exact position of any marked or unmarked CPB was recorded.
In the second study started on May 30, 1991, five marked
CPB (fingernail polish) were released per plant on eight flagged plants randomly located in the same potato field as above. CPB adults in study 1 and 2 were watched closely for
20 to 30 minutes after placement on plants to ensure that all CPB fed on or remained on the plant. If a CPB left the plant soon after placement, it was placed back on the plant and observed again. If a particular CPB continued to leave a plant then it was replaced by another marked CPB. The temperatures for study 1 ranged from 18°C to 32.8°C and for study 2 from 18.6°C to 30.4°C. Heavy rains occurred before
(3.3 cm) and after (0.65 cm) release of marked CPB in study
2 .
Section D; Geostatistical analysis of Colorado Potato beetle patterns of Infestation
In 1992, a commercial potato field was selected to measure the pattern of CPB infestation. The field (Denn 1992) was located 250 m west and 50 xn north of fields that were in potatoes during 1991. This field was sampled using two procedures designed to generate data for geostatistical analysis. In sampling procedure one, conducted on June 3, flags were set along the east and west edges of the field every 81 m. On the north and south edges, flags were placed every thirty-two rows starting on the fourth row from the east edge. At each intersecting point, between the east and west flags, and the north and south flags, five plants were randomly sampled and all the adults and egg masses on those five plants were recorded and averaged. On June 9 and 19, this same field was sampled using a second procedure, where flags were spaced 31 m apart on the east and west edges, and only one plant was sampled at the point of line intersection. This procedure increased the number of sample locations within the field.
These data, and data from commercial field Rho 1990 (see pattern of infestation study) were analyzed using two geostatistical techniques, the semi-variogram and kriging
(Geo-Eas 1.2.1, 1991). A semi-variogram is calculated from data that is taken at precise x and y coordinates. These data points are grouped by the distance separating points using a specified distance interval or lag distance (h).
The semi-variance for a given lag distance (h) can be estimated by equation (1); 44
1 N (h) Y*(h)=----- t [z(i)-z(i+h)]2 (1) 2N(h) i-1
Where N(h) is the number of pairs of observations [z(i), z(i
+h)] separated by a distance or lag (h) (Vieria et al. 1983,
Clark 1979). Y*(h) is plotted against h to produce a semi- variogram. Thus, the semi-variogram provides a measure of the differences between pairs of sample values, and how those differnces change with the distance between sample points.
A mathematical function (model) can be fit to the semi- variogram. Semi-variograms should be calculated for different compass directions, and also non-directionally
(omnidirectional semi-variogram). Anisotropy is said to occur when semi-variograms of differing directions produce different models. Anisotropy indicates that direction related differences in the pattern of variability among data points exists.
Kriging is a system of interpolation that uses the values of surrounding sampled points and a weighting factor K to estimate values at unsampled points or areas (block kriging). Kriging is represented by the general eguation
(2 );
N z*(x0) = Y, K z
Where the point to be estimated is z*(xo) and the surrounding points are z(xt). The weighting factor x is derived from the semi-variogram and geometry of the points z(Xj). For more information on kriging, see Clark (1979) or
Viera et al. (1983) .
Results and Discussion
Section A: Patterns of CPB Infestation in Commercial Fields in Smithville. Ohio for 1990 and 1991
In 1990, commercial potato fields Rho, Mooext, Don III, and Rho II had significantly higher populations of CPB per plant on one or more edge sections than in the field center
(an edge effect), (Table 14). Rho, Mooext, Don III, and Rho
II were adjacent to fields that were in potatoes in 1989.
In 1991, Rho 1, 2 & 3, Don 1 and Denn 4 & 5 had significant edge effects (Table 15). Rho 1 & 3 and Don 1 were located next to fields that were in potatoes in 1990. Individual field results are presented in Tables 24 through 45 (See
Appendix).
When results are pooled for 1990 and 1991, and all early fields are compared with late fields regardless of distance from the previous year's potatoes, 66.6% of early fields have edge effects, while only 20.0% of late fields have edge effects. A G-Test for equality of two percentages (CoStat,
1986) indicates that these differences are statistically significant (G=5.1, df=l, P=0.02). Similarly, when adjacent fields are compared with far-rotated fields, ignoring planting date, 72.7% of adjacent fields have significant edge effects, while only 16.6% of far-rotated fields have significant edge effects. A G-Test for equality of two percentages (CoStat, 1986) indicates that these differences are statistically significant (G=4.7, df=l, P=0.03). When pooled results of early-adjacent fields are compared with late-planted and far and close-rotated fields, the differences are pronounced with 75% of early adjacent having significant edge effects and no late-rotated fields having significant edge effects. A G-Test for equality of two percentages (CoStat, 1986) indicates that these differences are statistically significant (G = 6.7, df = 1, P = 0.006).
CPB flight muscles degenerate during diapause and regenerate soon after postdiapause (De Kort 1969). One hypothesis, to explain for the higher frequency of edge effects observed in potato fields that were adjacent to a field that was in potatoes the previous year, is that immediately after diapause CPB might not have fully regenerated flight muscles and would have to walk in search of host plants. The results from Chapter 3 (section c) are consistant with this hypothesis. Walking CPB would be more likely to encounter potato plants on a field edge and accumulate there. The farther a field is located from the over-wintering site, the less likely this field is to be reached quickly by walking CPB. Flying CPB might pass over 47 field edges and land anywhere in a potato field, thus resulting in no edge effect.
If temperatures are cold in spring, then fewer CPB will fly (Caprio and Grafius, 1990) and more CPB will encounter and colonize the edges of nearby fields. Therefore, cold temperatures may increase the edge effects in adjacent fields. Edge effects in early-planted fields could result from the generally colder temperatures in early spring; CPB are more likely to walk than fly as described above, and will tend to colonize the edges of fields.
Planting date and rotation distance also affect the absolute numbers of CPB that colonize a field. If the mean numbers of CPB from the center-of-field are averaged for the season for each field, the results are as follows, early- adjacent fields have a mean(±SEM) of 0.91±0.12 CPB per plant, early-remote = 0.10±0.05 CPB per plant, late-adjacent
= 0.23±0.02 CPB per plant, and late remote = 0.11±0.04 CPB per plant. The planting date and rotation distance factors can not be pooled, because of significant interaction (df=
1,18, F = 8.35, P = 0.01). In the analysis of main effects, however, the center-of-field counts of early adjacent fields were significantly greater (LSD, a= 0.05) than early-remote fields, late-adjacent fields and late-remote fields (ANOVA, df = 3,18, F = 17.49, P < 0.001).
Some fields in all groupings showed significant changes in CPB density over time (Tables 14 & 15). Significant 48
Figure 2 Pattern of Infestation: Commercial field Rho over four sampling dates in 1990. i
Mean Number of Adult CPB/Plant 50 0 .5 2 50 .5 0 2.00 0.00 50 .5 1 1.00
at 14 Es (-) etr et 58 Ws (1-4) West (5-8) West Center (5-8) East (1-4) East a 2 My 0 Le Jn 13 June 7 JLne 30 May 23 May il Scin at o et Rw No.) (Row West to East Section Field iue2 £ 2 Figure 50
Table 14. ANOVA results for pattern of infestation study of commercial potato fields in 1990.
Difference Difference Field Between Within Grouping Areas Field by Date1^ in Field Over Time Field & Dist.2 (df) F P (df) F P
Rho EA (4,91) 17.3 0.001 (3,273) 2.60 0.053 Rho II E A (1,58) 25.5 0.001 - Rho III E A (1,58) 4.97 0.030 - Don III E A (3,86) 6.49 0.001 —
Mooext L A (1,38) 33.4 0.001 (2,76) 5.03 0.009
Moo L CR (4,89) 1.34 0.263 (3,267) 7.74 0.000 Don L CR (3,76) 0.86 0.467 (1,76) 0.01 0.919 Fry 3 L FR (4,95) 0.40 0.807 (3,285) 9.64 0.000 Fry 1 L FR (4,95) 0.86 0.495 (2,190) 1.72 0.185
' e = early planting (plants up before June 1), L = late planting. 2 A = adjacent field (bordering 1989 potato field), CR = close rotated field (< 100 m from 1989 Potato field), FR = far rotated field (> 100 m from 1989 potato field). 51
Table 15. ANOVA results for pattern of infestation study of commercial potato fields in 1991.
Difference Difference Field Between Within Grouping Areas Field by Date^ in Field Over Time Field & Dist.2 (df) F (df) F
Don 3 E N (3,116) 0.58 0.057 (1,116) 0.69 0.407
Don 1 E A (1,98) 4.19 0.043 (1,98) 22.1 0.000 Don 2 E A (4,145) 0.99 0.415 - Rho 1 E A (4,145) 10.4 0.001 - Rho 3 E A (4,145) 4.72 0.001 —
Rho 2 E CR (4,145) 3.70 0.007 (1,145) 0.03 0.873 Snyder E FR (4,145) 1.84 0.124 (1,145) 1.00 0.320
Denn 4 M CR (4,145) 2.49 0.046 — Denn 5 M FR (4,145) 3.22 0.014 —
Rho 4 L A (2,87) 0.12 0.890 — Rho 5 L A (2,132) 2.87 0.060 —
Denn 1 L FR (4,145) 0.67 0.615 (1,145) 0.41 0.522 Denn 2 L FR (4,145) 0.75 0.560 -
1 E = Early planting (plants up before June 1), M = Mid-season planting (plants up on June 1), L = Late planting 2 A = adjacent field (bordering 1990 potato field), CR = Close rotated field (< 100 m from 1990 Potato field), FR = Far rotated field (> 100 m from 1990 potato field), N = not rotated. 52 linear, quadratic or cubic trends in CPB density over time were observed, but could not be correlated with field grouping. Edge effects were persistent in some fields over a period of weeks as illustrated by commercial field Rho,
(Figure 2); in 1989, a potato field (winter wheat in 1990) was located adjacent to this field on the east side.
However, increases in CPB density were observed in center sections of Rho on later sampling dates (Figure 2), whereas populations on the edge remained fairly constant over time.
Although edge effects were persistent, they became less pronounced with time in this field.
In six of the eight fields showing a significant edge effect, the edge highest in density was on the side of the field that was the closest to a field that was in potatoes the previous year. One of the two exceptional fields, Don
1, had a significant edge effect adjacent to the previous year's potato field, but not enough other sides were sampled in this field as a check. In the other field, Denn 4, the edge effect was so small that it was probably not biologically significant. The only major exception was field Don 2, which had fields that were in potatoes the previous year bordering the east and west edges of the field, but showed no edge effects.
This study does not rule out the possibility of mass unidirectional movement of postdiapause CPB in the spring as has been reported by some researchers (Ng and Lashomb 1983). My data suggest, however, that enough CPB search in all directions from an over-wintering site that any field in close proximity will not only be infested, but the most severely infested regions of the field will be closest to this over-wintering site. Furthermore, in Ohio many CPB over-winter either in or very close to the field in which they fed as larvae.
Section B: Colonization of a Potato Field bv Walking and
Flvina CPB
The results of this experiment are presented in Table
16. For no individual dates or season totals, are differences between enclosed and unenclosed areas significantly different (ANOVA for season total, df=l,838, F
= 3.34, P = 0.068). Most of the CPB that were colonizing this field did so by flight, since that is the only way they could have reached the enclosed areas of potatoes. CPB were observed flying into these enclosed areas as they were being assembled, and practically no plants were available anywhere in the field to be colonized at that time. This experiment supports the hypothesis that CPB fly to remote or late- planted fields. 54
Table 16. Mean Numbers (±SEM) of Adult and Eggs Masses in Unenclosed and Flashing Enclosed Areas.
June 15 June 18 Adults Unenclosed Area 0. 250±0.048 0.49210.097 Enclosed Area 0.178±0.066 0.31110.083
June 22 June 26 Adults Unenclosed Area 0.258±0.051 0.20810.050 Enclosed Area 0. 211±0.058 0.16710.040
Season Total Adults Unenclosed Area 0.302±0.03 Enclosed Area 0.217±0.03
June 26 Ecrci Masses Unenclosed Area 0.717±0.075 Enclosed Area 0.456±0.087
Section C: Post-■colonization Movement Studies
In study 1 of the post-colonization dispersal study, four marked CPB moved into the cleared area, five marked CPB were found in the two row wide release area and 11 were not located. Five marked CPB were outside the release area, 1
CPB was 5 m to the northeast, 1 CPB was 5.6 m away, 1 CPB was 2 m to the west, 1 CPB was 5.6 m to the northwest and 1
CPB was 4 m to the west. Twenty-seven unmarked CPB were found in the cleared area. We do not know whether these 27 were CPB from surrounding plants or new arrivals to the field; however, given that the marked group was so mobile, 55 it is likely that some of these were from surrounding plants.
In study 2, only one marked CPB was recovered on flagged plants, despite a release method that insured that
CPB were not immediately leaving due to handling. However,
14 marked CPB were recovered on non-flagged plants. The mean distance of recovery from the site of release was 2.83 m. Eighteen of 32 beetles either left the sampling arena or were not located within the sampling arena. Thirty-one of
32 CPB left the plant on which they were released.
Study 1 and 2 indicate that CPB, after establishing on a plant, will move relatively far within a field, even after only 24 hours. Heavy rain during study 2 might have been a factor in the high dispersal from flagged plants; however, heavy rains can occur with regularity during the spring and thus may increase dispersal of CPB within a potato field by knocking CPB from plants. My results contrast sharply with those of Bach (1985) who states that CPB tend to remain on plants that they originally colonize or on which they are placed.
Results of this study and section A indicate that controlling high populations of CPB on the edge rows of a potato field would be a useful strategy. Edge control may have to occur at frequent intervals to prevent rapid movement from the field edge to interior areas of the field, or a wide edge may have to be treated. In these situations, 56 effective control of field edge populations of CPB by physical, mechanical or insecticidal means will likely prevent significant numbers of CPB from reaching center areas of the field.
Section D: Geostatistical analysis of Colorado Potato Beetle
Patterns of Adult Infestation
All directional semi-variograms in Section A use a tolerance angle of 45° and a bandwidth of 64.5 m. These parameters determine how wide a band is sampled for pairs of points, in a particular direction, for semi-variogram analysis. If the band is too narrow, then too few points will be included in the directional semi-variogram. If the band is too wide, then the directionality of the semi- variogram is lost. The values I used here balance these two factors well for my data set.
The east/west semi-variogram of commercial field Rho
1990 is presented in Figure 3. The semi-variogram indicates pure nugget effect at a variance of approximately 0.7. The north/south semi-variogram (Figure 4) indicates a similar nugget effect. And finally the omnidirectional semi- variogram (Figure 5) also indicates a pure nugget effect at a variance of 0.8. A nugget effect occurs when the variation between the closest pairs of samples is similar to that of pairs that are at the maximum distance apart.
Despite the fact that in this field a significantly higher population of CPB occurred on one edge of the field than in the center or far edge (two sample T-test, df = 1, P <
0.05), the variation from plant to plant is so high that larger scale trends in variation are obscured. Figure 6 is an exact plot of the raw data from Rho on May 23, 1990.
Note the high plant-to-plant variation within the angled east edge. The sampling scheme used in this field was not designed specifically for geostatistical analysis, and this may have affected the results, but the local interplant variation might have produced similar variograms if samples had been spaced more uniformly.
Semi-variogram results for commercial field Denn 1992 are summarized in Table 17. A linear model fits most of the semi-variograms well. A linear model indicates that the increase in variation between points is directly proportional to distance. Nonlinear models used in geostatistics include the spherical, exponential, and
Gaussian (Clark 1979, Englund and Sparks 1991). Clumped distributions usually result in nonlinear shapes in the semi-variogram. (Schotzko and O'Keeffe 1990). The linear models fitted to these semi-variograms suggest that a distinct edge effect probably does not occur in this field.
Denn 1992 was a late-planted field that was rotated at a distance from previous year's potato fields. However, a 58
Figure 3 North/south semi-variogram of CPB in Rho field on May 23, 1990. Semi-variogram 00 .0 3 40 .4 2 60 .6 0 0.00 1.20 1.80 100 itne t e Pis n eet F in Pairs een etw B Distance 200 0 0 3 Figure 3 Figure 0 0 4 0 0 5 0 0 7 0 0 6 60
Figure 4. East/west semi-variogram of CPB in Rho field on May 23, 1990. Semi-variogram 00 .0 3 40 .4 2 60 .6 0 0.00 80 .8 1 1.20 0 sac Bewen ar i Feet F in Pairs een etw B istance D Figure 4 Figure 1000 2000 H Figure 5 Omnidirectional semi-variogram of CPB in Rho field on May 23, 1990. 3 .0 0 2 .4 0 1 .8 0 1.20 0 .6 0 0.00 0 1000 2000 Distance Between Pairs in Feet Figure 5 Figure 6 Plot of raw data from commercial field Rho on May 23, 1990. - • - •f • •f - f • - + • ■+ ■ ■+ 4 • + - f • 1 5 0 0 3 t, t 9 t t, 3 a 1.000 0.000 + 1000 E E + £ .OOO 2 a^ E 4- .OOO < .OOO # =£ 1 Northing ( feet) Figure 6 □ 5 0 0 nd Quartilo: nd Quartilo: rd Quartilo: < .OOO X — .OOO < .OOO □ =£ st Quartilo: st Quartilo: .OOO th Quartilo: th Quartilo: 1 2 4 3 - 6 0 0 4 0 0 - 200 UllBcq linear model might not fit all semi-variograms of postdiapause CPB populations in potato fields and more research needs to be done on fields that might have a different infestation pattern, such as an early-planted field that is adjacent to a field that was in potatoes the previous year. North/south, east/west and omnidirectional semi- variograms show anisotropy for adults on June 3 and 19 and isotropy for adults on June 9 (see Appendix for all Figures >13, Figures 14,15,16; 23,24,25 and 17,18,19 for June 3, 19 and 9, respectively). Anisotropy occurs when semi- variograms are not the same in all directions (Webster 1985). If anisotropy is severe, it may not be clear what model should be selected for kriging. For egg masses, the east/west and north/south semi-variograms indicate some 67 Table 17. Denn 1992. Semi-variograms Direction Nugget Sill Range Model Figure Adults June 3 north/south 0.09 0.09 2400 Linear 14 east/west Pure nugget effect 15 Omni- 0.08 0.085 2400 linear 16 Adults June 9 north/south 0.25 0.28 800 linear 17 east/west 0.29 0.32 2400 Linear 18 Omni- 0.29 0.32 2800 Linear 19 Adults June 19 north/south 0. 02 0.34 2400 Linear 23 east/west Pure nugget effect 24 Omni- 0.15 0.05 1600 Linear 25 Ecxas June 9 north/south 0.37 0.41 2500 Linear 20 east/west Pure nugget effect 21 Omni- 0.37 0,41 2500 Linear 22 Eaas June 19 north/south 0.40 0.6 2000 Linear 26 east/west Pure nugget effect 27 Omni- 0.39 0.45 1600 Linear 28 anisotropy on both dates sampled, June 9 (Figures 20,21,22) and June 19 (Figures 26,27,28), respectively. There is a north/south trend in the variation in the numbers of egg masses per plant, but not an east/west trend. Although an east/west trend in variation in adult counts was documented on June 9 (Figure 18), the adults may not have been ovipositing at the time. On other dates, no east/west trend in adults was observed. The adult semi-variograms change with respect to time. On the first sampling date, June 3, there were few CPB in the field and the plants were just starting to emerge from the soil. The north/south, east/west and omnidirectional semi-variograms (Figures 14,15,16, respectively) have relatively little slope compared with the same semi- variograms on June 9 (Figures 17,18,19), when there were many more CPB in certain areas of the field and thus more variation between sample pairs. However, the differences might also be due to the differences in the sampling methods between dates. The first sample method took fewer overall samples, each consisting of an average among five plants (to reduce the effect of local plant-to-plant CPB variation). This method might not have detected as much variation as the second, in which individual plants were sampled at more locations. On the last sample date (June 19, Figures 23,24,25), the slopes of the semi-variograms are flat compared with those on June 9. A hail storm that occurred prior to the June 19 sample date severely damaged potato plants and appeared to kill many CPB; counts dropped to near zero. This high CPB mortality could have reduced any variation in CPB density among different areas of the field. The egg mass semi-variograms are similar between the sampling dates June 9 and June 19 for the north/south (Figures 20,26, respectively) and east/west (figures 21,27, respectively), but the slope is less in the omnidirectional 69 semi-variogram on June 19 (Figure 28) than on June 9 (Figure 22) . The linear models fitted to the omnidirectional semi- variograms from the Denn 1992 field are appropriate for kriging eggs or adult values, because of the lack of severe anisotropy between semi-variograms of the same date and variable (egg or adult counts). The omnidirectional semi- variogram usually gives the best or smoothest semi-variogram (Englund and Sparks, 1991). Contour maps of Denn generated from kriged values using the omnidirectional linear model are provided in Figures 29, 31, 35 for adult densities on June 3, 9 and 19, respectively. The standard deviations of these adult estimates are provided in Figures 27,32,36, respectively. Contour maps of egg mass densities on the same dates are provided in Figures 24,37 and the standard deviations of these estimates are provided in Figures 34,38, respectively. Estimates of adult and egg densities correspond in the contour maps, although egg densities seem to be more widely distributed. This may indicate female CPB dispersal or mortality. The strongest population trends are seen on June 9 for eggs and adults Figures 31,33, respectively. These trends are in both a south to north and east to west direction, indicating CPB are probably entering the field from these directions. A large field was in potatoes directly to the east and could be the source of these CPB. Small "hot spots" of adults are apparent along the west edge of the field in Figure 31. One of these hot spots corresponds to a small field adjacent on that side to Denn 1992 that was in potatoes the previous year, and the other hot spot is near a house located next to the potato field. The high density estimated near this house is unusual. Perhaps there was a garden with potatoes at the house last year, or the house could have interfered with the movement of CPB through the field in the previous fall or this spring. The standard deviations for estimates on June 9 for adults are fairly low ranging from 0.02 to 0.14, so we can place some confidence in these estimates. The contour maps produced by geostatistical analysis with an associated measure of variation can be useful in identifying important patterns in CPB colonization of fields. They result in estimates of population density in areas not sampled. Kriging utilizes data from surrounding points, patterns of directional variation and distance between points to make these estimates. Kriging more effectively uses information available from the field of data to interpolate between points than other methods of interpolation. Interpolation methods such as inverse- distance, or inverse-distance squared assume that the relationship between points depends primarily on distance (Clark 1979), and not on complex distance variance relationships as does kriging. Kriging has some potential for direct use in integrated pest management. Spraying only parts of a field, to manage a pest but minimize pesticide use, could be more accurately directed with contour maps of pest density generated by kriging. If chemical or mechanical control is to be used on specific areas of the field, then kriged estimates could be used to more precisely define the points or areas in the field where the density of the CPB are above economic threshold. The contour maps listed above clearly show that spraying the entire field for CPB is not needed. A casual inspection of this field might not reveal these patterns as accurately. One problem with this approach might be that it took 284 samples over a period of 3.5 hours to get the data to generate contour maps of this 20 ha field, although this is only 10.5 minutes per ha. However, if the number of samples could be reduced without compromising accuracy, then it might be even more worthwhile. In this chapter, I showed that edge effects occur more frequently in fields planted early or adjacent to a previous year's potato field. This information could be used to structure sampling schemes that take more samples in fields or sections of fields that are likely to have distinct patterns in CPB. For example, a late-planted and far- rotated potato field would be very unlikely to have edge effects for adult CPB and could be sampled on a widely spaced grid, or a conventional sampling system. On the other hand, an early adjacent field would likely have strong edge effects and the edge effect would likely be on the side of the field nearest to the previous year's potatoes. The side of the field nearest the previous year's potatoes could be sampled the most intensively and the spacing of the samples might be increased as one moves away from that edge. If kriged maps showed any evidence for a contradiction of the anticipated patterns, then sections of the field could be resampled. Further research could also determine the minimum number of samples needed per acre to produce meaningful data sets for kriging. Presently, the methods of collecting and analyzing the two dimensional data required for kriging CPB counts seem cumbersome and difficult. However, with relatively inexpensive devices such as a hand held computer with a geostatistics data entry program and a measuring wheel, the collection and data entry time could be reduced considerably. Semi-variograms could also help us understand CPB colonization behavior. For example, a semi-variogram with pure nugget effect might indicate that CPB are arriving randomly at any point in a field. If any two pairs of sample points are equally likely to have a given number of CPB, then the semi-variance would not change much with increasing lag distance. This seems to most likely occur if 73 colonization is by flight from more than one direction. Walking CPB tend to accumulate in edge rows or areas of the field and this should produce a distinct pattern of variability. Nearest their overwintering site, flying CPB arriving from one direction also accumulate on one edge of the field. A linear semi-variogram model might indicate the steady movement of walking CPB from edge rows across the field. With a linear model, the differences in the numbers of CPB between any two points would increase proportionally with increasing lag distance. The linear model might also indicate arrival by flight from a specific over-wintering site. If flying CPB are not good at host location, some might fly over the field edge and land deeper in the field, and thus no distinct edge accumulation would occur. A semi-variogram with a nonlinear model could result from large and persistent edge effects. With a non-linear model, the differences in the numbers of CPB between any two points would increase sharply with increasing lag distance, then level off at a sill. This could suggest CPB are walking into the field and immediately colonizing plants and dispersing very little after initial colonization. However, it could also result from flying CPB that are able to locate plants guickly after entering the field, and like the scenario just described for walking CPB, they remain on the plants they initially colonize. The anisotropy observed in this study, could also provide information on colonization behavior. Where a linear model was seen in one direction and pure nugget effect in another could suggest CPB are moving into the field in the direction of the linear semi-variogram by one of modes described above. In the direction of the pure nugget semi-variogram, CPB could be entering the field by flight and landing on plants at quite variable distances from the field edge. Alternatively, few CPB could be entering the field in this direction, and the nugget effect may occur because differences in counts taken on a line perpendicular to the primary direction of CPB movemnt are consistant across the entire field, regardless of lag distance. CHAPTER IV The Orientation of Postdiapause Adult Colorado Potato Beetles to Potato Plants Materials and Methods Section A; Live-Plant Colonization Experiments 1991 Experiment I An experiment was initiated on May 10, 1991 to examine the effect of the presence of CPB on the attraction of additional CPB to plants, and to compare the attractiveness to CPB of potato tubers and potato plants. The first hypothesis in this experiment was that plants with CPB already present would attract more CPB than uncolonized plants, by an aggregation pheromone or other means. The second hypothesis was that tubers would attract as many CPB as uncolonized plants, and it tests whether potato tubers might attract and arrest CPB in a potato field before plants emerge from the soil. This experiment was conducted in a recently cultivated field and the design was a randomized complete block with nine replications. The blocking variable corresponded to location in the field and was necessary because of the hypothesized colonization gradient resulting from the arrival of adult CPB from an over-wintering location 15 m to 75 the Northwest. Treatments were replicated twice within each block and plots measured 6.1 m x 6.1 m. The three treatments were as follows: 1) a 25 cm high live potato plant (c.v. 'Katahdin') planted in the plot center, 2) a pile of 5-6 c.v. 'Katahdin' tubers (B sized) located in the plot center, and 3) a 25 cm high live potato plant planted in the plot center with two Colorado potato beetles caged inside a 22 cm wide by 40 cm long nylon mesh bag placed on one stem of the potato plant. On May 12 and May 14, all CPB found on plant or tuber treatments were removed and their numbers recorded. Any leaves with feeding damage or contaminated with frass were also removed. If a plant was severely fed upon, it was replaced. CPB counts were analyzed by ANOVA (Systat, 1991), and treatment means separated by Bonferonni pairwise comparison (Systat, 1991). The percentages of plants infested with one or more CPB in each treatment, were compared by a G-test, assuming a completely random design, (CoStat, 1990). Experiment II An experiment was initiated on May 14 in the same location as experiment I to test the effect of the nylon cages used in Experiment I on CPB colonization of potato plants. The experimental design was a randomized complete block with nine replications. The five treatments were as follows: 1) a 25 cm high potato plant (c.v. /Katahdin/), 2) a 25 cm high potato plant (c.v. 'Katahdin') with two adult CPB marked with purple fingernail polish and wings removed so they would be less likely to leave the plant, 3) a 25 cm live potato plant caged with two CPB as described in Experiment I, 4) a 25 cm high plant caged as in Experiment I, but with no CPB inside, and 5) a pile of tubers as described in Experiment I. Each treatment was replicated once per block, except the tuber treatment, which was replicated twice per block due to an excess of one plot per block. This experiment was sampled in a manner similar to Experiment I on May 15 and May 16. CPB counts were analyzed by ANOVA (Systat, 1991), and treatment groups (cage vs no cage, CPB vs no CPB) were compared using single degree of freedom contrasts (Systat, 1991). The percentages of plants infested with one or more CPB in each treatment were compared by a G-test, assuming a completely random design, (CoStat, 1990). Experiment III An experiment was initiated on May 22, 1991 to further test the effects of the nylon-bag cages in Experiment I on CPB colonization. The location of the Experiment III was the same as that for Experiment I. The experimental design was a randomized complete block with five blocks and two treatments were replicated three times per block. The two treatments were as follows: 1) a 25 cm high plant (c.v. 78 'Katahdin') planted in the plot center, and 2) a plant similar in size to treatment 1 was covered from the top and two sides with a 25 cm wide piece of same nylon mesh used to cage CPB in Experiment I. This cover allowed the odor of the plant to be released, while the visual stimuli were obscured from most angles. This experiment was sampled on May 23 and 24 in a manner similar to Experiments I and II. CPB counts were analyzed by ANOVA (Systat, 1991), and the percentage of plants infested by one or more CPB in each treatment was compared using a G-test (CoStat, 1990). Section B; Live-Plant Colonization Experiment 1992. This experiment was initiated on May 21, 1992 approximately in the center of a 49 m x 42 m oat field. The experiment was designed to test the ability of flying CPB to locate individual potato plants, and the ability of CPB to locate individual plants hidden in a plot of dense oats. The experimental design was a completely randomized design. Four treatments were each replicated 10 times. Individual plots were 3.1 m x 3.1 m. Fifteen meters to the northeast of the experimental site was a 1 ha field that was in potatoes the previous year and served as a source of colonizing beetles for this experiment. The four treatments were as follows: 1) a single potato plant (c.v. 'Katahdin') planted in the center of a of plot mowed to bare soil, 2) a 79 single potato plant (c.v. 'Katahdin') planted in the center> of a of plot with a dense stand of 0.75 in high immature oat plants, 3) a single potato plant (c.v. 'Katahdin') planted in the center of a plot mowed to bare soil and the potato plant surrounded by a 12.5 cm high x 45 cm diameter circular aluminum flashing barrier, sealed at soil level and the upper rim coated with TanglefootR to prevent walking beetles from reaching the plant, 4) a single potato plant (c.v. 'Katahdin') planted in the center of a of plot with oats as described above, and the potato plant surrounded by a circular aluminum flashing barrier as described above. The experiment was sampled twice daily (morning and evening) except weekends, from May 22 to June 26. The number of beetles on each plant was recorded and all beetles were removed from plants after sampling. CPB counts were analyzed by ANOVA (Systat, 1991), and treatment means were compared by Bonferonni pairwise comparison (Systat, 1991). The percentages of infested plants in each treatment were compared by a G-test (CoStat, 1990). Section C: Yellow Flight Traps Large Flight Traps On April 17, 1991, two large flight traps were placed 0.4 km apart to monitor flight activity next to a potato field. Flight traps were 2.4 m tall and 0.7 m wide. The top 1.8 m of the trap was fitted with a sheet of clear 80 plexiglas with a yellow backing for CPB attraction, and a 20 cm x 70 cm wide metal trough (filled with anti-freeze) was located below the backing to collect flying CPB that collided with the yellow pane. The wooden legs of the traps were coated with Tanglefoot11 to prevent walking beetles from entering the trough. The traps were sampled every other day and all beetles were removed. Small Flight Traps On May 15, 1991, eight small flight traps were placed along the edges of two fields to test the hypothesis that an odor source directly below the visual traps would increase the CPB catch. Traps were constructed by mounting perpendicular yellow plastic vanes (15 cm high x 12 cm wide) into the open end of an opaque white plastic 1 gallon jar. Inside four jars was a 15 cm high potted potato plant to serve as an odor source. All traps had a band of TanglefootR around the base to prevent walking beetles from entering the traps. Four flight traps, traps with odor source alternated with non-odor source traps, were placed 6.1m apart in a row along the east edge of a recently plowed field. Four more traps spaced and alternated in a similar manner were placed along the west edge of an adjacent recently plowed field. Traps were sampled daily and all beetles were removed. 81 On May 22, the traps were moved to a nearby 25 m by 25 m field that had potatoes in it the previous year in an effort to increase the catches of flying CPB. Two traps, one with odor source and one without, were evenly spaced along each edge of the field. The traps were sampled in a similar manner to that described above. Section D; Artificial-Plant Orientation Experiment An experiment was initiated on May 15, 1992 to test the effects of potato plant odor, form, and color on orientation of the Colorado potato beetle. The first hypothesis of this experiment was that orientation of the CPB to host plants is visual and models without odor would catch as many or more CPB than real plants. The second hypothesis was that plant form would be important in CPB host plant orientation and that plant models would catch as many or more CPB than yellow cylinders. The third hypothesis was that color is important in CPB host orientation, and yellow plant models would catch more CPB than green plant models. The experimental design was a randomized complete block with seven blocks and each treatment (models or real plants) was replicated twice within each block. The blocks were arranged from north to south, because a 1 ha field that was in potatoes last year was located 30 m to the north. It was expected from past experience that the beetles that had over-wintered in this field would enter the experimental field from the north and the experimental design must be able to handle this potential north to south gradient of beetle colonization. The treatments were as follows: 1) a no model control, 2) a 13.5 cm high x 12.5 cm diameter plastic cylinder painted with Dutch yellow (253) acrylic gloss enamel (Red DevilR), 3) a 15 cm high real potato plant (c.v. 'Katahdin') growing in a small covered pot (9 cm high by 10 cm diameter), 4) a 15 cm high green potato plant model made from artificial green silk plant foliage (Designer SilkR, Philodendron, Leeward's Store #800423) with six leaves cut to the shape of a potato plant. The leaves, paired in order from bottom to top, were approximately 8 cm long x 7.5 cm wide, 6 cm x 5.5 cm and 5 cm x 4.5 cm, and 5) a 15 cm high yellow potato plant model. The yellow models were made from green plant models painted with the same yellow paint as the plastic cylinders. The traps below each treatment were constructed by first cutting a 19 L bucket to a height of 20.5 cm and diameter of 28.5 cm. These buckets were buried, in a recently plowed field, so that the rim was flush with the soil surface. Buckets were spaced 3.1 m apart both within a block and between blocks. Smaller buckets (20.5 cm high and 24 cm diameter), with five small screen covered openings in the bottom to permit the movement of soapy water (A11R dye- free, perfume-free liquid laundry detergent), were placed inside each one of the larger buckets. Two pieces of wire 83 were used to hold the rim of the inner bucket at exactly 2 cm from the rim of the outer bucket. The sections of these wires between the inner and outer buckets were coated with TanglefootR to prevent walking CPB from reaching the inner bucket. The plant models were suspended using wire directly over the center of the inner bucket. In the case of the live plant, the small pot was wired so that the top of the pot was level with the inner bucket, so the real plant was the same height as other treatments. The trap was designed so that beetles that oriented directly to the model by flight and attempted to land on it would fall within the center bucket. Any beetles that attempted to reach the model by walking would fall into the outer bucket. Thus, the traps would distinguish between beetles that oriented directly to the model by flight, and those that either walked to the model or flew and landed near the model and walked to it. All traps were sampled two or three times per day each day except weekends. The numbers of CPB caught in all inner or outer traps were recorded at each sampling. For the last sample of each day and on Monday mornings, all CPB were removed from the traps and placed in containers labeled with the treatment type and whether the beetle was caught in the inner or outer bucket. At the end of the experiment all beetles were dissected to determine sex. 84 CPB counts were analyzed by ANOVA (Systat, 1991), and treatment means compared using orthogonal contrasts (Systat, 1991). Percent reflected light from 400 to 700 nm was taken on samples of all model and real plant surfaces using a Baush and Lomb, Spectronics 20 with a percent refectance attachment. Results and Discussion Section A: Live-Plant Colonization Experiments 1991 Experiment I Both the mean numbers of CPB and the percent of infested plants were significantly lower on the plants caged with beetles for both dates pooled (Table 18). On both May 12 and 14, the percentage of infested plants were significantly lower on the plants caged with beetles (Table 18). These were unexpected results. A reduction of CPB could have been due to the presence of beetles or the large nylon bags which might have visually blocked the plants from searching beetles. Based on the results of this experiment, Experiment II was designed to determine if the presence of the beetles, the cage, or both caused a reduction of beetle colonization. 85 Table 18. Colonization Experiment 1-1991. Treatment May 12 May 14 Pooled (Plant) Mean CPB 7.88±2.45 a 7.17±1.30 a 7.53±1.37 a % Colonized 72 ** 89 * 81 *** (Plant/CPB/Bag) Mean CPB 3 . 89±1.89 a 3.83±1.40 a 3 . 86±1.16 b % Colonized 22 61 42 (Tubers) Mean CPB 0.00±0.00 b 0.00±0.00 b O.OOiO.OO c % Colonized 0 0 0 Means in a column followed by the same letter are not significantly different (df=2,45, F = 15.225, Bonferroni pairwise comparison, P = 0.05). Asterisks = G-test comparison of percent colonized between plant and plant/CPB/bag treatments only. * = significantly higher at P < 0.05, ** = P < 0.005 and *** = P < 0.001. Experiment II Table 19 lists the results for each treatment. However, to properly assess the results for this experiment, common factors such as caged or not caged and CPB or no CPB can be pooled together as a contrast (Table 20). The mean numbers of beetles per plant were not significantly different between caged and uncaged (df=l,68, F = 3.226, P = 0.077). The mean number of CPB on plants without CPB already on them was slightly higher, but the difference was not significant (df = 1,68, F = 1.725, P = 0.193). Neither the percent infested plants for cage vs. no cage (P=0.09), or CPB vs. no CPB (P=0.49) was significantly different (Table 20). Results for this experiment do not conclusively determine whether the cages or the CPB caused the reduction in percent infestation or mean numbers of CPB observed on caged plants in Experiment I. This experiment does not prove, but suggests that, the reduction in beetles on the caged plants was due to the cage. 87 Table 19. Colonization Experiment 11-1991. Treatment May 15 May 16 Pooled (Plant) Mean CPB 6.89±3.32 1.33±0.65 4.11±1.77 % Colonized 78 56 67 (Plant/CPB) Mean CPB 1.22±0.46 2.33±1.72 1.77±0.88 % Colonized 67 56 61 (Plant/Bag) Mean CPB 1.44±0.53 1.11±0.77 1.27±0.46 % Colonized 67 33 50 (PIant/CPB/Bag) Mean CPB 1.33±0.78 0.44±0.24 0.89±0.41 % Colonized 44 33 39 (Tubers) Mean CPB 0 .00±0.00 0 .00±0 .00 O.OOiO.OO % Colonized 0 0 0 88 Table 20. Experiment II, 1991. Main effects of treatments for both sample dates pooled. Mean(±SE) % Infested Contrast CPB/Plant Plants Cage vs 1.08±0.30 44 No Cage 2 .94±1.00 64 CPB vs 1.33±0.63 50 No CPB 2.69±0.83 58 Experiment III Both the percentage colonization (P< 0.01) and mean numbers of beetles per plant (df = 1,28, F = 5.03, P = 0.03) for the two dates pooled (Table 21) were significantly higher on uncovered plants. This indicates that the cover did significantly reduce both the total number of CPB finding the potato plants and the number of plants found by one or more CPB. I conclude that host orientation can not be primarily olfactory, because I assume that CPB could equally detect and follow the odor plume of either covered or uncovered plants and find either with minimal searching effort, probably with much less effort than finding a host plant in a heterogenous plant community. If olfactory cues were of primary importance, I would expect nearly equal numbers of CPB for the two groups. 89 Table 21. Colonization Experiment III-1991. Treatment May 23 May 24 Pooled (Plant) Mean CPB 4.23 3.80 4.03 % Colonized 60 80 70 (Plant/Covered) Mean CPB 0.73 1.00 0.87 % Colonized 27 20 23 The best explanation for these large differences that is consistent with the results of the previous two experiments is that vision plays an important role in host orientation by the CPB. In this experiment, the nylon bags may have interfered with tactile cues or physically impeded the searching CPB. However, in Experiment I, the nylon mesh bags were only on one stem of the plant and were well off the ground, so the effect of the nylon bags on the tactile senses or physical interference with walking or even flying CPB would have been negligible. Yet in Experiment I, plants without the nylon bags caught significantly more beetles than plants with bags. The results from Experiment II imply that the bags were responsible for the reduction of beetles in Experiment I. In this experiment, CPB were observed in a few instances resting on the nylon bags and some covered plants did attract CPB. It is possible that the bags gave off some disagreeable odor, but if so it would probably be much less 90 Figure 7 Mean numbers of CPB caught during season in plant colonization experiment, 1992. Adult CPB per plant 80 - 0 .8 0 40 - 0 .4 0 0.00 - 0 .6 0 0.20 1.00 - U R U HR HU OR OU Figure 7 Figure pn Restricted Open pn Unrestricted Open idn UnRestrict. Hidden idn estricted R Hidden 92 than a CPB would encounter searching for host plants amoung non-host species. Section B: Live-Plant Colonization Experiment 1992. Mean numbers of adult CPB were higher on every sample date on unrestricted plants surrounded by bare soil (OU) than on any other treatment. Results pooled over all sample dates are presented in Figure 7. The OU treatment for pooled data is significantly higher than any other treatment (P < 0.001). Oats apparently disrupted the searching CPB. The disruption of CPB by the oats could be due to visual, olfactory or physical factors. The effects of the aluminum flashing indicate that CPB are either unable to land or orient directly to an individual potato plant, and that most individual plants are colonized by walking beetles. Because this experiment was located immediately adjacent to a large over-wintering site of CPB, and based on results in Chapter IV (Section A: pattern of infestation) on potato fields adjacent to over-wintering sites, large numbers of beetles could have been searching this area for host plants. Only 38% of OU plants were located by one or more CPB during this experiment (Figure 8). Figure 9 shows percent colonization plotted on a daily basis. CPB were never found on all 10 plants of any treatment on any sample date. These results could be interpreted in several ways. 93 Figure 8 Total infestation by CPB during season in plant colonization experiment, 1992. Percent of Plants Infested OU OR Figure 8 Figure HU idn Restricted Hidden pn Unrestricted Open pn Restricted Open idn Unrestrict. Hidden HR vo 95 Figure 9. Daily totals of plants infested during plant colonization experiment, 1992. "D 10 r 0 N C 0 8 - O U May 22 June 5 June 25 Date o — Open + Open •••<>••• Hidden —&— Hidden U. R. U. R. Figure 9 VO OV If large numbers of CPB were searching the area, then the dense stand of oats surrounding the experiment could have been a barrier to some walking CPB entering the experimental area. Flying CPB could also have passed over the entire oat field without landing and attempting to search the bare plots within the oats. If large numbers of CPB did enter the plots, many may have dispersed quickly, after initially failing to locate potato plants. Alternatively, CPB might not have dispersed after initially failing to locate a host, but were repeatedly searching the same area for host plants. However, few CPB were observed searching in the plots. Section C: Yellow Flight Traps Large Flight Traps Four CPB were trapped between April 17 and May 22. Two CPB were caught in the trap located on the OARDC Fry Farm on May 10 and 12. However, during this period many CPB were observed flying in the area, so it was concluded that these traps were not catching a very high percentage of the CPB flying in the area. Small Flight Traps Small flight traps captured CPB on May 15 and 16, 1991. The total catch for traps with plants inside was six CPB and traps without plants was five. These catches were too low 98 to draw any firm conclusions, and no trends were apparent. After May 16, no CPB were caught in any traps for five days and the traps were placed around the perimeter of an adjacent field, with two traps of each type on a common side of the field. Only one CPB was caught at this new location. In both locations, CPB could be found around the bases the of traps. I reasoned that if the traps were at ground level and the trap opening larger, the catch would be much higher. This ground level trap design was successfully adopted in the artificial plant orientation experiment. Section D: Artificial Plant Orientation Experiment The full results of this experiment are provided in Tables 22 and 23. No differences between male and female responses to models or real plants were observed. The inside bucket or outside bucket of all model types caught approximately 50% males and 50% females. Nearly 100% of beetles were trapped between noon and 6 p.m. This indicates that under the conditions of this experiment most of the CPB were searching for hosts in the afternoon and very little searching activity occured at other times of the day. The mean high daily temperature during this experiment was approximately 22.7°C. The 93 year averages for these same dates ranges from 21.2° to 26.2°C, so the temperatures during this experiment were cooler than normal. In Figure 99 Figure 10. Total daily CPB caught in bucket traps for artificial plant experiment. i \\ i \ / \ / \ i i » ; V / : v. 1 : V- 1 : \'- 1 : \'- 1: \ I: \ ’ • ; l: \ \ • / l: \ / / ^ i yi-l 1 1 \— J-— i 1—\— v.--- May 18 May 29 June 1 — In +• • • Out 0 T emp. Buckets Buckets Deg. C Figure 10 100 101 10, mean daily temperature is plotted against the number of CPB caught in the flying or walking bucket traps each day during this experiment. No capture of flying CPB occurred on days with a mean high temperature below 18°C in this experiment. This value is similar to flight initiation temperatures found by other researchers. Caprio and Grafius (1990) recorded flight initiation in CPB adults at temperatures as low as 15°C, while Johnson (1969) found a reported flight initiation temperature of 17°C. Flight in CPB in our experimental area could have occurred below 18°C, but CPB only began showing up in these flight traps when the daily high temperature were above 18°C. Results of this experiment were analyzed using contrasts to compare factors that might affect the orientation of the CPB to host plants. Numbers of CPB captured in the real plant traps were not significantly different than the green model for flying (inside buckets) CPB (df = 1,1325, F = 0.545. P = 0.461) or total CPB (inside plus outside buckets), (df = 1,2655, F = 3.06, P = 0.08). CPB numbers in the outside buckets alone were not analyzed, because this group also includes some flying CPB that landed close to the model and walked in, as well as CPB that walked the entire distance to the model. Because the size, shape and color were similar for both models, and the only major difference between these two models was odor, I hypothesize Figure 11. Combined CPB catch for treatments during season for artificial plant experiment. 12 YC = Yellow Cylinder YM = Yellow Model GM = Green Model RP = Real Plant CN = Control YC YM GM RP CN Model Type Figure 11 H O u Figure 12. Flying CPB catch for treatments during season for artificial plant experiment. YC = Yellow Cylinder YM = Yellow Model GM = Green Model RP = Real Plant CN = Control GM RP CN Model Type Figure 12 H o U1 106 that odor is not a major factor in the orientation of CPB to potatoes. In general, both of these treatments caught few beetles (Figures 11 & 12). The yellow plant model captured significantly more flying CPB (df = 1,1325, F= 13.6, P < 0.001) and total CPB (df = 1,2655, F = 9.09, P = 0.003), than the green plant model. Because these treatments differed only by color, while shape and height were identical, I conclude that color is an important factor in host orientation; particularly in flying CPB. The yellow model captured significantly more flying CPB than the real plant (df = 1,1325, F = 8.7 ,P = 0.003). In this case, an artificial plant with no odor caught more CPB than real plants of the same size and shape. The Yellow cylinder lure caught significantly more flying CPB (df = 1,1325, F = 44.1, P < 0.001) or total CPB (df = 1,2655, F = 39.3, P < 0.001) than the yellow model. The yellow cylinder model differed from the yellow plant model in that it had no potato plant shape, but had more surface area of yellow color. I hypothesize that the amount of the appropriate color (yellow) is more important than plant shape in attracting CPB, and finer details of plant structure are not important stimuli for CPB host orientation. The average number of CPB captured by the three models and the real plant was significantly greater than the catch Figure 13. Percent reflectance of model surface for artificial plant experiment. I I Percent Reflected Light 100 0 8 0 6 0 4 20 0 0 4 -— Yellow --Q— Cylinder 0 6 4 h — Real Plant 0 2 5 aeegh (nm) Wavelength Figure 13 Figure 0 E* Q- Q 'Q-- ET* ,0 A JP" ^ ^ " P J -A- Green • • o A "= A '"{=£ -A— Model — 05 0 7 0 4 6 0 8 a — -- Yellow Model 108 109 in the no model control for flying (df = 1,2655, F = 30.4, P < 0.001) and total (df = 1,2655, F= 32.1, P < 0.001) CPB. The no model control caught almost no beetles for the entire experiment (Figure 11, 12). CPB oriented to the models and plants used and the numbers falling into the traps while passing through the experimental area was minimal. The trapping efficiency of the models used in this experiment were not equal. It is possible that some CPB could have landed on the green or yellow plant models and flown away, although this was never observed. CPB could more easily land on the top of the yellow cylinder model than other treatments and fly away, and this was observed on one occassion. Furthermore, the area of the inner bucket open below the yellow cylinder model was less than all other treatments, so this should have actually reduced the catch of flying CPB for this model. The sides of the yellow cylinder, however, would be more difficult to land on than any of the other models or the real plant. CPB could feed on the real potato plants after landing, and after feeding on the potato foliage they would be more likely walk off the plant than fly (Caprio and Grafius, 1990). This should have given the real plants an advantage over all plant models. Escapes by walking CPB should have been minimal from all treatments, because CPB were observed having trouble walking on and would frequently fall off the type of wire that was 110 used to support the plants and plant models over the center of the inner bucket. Percent reflectance data is presented in Figure 13. The reflectance curves for the yellow cylinder and yellow plant models are very similar, and the reflectance curves for the real potato plants and green plant models are also nearly identical. The refectance curves indicate that the green plant model was a good mimic of the real plant in terms of percent of each light wavelength reflected. Because the percentage of light reflected at every wavelength from 400 to 700 nm is higher in the yellow cylinder models and yellow plant models than the real plants or green plant models, the overall brightness may also play a role in attracting CPB. CPB could be responding to yellow, because of the hue contrasts might play a stimulus role in distance detection by insects of vegetated vs non vegetated areas (Prokopy and Owens 1983). The brightness of the yellow stimulus could also play a role in the contrast between vegetated vs non-vegetated areas. The results of the artificial plant experiment are in agreement with those of Experiment I 1992. In Experiment I, CPB seldom colonized of potato plants that were surrounded by bare soil but were collared to prevent walking CPB from reaching them. In the artificial plant experiment, at least 57% of the CPB caught by the yellow cylinders flew directly to them, at least 51% of the CPB caught by the yellow plant models flew directly to them, at least 24% of the CPB (actual numbers were low) caught by the real plants flew to them, 0 % of the CPB caught by the green plant models were caught in the inner (flying) buckets, while too few CPB were caught in the control traps to conclude anything. Figure 10 shows that CPB were flying in the area while Experiment I was being conducted. CPB orient by flight best to bright yellow objects (such as the yellow cylinder or yellow plant models) of larger size or that are visually unobscured. CPB may have a limited ability to orient by flight directly to seedling or small potato plants that have green or dark green foliage. However, the larger the potato plant or the yellower the foliage, then the ability of flying CPB to orient directly to them should be better. Table 22. Daily mean (±SE) catches of adult CPB for inside traps (flying beetles) for artificial plant orientation experiment, 1992. Trap May 18 May 19 May 20 May 21 YC 0.29±0.16 0.71i0.16 0.50i0.17 1.1410.29 YM 0.00±0.00 0.50i0.14 0.14i0.10 0.5010.20 GM O.OOiO.OO O.OOiO.OO O.OOiO.OO O.OOiO.OO RP O.OOiO.OO O.OOiO.OO O.OOiO.OO 0.1410.10 CN 0.00±0.00 O.OOiO.OO O.OOiO.OO O.OOiO.OO Trap May 22 May 25 May 26 May 27 YC 1.36±0.48 0.14i0.10 O.OOiO.OO O.OOiO.OO YM 0.36±0.13 O.OOiO.OO O.OOiO.OO O.OOiO.OO GM O.OOiO.OO O.OOiO.OO O.OOiO.OO O.OOiO.OO RP 0.14±0.10 0.07i0.07 O.OOiO.OO O.OOiO.OO CN O.OOiO.OO O.OOiO.OO O.OOiO.OO O.OOiO.OO Trap May 28 May 29 June 1 June 2 YC 0. 42i0.20 O.OOiO.OO O.OOiO.OO 1.1410.35 YM 0.07i0.07 O.OOiO.OO O.OOiO.OO 0.3610.17 GM O.OOiO.OO O.OOiO.OO O.OOiO.OO O.OOiO.OO RP 0.OOiO.OO O.OOiO.OO O.OOiO.OO O.OOiO.OO CN O.OOiO.OO O.OOiO.OO O.OOiO.OO 0.1410.14 Trap June 3 June 4 June 5 June 7 YC 0.6410.27 O.OOiO.OO O.OOiO.OO 0.1410.10 YM 0.0710.07 O.OOiO.OO O.OOiO.OO 0.2910.16 GM O.OOiO.OO O.OOiO.OO O.OOiO.OO O.OOiO.OO RP O.OOiO.OO O.OOiO.OO O.OOiO.OO 0.0710.07 CN 0.0710.07 O.OOiO.OO O.OOiO.OO O.OOiO.OO Trap June 8 June 9 June 10 June 12 YC 0.36i0.17 O.OOiO.OO O.OOiO.OO 0.0710.07 YM 0.0710.07 O.OOiO.OO O.OOiO.OO 0.1410.10 GM O.OOiO.OO O.OOiO.OO O.OOiO.OO O.OOiO.OO RP 0.0710.07 O.OOiO.OO O.OOiO.OO 0.0710.07 CN O.OOiO.OO O.OOiO.OO O.OOiO.OO O.OOiO.OO Note: YC = Yellow cylinder model, YM = Yellow plant model, GM = Green plant model, RP = Real plant and CN = No lure control. 113 Table 23. Daily mean (±SE) catches of adult CPB for outside traps (walking beetles ) for artificial plant orientation experiment, 1992. Trap May 18 May 19 May 20 May 21 YC 0.07±0.07 0.50i0.17 0.14i0.10 0.79i0 64 YM 0.07±0.07 O.OOiO.OO 0.07i0.07 0.29i0 17 GM 0 .07±0.07 0.07i0.07 0.07i0.07 O.OOiO 00 RP O.OOiO.OO 0.21i0.11 0.21i0.11 0.14i0 10 CN O.OOiO.OO O.OOiO.OO O.OOiO.OO O.OOiO 00 Trap May 22 May 25 May 26 May 27 YC 0.79i0.33 0.71i0.57 O.OOiO.OO O.OOiO 00 YM 0.42i0.20 0.43i0.25 O.OOiO.OO O.OOiO 00 GM 0.21i0.11 0. 36i0.18 O.OOiO.OO O.OOiO 00 RP 0.36i0.20 0.50i0.20 O.OOiO.OO O.OOiO 00 CN 0. 07i0.07 0.14i0.10 O.OOiO.OO O.OOiO 00 Trap May 28 May 29 June 1 June 2 YC 0.14i0.14 O.OOiO.OO O.OOiO.OO 0.64i0 27 YM 0. 07i0.07 O.OOiO.OO O.OOiO.OO 0.14i0 14 GM 0. 07i0.07 O.OOiO.OO O.OOiO.OO O.OOiO 00 RP O.OOiO.OO O.OOiO.OO O.OOiO.OO O.OOiO 00 CN O.OOiO.OO 0.07i0.07 O.OOiO.OO O.OOiO 00 Trap June 3 June 4 June 5 June 7 YC 0.29+0.29 O.OOiO.OO O.OOiO.OO 0.14i0.14 YM 0.42i0.23 0.07i0.07 O.OOiO.OO 0.14i0.10 GM O.OOiO.OO 0.14i0.10 0.07i0.07 0.07i0.07 RP 0. 07i0.07 0.07i0.07 O.OOiO.OO 0.29i0.16 CN O.OOiO.OO O.OOiO.OO O.OOiO.OO O.OOiO. 00 Trap June 8 June 9 June 10 June 12 YC 0. 07i0.07 0.14i0.10 O.OOiO.OO 0.43i0.36 YM 0.14+0.10 O.OOiO.OO O.OOiO.OO O.OOiO. 00 GM 0.14i0.14 0.14i0.10 0.07i0.07 O.OOiO. 00 RP O.OOiO.OO 0.07i0.07 0.07i0.07 0.07i0.07 CN 0.07i0.07 O.OOiO.OO O.OOiO.OO 0.07i0.07 Note: YC = Yellow cylinder model, lure, YM = Yellow plant model, GM = Green plant model, RP = Real plant and CN = No lure control. CHAPTER V Summary and Conclusions This research supports the following results from previous studies (Caprio and Grafius, 1990) : if the temperature is warm enough (15°C to 18°C) many postdiapause CPB are capable of searching for host plants or dispersing to new habitats by flight. The results of Chapter 3 demonstrate that postdiapause CPB are capable of flight several days after emerging from the ground and can fly without feeding or ovipositing. This contrasts with summer generations of CPB that must feed after emerging from the pupal stage before flight is possible. Most of the research on host location in CPB has only focused on walking CPB, but any pest management strategy based on disrupting CPB dispersal or controlling CPB on field edges must take flying CPB into account. Host location by the Colorado potato beetle (CPB) is not a chance or random event. It has been demonstrated by others (Thiery and Visser, 1987) that walking CPB can orient at least over short distances to green leaf volatiles of potato foliage. Results of the artificial plant trapping experiment in Chapter 4 demonstrate clearly that flying or walking CPB seldom land in (no model) control traps, but 114 significantly greater numbers do get caught in traps with different types of models. However, fine details of plant shape do not appear to be important, because yellow cylinders caught significantly more CPB than yellow plant models. In live-plant colonization experiments (Chapter 4), visually obscured plants were colonized less frequently than unobscured plants. I conclude that size and color are the two most important cues that CPB use to orient to potato plants. Based on the results of plant colonization experiments, cartures of flying CPB in flight traps with models containing no odor, and flight trap captures descibed in chapter 4, I conclude that olfactory cues appear relatively unimportant to flying CPB. This research does not contradict research that olfactory cues are important for walking CPB. I hypothesize that visual cues, as described above, are also important to walking CPB. I have demonstrated that edge effects are present in most fields that border a field that was in potatoes the previous year, particularly when planted early. These edge effects persist over time, but become less distinct as more CPB disperse into center sections of the field. The results of the post-colonization movement studies suggest that CPB move frequently from plant to plant. In pattern of infestation studies, plants were often found with eggs but no adults. Contour maps of CPB density produced by kriging (Denn 1992) confirmed this broader distribution of eggs than 116 adults in a potato field, and imply that female CPB move from plant to plant. Therefore the process of dispersal into a potato field by postdiapause CPB continues after initial host location. Control strategies directed at large CPB populations on the edges of potato fields must take this CPB mobility into account. Flight studies (Chapter 2), although not done with postdiapause CPB, suggest that CPB that move around a field after initial colonization do so by walking, since well fed CPB are not likely to fly. Semi-variograms can give us insight into CPB colonization patterns and host-seeking behavior by illustrating and quantifying directional patterns of variability. Distinct patterns of variability between sample points of increasing lag distance apart could result from specific colonization conditions, processes or behaviors. 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Dalsze badania nad mikromigracjami stonki ziemniaczanej (Leptinotarsa decemlineata Say.).Rocznoki Nauk Rolniczych 78: 95-122. 122 Zehnder G.W. and J.L. Linduska. 1987. Influence of conservation tillage practices on populations of Colorado potato beetle (Coleoptera: Chrysomelidae) in rotated and non-rotated tomato fields. Environ. Entomol. 16: 135-139. Zehnder G.W. and J. Speese III. 1987. Assessment of Color response and flight activity of Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae) using window flight traps. Environ. Entomol. 16: 1199- 1202. Zehnder G.W. and G.K. Evanylo. 1989. Influence of extent and timing of Colorado potato beetle defoliation on potato tuber production in Eastern Virginia. J. Econ. Entomol. 82: 948-953. Zehnder G.W. and J. Hough-Goldstein. 1989. Use of straw mulch for suppression of Colorado potato beetle populations in potatoes. Virginia Coop. Ext. Serv. 44: 2-3. APPENDIX Table 24. CPB densities for sections of commercial field Rho, 1990. May 23 May 30 Field CPB CPB Section N /Plant N /Plant Center 20 0.23+0.09 20 0.08+0.22 North Edge 20 0.60±0.30 14 0.64+0.25 South Edge 20 0.33+0.13 22 0.5 5+0.22 East Edge* 20 1.45+0.2 8 21 1.29+0.42 West Edge 20 0.00+0.00 21 0.19+0.11 June 7 June 13 Field CPB Section N /Plant N /Plant Center 20 0.55+0.2 3 20 0.90+0.22 North Edge 20 0.7 0+0.19 20 0.90+0.22 South Edge 22 0.23+0.09 40 0.55+0.15 East Edge* 22 1.13+0.3 0 20 2.00+0.3 6 West Edge 20 0.30+0.18 20 0.00+0.00 * = edge bordering previous years potato field. Table 25. CPB densities for sections of commercial field Rho II, 1990. June 7 Field CPB Section N /Plant Center 30 1.2 6±0.21 North Edge* 30 3 .40+0.36 * = edge bordering previous years potato field. T&ble 26. CPB densities for sections of commercial field Rho III , 1990. June 7 Field CPB Section N /Plant Center 30 1.50+0.30 South Edge* 30 2.77±0.48 * = edge bordering previous years potato field. Table 27. CPB densities for commercial field Don III, 1990. June 14 Field CPB Section N /Plant Center 30 0.50+0.17 North Edge 20 0.25+0.12 S. West Edge* 20 0.70+0.23 N. East Edge* 20 1.60+0.33 * = edge bordering previous years potatoes Table 28. CPB densities for sections of commercial field Mooext, 1990. June 1 June 7 Field CPB CPB Section N /Plant N /Plant Center 24 0.42+0.17 30 0.30+0.17 West Edge* 20 2.00+0.45 20 1.25+0.24 June 14 Field CPB Section N /Plant Center 20 0.10±0.07 West Edge* 20 0.90+0.18 * = edge bordering previous years potato field. Table 29. CPB densities for sections of commercial field Moo, 1990. June 1 June 7 Field CPB CPB Section N /Plant N /Plant Center 15 0.07+0.07 20 0.40±0.15 North Edge 20 0.32+0.19 20 0.65+0.21 South Edge 22 0.00+0.00 20 0.50+0.21 East Edge* 20 0.10+0.07 20 0.35+0.18 West Edge 22 0.14+0.07 20 0.30+0.11 June 14 June 21 Field CPB CPB Section N /Plant N /Plant Center 20 0.15+0.08 20 0.00+0.00 North Edge 20 0.15+0.08 20 0.10±0.07 South Edge 20 0.10±0.07 20 0.05+0.05 East Edge* 20 0.40+0.17 20 0.25±0.12 West Edge 20 0.10+0.07 20 0.05+0.05 * = edge nearest to previous years potatoes Table 30. CPB densities for commercial field Don, 1990. June 14 July 5 Field CPB CPB Section N /Plant N /Plant Center 20 0.20+0.16 20 0.35+0.18 North Edge 20 0.60+0.17 20 0.40+0.18 S. West Edge* 20 0.50+0.14 20 0.35+0.15 S. East Edge 20 0.25+0.14 20 0.40+0.18 * = edge nearest previous years potatoes Table 31. CPB densities for OARDC field Fry 1, 1990. June 12 June 22 Field CPB CPB Section N /Plant N /Plant Center 20 0.2 5±0.20 20 0.20+0.09 North Edge 20 0.05+0.05 20 0.25±0.14 South Edge 20 0.30+0.13 20 0.45+0.17 East Edge 20 0.25+0.16 20 0.15±0.11 West Edge 20 0.30+0.13 20 0.05+0.05 July 6 Field cpb Section N /Plant Center 20 0.15+0.08 North Edge 20 0.05+0.15 South Edge 20 0.05±0.05 East Edge 20 0.15±0.08 West Edge 20 0.10+0.07 * = nearest in potatoes previous year not known. Table 32. CPB densities for OARDC field Fry 3, 1990. June 22 July 3 Field CPB CPB Section N /Plant N /Plant Center 20 0.20+0.14 20 0.20+0.12 North Edge 20 0.10+0.07 20 0.15+0.11 South Edge 20 0.00+0.00 20 0.35+0.15 East Edge 20 0.05+0.05 20 0.40+0.21 West Edge 20 0.00+0.00 20 0.55±0.17 July 13 June 18 Field CPB CPB Section N /Plant N /Plant Center 20 0.05+0.05 20 0.05+0.05 North Edge 20 0.15+0.11 20 0.05±0.05 South Edge 20 0.15+0.08 20 0.15+0.08 East Edge 20 0.25+0.09 20 0.00+0.00 West Edge 20 0.30+0.13 20 0.00+0.00 * = nearest in potatoes previous year not known. Table 33. CPB densities for commercial field Don 3, 1991. May31 July 9 Field CPB CPB Section N /Plant N /Plant Center 30 0.47+0.13 30 0.80+0.14 North Edge 30 0.67+0.16 30 0.40+0.11 S.West Edge* 30 0.43+0.13 30 1.10+0.26 S.East Edge** 30 1.17+0.27 30 0.87+0.19 * = Field not rotated, but edge bordered previous years potato field. ** = Edge bordered woods. Table 34. CPB densities for commercial field Don 1, 1991. May 17 May 23 Field CPB CPB Section N /Plant N /Plant Center 50 0.06+0.03 50 1.22+0.20 West Edge* 50 0.36+0.09 50 1.64+0.37 May 30 Field CPB Section N /Plant Center 50 0.45+0.14 West Edge* 50 0.68+0.15 * = edge bordering previous potatoes Table 35. CPB densities for commercial field Don 2, 1991. May 23 Field CPB Section N /Plant Center 30 0.73+0.13 North Edge 30 1.13±0.25 South Edge 30 0.80+0.17 East Edge* 30 0.90+0.14 West Edge* 30 1.13+0.22 * = edge bordering previous years potatoes Table 36. CPB densities for commercial field Rho 1, 1991. May 31 Field CPB Section N /Plant Center 30 0.87+0.21 North Edge* 30 0.67+0.14 South Edge 30 0.70+0.15 East Edge* 30 2.20+0.34 West Edge 30 0.40+0.20 * = edge bordering previous years potatoes. North Edge only party borders last years potatoes. Table 37. CPB densities for commercial field Rho 3, 1991. June 3 Field CPB Section N /Plant Center 30 0.57+0.20 West Edge* 30 1.37±0.29 South Edge 30 0.57+0.13 N. East Edge* 30 1.50+0.31 S . West Edge 30 0.43±0.19 * = edge bordering previous years potatoes. Table 38. CPB densities for commercial Rho 2, 1990. May 30 June 9 Field CPB CPB Section N /Plant N /Plant Center 30 0.16+0.08 30 0.13+0.06 North Edge 30 0.59+0.19 30 0.34+0.11 South Edge* 30 0.38+0.12 30 0.72+0.20 East Edge 30 0.31+0.13 30 0.25+0.11 West Edge 30 0.31+0.10 30 0.28+0.11 * = nearest edge to previous years potatoes. Table 39. CPB densities for OARDC field Synder, 1991. May 17 May 30 Field CPB CPB Section N /Plant N /Plant Center 20 0.00+0.00 30 0.30+0.15 North Edge 20 0.00+0.00 30 0.13+0.06 South Edge 20 0.00+0.00 30 0.03+0.03 East Edge 20 0.00+0.00 30 0.00±0.00 West Edge 20 0.00+0.00 30 0.07+0.05 June 9 Field CPB Section N /Plant Center 30 0.13+0.08 North Edge 30 0.27+0.11 South Edge 30 0.13+0.09 East Edge 30 0.27+0.12 West Edge 30 0.00+0.00 * = nearest field in potatoes previous year not known. Table 40. CPB densities for commercial field Denn 4, 1991. June 5 Field CPB Section N /Plant Center 30 0.00+0.00 North Edge 30 0.00+0.03 South Edge 30 0.00+0.00 East Edge 30 0.17+0.10 West Edge 30 0.00+0.00 * = edge nearest to previous years potatoes not known. Table 41. CPB densities for commercial field Denn 5, 1991. June 9 Field CPB Section N /Plant Center 30 0.00+0.00 North Edge 30 0.00+0.00 South Edge* 30 0.10+0.05 East Edge 30 0.00+0.00 West Edge 30 0.00+0.00 * = edge nearest to previous years potatoes. Table 42. CPB densities for commercial field Rho 4, 1991. June 5 Field CPB Section N /Plant Center 30 0.23+0.11 S . West Edge* 30 0.30+0.12 N. East Edge* 30 0.17+0.08 * = edge bordering previous potatoes Table 43. CPB densities for commercial field Rho 5, 1991. June 5 Field CPB Section N /Plant Center 45 0.20+0.08 S . West Edge* 45 0.42+0.12 N. East Edge* 45 0.13+0.06 * = edge bordering previous potatoes Table 44. CPB densities for commercial field Denn 1, 1991. May 30 June 5 Field CPB CPB Section N /Plant N /Plant Center 30 0.00+0.00 30 0.00+0.00 North Edge 30 0.07+0.05 30 0.00±0.00 South Edge 30 0.03±0.03 30 0.00+0.00 East Edge 30 0.00+0.00 30 0.10+0.07 West Edge 30 0.07±0.05 30 0.00±0.00 * = nearest edge to previous years potatoes is unknown. Table 45. CPB densities for commercial field Denn 2, 1991. May 30 June 5 Field CPB CPB Section N /Plant N /Plant Center 30 0.00+0.00 30 0.00+0.00 North Edge 30 0.00+0.00 30 0.00+0.00 South Edge 30 0.03+0.03 30 0.00±0.00 East Edge 30 0.03+0.03 30 0.00+0.00 West Edge 30 0.00+0.00 30 0.00+0.00 * = nearest edge to previous years potatoes is unknown. 136 Figure 14. North/south semi-variogram of adults in Denn field on June 3, 1992. Semi-variogram 40 .4 0 0 .6 0 80 .8 0 0.00 0.20 1.00 0 0 0 3 0 0 0 2 0 0 0 1 0 itne t e Pis n eet F in Pairs een etw B Distance Figure 14 Figure 137 138 Figure 15. East/west semi-variogram of adults in Denn field on June 3, 1992. Semi-variogram 80 .8 0 60 .6 0 40 .4 0 0.20 0.00 1.00 0 0 0 1 0 0 9 0 0 8 0 0 7 0 0 6 0 0 5 0 0 4 0 0 3 0 0 2 0 0 1 0 itne t e Pis n eet F in Pairs een etw B Distance Figure 15 Figure 139 140 Figure 16. Omnidirectional semi-variogram of adults in Denn field on June 3, 1992. | Semi-variogram 80 .8 0 0.00 0.20 0 .4 0 0 .6 0 1.00 0 itne t e Pis n eet F in Pairs een etw B Distance 1000 Figure 16 Figure 2000 0 0 0 3 141 142 Figure 17. North/south semi-variogram of adults in Denn field on June 9, 1992. 1.00 0 .8 0 0 .6 0 0 .4 0 0.20 0.00 0 1000 2000 3 0 0 0 Distance Between Pairs in Feet Figure 17 144 Figure 18. East/west semi-variogram of adults in Denn field on June 9, 1992. 1.00 0 .8 0 0 .6 0 0 .4 0 0.20 0.00 0 100 200 300 400 500 600 700 800 900 1000 Distance Between Pairs in Feet Figure 18 146 Figure 19. Omnidirectional semi-variogram of adults in Denn field on June 9, 1992. Semi-variogram 0.00 0.20 0 .4 0 0 .6 0 80 .8 0 1.00 0 sac Bewen ar i Feet F in Pairs een etw B istance D 1000 Figure 19 Figure 2000 0 0 0 3 147 148 Figure 20. North/south semi-variogram of egg masses in Denn field on June 9, 1992. I Figure 20 Figure I i i Semi-variogram 0.20 0 .6 0 40 .4 0 o.oo 0 .8 0 1.00 sac Bewen ar i Feet F in Pairs een etw B istance D 1000 2000 0 0 0 3 149 Figure 21. East/west semi-variogram of egg masses in Denn field on June 9, 1992. I ! Semi-variogram 0.00 0 .6 0 0 .8 0 0.20 40 .4 0 1.00 0 0 0 1 0 0 9 0 0 8 0 0 7 0 0 6 0 0 5 0 0 4 0 0 3 0 0 2 0 0 1 0 itne t e Pis n eet F in Pairs een etw B Distance Figure 21 Figure 151 152 Figure 22. Omnidirectional semi-variogram of egg masses in Denn field on June 9, 1992. Semi-variogram 0.00 0.20 0 .6 0 0 .8 0 40 .4 0 1.00 0 0 0 3 0 0 0 2 0 0 0 1 0 sac Bewen ar i Feet F in Pairs een etw B istance D Figure 22 Figure 153 154 Figure 23. North/south semi-variogram of adults in Denn field on June 19, 1992. Semi-variogram 0.00 0 .4 0 0 .8 0 0 0 . 2 1.20 0 .6 1 0 sac Bewen ar i Feet F in Pairs een etw B istance D 1000 Figure 23 Figure 2000 0 0 0 3 155 156 Figure 24. East/west semi-variogram of adults in Denn field on June 19, 1992. Semi-variogram 0 0 . 2 40 .4 0 0.00 0 .8 0 1.20 0 .6 1 0 0 0 1 0 0 9 0 0 8 0 0 7 0 0 6 0 0 5 0 0 4 0 0 3 0 0 2 0 0 1 0 sac Bewen ar i Feet F in Pairs een etw B istance D Figure 24 Figure 157 158 Figure 25. Omnidirectional semi-variogram of adults in Denn field on June 19, 1992. Semi—variogram 0.00 40 0 .4 0 80 0 .8 0 2.00 1.20 60 0 .6 1 0 sac Bewen ar i Feet F in Pairs een etw B istance D Figure 25 Figure 1000 2000 2000 159 Figure 26. North/south semi-variogram of egg masses Denn field on June 19, 1992. Semi-variogram 0.00 0 .8 0 0 0 . 2 40 .4 0 60 .6 1 1.20 itne t e Pis n eet F in Pairs een etw B Distance 1000 Figure 26 Figure 2000 0 0 0 3 161 162 Figure 27. East/west semi-variogram of egg masses in Denn field on June 19, 1992. Semi-variogram 0.00 0 .8 0 0 0 . 2 40 .4 0 1.20 0 .6 1 100 200 300 400 500 600 700 800 900 1000 0 0 1 0 0 9 0 0 8 0 0 7 0 0 6 0 0 5 0 0 4 0 0 3 0 0 2 0 0 1 O itne t e Pis n eet F in Pairs een etw B Distance Figure 27 Figure 163 164 Figure 28. Omnidirectional semi-variogram of egg masses in Denn field on June 19, 1992. 2 . 0 0 1 .6 0 1.20 0 .8 0 0 .4 0 0.00 1000 2000 Distance Between Pairs in Feet Figure 28 166 Figure 29. Contour map using kriged estimates of adult populations in Denn 1992 field on June 3. NORTHING 2641.0 2112.8 1056.4 1584.6 528.2 0.0 0 25 .2 0 020 321 EASTING 642 70 .7 0 5 .0 0 963 167 168 Figure 30. Contour of standard deviations of kriged estimates of adult populations in Denn 1992 field on June 3. NORTHING 2641.0 1056.4 1584.6 528.2 0.0 2.8 0 321 EASTING 642 963 169 170 Figure 31. Contour map using kriged estimates of adult populations in Denn 1992 field on June 9. NORTHING 2112.8 2112.8 2641.0 2376.9 2376.9 1056.4 1056.4 1320.5 1320.5 1584.6 1848.7 1848.7 264.1 528.2 792.3 792.3 0.0 31 4 963 642 321 0 EASTING 171 172 Figure 32. Contour of standard deviations of kriged estimates of adult populations in Denn 1992 field on June 9. NORTHING 2641.0 2112.8 1584.6 1056.4 528.2 0.0 642 0 321 EASTING 963 Figure 32 173 Figure 33. Contour map using kriged estimates of mass populations in Denn 1992 field on June 9. NORTHING 2112.8 2641.0 1056.4 1584.6 528.2 0.0 0 .4 0 321 EASTING 642 .4 0 0.4 963 Figure 33 175 176 Figure 34. Contour map of standard deviations of kriged estimates of egg mass populations in Denn 1992 field on June 9. NORTHING 2641.0 2112.8 1584.6 1056.4 528.2 0.0 0 321 EASTING 642 963 177 178 Figure 35. Contour map using kriged estimates of adult populations in Denn 1992 field on June 19. NORTHING 2641.0 2112.8 1584.6 1056,4 528.2 0.0 2 642 321 0 EASTING 963 Figure 35 179 180 Figure 36. Contour of standard deviations of kriged estimates of adult populations in Denn 1992 field on June 19. NORTHING 2641.0 2112.8 1684.6 1056.4 528.2 0.0 321 EASTING 642 963 181 Figure 37. Contour map using kriged estimates of egg mass populations in Denn 1992 field on June 19. No^'-g^ 2641.0 2112.8 584.6 056.4 528.2 0.0 31 4 963 642 321 0 0.6 EASTING 0.2 Figure 37 183 184 Figure 38. Contour map of standard deviations of kriged estimates of egg mass populations in Denn 1992 field on June 19. 2641.0 2112.8 1584.6 84 1056.4 528.2 0.20 0.0 0 321 642 963 EASTING