Subterranean termite infestation of urban structures in the Tucson basin: Patterns and influences.

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Subterranean termite infestation of urban structures in the Tucson basin: Patterns and influences

Colwell, Curt Edward, Ph.D. The University of Arizona, 1987

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U'MI f. 1

SUBTERRANEAN TERMITE INFESTATION OF URBAN STRUCTURES IN THE TUCSON BASIN: PATTERNS AND INFLUENCES

by Curt Edward Colwell

A Dissertation Submitted to the Faculty of the DEPARTMENT OF ENTOMOLOGY In Partial Fulfillment of the Requirements For the Degree of DOCTOR OF PHILOSOPHY In the Graduate College UNIVERSITY OF ARIZONA

1987 1- .

2 THE UNIVERSITY OF ARIZONA GRADUATE COLLEGE

As members of the Final Examination Committee, we certify that we have read the dissertation prepared by ------Curt Edward Colwell entitled SUBTERRANEAN TERMITE INFESTATION OF URBAN STRUCTURES

IN THE TUCSON BASIN: PATTERNS AND INFLUENCES

and recommend that it be accepted as fulfilling the dissertation requirement

Doctor of Philosophy

Date

Date 11/16/87

Date 11/16/87

Date 11/16/87

Date

Final approval and acceptance of this dissertation is contingent upon the candidate's submission of the final copy of the dissertation to the Graduate College.

I hereby certify that I have read this dissertation prepared under my direc' and nd that it be accepted as fulfilling the dissertation

Date 11/¥6J87! I ) 3

STATEMENT BY THE AUTHOR

This dissertation has been submitted in partial fulfillment of requirements for an advanced degree at the University of Arizona and is deposited in the University Library to be made available to borrowers under rules of the Library. Brief quotations from this dissertation are allowable without special permission, provided that accurate acknowledgment of source is made. Requests for permission for extended quotation from or reproduction of this manuscript in whole or in part may be granted by the head of the major department or the Dean of the Graduate College when in his or her judgment tha prposed use of the material is in the interests of scholarship. In all ohter instances, however, permission must be obtained from the author.

SIGNED: " C

r. 4 ACKNOWLEDGMENTS

The author gratefully acknowledges selection as first recipient of the Truly Nolen Urban Pest Management Fellowship Award established by the Truly Nolen Company. without the company's continuing support, this study would not have been possible. I also thank Bill Spaulding, Bob Hartley, Bill Nolen, and Lauren Schaap, all of Truly Nolen Company, for their support and expert advice. Additional appreciation is expressed to Dr. Robert L. Smith for services rendered as Committee Chairman, and to all Committee participants: Dr. Leon Moore, Dr. Michael K. Rust, Dr. Astrid Kodric-Brown, Dr. James H. Brown, and especially to Dr. William L. Nutting for masterful insight, advice, and sincere interest in my general welfare. I am also indebted to Dr. Michael W. Trosset of the University of Arizona, Department of Statistics, who unselfishly provided invaluable statistical expertise throughout. Finally, I am deeply appreciative of my parents, whose constant support and encouragement inspired me to achieve. 5

TABLE OF CONTENTS Page

LIST OF FIGURES. 6

LIST OF TABLES. 7

ABSTRACT ••••• 9 INTRODUCTION. 11 METHODS and MATERIALS .• 16

Termite Control Questionn~ire ••• 16 Bait Study ••••••.•• 16 Termite Contracts •••••••••• ~ .• 19 Analysis ...... 24 Termite Control Questionnaire. 24 Bait Study .•••••••• 26 Termite Contracts .•••••••••••• 26

RESULTS. • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 28 Questionnaire Response...... 28 Bait study...... 33 Termite Contract Dispersion Analysis.. 47 Retreatment Rate Analysis...... 61

DISCUSSION •••••••••••••.•••••••.•••.•••.•••• 72 Interpretation of Questionnaire Response...... 72 Interpretation of Termite Foraging Activity.... 82 Interpretation of Termite Contract Dispersion.. 87 Influences on Retreatment Rate...... 89 CONCLUSION • ...... 91 APPENDIX A - TERMITE CONTROL QUESTIONNAIRE. 95

LITERATURE CITED •••••••••••••••••••.••••••• 97 6

LIST OF FIGURES

Page Figure 1. Bait site locations •••••••••••••••••••••••• 17 Figure 2. Historical expansion of Tucson, Arizona •••• 22 Figure 3. Numbers of termites observed at bait sites during weekly observations ••••••••••••••••• 38 Figure 4. Numbers of termites observed at site 1 during weekly observations ••••••••••••••••• 39 Figure 5. Numbers of termites observed at site 3 during weekly observations ••••••••••••••••• 40 Figure 6. Numbers of termites observed at site 4 during weekly observations ••••••••••••••••• 41 Figure 7. Numbers of termites observed at site 5 during weekly observations ••••••••••••••••• 42 Figure 8. Numbers of termites observed at site 8 during weekly observations ••••••••••••••••• 43 Figure 9. Numbers of termites observed at site 9 during weekly observations ••••••••••••••••• 44 Figure 10. Numbers of termites observed at site 10 during weekly observations •••••••••••••••• ~ 45 Figure 11. Numbers of termites observed at site 12 during weekly observations ••••••••••••••••• 46 Figure 12. Dispersion of subterranean termite contracts held by primary cooperator...... 78 Figure 13. Dispersion of subterranean termite contracts held by primary cooperator ••••••• 79 Figure 14. Dispersion of subterranean termite contracts held by cooperating pest control companies, excluding primary cooperator •••• 80 Figure 15. Dispersion of subterranean termite contracts held by cooperating pest control companies including primary cooperator ••••• 81 7

LIST OF TABLES

Page TABLE I. Termiticide use by pest control companies in Tucson, Arizona, 1986-1987 •••••••••• 31 TABLE II. Termiticide use by jobs performed in Tucson, Arizona, 1986-1877 ••••••••••••• 32 TABLE III. Predominant vegetation at bait sites ••••••• 34 TABLE IV. site characteristics and termite species observed. • • • • • • • • • • • • • • . • • • • • • • • • • • • • •• 35 TABLE V. Termite observations by species •••••••••••• 36 TABLE VI. Contingency table; termite contract density by wall material ••••••••••••••• 48 TABLE VII. Contingency table; termite contract density by air-conditioning type ••••••• 49 TABLE VIII. Contingency table; termite contract density by exterior structures ••••••••• 50 TABLE IX. contingency table; termite contract density by foundation type ••••••••••••• 51 TABLE X. Contingency table; termite contract density by soil grade •••••••••••••••••• 52 TABLE XI. Contingency table; termite contract density by soil permeability ••••••••••• 53 TABLE XII. Contingency table; termite contract density by caliche depth ••••••••••••••• 54 TABLE XIII. Contingency table; termite contract density by swimming pool presence or absence. • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •• 55 TABLE XIV. Contingency table; termite contract density by structure age ••••••••••••••• 56 TABLE XV. Contingency table; termite contract density by floor area ...... •...... 57 TABLE XVI. Contingency table; termite contract density by consumer affluence •••••••••• 58 8

TABLE XVII. contingency table: termite contract density by housing density ••••••••••••• 59 TABLE XVIII. Significance of site characteristics as influences on termite contract distribution ...•...... •.••.....•...... 60 TABLE XIX. contingency table: structure age by housing density •••••••••••••••••••••••• 62 TABLE XX. contingency table: structure age by consumer affluence ••••••••••••••••••••• 63 TABLE XXI. contingency table: structure age by soil permeability...... 64 TABLE XXII. Contingency table: consumer affluence by soil permeability •••••••••••••••••••••• 65 TABLE XXIII. Contingency table; consumer affluence by housing density ••••••••••••••.••.•..•.. 66 TABLE XXIV. Contingency table: soil permeability by housing density ...... •...... •..... 67 TABLE XXV. Significance of interrelationships between influences on termite contract dispersion •••••••••••••••••••• 68 TABLE XXVI. Significance of influences on retreatment rate...... 69 TABLE XXVII. Significance of wall materials and foundation types as influences on retreatment rates •••••••••••••••••••••• 71 9 ABSTRACT

A three-part study was conducted to characterize and assess the impact of subterranean termite infestation of urban structures in Tucson, Arizona. A termite control questionnaire was administered to all Tucson-based pest control firms offering termite control services, of which 52 percent responded. Twelve study sites were established in and around the city , wi th toilet paper rolls serving as termite bait at each site. In addition, 5943 active termite control contracts were accessed from Tucson's largest pest control company, and analyzed with accompanying data from various sources including those pertinent to structure location, construction, treatment history, and surrounding soil types.

An estimate of over $3 million for gross annual income derived from commercial termite control services performed in Tucson, was calculated from questionnaire responses. Termide (heptachlor + chlordane) was the most frequently used termiticide. Approximately 45 percent of commercial termite control jobs were performed with Termide, the principal termiticide used by 85.7 percent of companies offering termite control services. Gnathamitermes perplexus (Banks) was most prevalent in the toilet paper rolls at bait sites, followed by Heteroter­

~ aureus (Snyder) and Reticulitermes tibialis Banks. Q. perplexus infested bait at sites that resembled the sur- 10 rounding desert while H. aureus and B. tibialis generally infested those which had been significantly altered by irrigation and landscaping. H. aureus and, to a lesser degree, B. tibialis, are by far the most economically important of the 18 termite species inhabiting Tucson and the surrounding area. significant interrelationships were found between termite contract density, customer affluence, housing density, structure age, and soil permeability, and also between retreatment rate, foundation type, and materials used in wall construction. The percentage of structures under contract requiring retreatment was estimated to be between 17.3 percent and 42.7 percent per year. Analysis utilizing termite control contracts is suggested as a unique and effective approach providing critical insight into factors influencing termite com­ munities and patterns of infestation in the urban environ­ ment.

f 11

INTRODUCTION

Some 2200 termite species exist worldwide with at least 45 species occurring in the united states (Snyder 1954, Wilson 1971). Termites can be found in every u.s. state except Alaska. Eighteen species inhabit Arizona, more than are found in any other state, and 13 of these are subterranean species (Nutting 1960). Termites are impor­ tant pests of crops, forests, grasslands, stored foods, wood products, and other commodities. Yet the order gains notoriety primarily from destruction of man-made structures in all areas of the world except the arctic and antarctic regions. Termites, especially the Rhinotermitidae, may represent the most economically destructive family of animals on earth. But few scientifically-based estimates of their economic impact exist. Such assessments vary accord­ ing to the period examined, inflation rates, method of estimation, and selective inclusion of prevention, control, and repair costs. Gentry (1966) calculated the annual cost of subterranean termite control and damage in the United states at $250 million. Based on earlier u.S. evaluations, Ebeling (1968) arrived at $500 million for the economic impact of termites. A united states Department of Agricul­ ture (USDA) estimate of $500 million was given by Johnston et al. (1980) for the annual u.S. impact of termites, i.

12 including damage and control costs. From income information obtained by a survey of pest control companies, Pinto (1981) suggested that termites cost u.s. residents $700 million in 1980. For the year 1982, Granovsky (1983) estimated an impact of $1.17 billion for termites in the U.S., based on USDA figures. A more recent assessment places the annual cost of termites in the U.S. at $2.5 billion (Fellman 1985). The cost of termiticide application is the prin­ cipal component of termite impact assessment, as measured by the magnitude of monetary expenditures and concerns regard­ ing human health. Based on Environmental Protection Agency (EPA) estimates for the year 1981 (Immerman and Drummond 1985), 78.5 percent of pesticides applied in the urban sector were insecticides, as measured by pounds of active ingredient (A.I.) applied. In urban arElas, 61.0 percent of insecticide applications by pounds A.I. were made to structures, and 24.4 percent of applications to structures were made with the cyclodiene termiticides chlordane, heptachlor, and aldrin. In 1981, excluding IIrefined petroleum hydrocarbons II , Le. oils presumably including those used as carriers, more pounds A.I. of chlordane were applied than any other insecticide used in the urban sector. EPA estimates of household pesticide use (Savage et ale 1979) indicate that 26.1 percent of U.S. households were treated for termites, approximately 3.9 million pounds of chlordane were used in U.S. households during a one-year 13 period, 1976-1977. Despite the apparent emphasis on prevention and control of termites, there is no indication that the impact of termites is being reduced. The distributions of some termite species continue to expand. Ironically, this can be attributed to human manipulations. Subterranean termites pose a new threat by range extension facilitated by central heating which allows them to survive in formerly uninhabit­ able areas of the northern u.S. and Canada (Ebeling 1975). An even greater economic threat is represented by range extension of the Formosan termite, coptotermes formosanus Shiraki. This highly destructive species indigenous to Asia, was apparently transported aboard ship in infested wood and first discovered in the continental u.S. in 1965. Inadvertently transported by commercial vehicles, the species is now present in all gulf states and has been reported as far north as Tennessee (Mix 1985). Control measures directed against this enormous and growing termite problem have remained essentially unchanged for 35 years-- soil treatment with termiticides. Non-chemical control methods including moisture control and avoidance of wood-soil interfaces in and around structures have been valuable only as supplements to termiticide application. The efficacy of cyclodiene termiticides, when properly applied, is indisputable. However, their potential for compromising human safety has come to be the subject of 14 fierce debate. Action taken by the EPA in August 1987 indi­ cates a forthcoming curtailment of cyclodiene use. Alternative termiticides have been available for some time but may lack the extended residual life characteristic of cyclodienes. Moreover, the monetary costs of using alter­ nates such as organophosphates and pyrethroid termiticides are currently about twice those of cyclodienes (Mampe 1987). Through incidental "cohabitatation" with humans, and resultant property damage, termites are viewed as insidious and costly pests. For information on such pests, homeowners depend primarily on pesticide retailers and pest control operators (Byrne and Carpenter 1983, Levenson and Frankie 1983). Yet in urban areas such as Tucson, Arizona, where several termite species exist, PCOs often discriminate only between subterranean and drywood termites, and may be unaware of interspecific ecological distinctions. Yet definitive knowledge of the habits of termite species present in urban environments and the contributions of each to the local termite problem can be important to all concerned. For decades entomologists at the University of Arizona have conducted research to explain the habits of subterranean termites in the Sonoran Desert surrounding Tucson. Termite research has typically centered on termite populations in relatively natural areas or in the labora­ tory, where species have been extensively counted, cata- 15 logued, and characterized by researchers. Much has and continues to be gained from these studies, but scientific investigation of subterranean termite activity within urban environments has been lacking. This study was undertaken to characterize subter­ ranean termite infestation of urban structures and its impact in Tucson, Arizona. This involved estimating the magnitude of economic loss attributable to subterranean termite activity, determining the relative importance of indigenous species as structural pests, and understanding subterranean termite activity relative to an urban ecosys­ tem. 16

METHODS AND MATERIALS

Termite Control Ouestionnaire

All Tucson-based pest control companies offering termite control services were contacted by telephone and asked to complete and return a proposed termite control questionnaire. Having secured verbal agreements from personnel of all 42 companies, copies of the one-page questionnaire were mailed to each company (Appendix A). Each questionnaire was accompanied by an explanatory covering letter and a stamped, self-addressed envelope for returning the completed form. By checking the appropriate box on the questionnaire, respondents could request a summary of information obtained from completed question­ naires. Responses were obtained from 22 or 52.4 percent of the 42 companies surveyed. All but one requested and was provided with a copy of the summary results.

Bait Study

To determine the relative occurrence of economi­ cally important subterranean termite species in the Tucson area, twelve bait sites were established in widely separate locations in and around the city (Fig. 1). At each site samples of predominant vegetation were taken and submitted to the University of Arizona Herbarium for identification. The extent of landscape development was visually estimated 17

9 Coronado National Forest

10 5

Saguaro National Monument

San Xavier Indian Reservation

Figure 1.' .B..ai,t site "locations. Numbers 'indicate site' location. Shaded area 'indicates city of Tucson, Arizona. 18 for each site. Landscape development was noted as "high" at sites where groundcover was uniform, as in the case of turfgrass lawns where woody surface debris was absent and where watering was routine. sites listed as "moderate" for landscape development lacked uniform groundcover, had little woody surface debris, and were occasionally watered. Sites of "low" landscape development also lacked uniform groundco­ ver, contained some woody surface debris, and were rarely watered. sites of "very low" landscape development also lacked uniform groundcover, contained appreciable woody surface debris, and were never watered. Rolls of white, unscented CrownR HumboldtR toilet paper, each roll consisting of 1000 11.4 cm by 11.4 cm sheets, were wrapped in 5.0 cm wide duct tape. At each of 12 sites, 25 wrapped rolls were staked down with stakes of #9 gauge galvanized steel wire, each 24 cm in length. Toilet paper rolls at each site were spaced 1 m apart. Every fifth roll was numbered with a felt-tipped marker. Rolls at each site were set out in an "L"-shaped pattern, except at site 6 where space constraints would not permit this pattern. Rolls were moved within site 2 on day 16 of the experiment as they had become increasingly waterlogged from lawn watering. A few rolls at sites 8, 10, 11, and 12 were occasionally missing or damaged, presumably by rodents, and were replaced. 19 Sites were visited weekly for ten weeks beginning 1 April and ending 12 June 1987. All rolls at the twelve sites were inspected during a 6 to 7 hour period. starting times were adjusted each week to allow observation at times when ambient temperatures were expected to be optimal for termite foraging. The order of site inspection was varied each week to minimize temporal sampling bias among sites. At each site, species (verified by collections and iden­ tifications of soldiers whenever possible), estimated number of soldiers and non-soldiers, and the numbers of the infested rolls were recorded. After examination each roll was staked in its original position.

Termite Contracts

Data contained in 5943 active subterranean termite contracts were accessed from Tucson's largest pest control company (hereafter referred to as the "primary" cooperating company or cooperator). Each contract record included the location of the structure under contract, the date of contract initiation, structure's foundation type, and dates of all retreatments performed there by the company after contract initiation. For each of the 5943 contracted structures, coordinates were assigned representing the specific square­ mile area in which each was located within a 1764 square mile (4571 sq. km) area of the Tucson Basin, with sides 42 20 miles (67.6 kIn) long and with USGS R10E-T11S, R16E-T11S, R10E-T17S, and Rl16E-T17S sections forming the four corners (Anon. 1986). A second grid was employed to facilitate production of a contour map depicting dispersion of the company's termite contracts. This grid focused on a smaller

area with sides 24 miles (38.6 km) long and with the eastern halves of R12E-T12S and R12E-T15S and western halves of R16E-T12S and R16E-T15S forming the corners. This 576

square mile (1493 square kIn) area encompassed the locations of 5877 or 98.9 percent of the 5943 contracted structures. The X and Y coordinates of each square mile (1.6

square km) cell containing one or more of the contracted structures were used along with the number (the Z coor­ dinate) of contracted structures located within the cell to generate a contour map of termite contract dispersion using the Kriging algorithm (Krige 1951) utilized by Golden Graphics System software (Golden Software Incorporated 1985). A subset consisting of 100 of the 5943 contracted structures was randomly selected for detailed analysis. contract initiation dates of the 100 structures ranged from 1957 to 1985. Using the contour map of contract dispersion a contract density value ranging from 20 to 160 contracts per square mile was assigned to each of the 100 structures, corresponding to the greater of two contour lines nearest a structure • s location on the map. Foundation type, i. e. 21 basement, crawlspace, or slab, was also noted for each structure. Retreatment rates, i.e. numbers of retreatments per year, were also calculated, using numbers and dates of all retreatments performed on each structure. Historical perimeters of urban development were determined for ten-year intervals using Tucson city maps (Anon. 1930, 1940, 1950, 1960, 1970) (Fig. 2). Without regard to official city limits, perimeters were drawn to represent urban-rural interfaces, i. e. between areas of substantial street development and areas where few or no streets had yet been constructed. Distance (m) to un­ developed land was also recorded for each structure and corresponded to the shortest distance from a structure's location to the perimeter of urban development most ap­ propriate to the year of contract initiati.on for that structure. structures located outside a perimeter were assigned a distance value of zero. Additional data collected for each of the 100 structures included the calculated minimum depth to the water table. Minimum depth to water was determined by noting each structure's location on a depth to water map (Johnson et al. 1986) and recording the depth to water figure corresponding to the lesser of two contour lines between which the structure was located. Depth to water ranged from 0 to 300 feet (0 to 91.2 m) by 50-foot (17 m) intervals. \' ~. j ;1;.

22

- 1930 ---- 1940 •••••••• 1950 -.- 1960 - ... - 1970 --- 1980

: I .. ,-: l[1--!! DIV0r-~

. r-L i / I _I ~! . I - -&.- I .I : r:.-r- j ...... 'r J I ,,""-"'!.I 7 : ,','-"',-,'" - --- -: :. \... LI I: . "', '\. ---.. :I .j:.: . .:....,: 'I I .. _ .... _ .. 1--.: .....•. ,.: ___, . l country L--- Club Road

Figure 2. Historical expansion of Tucson, Arizona. Lines indicate perimeters of urban development. t l ..

23 Records accessed from the Pima County Tax Asses­ sor's Office (Pima County 1986) provided construction data for each of the structures including: 1) structure age, 2) floor area in square feet, 3 ) wall construction material (categorized as concrete, brick and brick veneer, adobe, stucco, and wood and wood/concrete block), 4) accompanying exterior structures (categorized as patio and/or porch present, carport and/or garage present, patio and/or porch and carport and/or garage present, or none present), 5) presence or absence of a swimming pool, and 6) presence and type of air-conditioning (categorized as evaporative, refrigerative, or absent). Information obtained from the USDA Soil Conserva- tion Service (USDA 1972, USDA 1985) permitted determination of soil mapping units representing soil types at each structure's location. Soil type descriptions provided data on: 1) soil permeability (categorized as slow, moderate, or rapid), 2) depth to caliche bedrock layer (categorized as shallow: 4-20 inches (10.1 cm - 50.4 cm), intermediate: 8 inches (20.2 cm) to deep, and deep: simply listed as "deep", Le. greater than 20 inches, in soil type descriptions), 3) soil grade, i.e. slope (categorized as shallow: 0 to 8 percent, or steep: 5 to 35 percent). In categorizing soil characteristics, some degree of category overlap was unavoidable as mapping units typically represented more than one type of soil, and soil types were broadly described. 24 For each structure the relative affluence of the neighborhood was categorized as lower, middle, or upper income from wealth ratings based on United states Census Bureau figures, block canvassing and real estate evaluation data (Anon. 1987b). Finally, from Tucson zoning maps (Anon. 1987b) each of the structures was assigned a housing density category based on the following lot sizes: Low (16000 sq. ft., 4864 sq. m, or greater), moderate (7000 to 16000 sq. ft., 2128 to 4864 sq. m), or high (less than 3000 sq. ft., 912 sq. m). In addition to termite contracts, 528 inspection reports for termite inspections performed by the primary cooperating company during the years 1986 and 1987 were accessed. For each structure, information was collected regarding; 1) the presence of subterranean termites, 2) presence of active infestations, 3) premise characteristics conducive to termite infestation (faulty grades, excessive moisture, and wood-soil contact) " and 4) termite contract status.

Analysis

Termite Control Questionnaire

Gross annual income estimates for termite control service were totaled and used with respondents' estimates of percent gross annual income derived from general pest 25 control service, to determine gross annual income from general pest control service. The numbers of subterranean termite control pretreatments, retreatments, and active contracts listed by respondents were also totaled. Percent gross annual income from drywood and dampwood termite treatment were averaged and used to determine percent gross annual income from subterranean termite control. The numbers of respondents listing particular months as those in which the greatest and fewest termite control requests were received were also tallied. Percentages of respondents specifying use of various termiticides were calculated. Estimated numbers of active contracts specified by respon­ dents were used with termiticide use percentages to calcu­ late percentages of subterranean termite control services performed with various termiticides in Tucson. In addition to compilation of the above responses, each respondent's estimate of the number of active (uncan­ celed) termite contracts held by their company, and es­ timated percentages of structures under contract wi thin 2 miles (3.2 km) and within 5 miles (8.1 km) of the company's geographical location, were used to generate two additional contour maps of termite contract dispersion. The first map excluded contract information obtained from the primary cooperating company. The latter map included this informa­ tion along with that obtained from all other companies responding to the questionnaire, and thus was a composite of 26 the previous two contour maps.

Bait study

Estimated numbers of soldiers and non-soldiers observed and numbers of toilet paper rolls infested by each termite species were calculated, along with bait site characteristics.

Termite Contracts

Frequency analysis was performed on the subset of 100 contracted structures using SAS (Joyner et al. 1986), and produced two-way contingency tables between all categor- ical variables and termite contract density. For this analysis contract density was classified as peripheral: 0 to 79 contracts per square mile, or central: 80 to 160 con­ tracts per square mile. To facilitate the analysis, categories were necessarily expanded to reduce the number of categories for certain variables. Likelihood Ratio Chi­ square statistics were used to obtain probability (p) values. Subsequent analyses were performed on variables classified as statistically significant. In addition, analysis of covariance was performed employing the SAS GLM procedure. Retreatment rates of the sample 100 structures, excluding seventeen with retreatment rates equal to zero, were normalized by loglO transformation and served as the model's dependent variable. Independent 27 variables incorporated into the model were: initial infesta­ tion date, structure age, minimum depth to water, minimum distance to undeveloped land, wall construction material, air-conditioning presence and type, exterior structures' presence and type, floor area, foundation type, soil grade, soil permeability, and caliche depth. Probablility (p) values for partial sums of squares were used to assess the extent of retreatment rate variability explained by the independent variables. Significant influences on retreat- ment rate, as determined by this analysis were incorporated into subsequent GLM models and further analyzed. 28 RESULTS

Questionnaire Response

Twenty-two of the forty-two Tucson-based companies offering termite control services submitted completed questionnaires. The number of respondents for individual questions ranged from twenty (48 percent) to twenty-two (52 percent). Estimates of company gross annual income derived from termite control ranged from $1000 to $600,000 with a per-company mean of $83,090 and median of $21,150. Gross annual income from general pest control, based on percentage estimates, varied from $1500 to $1,400,000 with a mean of $146,765 and median of $69,850. Responses to questions 1 and 2 facilitated calculation of the respondents' gross annual income from termite control services, which totaled $1, 661, 800, and from general pest control services, which totaled $2,935,300 or 63.9 percent of the total gross annual income from control services performed by the twenty-two responding companies. Thus 36.1 percent of the companies' total gross annual income from pest control is attributable to income from termite control services. Percentages of gross annual termite control income derived from drywood and dampwood termite control services ranged from 0 to 15 percent and 0 to 24 percent , with means of 1. 5 and 1. 4 percent, respectively. 29 Estimates of percent annual termite control income derived from "desert" termites, a local common name for Gnathamitermes perplexus (Banks) varied greatly. Twelve of twenty responding companies reported that so-called desert termites accounted for 95 to 100 percent of their gross annual income from termite control, while five companies attributed only 3 percent or less of their termite income to desert termite control. Responses to question 3 regarding the number of pretreatments for subterranean termite control performed per year, ranged from 0 to 1000 with a per-company mean of 83, median of 12.5. A total of 1660 pretreatments were per­ formed by responding companies. Responses to question four, estimation of retreatments performed annually on structures a company previously treated, totaled 2949 and ranged from 0 to 2000 with a mean of 134 per company and median of 10.5. Estimates of the number of active subterranean termite contracts held, question 6, totaled 17095 and ranged from 50 to 6000 with a mean of 814 and median of 270. In addition to treatment estimates obtained from questionnaire response, an informal telephone survey in which 33 homeowners were asked if their home had been treated for termite control prior to, during, or at anytime after construction, found that 90 percent of homeowners who claimed to know their home's termite treatment history said their home had at some time been treated for termites. 30 Responses to question 5 indicated Gold CrestR Termide (heptachlor plus chlordane) as the principal termiticide used by 85.7 percent of pest control companies in Tucson. Dursban™ TC (chlorpyrifos) was the principal termiticide for 9.5 percent of companies and Gold CrestR C- 100 (chlordane) for 4.8 percent (Table I). Termide and/or C-100 and/or Dursban TC were the only termiticides used by 77.2 percent of responding companies (Table II). Sixty percent of the respondents listed August as a month during which their company received the greatest number of requests for termite control services, while 60 percent listed September, 50 percent listed July, and 35 percent listed the month of March as well (most respondents listed several months). Months of fewest requests for termite control services included December: listed by 55 percent of the respondents, July: listed by 35 percent, January: listed by 30 percent, and June: also listed by 30 percent. Through examination of the 528 termite inspection reports accessed from the primary cooperator, 59.5 percent of structures inspected during 1986 and 1987 were found to have no visible evidence of wood-destroying insects, 17.2 percent showed visible evidence of previous (presently inactive) termite infestation, 14.2 percent showed visible termite damage from active or inactive infestations, and visible evidence of active termite infestation was found in 31 TABLE I. Termiticide use by pest control companies in Tucson. Arizona. 1986-1987. Percent Companies Percent Percent Companies Using Termiticide jobs Termiticide using Termiticide on most jobs Performed Termide 86.4 85.7 45.0 Dursban TC 36.4 9.5 38.5 C-100 36.4 4.8 15.2 Torpedo 13.6 0 <1 Ficam 13.6 0 <1 Lindane 4.5 0 <1

[ '.-. ~'..

32

TABLE II. Termiticide use by jobs performed in Tucson, Arizona. 1986-1987. Termiticide Used and Mean Percent of Jobs Performed Percent of companies Termide (100) 27.3 Termide (78) and C-100 (22) 22.7 Termide (94.7) and Dursban TC (S.3) 13.6 Dursban TC (87.S) and C-100 (12.S) 9.1 C-100 (100) 4.S

Termide (90) and Torpedo (10) 4.S Termide (98) and Ficam (2) 4.S Termide (93), Dursban TC (S), and Torpedo (2) 4.S

Termide (90), Dursban TC (7), and Ficam (3) 4.S Termide (8S), Dursban TC (10), Torpedo (4), Ficam «1) and Lindane «1) 4.S

Total is less than 100% due to rounding of percent figures. 33 the remaining 9 • 1 percent. Faulty grades were listed as present at 9.1 percent of the premises inspected, wood-soil contact was recorded for 6.6 percent of the structures, and excessive moisture was listed present at 1.3 percent. Of the 528 inspected structures, 198 were under contract with the company at the time of inspection.

Bait Study

Predominant vegetation and other bait site characteristics are summarized in Tables III and IV. After ten weekly observations an estimated total of 5152 Gnathami- termes perplexus individuals, including 21 (0.4 percent) soldiers, were recorded in 50 (20 percent) of the 250 toilet paper rolls at bait sites (Table V). 2. perplexus, the tube-building desert termite, was recorded at five of the twelve bait sites during the initial observation period (day 7, April 7), seven days after toilet paper rolls were set in place. Landscape development at these five sites was characterized as very low or lOW, and all were more than 7.0 km distant from the center of termite contract distribution. 2. perplexus was observed at sites 5, 10, and 12 during all weekly observations, and sporadically at sites 8 and 9. An estimated 985 Heterotermes aureus (Snyder) individuals, including 34 (3.5 percent) soldiers, were observed infesting 7 (2.8 percent) of available toilet paper rolls (Table V). H. aureus, the desert subterranean r-:------34 TABLE III. Predominant vegetation at bait sites. Site Plant species Present 1 turfgrass 2 Nerium oleander (oleander), turfgrass 3 Erodium cicutarium (filaree) 4 turfgrass 5 Bahia absinthifolia (bahia), Larrea tridentata (creo sote bush), Cercidium microphyllum (foothills palo verde) 6 turfgrass 7 turfgrass 8 Aristida purpurea (purple three-awn), Ambrosia del­ toidea (burrobush), Encelia farinosa (brittle bush)

9 Ambrosia deltoidea, ~. microphyllum 10 Larrea tridentata 11 Schismus barbatus (Meditteranean grass), Haplopappus tenuisectus (burroweed) 12 Erodium cicutarium, Larrea tridentata 35

TABLE IV. Site characteristics and termite sI;!ecies observed. Distance from center of Termite contract Landscape Species Site Distribution (Jan) Development Observed

1 3.2 moderate RT

2 4.5 high

3 4.7 moderate HA 4 5.0 moderate HA 5 7.2 low GP,HA

6 7.7 high

7 9.2 moderate

8 10.7 very low GP 9 11.9 very low GP

10 12.1 very low GP 11 12.1 very low 12 14.4 very low GP

RT: Reticulitermes t!~ialis HA: Heterotermes aureus GP: Gnathamitermes pe~lexus.

"""'f..,...------36 TABLE V. Termite observations by species.

Number Number Number Workers Soldiers Percent Rolls Species Observed Observed Soldiers Infested

Q. perplexus 5131 21 0.4 50 H· aureus 951 34 3.5 7 B· tibialis 30 3 9.1 1 37 termite, was recorded at three sites, first at site 4 on day 24 (April 24), and later during observations at sites 3 and 5 on day 30 (April 30). H. aureus was observed during all subsequent observations at site 4, sporadically at site 3, and only once again at site 5. site 5 was the only site at which more than one termite species was observed. Landscape development at sites 3, 4, and 5 was characterized as low or moderate, and distance from the center of termite contract distribution ranged from 4.7 km to 7.2 km. Reticulitermes tibialis Banks, the arid land subterranean termite, was discovered in one roll at site 1 on day 52 (May 22) when 33 E,. tibialis individuals were observed, including 3 (9.1 percent) soldiers (Table V). Landscape development at site 1 was characterized as moderate. site 1 was the site closest (3.2 km) to the center of termite contract distribution. No termites were observed at sites 2, 6, 7, and 11. Estimated numbers of termites observed during each observation period are represented in Figure 3, and by site in Figures 4 through 11. The greatest numbers of termites of all species were recorded during observation periods on days 37, 45, 52, and 58. Peak numbers were noted on day 58 when 1639 termites were observed; 1631 Q. perplexus and 8 H. aureus. This was the highest number of Q. perplexus observed during the study. Highest numbers of H. aureus and R. tibialis, 699 and 33 respectively, were recorded on day 38

1800

1600

1400

1200

~v ~ .,u 1000 .a 0 !! u .a BOO E ::J Z

~OO

400

200

30 MAY 7 15 22 2R JUN 5 12 Observation Day IZZZZZI Q. p-erplexus 1TImI!!. ~ 1ZZl~. ~

Figure 3. Numbers of termites observed at bait sites during weekly observa­ tions. 39

1200

1000

800 "0 4) ~ ~ ..Q Q

~ 4) 600 ..Q E :::J Z

400

200

Observation Day rIIII1J Reiicul iiermes !.l!2.!2!JlI Figure 4. Numbers of termites observed at site 1 during weekly observations. 40

800 '"Q ~ Q In ..Q 0 "- Q 600 ..Q E z:;,

400

7 16 24 30 37 45 52 58 66 73 Observation Day rIIIlJJ Heterotermes ~ Figure'S. Numbers of termites observed at site 3 during weekly observations. 41

1200

1000

BOO '0 U ~ U 1/1 .<> 0 "-u 600 .<> E :J Z

400

200

7 16 24 30 37 45 52 56 66 73 Observation Day IZZZZZl Heterotermes ~ Figure 6. Numbers of termites observed at site 4 during weekly observations. 42

BOD 'U U ~ u .8 0 u"- 600 .0 E :J Z

... 00

7 16 24 30 37 ... 5 52 58 66 73 Observation Day rILlI1J Gnathomiterme8 perplexu8 ~ Heteroterm88 aureU8

Figure 7. Numbers of termites observed at site 5 during weekly observations.

f" [ .

43

1200

1000

800 "0 Ut lit .0 0 ...u 600 .0 E :l Z

400

200

rnT7I or7T171 I 7 16 24 30 37 45 52 58 66 73 Observation Day rIIIZlJ Gnathomilermes perplex us

Figure 8. Numbers of termites observed at site 8 during weekly observations. 44

1200 .

1000

BOO "'0 ~ u., ..a 0 ...u 600 ..a E :::J Z

400

200

O~~----~----r----r----~---'---~~~~~----'-----~ 7 16 24 30 37 45 52 58 66 73 Observatian Day rIIIZJJ Gnathamitermes perplexus Figure 9. NlmWers of termites observed at site 9 during weekly observations.

f i....

45

... .8 E :J Z

7 16 24 30 37 45 52 58 66 73 Observation Day IZZZZZI Gnothomitermes perplexus Figure 10. Numbers of termites observed at site 10 during weekly observa­ tions. 46

800 "V., b .c." 0 .,"- 600 .c E ::J Z

400

Observation Day rI1IIJJ Gnathamitermes perplexus

Figure. 11. Numbers of termites observed at site 12 during weekly observa­ tions. 47 52. The four observations in May accounted for 4849, or 71:1: 6 percent of the estimated 6170 termites observed during the ten-week period. Minimal numbers of termites were observed during the first two and last two weekly observations, i.e. days 7 April 7) and 16 (April 16), and days 66 (June 5) and 73 (June 12), with fewest termites (27) observed on day 16. Lowest numbers of the three species were wi tnessed during the first and last weekly observation periods. Thus the patterns above, regarding numbers of termites observed, were similar for all three species.

Termite Contract Dispersion Analvsis

Two-way contingency tables for termite contract density and twelve categorical variables are presented in Tables VI through XVII. statistically significant relation­ ships were revealed between termite contract density and customer affluence (p=. 002), soil permeability (p=. 006) , housing density (p=.012), and structure age (p=.014) (Table XVIII). As the density of termite contracts increased, affluence decreased, soil permeability decreased, housing density increased, and structure age increased. No statis­ tically significant relationships were detected between contract density and floor area, foundation type, wall material, exterior structures, air-conditioning type, soil grade, and depth to caliche. 48 TABLE VI. contingency table: termite contract density by wall material. Termite contracts Wall Construction Material per Square Mile concrete brick adobe stucco wood o to 80: (peripheral)

Number 8 16 12 5 9 Row percent 16 32 24 10 18 Column percent 67 42 71 29 56 81 to 160: (central) Number 4 22 5 12 7 Row percent 8 44 10 24 14 Column percent 33 58 29 71 44 49 TABLE VII. contingency table; termite contract density by air-conditioning type. Termite contracts Air-conditioning Type per Sguare Mile Refrigerative Evaporative o to 80: (peripheral)

Number 20 29 Row percent 41 59 Column percent 48 52 81 to 160: (central)

Number 22 27 Row percent 45 55 Column percent 52 48

Note: Two of 100 sample structures were not equipped with air-conditioning, and were excluded from this analysis. 50 TABLE VIII. contingency table; termite contract density by exterior structures. Exterior structures Present Termite Contracts Patio Carport Patio/Porch + 12er Sgyare Mile None LPorch LGarage CamortLGarage o to 80: (peripheral) Number 6 7 17 20 Row percent 12 14 34 40 Column percent 46 41 59 49 81 to 160: (central) Number 7 10 12 21 Row percent 14 20 24 42 Column percent 54 59 41 51 51 TABLE IX. contingency table; termite contract density by foundation type. Termite contracts Foundation Type per Square Mile Slab Basement or Crawlspace o to 80: (peripheral)

Number 45 5 Row percent 90 10 Column percent 52 36 81 to 160: (central)

Number 41 9 Row percent 82 18 Column percent 48 64 52 TABLE X. contingency table; termite contract density by soil grade. Termite contracts Soil Grade per Square Mile o to 8 percent 5 to 35 percent o to 80: (peripheral)

Number 6 44 RpW percent 12 88 Column percent 40 52 81 to 160: (central)

Number 9 41 Row percent 18 82 Column percent 60 48 ~i .

53 TABLE XI. contingency table: termite contract density by soil permeability. Termite contracts Soil Permeability per Square Mile Slow Moderate Rapid

o to 80: (peripheral) Number 21 18 11 Row percent 42 36 22 Column percent 43 78 39

81 to 160: (central)

Number 28 5 17 Row percent 56 10 34 Column percent 57 22 61 54

TABLE XII. contingency table; termite contract density by caliche depth. Caliche Depth Termite contracts Shallow: Deep: per Square Mile « 21 inches) (> 7 inches) o to 80: (peripheral)

Number 13 37 Row percent 26 74 Column percent 42 54 81 to 160: (central)

Number 18 32 Row percent 36 64 Column percent 58 46 t.

55 TABLE XIII. contingency table; termite contract density by swimming pool presence or absence. Termite contracts swimming Pool per Square Mile Present Absent

o to 80: (peripheral)

Number 37 13 Row percent 74 26 Column percent 47 62 81 to 160: (central)

Number 42 8 Row percent 84 16 Column percent 53 38 56 TABLE XIV. Contingency table; termite contract density by structure age. Termite Contracts structure Age per Sauare Mile 1 to 21 yrs. 22 to 37 yrs. >37 yrs. o to 80: (peripheral)

Number 11 29 10 Row percent 22 58 20 Column percent 73 55 31 81 to 160: (central)

Number 4 24 22 Row percent 8 48 44 Column percent 27 45 69 57 TABLE XV. Contingency table: termite contract density by floor area. Termite Contracts Floor Area (sq.ft.) per Square Mile <1500 1500-2500 >2500 o to 80: (peripheral) Number 17 23 10 Row percent 34 46 20 Column percent 41 51 71

81 to 160: (central)

Number 24 22 4 Row percent 48 44 8 Column percent 59 49 29 ;' L

58

TABLE XVI. contingency table: termite contract density by consumer affluence. Termite contracts Consumer Affluence (income rating) per Square Mile low middle high o to 80: (peripheral)

Number 16 6 28 Row percent 32 12 56 Column percent 47 24 68

81 to 160: (central)

Number 18 19 13 Row percent 36 38 26 Column percent 53 76 32 59

TABLE XVII. contingency table; termite contract density by housing density. Termite contracts Housing Density per Square Mile Low Medium High o to 80: (peripheral)

Number 14 20 16 Row percent 28 40 32 Column percent 78 38 53 81 to 160: (central)

Number 4 32 14 Row percent 8 64 28 Column percent 22 62 47 60 TABLE XVIII. Significance of site characteristics as influences on termite contract dispersion. site Characteristic Significance Cp) affluence .002 soil permeability .006 housing density .012 structure age .014 wall material .075 floor area .144 swimming pool .218 foundation type .246 caliche depth .279 soil grade .399 exterior structures .682 air-conditioning type .683 61 Affluence, soil permeability, housing density, and structure age data were then cross-analyzed, again by frequency analysis (Tables XIX-XXIV). Significant rela­ tionships existed between housing density and affluence (p=. 000), housing density and soil permeability (p=. 036) , and affluence and structure age (p=.010) (Table XXV).

Retreatment Rate Analysis

Covariance analysis of a preliminary model with retreatment rate as the dependent variable and fourteen site characteristics as independent variables yielded significant p values for partial sums of squares for two of the site characteristics, wall material (p=.0109) and foundation type (p=. 0182) • Of near significance were initial infestation date (p=.1762) and termite contract density at the sites (p=.1891) (Table XXVI). Covariance analysis of a model including only these four most significant characteristics showed the model to be significant (p=.0009) and explaining 27 percent of retreatment variability (rsquare=.271759). Analysis of the model indicated foundation type as most significant (p=.0003) in predicting retreatment rate, followed by wall material (p=.0141), and initial infestation date (p=.0243). Termite contract density remained less significant (p=.0860). Analysis excluding the contract density variable from the model indicated foundation type (p=.0003) and initial infestation date (p=.0083) as sig- 62 TABLE XIX. contingency table: structure age by housing density. structure Housing Density Age Cyrs.) low medium high 1 to 21:

Number 6 4 5 Row percent 33 8 17 Column percent 40 27 33

22 to 37:

Number 8 32 13 Row percent 44 62 43 Column percent 15 60 25 >37:

Number 4 16 12 Row percent 22 31 40 Column percent 13 50 38 63

TABLE XX. contingency table: structure age by consumer affluence.

structure Consumer Affluence (income rating) Age Cyrs. ) low middle high 1 to 21:

Number 2 1 12 Row percent 13 7 80 Column percent 6 4 29 22 to 37:

Number 17 16 20 Row percent 32 30 38 Column percent 50 64 49 >37:

Number 15 8 9 Row percent 47 25 28 Column percent 44 32 22 64 TABLE XXI. contingency table: structure age by soil permeability. structure Soil Permeability Age Cyrs.) Slow to Moderate Moderate to Rapid 1 to 21:

Number 8 7 Row percent 16 14 Column percent 53 47 22 to 37:

Number 30 23 Row percent 61 45 Column percent 56 43 >37:

Number 11 21 Row percent 22 41 Column percent 34 66

""""r-·-_ .... _... .._ .. _-- 65 TABLE XXII. contigency table: consumer affluence by soil permeability. Consumer Affluence Soil Permeability (income rating> Slow to Moderate Moderate to Rapid Low:

Number 20 l.4 Row percent 59 41 Column percent 41 27 Middle:

Number 12 13 Row percent 48 52 Column percent 24 25 High:

Number 17 24 Row percent 41 59 Column percent 35 48 66 TABLE XXIII. Contigency table: consumer affluence by housing density. Consumer Affluence Housing Density (income rating) low medium high

Low:

Number o 10 24 Row percent o 29 71 Column percent o 19 80 Middle:

Number 2 19 4 Row percent 8 76 16 Column percent 11 37 13 High:

Number 16 23 2 Row percent 39 56 5 Column percent 89 44 7 ~ ...

67 TABLE XXIV. contingency table: soil permeability by housing density. Soil Housing Density Permeability low medium high Slow to Moderate:

Number 4 29 16 Row percent 8 59 33 Column percent 22 56 53 Moderate to Rapid:

Number 14 23 14 Row percent 27 45 27 Column percent 78 44 47 68 TABLE xxv. Significance of interrelationships between influences on termite contract dispersion. Significance (p) Structure Housing Soil Influence Age Density Permeability Affluence affluence .010 .000 .119 soil permeability .127 .036 .119 housing density .092* .036 .000 structure age .092* .127 .010

* 22 percent of contingency table cells had expected counts less than 5, therefore p value may not be a valid indicator. 69 TABLE XXVI. Significance of influences on retreatment rate. Percent Variability Significance (p) * Model Explained Model FDN WALL INF DENS preliminary 34.5 .0891 .0182 .0109 .1762 .1891

FDN,WALL,INF,DENS 27.2 .0009 .0003 .0141 .0243 .0860

FDN,WALL,INF 24.2 .0014 .0003 .0353 .0083

* FDN: foundation type (slab, crawlspace/basement) WALL: wall type (brick, wood, concrete, stucco, adobe) INF: infestation date, initial DENS: density of termite contracts at location. 70 nificant. stucco (p=.0001) , brick (p=.0005) , and wood (p=.0015) walls, and slab foundations (p=.0001), were found to have highly significant effects on retreatment rate, while adobe and concrete walls, and structures with base­ ments or crawlspaces had no such effects (Table XXVII). 71 TABLE XXVII. Significance of wall materials and foundation types as influences on retreatment rates.* Number Mean significance included retreatment Type (p) in Analysis rate (no. /yr.) WALL: stucco .0001 15 .594 brick .0005 32 .450 wood .0015 16 .698 adobe .1402 13 .428 concrete .3487 7 .387 FOUNDATION: slab .0001 67 .604 crawlspace or basement .5095 16 .117

* model=foundation type, wall type, and initial infestation date. NOTE: "brick" includes structures with walls listed as "brick" and "brick veneer", "wood" includes structures recorded as "wood" and "wood/concrete block". 72

DISCUSSION

Interpretation of Ouestlonnaire Response

As approximately fifty percent of companies surveyed responded to the questionnaire, the figure obtained for gross annual income from termite control might be doubled to provide a somewhat crude estimate of the total cost of termite control per year in Tucson; $3,323,600. Behr (1973) estimated $1.6 million for remedial control of subterranean termites in the state of Michigan, based on a survey of pest control companies. From 1977 through 1979, Kamble et ale (1984) also surveyed pest control personnel, and estimated the annual cost of subterranean termite treatment and prevention in Nebraska at $1.2 million. Allowing for inflation effects on the two state estimates, the impact of termites on cities in the southern United states, such as Tucson, is arguably greater than the impact of termites on northern states. For the cost of subterranean termite and wood­ destroying beetle prevention, control, and damage repair in single-family dwellings across eleven southern states in 1976, Williams and Smythe (1979) estimated $143 million, or approximately $200 million including the costs of damage repair and treatment performed by private individuals. Termites apparently exert their greatest economic effect on southern cities. Granovsky (1983) surveyed pest control 73 companies during 1979-1980 and estimated an annual economic impact of approximately $3.7 million for termites in Corpus Christi, Texas. This estimate included $1.1 million in repairs presumably performed by homeowners. Repair costs were not included in the $3.3 million estimate for Tucson. Mix (1987), from a 1986 nationwide survey of pest control companies, estimated the annual percentage of gross annual income that pest control companies derived from termite control services as 30.6 percent. This figure appears reasonably consistent with the 36.1 percent estimate for pest control companies in Tucson. Evidently confusion surrounded use of the term "desert termites" in the questionnaire. Some respondents, i.e. those attributing 3 percent or less of their company's gross annual termite control income to control of desert termites, apparently perceived only 2. perplexus as desert termites , as was intended. "Desert" termite is a local common name for g. perplexus. The species is not known to do structural damage to milled lumber, and control is rarely warranted. Respondents who estimated control of desert termites as contributing 95 to 100 percent of their com­ pany's gross annual income from termite control apparently viewed all local termites as desert termites. Moreland (1981) claimed that subterranean termites account for 95 percent of all termite damage in the United States, but did not present any corroborating evidence. 74 Subtracting percentage estimates for the relative contribu­ tions of drywood and dampwood termite control to gross annual incomes, services performed for control of subter­ ranean termites were found to contribute approximately 97.1 percent of the annual income from termite control in Tucson. Using totals of respondents' estimates for numbers of active subterranean termite contracts held (17095), and retreatments performed (2949), the percentage of contracted structures retreated during any particular year is estimated as 17. 3 percent. Such retreatment presumably results from initial treatment that is inadequate, modifications to the premises, or other factors allowing reinfestation of the structure. Information from the primary cooperating company regarding retreatment frequency can be used for comparison. The mean number of retreatments performed on the sample of 100 contracted structures was 0.427 retreatments per year. Thus in anyone year, an estimated 42.7 percent of struc­ tures under contract would require retreatment. The apparent descrepancy between the two estimates, 17.3 percent from questionnaire totals, and 42.7 percent from the sample 100 contracted structures, may be due to questionnaire respondents' over-estimations of contract numbers, resulting from possible ambiguity of the term "contract" as used in the questionnaire, or from under-estimation of the number of retreatments performed due to reluctance of respondents to 75 specify high retreatment rates. It is also noted that, using the known number of active termite contracts held by the primary cooperating company, approximately 6000, and the number of retreatments estimated by that company on the questionnaire, 2000, an estimate of 33.3 is obtained for the percentage of contracted structures requiring retreatment in anyone year. Perhaps this lends some support to the notion that the number of retreatments performed per year was under-estimated by questionnaire respondents. The true percentage may lie between 17.3 and 42.7, but is probably closer to the higher of these figures. Mix (1987) ranked Termide as the principal termiticide of 43.2 percent of respondents (each of which presumably represented a different company) in a 1986 survey of u. S. pest control operators. Chlordane and Dursban were listed as the principal termiticides by 35.6 percent and 33.8 percent of respondents. In terms of the variety of termiticides used, Mix found 63.6 percent of companies used Dursban to some extent, 55.4 percent used Termide, 52.3 percent used C-100, 7.7 percent used Torpedo™ (permeth- rin) , and 3.2 percent used Dragnet™ (permethrin) • Most respondents in the Mix survey represented companies in the southeastern part of the country. This, coupled with the much greater use of Termide relative to other termiticides used in Tucson (Table I), suggests that the type and extent of termiticides used may vary with geographic location.

ItIj,- 76 The number of requests received by pest control companies for termite control is undoubtedly linked to public awareness. Fowler (1984) found a significant relationship between the number of complaints from urban residents regarding subterranean termites and carpenter ants, and the annual appearance of termite and ant alates. Thirteen of seventeen termite species known to inhabit the Tucson area, including H. aureus, Q. perplexus and all local drywood and dampwood species, typically fly during the summer months, June through September. Only three species, including B. tibialis, have been observed October through April (Nutting 1960). Thus the timing of termite flights might result in greater termite control requests during July, August, and September, when the majority of termite species take wing in Tucson. Likewise, fewer requests would likely be made during October, November, and December during which no

Tucson termite species are known to fly. Howevel:'~ question­ naire responses were not in complete agreement with this. The listing of July, by 50 percent of questionnaire respon­ dents, as a month in which the greatest numbers of termite control service requests were received is obviously incon­ sistent with the fact that this same month was reported by 35 percent of respondents as a month in which their com- panies received fewest requests. The responses of three companies were especially contrary to those of the majority, 77 hinting that some respondents misinterpreted these two questions. The primary cooperating company's location was quite close, within 1 km, of the center of termite contract dispersion for that company (Fig. s 12 and l.3), intimating that dispersion of a company's termite contracts might be dependent upon company location. However, contract disper­ sions for the primary cooperator (Fig. l.3) and for all other responding companies (Fig. l.4), were similar while the locations of the companies varied. Therefore it seems doubtful that company location influences termite contract dispersion to any great degree. A composite contour map including both the primary cooperator's contracts and those of other questionnaire respondents depicts the known termite contract dispersion for Tucson (Fig. ,l.5). From compilations of termite inspection report data, 40.5 percent of structures in Tucson were found to be infested by termites at the time of inspection or at some time in the past. since many infestations undoubtedly go undetected, it can be assumed that more than half the structures in Tucson will at some time in their history be infested by subterranean termites. This is particularly notable since most structures in Tucson are pretreated for prevention of subterranean termite infestation. 78

Wilmot Road

Park Ave.

- Ina Road

Grant Road

Figure 12. Dispersion of subterranean termite con­ tracts held by primary cooperator. Location of primary cooperator indicated hy (x). 79

'I'WIX = 25.15

Coronado National Forest

Saguaro National Monument

Figure 13. Dispersion of subterranean termite contracts'held by primary cooperator.

Location of primary cooperator indicated by (0). Numbers indi­ cate mean numbers of termite con­ tracts per square mile. Shaded area indicates city of Tucson, Arizona. ..

80

"nWC = 25.15

Coronado National Forest

Saguaro National Monument

., ri...

Figure 14. Dispersion of subterranean termite contracts held by coop­ erating pest control companies, excluding primary cooperator.

Locations of cooperating compa­ nies indicated by (0). Numbers indicate ~ean numbers of termite contracts per square mile. Shaded area indicates city of Tucson, Arizona.

f 81

WAX = 25.15

Coronado National Forest

Saguaro National Monument

~ ...ori I I-19

Figure 15. Dispersion of subterranean termite contracts held by coop­ erating pest control companies including primary cooperator.

Numbers. indicate mean numbers of termite contracts per square mile. Shaded area indicates city of Tucson, Arizona. i:

82

Interpretation of Termite Foraging Adl... lty

Differences in estimated numbers of the three termite species encountered do not appear to reflect an interspecific sampling bias resulting from the use of toilet

paper bait nor its placement. La Fage et ale (1973) provided the original description for use of toilet paper in

sampling subterranean termite populations. Both~. perplex­

y§ and H. aureus were observed to forage somewhat different­ ly but continuously, night and day throughout the year at toilet paper rolls, while only minimal foraging was seen at wood blocks on the soil surface. Haverty et ale (1975) tested the sampling ef­ ficiency of toilet paper bait against superficial and partially buried dead wood. H. aureus was found to be most

numerous in the wood while ~. perplexus was much more numerous in the toilet paper. The apparent preference of H. aureus for wood was presumed artificial due to temporal sampling bias, the wood being sampled at times more favora­

ble to termite foraging, while the apparent preference of ~.

perplexus for toilet paper was related to this species I habit of foraging superficial items such as grasses and cattle dung. Four additional subterranean species, Amiter­ mes spp., were recorded from the wood and not from the toilet paper. This was attributed to their habit of foraging on "sound" wood. Another subterranean, Paraneotermes simplicicornis (Banks) was found in very low numbers in both 83 wood and toilet paper. A similar study by Haverty and Nutting (1975) again found H. aureus much more numerous in superficial dead wood than ~. perplexus, in fact more numerous than all other termite species combined. Ettershank et ale (1980) found bait position to be more important than bait composition in sampling for the subterranean termites, Gnathamitermes tubiformans (Buckley) and Amitermes wheeleri (Desneux) in New Mexico, and sug­ gested that subterranean termites locate food sources by detection of thermal "shadows" beneath surface debris. Hence surface placement of baits was preferabl.e to subsur­ face placement for these species. It seems reasonable to conclude that the use of toilet paper rolls as bait, as opposed to the use of other bait materials such as wooden blocks or stakes, is ad­ vantageous in sampling for ~. perplexus and perhaps H. aureus and B. tibialis as well, while probably less effec­ tive in sampling for certain other subterranean species such as Paraneotermes simplicicornis which in fact rarely infests structures in Tucson (Nutting, 1960).

The percentage of rolls infested by ~. perplexus and H. aureus, 16.7 and 2.3 percent respectively, is similar in terms of the ratio of rolls infested by the two species, 96 and 14 percent, obtained from a year-long toilet paper bait study by La Fage et ale (1973). 84 Also consistent with other studies were per­ centages of g. perplexus and H. aureus soldiers observed. Only 0.4 percent of observed g. perplexus were soldiers, while 3.5 percent of observed H. aureus were soldiers. Nutting (1970) and Nutting et al. (1973) found 0.4 to 1.3

percent soldiers for g. perplexus, and O. 7 to 4. 0 percent soldiers for H. aureus. However, Jones (1987) found an average of 8.6 percent soldiers in H. aureus foraging parties. Soldier percentage for B. tibialis, 9.1 percent, was inconsistent with the 1. 9 percent soldiers figure of Banks and Snyder (1920). Because the total number of B. tibialis individuals observed was relatively small, the 9.1 percent figure might be assumed less valid than soldier percentages obtained for the other species.

Foraging activity ip~terms of numbers of termites observed during the ten-week bait study was similar for all three species, and also consistent with previous studies

(Haverty et al. 1974, La Fage et al. 1976, Jones et al. 1987). A positive relationship (rs=.893, significant at alpha=.05) was found by Spearman rank correlation between number of rolls infested and number of individuals observed. Differences in nest-making, foraging, feeding, and climate tolerance have facilitated coexistence of termite species in grassland (Sands 1965) and rainforest (Matsumoto and Abe 1979) communities. In the Sonoran Desert community, g. perplexus and H. aureus are general feeders with con- 85 siderable diet overlap in terms of plant species foraged (Haverty and Nutting 1975): thus some degree of competitive interaction through exploitation of food resources probably occurs. The two species do differ in foraging preferences and means of foraging which undoubtedly contribute to their coexistence there (Haverty et ale 1975, Nutting et ale

1987) • Unlike those of Q. perplexus and H. aureus, the distributions of H. aureus and B. tibialis are almost mutually exclusive, apparently the result of interspecific requirements of temperature and moisture. In the desert surrounding Tucson, H. aureus generally occurs below 1000 m while B. tibialis is typically found at higher elevations. Throughout more than ten years of toilet paper bait studies conducted at 950 m elevation within the Santa Rita Ex­ perimental Range near Tucson, B. tibialis was never en­ countered. The atypical occurrence of B. tibialis in Tucson, at approximately 730 m, apparently results from urbanization providing greater moisture and reduced soil temperatures (Haverty and Nutting, 1976). certain profiles of infestation are evident for the three termite species observed. These profiles include the geographic location of sites relative to the center of termite contract dispersion (and center of Tucson), and by landscape development as defined by the extent and type of vegetation present, presence of woody debris, and human water management practices. Landscape development at bait ~.

86

sites was negatively correlated (rs~-.7285, alpha=.05) with distance of sites from the center of termite contract dispersion. Thus site location and landscape development appear to be interrelated factors. Peripherally located sites tended to be less manipulated, perhaps less disturbed, than sites closer to the center of contract dispersion and center of TUcson. wilcoxon's signed rank tests showed significant differences between g. perplexus and H. aureus

in terms of landscape development at infested bait sites I and in rapidity of attack as measured by dates of initial observation. Again, the occurrence of each termite species can be explained, at least in part, by species-specific foraging habits. g. perplexus appeared only at sites where quan­ tities of woody litter were present on the soil surface, Le. where appropriate forage was available. H. aureus occurred at one site of "low" landscape development, but was observed in far greater numbers at each of two sites with more "moderate" landscapes. This corroborates suggestions of Haverty and Nutting (1975), Haverty et ale (1976), and Nutting et ale (1987), that H. aureus tends to forage more solid, substantial items on the soil surface or below, while the more superficial attacks of g. perplexus are primarily upon woody surface debris. B. tibialis was also observed at a site of moderate landscape development similar in charac­ ter to sites where H. aureus was found. The habits and 87 workings of B. tibialis are said to be remarkably like those of H. aureus, although B. tibialis may prefer wood that is somewhat more moist, more decayed, and hence less sound than that preferred by H. aureus (Pickens and Light 1934).

Interpretation of Termite Contract Dispersion

Like termite infestation patterns in the urban environment, termite contract dispersion patterns appear to be governed by human activity. Explanations for the interrelation of housing density, structure age, and consumer affluence, which together influence the dispersion of termite contracts, are apparent. The relationship between consumer affluence and housing density was found to be most significant (p=.OOO). Housing density per unit area decreased with increasing affluence. Housing age increased with decreasing affluence, and with housing density. Noting that termite contract density contours radiate from the approximate center of TUcson as do historical perimeters of city expansion (Fig. 2), contract density may be thought of as a rough indicator of distance from the city I S center. Thus contract density decreases as one proceeds from the center of Tucson toward suburban areas. These results substantiate obvioius notions that, by comparison with more centrally located residential areas, outlying suburban areas generally tend to be less dense in terms of housing, are composed of newer housing, and are (.' ·l

88 occupied by individuals of greater affluence. Housing age appears to be related to termite contract dispersion largely as a result of its inverse relationship to affluence. Since termite contract density was lower in suburban areas, i. e contract density decreased as housing density decreased, the distribution of structures seems to be the principal influence on the distribution of termite contracts in Tucson. Also significantly related to termite contract distribution was soil permeability. Soil permeability decreased as contract density increased and as housing density increased. Thus soil permeability increased with increasing distance from the city's center, and regions with higher numbers of termite contracts per unit area were generally those with less permeable soils. Williams (1934) explained the importance of climate, vegetation, and soil slope and structure in limiting termite distribution. Haverty and Nutting (1975) discounted the effect of climate on small geographic areas, stating that soil water-holding capacity, and shade and food resources provided by vegetation, interact to affect termite abundance and dispersion. The generally higher permeability of coarser soils allows increased hydrostatic or downward­ flowing water which is more easily utilized by termites in comparison with the increased particle-bound water typical of finer soils. Thus to be conducive to termite habitation, 89 a higher overall water content may be necessary in finer, generally less permeable soils. Johnson and Whitford (1975) found subterranean termites in the Chihuahuan Desert virtually absent from fine, clay soils and areas where caliche was less than 30 cm beneath the soil surface. There, fifty percent fewer toilet paper rolls were attacked on shallower soils compared to rolls set on deeper soils.

In Tucson, soil depth as m' .:&sured by depth to caliche layers was not significantly related to the disper­ sion of termite contracts, nor was it related to soil grade or slope. The negative relationship found between soil permeability and contract dispersion is inconsistent with notions of soils with greater permeability being more habitable by termites. It seems the influence of soil permeability on termite dispersion may be reduced in urban environments where soil water content is elevated by irrigation and other artificial water sources, and from increased shade created by the presence of ornamental vegetation and buildings.

Influences on Retreatment Rate

The significance of wood frame construction in stucco, brick, and wood walls, in the prevention and control of subterranean termites is not surprising. certain types of stucco walls have been noted as generally unsatisfactory and requiring special inspection techniques as infestations 90 are easily masked by stucco facades. Reconstruction is suggested as the only viable control option except in areas of low termite incidence. Moreover, city building codes may not permit construction of certain types of stucco walls (Mampe 1973). Brick structures too possess the inherent potential for infestation through disintegrating mortar joints. That walls constructed primarily of wood facilitate termite infestation is also obvious. Conversely, adobe and concrete walls appear much less conducive to termite infestation in Tucson. similarly, slab-on-ground construction warrants special inspection and treatment techniques (Ebeling 1975, Mallis 1982, Mampe 1973). The significantly higher retreat­ ment rates for structures resting on slabs (Table XXVII) undoubtedly result from the difficulty of discovering and adequately treating termite infestations in these structures as opposed to those with crawlspaces or basements. 91

CONCLUSION

Termites exert a profound economic effect on the human inhabitants of Tucson, Arizona. Subterranean species are responsible for nearly all damage to structures but drywood and dampwood species also contribute to the city's estimated annual cost of well over three million dollars for prevention and control of termites. Despite the fact that most homes are pretreated and many are under contract with pest control companies for prevention and control of subterranean termite infestation, most will sooner or later, become infested. Heterotermes aureus is of greatest economic importance among the 18 termite species occurring in an around Tucson, followed by Reticulitermes tibialis. While H. aureus was undoubtedly indigenous to the land now occupied by the city of Tucson, B. tibialis occurred primarily at higher elevations. Urbanization allowed B. tibialis, possibly t'rom riparian habitats at lower eleva­ tions, to colonize urban locales with artificially high soil moisture content and reduced soil temperatures resulting from urbanization. In this manner another beneficial species assumed pest status through human manipulation of the environment. Transformation of the desert landscape into immaculate lawns has perhaps reduced the influence of species such as Gnathamitermes perplexus in urban environ- 92 ments. The importance of competition, if it occurs between

~. pernlexus and H. aureus, has thus been minimized by removal of woody debris from yards, perhaps making them more conducive to colonization by destructive H. aureus, and less so to colonization by non-destructive ~. pernlexus. B. tibialis naturally occurs in habitats different: from those of H. aureus and as such does not compete with it for resources. In essence, the destructive species, B. tibi­ alis, has been to a degree substituted for an economically harmless potential competitor, ~. perplexus, which normally exists alongside H. aureus and may exert some pressure on its populations through exploitation of resources. The most significant influence on H. aureus infestation in metropolitan Tucson, as measured by the dispersion of termite contracts held by pest control companies, is housing density. The degree of influence exerted by each of the interrelated considerations, housing density, structure age, and affluence, probably cannot be determined due to their inseparability. It is very likely that H. aureus infestation of structures in Tucson simply followed the spread of construction across the desert landscape. Moreover, while certain construction types, i.e. slab foundations and stucco, brick, and wood frame walls, have proven to require retreatment for termite control more frequently than other construction types, this can not be 93 interpreted as preferential infestation. since H. aureus searches more or less randomly and opportunistically for food resources, no wood-containing structure is likely to be ignored by foragers. Therefore the probability of becoming infested by subterranean termites appears essentially the same for all structures in an urban environment such as Tucson. The longer a structure stands, the more likely it is to become infested. Accordingly, the incidence of subterranean termii:e infestation follows the incidence of construction, as evidenced by the centralized dispersion of termite contracts, and the positive relationship between structure age, contract density, and housing density. Termite infestation of man-made structures is concomitant with human inhabitation of natural areas. A rapidly increasing human population resulting in increased urbanization will certainly be followed by a corresponding expansion of the termite problem. FUrther manipulation of the environment along with unwitting transportation and introduction of exotic termite species such as the Formosan termite will intensify this problem in the future. The recent proposal of the Velsicol corporation to end produc­ tion of cyclodiene insecticides, including the principal termiticides presently used by nearly all Tucson pest control companies, would necessitate the use of more expensive alternatives. Such facts indicate a potential if not probable multiplication of the already extreme economic 94 impact of termites in the United states, and suggest continued and intensified efforts to counteract this consequence. This study is unique in utilizing new and largely untapped sources of data, providing both historical and ecological perspectives to the study of urban termite communities. Through the use of tennite contract data, patterns of infestation and factors influencing those patterns were demonstrated, and a basis for understanding termite dispersion was supplied. An extensive bait study would also contribute greatly to our knowledge by furnishing fundamental and otherwise unobtainable information on termite distribution and abundance. Considering the great size of metropolitan Tucson, encompassing approximately 600 square miles, such a study would be labor-intensive, and would undoubtedly encounter problems unique to field .research in heavily populated urban environments. The chief advantages in using termite contract data are accessibility, quantity, and singularity in being the primary source of historical information regarding structural infestation. Thus a city­ wide bait study augmented by termite contract analysis would supply valuable information on subterranean termite infesta­ tion of urban structures-- information that might contribute to less hazardous and more effective prevention and control practices, for which the need has become acute.

".------_... - _._- ~~. 1.',.- t

95 APPENDIX A. Termite Control Questionnaire

1) Estimate your company's gross annual income from TERMITE control services alone: $ What PERCENTAGE of this figure is from:

drywood termite control services; %

dampwood termite control services; %

"desert" termite control services; % 2) What PERCENTAGE of your company's gross annual income is from general pest control not including termite control:

% 3) Estimate the number of PREtreatments for subterranean termite control your company performs per year: 4) Estimate the number of REtreatments for subterranean termite control your company performs per year (on structures previously treated by your company): 5) List the PERCENTAGE of subterranean termite control jobs your company performs using each of the following termiticides: Chlordane (Velsicol Gold Crest C-IOO): % Heptachlor + Chlordane (Velsicol Termide): % Chlorpyrifos (Dow Dursban TC): % Permethrin (ICI Torpedo): % Permethrin (FMC Dragnet): % other, please specify material: % 96

6) Estimate the number of active contracts your company currently holds for subterranean termite inspection and control: 7) During which month(s) does your company receive: the most requests for termite control; the fewest requests for termite control; 8) Approximately what PERCENT of your company's subterranean termite contract services are performed:

within 2 miles of your company's location; %

within 5 miles of your company's location; %

more than 5 miles form your company's location; ______% 97

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