An Inside Look atMole Cricket ManagementUnderstanding these pests' behavior is vital to controlling their numbers.by M. G. VILLANI, Ph.D., andR L. BRANDENBURG, Ph.D.

nospecies of mole crickets, thetawny mole cricket (Scapteriscusvicinus) and the southern mole

cricket (S. borellii) are among the mostdevastating insect pests in the south-eastern United States. The tawny molecricket is primarily a root feeder, whilethe southern mole cricket is a predatorof other soil arthropods (insects).

The cost of control and the impactof damage often is measured in tens ofthousands of dollars per golf course inmany areas. Neither of these pests isnative to the U.S.; they were introducedto several locations along the Southeastcoast in the early 1900s. Since that time,they have migrated northward wellinto North Carolina and westward toeastern Texas. Soil type and tempera-ture should. limit much additionalspread, but a few isolated infestationsare also showing up in the southwest-ern United States.

The costs associated with controllingmole crickets, the lack of effective con-trol following insecticide application,and the lack of an adequate under-standing of mole cricket ecology andbehavior prompted the development ofa proposal to the USGA Green SectionResearch Committee in 1992. A col-laborative effort was established totake advantage of the applied researchprogram on mole crickets at NorthCarolina State University under thedirection of Dr. Rick L. Brandenburgand the soil insect ecology programdirected by the late Dr. Mike Villani atCornell University.

This team received funding fromUSGA and for the next seven yearsembarked on an ambitious program tobetter understand the biology, ecology,and behavior of this most troublesometurfgrass insect pest. The research pro-gram focused on several field andlaboratory research projects. Each ofthese projects was targeted towarddeveloping information that will com-plement economically and environ-mentally sound mole cricket manage-ment programs.

6 USGA GREEN SECTION RECORD

Field Research

Field research was conducted onseveral golf courses in New Hanoverand Brunswick counties along thesoutheastern coast of North Carolina.Additional studies were conducted inlaboratories and greenhouses at NorthCarolina State University in Raleigh,N.C.

A study to monitor mole cricketdevelopment and to develop an equa-tion to forecast or predict mole cricketegg hatch was initiated early in theresearch program. Acoustic sound trapsthat synthetically produced the matingcall of the male mole cricket were usedto monitor mating flights. These wereplaced at two golf courses in BrunswickCounty. In addition, a network of auto-mated soil and air temperature record-ing units was installed throughout thetwo-county area to monitor degree-dayaccumulation.

Course fairways were monitoredweekly from late spring to late summer.Intensive sampling consisted of using a2% soapy water solution applied tosquare meter areas to bring molecrickets to the surface. Crickets werecollected, returned to the laboratory,and recorded for species, size, and stageof growth. These data provided indi-cations of egg hatch and cricketdevelopment as related to soil and airtemperature. Monitoring over a three-year period of time provided situationswith significant variations in degree-dayaccumulations, but did not establish astrong relationship with cricket egghatch, development, or mating flightpatterns.

Subsequent greenhouse evaluationsat North Carolina State Universitydetermined that soil moisture doesplaya significant role in the egg layingprocess. Soil moisture affects the timingand intensity of mole cricket egg laying.Mole crickets prefer adequate soilmoisture if they are to lay their eggs.Thus it appears there is an importantinteraction between soil moisture and

soil temperature that influences molecricket development each year.

Additional studies sought to defineturf areas that could be considered athigh risk for mole crickets. This projectfocused on the mole cricket abundanceas influenced by soil moisture, varioussoil parameters, and topography. Inaddition, the relationship between thepresence of adults in the spring andthe subsequent outbreaks of the nextgeneration of crickets in late summerwas investigated.

The intensity of adult abundance wasmeasured in the spring through astandardized grid rating system. A widerange of turf areas were monitored,including those with little or no dam-age. Soapy water flushes were thenused in the same areas late in thesummer to determine the abundance ofrecently hatched mole cricket nymphs.Soil samples were taken weekly andsoil moisture, texture, silt and clay con-tent, as well as pH and organic matterwere determined. General observationson topography were also noted.

Results show a strong relationshipbetween the presence of adults in thespring in a specific area and subsequentoutbreaks of nymphs and turf damagelater in the summer. This correlation isimportant since the majority of con-ventional insecticide applications aremost effective when applied againstsmall mole cricket nymphs long beforeobvious surface damage is visible. Sucha relationship allows a superintendentto map areas of adult damage in thespring and strategically apply insecti-cides in those locations during thesummer as egg hatch occurs.

This study also provided preliminaryindications concerning the relationshipof certain soil conditions and molecricket abundance. Of greatest impor-tance appears to be clay and silt con-tent. Slight increases in clay or siltcontent of the soil were generallyassociated with reduced mole cricketabundance. While this relationshipneeds to be studied more closely, it does

indicate two possible managementoptions. One is that certain areas maybe defined as "high risk" based on soilcharacteristics. Such information couldbe useful in managing these pests.

Research investigating the impact ofirrigation, both before and after theapplication of insecticides, proved in-conclusive. Large plots (50 ft. x 50 ft.)were established and subjected tovarious treatments and irrigation regi-mens. Treatments included no irriga-tion, pre-treatment irrigation, post-treatment irrigation, and both pre- andpost-treatment irrigation on replicatedplots. When the effects of these irriga-tion schedules were studied in conjunc-tion with the use of several syntheticpyrethroid insecticides, the results werevery inconsistent.

Two factors possibly added to thisinconsistency. One is that as morewater was applied (as either pre- orpost-treatment irrigation), surfaceactivity increased in spite of the insecti-cide. However, the extent to whichsurface activity increased with in-creasing soil moisture was difficult toassess in this experiment as it wasdesigned.

Another important factor adding toinconsistent control is an avoidancebehavior of the mole crickets when aninsecticide is applied to the soil. Theexact nature of this avoidance is notwell understood, nor has the degree towhich it occurs in the field been fullyexplored. However, reversed-rate re-sponses in pesticide field testing trialsare not uncommon. In other words,due to the insects' ability to detect andavoid the insecticide, higher insecticideapplication rates sometimes result inless control of the pests.

The field behavior of mole cricketswas examined by creating castings ofcricket tunnels with the use of a fiber-glass resin. The resin, commonly usedfor auto body repairs, provided an easy-to-pour material that flowed smoothlyinto the tunnels in the soil and hard-ened quickly with the addition of acatalyst. The casting material formed alightweight, durable casting that couldbe easily excavated from the soil. Thefiberglass resin also often encased thecricket occupying the tunnel, makingspecies identification easy.

Tunnels for the root-feeding tawnymole cricket almost always producedthe "Y"-shaped castings consistent withthose observed in the laboratory soilradiographs. The structure recoveredfrom the predatory southern molecricket consisted of a meandering type

of tunnel that might be associated withgeneral searching in the soil. Castingsfrom this species of mole cricket werealso consistent with radiographs takenin the laboratory. The castings docu-ment a consistent tunneling pattern foran individual species and markeddifferences between the two species.These are obviously related to thegeneral diet of the two species and tothe behavior required to meet thosedietary needs.

Greenhouse studies of field-collectedcrickets also indicate differences inresponse and possible susceptibility tospecific insecticides by the two species.The actual effect of behavioral differ-ences and individual cricket suscepti-bility to contact with a particularinsecticide needs further investigation.These species differences, in addition tosoil type and climate, may account forthe variability in product performanceoften observed by superintendents in aspecific region.

An additional area of researchfocused on the use of a fungal pathogento help add insight into the findingsof specific laboratory experiments.Several strains of the pathogen Beau-vena bassiana were applied for molecricket control on golf course fairwaysand the effect on the population wasmonitored. Treatments included severalstrains of this pathogen applied withboth surface and subsurface applicationequipment.

The results of their trials are notimpressive in terms of level of controltypically desired by golf course super-intendents. However, the study doesprovide insight into the use of suchcontrol agents. The use of subsurfaceapplication equipment appears to im-prove the efficacy of these products,

possibly by reducing the likelihood ofexposure to sunlight or desiccation ofthe fungal spores. The results are con-sistent with laboratory findings examin-ing fungal pathogens and mole cricketbehavior.

Laboratory ResearchTo further our understanding of the

impact of environmental factors anddisease on mole crickets, a clear pictureof "typical" tawny mole cricket and

The southern (left)and tawny molecricketsare the mostserious soilinsect pests inthe southeasternUnited States.

southern mole cricket behavior wasnecessary. Studies were initiated usingradiographic technology (x-rays) tovisualize the movement and feedingpatterns of both tawny mole cricketsand southern mole crickets in the soilmatrix. Mole crickets were placed inplexiglass soil arenas (1.5 x 12 x 15inches). Through the placement of asmall lead tag on each cricket, tunnelconstruction and cricket movement inthe tunnel could be monitored overextended periods of time.

A series of radiographs indicate aconsistent behavior of a single late-instar tawny mole cricket nymph. Thisnymph produces a characteristic "Y"-shaped tunnel that allows two escaperoutes to the surface and down intothe soil to escape predators, includinglarger southern mole crickets, and along tunnel into the soil profile thatmost likely aids in thermal and waterregulation.

Tawny mole crickets typically feed atthe root! soil interface between the "Y"arms and are therefore always near anescape route. As tawny mole cricketsgrow, their tunnels widen and extendfurther into the soil profile, suggestinga possible cause for the difficulty inbringing older crickets to the surfacethrough soap flushes and baits. Crickets

SEPTEMBER/OcrOBER2001 7

also seem to maintain their tunnelsystem, rebuilding collapsed tunnelsovertime.

The "Y" tunnel patterns of the tawnymole cricket do not seem to change inthe presence of predatory southernmole crickets. Tawny mole cricketsappear to "wall-off" their tunnels whensouthern mole crickets are present, butfurther studies are needed to confirmthis behavior.

By comparison, southern molecrickets will move as far from eachother as possible when placed togetherin a chamber. This behavior suggeststhe presence and activity of a chemi-cally mediated avoidance behavior inthis species. There is also an indicationthat mole crickets can detect and avoidconventional synthetic insecticides inthe soil.

Additional studies on cricket be-havior utilized arenas (12 x 20 x 8inches) filled with moist sandy loamsoil and topped with a commercialsod. A single tawny mole cricket wasplaced in the arena and allowed totunnel into the surface. At the end ofseven days, each arena was sampled todetermine the tunneling pattern of thecricket. To form a paraffin cast, theentrance to the mole cricket tunnel waslocated by looking for a disturbed areaof turf. Solid paraffin wax was heateduntil liquid and poured slowly, to allowescape of air bubbles, into the tunnelentrance. After a short time (about 10minutes), soil was carefully excavatedfrom around the hardened wax and thefull casting was retrieved.

To reveal the tunnel of a single tawnymole cricket over a one-week period,soil was removed at 1.5-inch intervalsfrom the surface to reveal the tunnel asit descended into the soil profile. Thered-tinted casting represents that por-tion of the tunnel revealed by removingsoil in that 2.5-inch layer (previouslyexposed tunnels are white). The cast-ings showed the typical "Y"-shapedconstruction and extensive tunneling atthe root-soil interface where the cricketforaged for food.

Preliminary studies with spray appli-cations of the fungal pathogen B.bassiana indicate that reverse-rateresponses often occur with higher rates.This may be the result of avoidancebehavior associated with higher rates.Mole crickets detect and avoid formu-lations containing pathogenic fungi byremaining deep in the soil profile. Thisbehavior allows mole crickets to avoidthe fungal pathogen until it becomesinactive.

8 USGA GREEN SECfION RECORD

Laboratory studies were initiated toevaluate mole cricket behavior towardsoil-borne, entomopathogenic fungi(fungi that cause disease in insects) andto evaluate the efficacy of subsurfaceand surface fungal applications. Inthese experiments, tawny mole cricketshad no choice but to tunnel through alayer of fungal-treated sand in order toreach a sod food source. One late-instartawny mole cricket was placed in eacharena and allowed to tunnel for onehour before strips of sod were placedon top of the sand. After four days, thesod was removed and two inches offungal-treated sand was added to thesurface of the sand. An equivalentlayer of clean sand was added incontrol treatments.

Two hours after treatment, 40% ofthe tawny mole crickets in both treatedand untreated arenas had tunneledthrough the treatment layer and re-turned to the surface. After three andsix days, 60% of treated and 80% ofuntreated tawny mole crickets hadtunneled through to the surface sod.The amount of tunneling in the treat-ment layer area was significantly lowerin arenas treated with the entomo-pathogenic fungi compared to thearenas containing the clean sand layers.Tunneling in the untreated layer belowthe interface was not significantly dif-ferent in any treatment.

These findings of avoidance behaviorin mole crickets suggest that placementof fungal pathogens in the soil profilemay influence the effectiveness of aproduct to control mole cricket damageto turf. The avoidance response seen inthese experiments may be evidence ofan evolutionary adaptation to avoidinfected insects and areas of soil withhigh concentrations of fungal spores.Avoidance behavior may explain theinconsistent results found in the fieldwith high doses and surface applica-tions of fungal pathogens. Subsurfaceapplications of fungal pathogens, how-ever, may lengthen the time a pathogenremains viable compared to pathogensurvival after surface application.

This field and laboratory researchdemonstrates the value of a goodunderstanding of pest biology andecology. These studies help us betterunderstand the reasoning behind someof our strategies for mole cricket man-agement. At the same time, they alsoreveal why mole crickets continue to besuch a difficult pest to manage. Furtherstudies will help ensure our ability tocost effectively manage this seriouspest.

Additional ReferencesBrandenburg, R. L. 1997. Managing molecrickets: Developing a strategy for success.Turf Grass Trends 6:1-8.Brandenburg, R. L., and M. G. Villani. 1995.Handbook of turfgrass insect pests. Ento-mological Society of America. Lanham, Md.Brandenburg, R. L., P. T. HertI, and M. G.Villani. 1997. Integration and adoption ofa mole cricket management program inNorth Carolina, USA. Pages 973-979. In:International Turfgrass Society ResearchJournal, Vol. 8. Part 1. Univ. PrintingService, Univ. of Sydney, New South Wales,Australia.Brandenburg, R. L., P. T. Hertl, and M. G.Villani. 2000. Improved mole cricket man-agement through an enhanced understand-ing of pest behavior. Pages 397-407. In: J. M.Clark and M. P. Kenna (eds.). Fate and'Management of Turfgrass Chemicals. Sym-posium Series 743. Amer. Chern. Soc.,Washington, ne.Fowler, H. G. 1988. Dispersal of earlyinstars of the mole cricket, Scapteriscustenuis, as a function of density, food,pathogens (Orthoptera: Gryllotalpidae).Entomo!. Gener. 13:15-20.Fowler, H. G. 1989. Natural microbialcontrol of populations of mole crickets(Orthoptera: Gryllotalpidae), Scapteriscusborellii, regulation of populations in timeand space. Res. Bras. Bio!' 49:1039-1052.Hertl, P. T., and R. L. Brandenburg. 1997.Evaluation of Beauveria bassiana sporeapplications for control of mole cricketnymphs in turf. Arthropod ManagementTests 23:323.Hudson, W G., J. H. Frank, and J. L.Castner. 1988. Biological control of Scap-teriscus spp. mole crickets (Orthoptera:Gryllotalpidae) in Florida. Bull. Entomo!.Soc. Am. 34:192-198.Villani, M. G., and R. J. Wright. 1988. Useof radiography in behavioral studies ofturfgrass-infesting scarab grub species(Coleoptera: Scarabaeidae). Bull. Entomo!.Soc. Am. 34:132-144.Villani, M. G., L. L. Allee, A. Diaz, and P. S.Robbins. 1999. Adaptive strategies ofedaphaic arthropods. Ann. Rev. Entomo!.44:233-256.Vittum, P., M. G. Villani, and H. Tashiro.1999. Turlgrass insects of the United Statesand Canada. Second Edition. Cornell Uni-versity Press, Ithaca, N.YXia, Y, and R. L. Brandenburg. 2000. Effectof irrigation on the efficacy of insecti-cides for controlling two species of molecrickets (Orthoptera: Gryllotalpidea) ongolf courses. J. Econ. Entomol. 93:852-857.

The late DR. MIKE VILLANI was Profes-sor of Entomology at Cornell University inGeneva, N. Y, and DR. RICK BRANDEN-BURG is Professor of Entomology at NorthCarolina State University in Raleigh, N. C.