STORED-PRODUCT AND QUARANTINE ENTOMOLOGY

Activity of Plodia interpunctella (Lepidoptera: Pyralidae)in and Around Flour Mills

CARL W. DOUD1 AND THOMAS W. PHILLIPS2

Department of Entomology and Plant Pathology, 127 Noble Research Center, Oklahoma State University,Stillwater, OK 74078

J. Econ. Entomol. 93(6): 1842Ð1847 (2000)

ABSTRACT Studies were conducted at two ßour mills where male Indian meal moths, Plodiainterpunctella (Hubner), were captured using pheromone-baited traps. Objectives were to deter-mine the distribution of male P. interpunctella at different locations in and around the millsthroughout the season, and to monitor moth activity before and after one of the mills was fumigatedwith methyl bromide to assess efÞcacy of treatment. Commercially available sticky traps baited withthe P. interpunctella sex pheromone were placed at various locations outside and within the largerof the two mills (mill 1). Moths were captured inside mill 1 after methyl bromide fumigations. Thehighest numbers of P. interpunctella were caught outside the facility and at ground ßoor locationsnear outside openings. Additional traps placed in the rooms above the concrete stored-wheat silosat mill 1 during the second year captured more moths than did traps within the millÕs productionand warehouse areas. In another study, moths were trapped at various distances from a smaller ßourmill (mill 2) todetermine thedistributionofmoths outdoors relative to themill. Therewas anegativecorrelation between moth capture and distance from the facility, which suggested that moth activitywas concentrated at or near the ßour mill. The effectiveness of the methyl bromide fumigations insuppressing moth populations could not be assessed with certainty because moths captured afterfumigation may have immigrated from outside through opened loading bay warehouse doors. Thisstudy documents high levels of P. interpunctella outdoors relative to those recorded inside a foodprocessing facility. Potential for immigration of P. interpunctella into ßour mills and other storedproduct facilities from other sources may be greater than previously recognized. Moth entry into afood processing facility after fumigation is a problem that should be addressed by pest managers.

KEY WORDS Indian meal moth, stored-products, fumigation, methyl bromide

THE INDIAN MEAL moth, Plodia interpunctella (Hub-ner), is a serious and widespread pest of many storedfood commodities (Hinton 1943, Sedlacek et al. 1996).Female P. interpunctella and females of other stored-product moths of the subfamily Phycitinae produceZ-9, E-12-tetradecandienyl acetate as a component oftheir sex pheromone blends (Brady and Nordlund1971; Brady et al. 1971; Kuwahara et al. 1971a, 1971b).Traps baited with synthetic pheromone are effectiveand widely used to monitor male stored-productmoths (Vick et al. 1981, Chambers 1990). Pheromone-baited traps have proven successful in detecting lowlevel infestations of these moths (Vick et al. 1981).

Although many studies have focused on capturingphycitine moths inside storage and food processingstructures (reviewed in Plarre 1998), only a few stud-ies have documented outdoor activity of P. interpunc-tella. Ganyard (1971) used traps baited with virginfemales as natural pheromone sources and capturedless than one male moth per trap per day at outdoorlocations up to 1.2 km from grain storages. A limited

trapping study by Vick et al. (1981) with syntheticpheromone found P. interpunctella and the almondmoth, Cadra cautella (Walker), inside a food ware-house, but no moths were trapped outdoors on theloading dock. Cogburn and Vick (1981) trapped C.cautella at rates of 18.8 and 23.8 moths per trap perweekboth inside and immediately outside rice storagebins, respectively, but recorded only 0.1Ð0.4 mothsper trap per week at Þeld sites 10Ð40 km away. Vicket al. (1987) placed pheromone traps for four speciesof storage moth pests in Þve outdoor locations alonga 56-km transect from a peanut warehouse and onlytrapped substantial numbers of P. interpunctella in thearea immediately outside the structure. These studiessuggest that outdoor occurrences of moths such as P.interpunctella and C. cautella can be attributed to em-igration from nearby storages, and that these speciesdo not breed in outdoor habitats. Some researchershave concluded that moth infestations inside foodprocessing facilities are mainly attributed to the in-troduction and storage of infested product (Levinsonand Buchelos 1979) rather than to immigration ofadults from outdoor locations.

In the current study we monitored P. interpunctellain and around twoßourmills in 1997 and1998. SpeciÞc

1 Current address: Navy Disease Vector Ecology Control Center,P.O. Box 43, Naval Air Station, Jacksonville, FL 32212Ð0043.

2 To whom correspondence should be addressed.

0022-0493/00/1842Ð1847$02.00/0 q 2000 Entomological Society of America

objectives of the study were to document variation inmoth activity at different locations and times bothinside and outside the building, to determine P. inter-punctella activity before and after methyl bromidefumigations, and to evaluate the outdoor occurrenceof the moths at various distances from a mill.

Materials and Methods

Traps and Lures. Two types of sticky traps designedfor ßying insects, manufactured by Trece (Salinas,CA), were used in these studies. The Pherocon III D,a delta-shaped sticky trap with constricted openingsfor moth entry, was used inside and immediately out-side the ßour mill in most experiments. The design ofthe Pherocon III D trap was ideal for this study be-cause the small openings for insect entry also reducedfoulingof the trapby thehigh levels of dust in theßourmill environments. The Pherocon II trap, a diamond-shaped sticky trap with larger openings than thePherocon III D, was used to study outdoor moth ac-

tivity inoneexperiment. Traps in all experimentswerebaited with pheromone lures provided by the manu-facturer. Lures consisted of a rubber septum that re-leased a single pheromone component, Z-9, E-12-tet-radecadienyl acetate, and were placed on the trapÕsbottom inner sticky surface. Lures were replaced ev-ery four wks. Traps were replaced when needed be-cause their sticky surfaces became covered withmoths or dust, or at 4-wk intervals.

Flour Mill Studies. Mill 1 was a large commercialwheat ßour mill that typically operated 24 h a day, 7 da week. Traps were deployed in four areas of mill 1 forstudies conducted in 1997 and 1998: the bulk grainstorage area (comprised of concrete silos and eleva-tors), an eight-story building housing milling andpackaging operations, a bulk ßour storage area, andtwo Þnished product warehouse areas (Fig. 1A). In-door traps were hung from pipes or conduits two mabove the ßoor, and were spaced from three to 10 mapart, depending on the size of the area monitored, ina line approximately centered along the roomÕs long

Fig. 1. (A) Facility components for mill 1, side view. Warehouse 1 was located directly behind warehouse 2 in this view.(B) Placement of moth traps around mill 2 for the spatial occurrence study. Stars represent traps, lines represent residentialstreets, thedotted line represents train tracks, and the single circle '200mnorthof themill represents a separate storedwheatbin.

December 2000 DOUD AND PHILLIPS: TRAPPING INDIAN MEAL MOTHS AT FLOUR MILLS 1843

dimension. During the 1997 study (1 MayÐ26 Novem-ber), traps were checked biweekly and all P. inter-punctella counted. In 1997, two traps were placed onßoors 3 through 8 of the mill area, two each in therooms above andbelow thebulk-storedßour bins, twoin warehouse 1 and four in warehouse 2. On 29 August1997, two traps were placed 30 m apart outdoors in aÞeld 50 m south of the mill and two other traps wereput outdoors directly adjacent to the south side of thebuilding, one trap near the rail car mill entrance andanother on the south loading dock. Outdoor traps atmill 1 were positioned 2 m above the ground and werehung from tree branches or building hardware.

Mill 1 was also used for the 1998 study (16 JuneÐ5November) in which traps were checked weekly andsimilarly deployed. No traps were placed on ßoors 4through 8 or in the rooms above the bulk stored ßourbecause of low moth capture in those areas in 1997.Traps were placed outside the mill at the beginning ofthe 1998 study: one in a Þeld 50 m south of the mill,another 50 m north of the mill, a third 2 m south of themill on the south loading dock, and a fourth trapattached to the outside wall of the mill on the westloading dock. An additional trap was placed in each ofthe three gallery areas above the wheat silos on 10September.

Fumigations were conducted at mill 1 on 31 May1997, 30 August 1997, and 4 July 1998 by a contractedfumigator. All areas of the mill were fumigated withthe exception of warehouse 2 and the stored wheatsilos. Flour inside the bulk storage bins was fumigatedwith magnesium phosphide, whereas the eight-storymillingbuilding,warehouse1, andadjacent areasweretreated with methyl bromide. All traps were removed1Ð3 d before fumigations and replaced as soon aftertreatment as possible.

Outdoor Trapping Study. The outdoor area sur-rounding mill 2 was used in 1998 for a study of mothcapture in pheromone traps relative to the distancefromamill.Mill 2was in adifferent city frommill 1 andwas about one-half the size andproduction capacity ofmill 1. We selected mill 2 because it was located in aneighborhood that had few other obvious sources ofIndianmealmoths relative to theneighborhoodofmill1,whichwas located close to several commercial grainstorage facilities. Twenty-eight traps were positionedthroughout the residential area surrounding mill 1 atdistances from 6 to 440 m in various directions (Fig.1B). Traps with lures were attached '3 m high onutility poles on 24 September, collected after 1 wk on1 October, and the number of P. interpunctellacounted. The distance of each trap from the mill wasdetermined using a survey laser instrument (modelCriterion 400, Laser, Technology, Englewood, CO),sited fromthe trap location to the topof themillÕs grainelevator. The geographic position of each trap relativeto the mill was recorded by designating one of fourdirectional quadrants (northeast, northwest, south-east, and southwest). All but the southwest quadrantcontained seven traps; data from only four traps wererecorded in the southwest quadrant because threetraps were lost.

Data Analyses. Moths caught per trap per trappingperiod at each designated location at mill 1 were plot-ted on a biweekly (1997) or weekly (1998) basis.Analysis of variance was performed in SAS usingPROC MIXED followed by a means separation (LS-MEANS) to test for differences in capture by location(SAS Institute 1996). Seasonal moth activity duringthe 1997 and 1998 studies atmill 1was plottedbymeannumber trapped per day using the sum of mothscaught at all locations during each trapping period.Moth captures from the outdoor study at mill 2 wereanalyzed by linear regression of square root trans-formed moth capture against distance in meters fromthe facility using PROC REG (SAS Institute 1996).Trap captures were analyzed for differences amongquadrant directions and between north and south ofthe mill using PROC GLM; comparisons by directionwere adjusted by using distance as a covariate (SASInstitute 1996).

Results

Capture of P. interpunctella in different locations atmill 1 during 1997 was signiÞcantly different by loca-tion(F55.28; df510, 15;P50.0021),with thehighestcaptures occurring in warehouses 1 and 2 and theroom at the bottom of the bulk ßour storage (Fig. 2).Locations with the highest moth activity were all sit-uated on the ground ßoor close to large outside open-ings. In 1998 the highest numbers of moths were re-corded from traps in warehouse 2 (Fig. 3), butstatistical analysis found no signiÞcant differencesamong the four locations studied (F 5 3.54; df 5 3, 4;P 5 0.1269).

Moth activity in 1997 gradually increasedduring theseason to a peak on 29 August, followed by decline tothe end of the study (Fig. 4A). Moths were capturedaftereach fumigation in1997, and themothpopulation

Fig. 2. Capture of P. interpunctella by location in mill 1during 1997. Each mean represents 13 biweekly observationswith four traps in warehouse 2 and two traps in all otherlocations. Means with the same letter are not signiÞcantlydifferent (LS MEANS comparison).

1844 JOURNAL OF ECONOMIC ENTOMOLOGY Vol. 93, no. 6

was clearly not eliminated as a result of these treat-ments. The seasonal pattern of moth capture in 1998was similar to that in 1997, and moths were still cap-tured after the 4 July fumigation (Fig. 4B). Trapsoutside mill 1 during 1997 captured more moths thandid traps inside the mill (Fig. 5A). We observed a36-fold higher capture of moths on outside traps com-pared with inside traps during the Þrst comparisonperiod that ended 16 September. Moth activitysteadily declined in subsequentweeks both inside andoutside the facility. Responses of moths to traps out-sidemill 1 or in the gallery of the grain silosweremuchhigher in most cases than responses to traps inside(Fig. 5B). SigniÞcantly more moths were caught out-doors compared with indoors from 24 June through 10September (PROC MIXED, P , 0.05 for all pairwisecomparisons at each date), and captures in the galleryrooms of the grain silos were similar to or greater thanthoseoutside from24September through5November(Fig. 5B).

The numbers of P. interpunctella trapped at variousdistances from mill 2 ranged from two moths at 202 mto120moths at 6mduring a 1-wk trappingperiod(Fig.6). Regression analysis revealed a signiÞcant negativerelationship (b 5 20.0076, r2 5 0.1883, P 5 0.0302) ofmoth capture with distance from the mill. After thisstudy was completed an isolated bin of stored wheat,200 m north of mill 2, was discovered (Fig. 1B). Thisbin could have served as a source of moths north ofmill 2. A comparison of mean number of moths pertrapnorth (43.2 6 8.4 SE) versus south (17.8 6 4.0 SE)of the mill was nearly signiÞcantly different (F 5 3.90,df 5 1, P 5 0.0623). Differences in moth captureamong the four quadrants around the mill were notsigniÞcant (F 5 2.24, df 5 3, P 5 0.1145).

Discussion

Three observations can be drawn from the studiesreportedabove.First,P. interpunctellacanbecaptured

regularly in high numbers outside ßour mills duringthe summer and early fall months, and occur in highernumbers close to the mill compared with far from themill. Second, some of the P. interpunctella trappedinside mill 1 may have come from outside the buildingvia the open doorways on the ground ßoor. Lastly, thewheat storage silos of mill 1 may have been a predom-inant source of moths captured both inside and out-side the mill buildings.

An a priori assumption of this research was that P.interpunctella populations perpetuate inside the millfacility as a closed system. There was no expectationthat moth activity outside the facility would be im-portant to the spatial or population dynamics of mothsin the mill. Thus, we initially deployed traps onlyinside themainbuilding thathoused themillingequip-ment and warehouses. However, substantial moth ac-tivity was observed inside the mill immediately afterfumigations, and moth captures were consistentlyhigher in areas of the mill near large outside openings.Additional trapswere subsequentlyplacedoutside themill in late August 1997. The resulting high mothcapture outside led us to suspect that some mothstrapped inside the mill may have immigrated into the

Fig. 3. Capture of P. interpunctella by location in mill 1during 1998. Each mean represents 18 weekly observationswith two traps in each area.

Fig. 4. (A) Daily indoor capture of P. interpunctella atbiweekly intervals for all locations combined in 1997 at mill1. Means represent 24 traps. Arrows denote methyl bromidefumigations on 31 May and 30 August. (B) Daily indoorcapture of P. interpunctella at weekly intervals in 1998 at mill1. Means represent observations from eight traps. Arrowdenotes methyl bromide fumigation on 4 July.

December 2000 DOUD AND PHILLIPS: TRAPPING INDIAN MEAL MOTHS AT FLOUR MILLS 1845

building from outside via large doors that were fre-quently left open. Based on these observations, mothactivity in the mill immediately after methyl bromidefumigation may reßect the immigration of moths fromoutdoors rather than low effectiveness of the fumi-gant.

Failure to suppress moth populations in a ßour millafter fumigation has been noted in the past. Popula-tions of P. interpunctella and C. cautella in a ßour millin Greece were only slightly reduced following phos-phine fumigation, but those of Sitotroga cerealella(Olivier) and Ephestia kuehniella Zeller were reducedtobeloweconomically damaging levels (Levinson andBuchelos 1979). It is possible that P. interpuctella andC. cautella, which are ecologically similar species(Hinton 1943), are more inclined to ßy outdoors thanother storage moths, and readily reinvade structuresafter fumigation. Alternatively, capture of adult mothssoon after structural fumigaitonmay result fromemer-gence of new adults from pupae that survived thefumigation (Levinson and Buchelos 1979).

In the current study, more moths were captured inthe indoor gallery rooms above the grain silos thaninside the ßour mill building. Furthermore, numbers

ofmoths captured in thegallerieswere similar to thosecaught outdoors, and moths were active in the silogalleries longer in the season (into the period of coolweather) than those outdoors. Therefore, it seemslikely that many of the moths captured outdoors orig-inated in the grain silos that contained an abundantfood supply. Moths dispersing from the grain siloscould easily invade the warehouse and other indoorareas through openings. Further study is required tosubstantiate this hypothesis.

The study of outdoor spatial occurrence of P. inter-punctella around mill 2 found a signiÞcant negativecorrelation of trap catch with distance from the mill,but the relatively low regression value suggests thatsources of moths, in addition to the mill, existed.Homes in the area could have been sources of P.interpunctella. Additionally, the sampling radius con-tained another single wheat silo in the northeasternquadrant (Fig. 1B) and two commercialwheat storagefacilities were located within a kilometer (northeastand southeast) of the study area. The wheat storagefacilities north of the mill 2 may have accounted forthe greater number of moths trapped in the northversus the south quadrants. P. interpunctella males candisperse up to 1.6 km in 24 h (Ganyard 1971), andmoths captured in this study could have easily dis-persed from any of the potential breeding sites withinand outside the study area. Although this study maysuggest thatP. inerpunctella are concentratednearmillfacilities, we cannot determine if the ßour mills act assources or sinks for moths without further study usingmarked individuals.

In summary, these studies document high levels ofoutdoor activity of P. interpunctella, particularlyaround ßour mills, and indicate the potential for im-migration into food processing facilities. Infestation offood plants by Indian meal moths could occur both bystorage of contaminated products and by immigrationof ßying moths. The current study only addressedactivity of male P. interpunctella, and research on spa-

Fig. 5. (A) Numbers of P. interpunctella captured inpheromone traps outside and inside on ground ßoors at mill1 during 1997. (B) Numbers of P. interpunctella captured inpheromone traps outside the mill, inside the mill and in thegallery rooms above the bulk-stored wheat silos at mill 1 in1998. Means with the same letters are signiÞcantly differentfor agivendate.Differencesbetween insideandoutside trapswere signiÞcant at each date before 17 September.

Fig. 6. Numbers of P. interpunctella captured in 1 wk atvarious distances from mill 2. Data points are the squareroot-transformed number of moths caught in 25 traps posi-tioned 6Ð440 m from the mill.

1846 JOURNAL OF ECONOMIC ENTOMOLOGY Vol. 93, no. 6

tial distribution and movement of female moths isneeded. Additionally, the source of moths inside andoutside food processing buildings needs to be deter-mined. If wild populations occur, possibly developingon suitable food material in nonagricultural habitats,they would only increase the potential for moth in-festation via immigration. Regardless of the source ofimmigrating moths, P. interpunctella populations willbe difÞcult to suppress with fumigation unless bettermeasures are taken to prevent moth entry into mills.Methods of limiting moth immigration are the use andmaintenance of screens on doors and windows as wellas limiting the time that large loading bay doors areopen.

Acknowledgments

We thank Kristopher Giles and Phillip Mulder for review-ing an earlier draft of the manuscript. We are very gratefulto Mark Payton for advice and assistance with statisticalanalyses. We appreciate the loan of the distance-measuringdevice fromLarryGeringandMikeHuebschmann.WethankBill Lingren (Trece) for his generous donation of traps andlures for this study. Work at the ßour mills was made possibleby the helpful cooperation of industry colleagues. This re-search was supported by the Food Research Initiative Pro-gram of the Oklahoma Agricultural Experiment Station, andwas approved for publication by OAES.

References Cited

Brady, U. E., and D. A. Nordlund. 1971. cis-9, trans-12-Tet-radecadien-1-yl acetate in the female tobacco moth,Ephestia eutella (Hubner), and evidence for an additionalcomponent of the sex pheromone. Life Sci. 10: 797Ð801.

Brady, U. E., J. H. Tumlinson, R. G. Brownlee, and R. M.Silverstein. 1971. Sex stimulant and attractant in the In-dian meal moth and in the almond moth. Science 171:802Ð804.

Chambers, J. 1990. Overview on stored-product insectpheromones and food attractants. J. Kans. Entomol. Soc.63: 490Ð499.

Cogburn, R. R., and K. W. Vick. 1981. Distribution ofAngoumois grain moth, almond moth, and Indian meal

moth in rice Þelds and rice storages in Texas as indicatedby pheromone baited adhesive traps. Environ. Entomol.10: 1003Ð1007.

Ganyard, M. C. 1971. Studies on the attractive properties ofthe sex pheromone of the Indian-meal moth, Plodia in-terpunctella, and related species, in indoor and outdoorenvironments. Ph.D. dissertation, University of Georgia,Athens.

Hinton, H. E. 1943. The larvae of the Lepidoptera associ-ated with stored products. Bull. Entomol. Res. 34: 163Ð212.

Kuwahara, Y., H. Hara, S. Ishii, and H. Fukami. 1971a. Thesex pheromone of the Mediterranean ßour moth. Agric.Biol. Chem. 35: 447Ð448.

Kuwahara, Y., C. Kitamura, S. Takahashi, H. Hara, S. Ishii,and H. Fukami. 1971b. Sex pheromone of the almondmoth and Indian meal moth: cis-9, trans-12 tetradecadi-enyl acetate. Science 171: 801Ð802.

Levinson, H. Z., and C. Th. Buchelos. 1979. Surveillance ofstorage moths species (Pyralidae, Gelechiidae) in a ßourmill by adhesive traps with notes on the pheromone-mediated ßight behavior of male moths. Z. Angew. En-tomol. 92: 233Ð251.

Plarre, R. 1998. Pheromones and other semiochemicals ofstored-product insects, a historical review, current appli-cation, and perspective needs. Mitt. Biologischen Bude-sanst. Land-Forstwirtsch. Berl. 342: 13Ð83.

SAS Institute. 1996. SAS/STAT userÕs guide for personalcomputers, version 6.12 ed. SAS Institute, Cary, NC.

Sedlacek, J. D., P. A. Weston, and R. J. Barney. 1996. Lep-idoptera and Psocoptera, pp. 41Ð70. In B. Subramanyamand D. W. Hagstrum [eds.], Integrated management ofinsects in stored products. Marcel Dekker, New York.

Vick, K. W., J. A. Coffelt, and R. W. Mankin. 1981. Recentdevelopments in theuseofpheromones tomonitorPlodiainterpunctella and Ephestia cautella, pp. 19Ð28. In E. R.Mitchell [ed.], Management of insect pests with semio-chemicals. Plenum, New York.

Vick, K. W., J. A. Coffelt, and W. A. Weaver. 1987. Presenceof four species of stored-product moths in storage andÞeld situations in north-central Florida as determinedwith sex pheromone-baited traps. Fla. Entomol. 70: 488Ð492.

Received for publication 22 December 1999; accepted 16August 2000.

December 2000 DOUD AND PHILLIPS: TRAPPING INDIAN MEAL MOTHS AT FLOUR MILLS 1847