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Biological Control 14, 85–95 (1999)Article ID bcon.1998.0679, available online at http://www.idealibrary.com on

Establishment and Early Effects of Omphalapion hookeri (Kirby)(Coleoptera: Apionidae) as a Biological Control Agent

for Scentless Chamomile, Matricaria perforataMerat (Asteraceae)

Alec McClay* and Rosemarie De Clerck-Floate†*Alberta Research Council, PO Bag 4000, Vegreville, Alberta T9C 1T4, Canada; and †Agriculture and Agri-Food Canada,

Lethbridge Research Centre, PO Box 3000, Lethbridge, Alberta T1J 4B1, CanadaE-mail: alec@aec.arc.ab.ca

Received March 27, 1998; accepted October 11, 1998

[Aosw1gSp(ilapdasedlspalyrow(opyc

Omphalapion hookeri (Kirby) (Coleoptera: Apioni-ae) (5 Apion hookeri Kirby) was released and estab-

ished in four provinces in western Canada (Britisholumbia, Alberta, Saskatchewan, and Manitoba) as aiological control agent for scentless chamomile, Mat-icaria perforata Merat (Asteraceae), a rapidly spread-ng, introduced, annual weed of disturbed ground.arvae of this univoltine European weevil feed oneveloping achenes in the capitula of scentless chamo-ile. Overall, 74% of releases resulted in establish-ent; these included both releases of prediapause

dults in late summer or fall and postdiapause adultsn early summer. In experimental plots in Alberta, O.ookeri persisted for five consecutive growing seasons

rom an initial release of 38 adults. Populations inhese plots showed year-to-year increases of up to7-fold, and in mass rearing cages net reproductiveates of up to 64-fold were obtained. Up to 17 O. hookerieveloped in a single scentless chamomile seed head inhe field. In the field plots each individual of O. hookeriompleting development reduced seed production in aead by 11.2 seeds; unattacked heads produced anverage of 171 seeds. A host choice test confirmed that. hookeri would not develop in the herbal chamomile,hamomilla recutita. Adult O. hookeri dispersed up to50 m between emergence and oviposition. Our resultsuggest that O. hookeri can be established across thecentless chamomile-infested areas of the Canadianrairies and that it has potential for reducing theeed’s reproductive output. r 1999 Academic Press

Key Words: scentless chamomile; Matricaria perfo-ata; Tripleurospermum perforatum; Omphalapionookeri; Apion hookeri; Chamomilla recutita; biologi-al control; establishment; weeds; dispersal; seed pro-uction.

S

85

INTRODUCTION

Scentless chamomile, Matricaria perforata Merat5 Tripleurospermum perforatum (Merat) Wagenitz],steraceae, is an annual or short-lived perennial plantf European origin which is becoming an increasinglyevere weed problem in cropland and waste areas inestern Canada (Douglas et al., 1991, 1992; Woo et al.,991; Bowes et al., 1994). It occurs widely in the black,rey, and dark brown soil zones of Alberta andaskatchewan and can spread rapidly because of itsrofuse seed production, up to 1.8 million seeds m22

Woo et al., 1991). It occurs in a wide variety of habitats,ncluding annual and perennial crops, pastures, waste-and, roadsides and ditches, urban, and industrialreas (Woo et al., 1991); in agricultural land it isarticularly common along slough margins, in fieldepressions, and in transition areas such as fence linesnd right-of-ways (Bowes et al., 1994). It can causeignificant problems by competing with crops. In farm-rs’ fields in Saskatchewan, scentless chamomile at aensity of 20 plants m22 in spring wheat caused yieldosses ranging from 30 to 80%. Actual densities ofcentless chamomile in these fields ranged up to 70lants m22. Plot experiments indicated that the winternnual form is particularly competitive and that yieldosses due to scentless chamomile were greater in moistears (Douglas et al., 1991). Yield of winter wheat waseduced by summer annual scentless chamomile plantsnly in a moist year, whereas yields were reduced byinter annual plants in a year of normal precipitation

Douglas et al., 1992). In Alberta, scentless chamomileccurs mainly in central and northern areas and causesroblems particularly on solonetzic soils and in weak oroung stands of forage crops (Cole, 1994). Scentlesshamomile is legislated as a noxious weed in Alberta,

askatchewan, Manitoba, and part of British Colum-

1049-9644/99 $30.00Copyright r 1999 by Academic Press

All rights of reproduction in any form reserved.

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86 MCCLAY AND DE CLERCK-FLOATE

ia, and as a class 3 secondary noxious weed under theanada Seeds Act (Woo et al., 1991).Several products are available for chemical control of

centless chamomile in cereals; however, in other cropsnd in uncultivated land, chemical control options forcentless chamomile are limited or absent. In canola,nly one product, clopyralid, is registered for scentlesshamomile control. In seedling forage legumes, in haynd grazing land with legumes, and in other crops suchs beans, corn, lentils, peas, and potatoes, no chemicalontrol is available (Ali, 1995).Scentless chamomile was proposed as a target for

iological control by Peschken et al. (1989), and the firstiological control agent screened against it was anchene-feeding weevil, Omphalapion hookeri (Kirby)Apionidae). In previous literature this was referred tos Apion hookeri Kirby; the subgenus Omphalapion inhich it was placed is now treated as a genus (Alonso-arazaga, 1990; Ehret, 1990). The biology of O. hookerias described by Freese (1991) and by Peschken andawchyn (1993). It is univoltine. Adult females lay eggs

nto the flower buds of M. perforata when they begin topen in early summer. The larvae feed on the tubularorets and developing achenes, and pupate among thechenes in a cell formed of chewed plant tissue. Adultsmerge from the heads in late summer and overwinter,resumably in litter or soil. O. hookeri is widely distrib-ted in Europe and western Asia (Peschken and Saw-hyn, 1993). Recently an adventive population wasound in Nova Scotia, Canada (Peschken et al., 1993),ut it is not known how or when this population wasntroduced. O. hookeri was approved for release inanada in 1992, and this paper reports on the releases,stablishment, and dispersal of this insect at field sitesn western Canada, its population development onxperimental plots, and its effects on seed production.

MATERIALS AND METHODS

ource of Materials

O. hookeri was obtained from the breeding colonytudied by D. P. Peschken at the Agriculture Canadaegina Research Station (originally derived from in-

TAB

Summary of Mass Rearing of Omphalapion

Year Source of parentsDate placed

in cage

994 Sherwood Park, ABBayreuth, Germany

June 24July 5

995 Progeny from 1994 July 6996 Progeny from 1995 June 12997 Field sites (Vegreville, Edmonton) June 3–July 8

ects collected at Bayreuth, Germany), directly from a d

eld population at Bayreuth, Germany, and from thedventive Nova Scotia population.

ass Rearing

O. hookeri was reared every year from 1994 to 1997t the Alberta Research Council, Vegreville, in a fieldage 1.8 3 3.6 3 1.8 m containing approximately 25–30lants of M. perforata in 30-cm-diameter pots. Adultsere placed in the cage in early summer when the

centless chamomile plants were in bud stage; num-ers, sources, and dates of introduction of adults arehown in Table 1. Heads were clipped as they ripenednd before adult O. hookeri emerged (Table 1). Seedeads were allowed to dry for a few days in the

aboratory. To speed the collection of adults, the ripeeed heads were then tumbled for a few seconds in aeed scarifier (Forsbergs, Inc., Thief River Falls, MN) toreak the achenes loose from the receptacles; therumbled heads were placed in a screened cage anddults were collected as they emerged. Emerged adultsere then placed in 1.7-liter plastic containers with

creened ventilation holes, containing bouquets of scent-ess chamomile foliage, in incubators at 4°C for overwin-er storage from mid October to mid May.

ost Choice

The herbal chamomile, Chamomilla recutita (L.)auschert, used in the preparation of teas and essen-

ial oils, is the most economically important specieslosely related to scentless chamomile. Peschken andawchyn (1993) found that in no-choice tests O. hookeriould oviposit in buds of C. recutita at a similar rate to

hat shown on scentless chamomile. However, no adultsmerged from C. recutita plants exposed to ovipositiony O. hookeri, indicating that this plant will not sup-ort complete development of O. hookeri. In 1994, as aurther test of this conclusion, 10 plants of C. recutita,n a flowering stage similar to that of the M. perforatalants, were placed in the mass rearing field cagenterspersed among the 33 plants of M. perforata. Seedeads of C. recutita were collected separately fromhose of M. perforata and processed in the same way to

1

okeri in Outdoor Field Cages at Vegreville

Date firstharvested

Number ofparents

Number ofprogeny

Reproductiverate

July 27 6177 597 3.26

August 23 111 2,558 23.05July 17 92 1,316 14.30July 22 315 20,248 64.28

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87ESTABLISHMENT OF Omphalapion hookeri ON SCENTLESS CHAMOMILE

ield Plots

Six field plots, each 1.8 3 3.6 m, were set up at thelberta Research Council, Vegreville, Alberta. Theselots were primarily intended as sites for the releasend establishment of O. hookeri and of other biologicalontrol agents for scentless chamomile as these becamevailable, rather than as a strictly replicated study. Itas initially intended that one caged plot would serves a release site for O. hookeri, and a second plot waslso caged to observe the effects of shading on scentlesshamomile in the absence of the insect. By 1994 it waspparent that O. hookeri could not be confined in theages, so sampling was extended to all six plots until996 to observe the development of scentless chamo-ile and O. hookeri populations.The plots were seeded with M. perforata on May 6,

993. Because of dry conditions and slow germination,0 additional greenhouse-grown rosettes of M. per-orata were transplanted into each plot on June 14,993, to bring the plant population close to 100%centless chamomile cover. On June 16, 1993, two of thelots were covered by walk-in cages 1.8 3 3.6 3 1.8 migh screened with 32 mesh-per-inch Saran fabricSynthetic Industries, Gainesville, GA). Thirty-eightdult O. hookeri collected from the Sherwood Park,lberta, release site (see Table 2) were released intone of the caged plots (Plot 3) on July 7, 1993. The cagecreens were removed from these plots on August 19,993 because a heavy infestation of aphids had devel-ped in the cages. Subsequently the cage covers onhese two plots were replaced each spring (April 26,994 and April 18, 1995) and removed in the fallSeptember 29, 1994 and September 21, 1995). Plotsere not caged in 1996 or 1997. At 3-week intervalsuring the growing season, seedlings (#6 true leaves),osettes (.6 true leaves), bolted plants, stems andercentage cover of scentless chamomile were countedn 20 0.1-m2 quadrats within each plot, the predomi-ant flowering stage of plants in the quadrat wasetermined according to a scale modified from Freese1991) (Table 3), and visual observations were made toetermine the presence of O. hookeri adults on thelants. The total percentage cover of other plant speciesas also recorded from 1994 onwards. In 1994, 1995,nd 1996, any surviving overwintered rosettes wereounted separately and tagged to distinguish themrom the current season’s rosettes.

Each year in late summer, when most seed headsere ripe, 50 stems were collected at random from eachlot. These collections were made on September 13,993; August 8, 1994; August 15, 1995; and August 21,996. The later sampling date in 1993 reflects the latermergence and flowering of scentless chamomile inhat year due to the dry conditions in spring. Theumbers of flower heads in each of the 4 flowering

tages on each stem were recorded. Separately, a

ample of 100 heads in each of stages 3 and 4 wasollected from each plot. The number of living and dead. hookeri larvae, pupae, and adults, empty pupal cells,nd number and weight of achenes were recorded fromach head. In 1995 and 1996, achenes from each headere tested for germination on moist filter paper inetri dishes at a photoperiod of 16 h and day/nightemperatures of 25°C/20°C, respectively. In 1995, theiameter of each head (excluding the ray florets) waseasured using a vernier caliper, and in 1996 the

iameter and height (from the base of the involucre) ofach head were measured.

ffects on Seed Production

The effect of O. hookeri on seed production in the fieldlots in 1996 was evaluated by analysis of covariance,ith number and weight of seeds per head as depen-ent variables, flowering stage and plot as independentariables, and seed head volume (height 3 diameter2)nd number of O. hookeri per head as covariates. Headshich produced no seed were omitted from the analy-

is; in many of these seed development had failed due tottack by a phytoplasma pathogen (H. Khadhair, pers.omm.). The effects on seed production in the massearing cage were also assessed by multiple regressionf number and seed weight on seed head volume and O.ookeri number for 200 stage 4 heads.

ield Releases and Monitoring

Documented field releases (Fig. 1) were made at 2ites in British Columbia, 10 sites in Alberta, 53 sites inaskatchewan, and 4 sites in Manitoba between 1992nd 1996. Dates, locations, and numbers of weevilseleased are provided for those sites that were moni-ored for weevil establishment (Table 2). Until 1995,ost releases in Alberta were made in early summer

sing overwintered (postdiapause) adult weevils whichere ready to begin ovipositing; in the other provinces,nd in Alberta after 1995, most releases were maden late summer using prediapause adults. In Sas-atchewan, 19 recorded releases were made between992 and 1994, and 55 were made in 1995. Mosteleases made in Saskatchewan in 1994, using weevilsrom Nova Scotia, were not documented. However, it isnown that about 10,000 weevils were shipped toaskatchewan (Glen Sampson, Nova Scotia Agricul-ural College, pers. comm.) and were divided into lots of00 for release. All O. hookeri released in 1995–1996 inaskatchewan were from Nova Scotia. In 1997, four-een additional releases of 287–1000 prediapause adultsere made in Alberta and two releases of 450 predia-ause adults were made in Manitoba; these have notet been monitored for establishment.

In Alberta, sites were monitored in early summer

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88 MCCLAY AND DE CLERCK-FLOATE

June–mid July) by searching for adult weevils on thelants, and in late summer (August–September) byollecting and dissecting samples of 100 or 200 ripeeads from each location and dissecting to determineumbers of each life stage of O. hookeri present. Headsrom which adult O. hookeri had already emerged coulde easily identified by the presence of an empty pupa-ion cell or cells surrounded by chewed achene tissue.ites in British Columbia, Saskatchewan, and Mani-oba were monitored by collecting 300 ripe seed headsn average (40–1200 depending on availability of plants)rom each location in August or September. Someaskatchewan sites were also visited in spring 1996nd checked for adults. At most sites, the seed headsere collected within 10 m of the original release point,ut at Fort St. John (site 2), seed heads were collectedear the release point (,10 m and 10–20 m), and at aontrol site 100 m away.

ispersal

Between July 25 and 29, 1996, patches of scentlesshamomile in the vicinity of the release plots at Vegre-ille were searched for adult O. hookeri. At this time ofear adults are easily visible on the flower buds.ocations of the plants and O. hookeri were plottedsing a portable differential GPS unit (CMT PC-5,orvallis Microtechnology). The same method was usedn July 26, 1996, and on July 21, 1997, to plot dispersalrom the Terwillegar Park release site in Edmonton.

FIG. 1. Release sites of Omphalapion hookeri in western Canada,nd breeding observed at least in the year after release). Open cinsuccessful releases in same area.

RESULTS AND DISCUSSION

ass Rearing

Results of the mass rearing from 1994 to 1997 arerovided (Table 1). The lower reproductive rate in 1994as probably because most of the adults used for

earing in this year were collected from the field inermany relatively late in the season, and females maylready have laid many of their eggs before they wereollected. The results from 1995 to 1997 indicate thatearing of O. hookeri on potted scentless chamomilelants in outdoor field cages is a simple and effectiveay to produce large numbers of the insect for field

eleases. Up to 30 adult O. hookeri were found to haveompleted development in a single scentless chamomileower head in the mass rearing cage.Survival of O. hookeri in overwinter storage was very

ariable. From 1994 to 1995, 37% of adults placed intorage were recovered alive, while from 1995 to 1996urvival was only 6%. Further work is currently underay to determine optimum overwinter storage condi-

ions for O. hookeri.

ost Choice

Only one adult O. hookeri emerged from flower headsf C. recutita in 1994. Assuming that this individualad actually completed development on C. recutita andas not a stray, the reproductive success on this plantas only 0.17% of that on scentless chamomile, confirm

2–1995. Filled circles: successful establishment (overwinter survivals: no establishment. Circles with enclosed square: successful and

199rcle

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TAB

Releases and Recoveries of Omphalapion hooker

Locality Date of releaseNumberreleased So

British

ort St. John (56°148N,120°558W)

Site 1 August 28, 1992 53Site 2 August 28, 1992 116

Site 2 August 25, 1993 200

Al

ezanson (55°138N,118°288W)

September 26, 1996 200

rayton Valley (53°058N,114°478W)

September 12, 1996 200

dmonton (53°338N,113°288W)

June 29, 1995 47

dmonton (53°358N,113°378W)

October 3, 1996 200

rande Prairie (55°128N,118°288W)

September 26, 1996 200

illcrest (49°358N,114°238W)

June 3, 1993 18

isku (53°208N,113°328W)

June 16, 1995 44

herwood Park (53°318N,113°198W)

June 30, 1992 105

egreville (53°308N,112°038W)

July 7, 1993 38

iking (53°068N,111°468W)

August 25, 1993 200

Saskat

ylsham (53°128N,103°498W)

Site 1 August 24, 1995 c. 500

Site 2 September 6, 1996 c. 500algonie (50°298N,

104°168W)August 25, 1993 200

ethune (50°438N,105°138W)

Site 1 July 30, 1995 c. 500Site 2 September, 1996 c. 500

roadview (50°228N,102°358W)

September 1, 1995 c. 500

anwood (53°228N,106°368W)

Site 1 August 31, 1995 c. 500Site 2 August 31, 1995 c. 500

Site 3 August 31, 1995 c. 500

Site 4 August 31, 1995 c. 500

ubuc (50°418N,102°288W)

Fall, 1995 c. 500

dgeley (50°388N,103°598W)

Site 1 Fall, 1995 c. 1000Site 2 Fall, 1995 c. 500

LE 2

i against Matricaria perforata in Western Canada

urceaPre- or

post-diapause

Years recoveredb

Site descriptionand remarks93 94 95 96 97

Columbiac

G Pre N — N — — Edge of wheat fieldNS Pre Y Y Y — Y Poplar bluff in center of

fieldNS Pre Y Y — Y Same site as previous

berta

G Pre N

G Pre Y Pasture

NS Post Y Y Park

G Pre Y Industrial area (claystorage mound)

G Pre Y

R Post N — — N Roadside along river,near town

NS Post Y — Roadside

R Post Y Y N — — Park, caged release

R Post Y Y Y Y Experimental plots, cagedrelease

NS Pre N N — — Waste ground, heavilygrazed and trampled bycattle in spring 1994

chewand

NS Pre Y — Edge of slough/field,plowed in 1997

NS Pre Y Farm yard, along roadNS Pre Y Y Y — Edge of hay field, site

plowed in 1997

NS Pre Y Y Near slough, along roadNS Pre Y Alfalfa field, none in seed

heads, adults seen in1997

NS Pre — N Near farm yard, alongpasture

NS Pre Y Y Gravel pitNS Pre Y — Roadside, edge of field,

site plowed in 1997NS Pre N Y Roadside, field edge, 11%

heads attacked 1997NS Pre Y — Roadside, edge of field,

site mowed in 1997NS Pre Y Y Edge of field/slough

NS Pre — N Edge of slough/fieldNS Pre — N Edge of slough/field

89

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TABLE 2

Locality Date of releaseNumberreleased So

sterhazy (50°398N,102°058W)

Site 1 Fall, 1995 c. 500Site 2 September 1, 1995 500afford (52°438N,

107°218W)Site 1 August 1996 c. 500

Site 2 August 1996 c. 500

endon (52°058N,103°508W)

August 29, 1995 c. 500

oldfast (50°588N,105°258W)

August 1, 1995 c. 500

ndian Head (50°328N,103°408W)

September 1, 1995 c. 1000

elvington (52°108N,103°328W)

September 15, 1995 500

loydminster (53°178N,110°008W)

Site 1 August 27, 1994 400

Site 2 August 27, 1994 400acNutt (51°058N,

101°368W)Fall, 1996 c. 500

cLean (50°318N,104°048W)

Site 1 September 1, 1995 c. 500Site 2 September 1, 1995 c. 500Site 3 September 1, 1995 c. 500elville (50°558N,

102°488W)Site 1 August, 1994 c. 500

Site 2 August, 1994 c. 500

oosomin (50°088N,101°408W)

September 2, 1996 c. 500

u’Appelle (50°338N,103°538W)

September 1, 1995 c. 500

ocanville (50°238N,101°428W)

Site 1 September 1, 1995 c. 500

Site 2 September 2, 1996 c. 500t. Walburg (53°398N,

109°128W)June 29, 1992 c. 700

tockholm (50°398N,102°188W)

Fall, 1995 c. 400

—Continued

urceaPre- or

post-diapause

Years recoveredb

Site descriptionand remarks93 94 95 96 97

NS Pre Y Y 17% heads attacked 1997NS Pre Y N Roadside

NS Pre Y In grass field, 5% headsattacked 1997

NS Pre Y In grass field, 6% headsattacked 1997

NS Pre Y — Site flooded in 1997

NS Pre N N Low area in middle offield

NS Pre Y N Waste site near grainelevator, mowed in1996 adults seen July1996

NS Pre N — Part of site bulldozed1996, site flooded in1997

NS Pre — Y — Slough, cultivated fieldedge, 5% headsattacked in 1996, noplants in 1997

NS Pre — — N In ditch along roadNS Pre Y Edge of barley field

NS Pre N N RoadsideNS Pre Y N Edge of pastureNS Pre N N Waste area along fence

NS Pre Y Y — Edge of cultivated field,sprayed with herbicidein 1997, adults seenJuly 1996

NS Pre N N — Edge of cultivated field,sprayed with herbicidein 1997

NS Pre Y Along railway

NS Pre Y — Abandoned farm yard,none in seed heads butadults seen July 1996

NS Pre Y Y Roadside, 15% headsattacked 1996

NS Pre Y RoadsideR N/A N — — — Y In ditch on alfalfa field

edge, potted chamomilewith O. hookeri eggs inflower heads trans-planted into stand, 10%heads attacked 1997

NS Pre Y Y Edge of slough

90

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TABLE 2—Continued

Locality Date of releaseNumberreleased Sourcea

Pre- orpost-diapause

Years recoveredb

Site descriptionand remarks93 94 95 96 97

isdale (52°518N,104°038W)

Site 1 August 24, 1995 c. 500 NS Pre Y Y Edge of slough/field, 13%heads attacked 1997

Site 2 August 24, 1995 c. 500 NS Pre N Y Along ditch of farm roadSite 3 September 8, 1996 c. 500 NS Pre N Edge of fieldSite 4 September 9, 1996 c. 500 NS Pre Y Edge of field/farm yard,

6% heads attacked1997

apella (50°168N,101°588W)

Site 1 September 1, 1995 c. 500 NS Pre Y — Edge of oat field, siteflooded 1997, 6% headsattacked 1996

Site 2 September 2, 1996 c. 500 NS Pre Y Edge of sloughatrous (51°408N,

105°288W)Site 1 September 14, 1995 c. 100 NS Pre N Y In windbreak hedge, field

edgeSite 2 September 14, 1995 c. 100 NS Pre Y — In windbreak hedge, field

edgeSite 3 September 14, 1995 c. 100 NS Pre N N Field edgeSite 4 September 14, 1995 c. 100 NS Pre Y N Field edgehitewood (50°208N,

102°168W)Site 1 September 1, 1995 c. 500 NS Pre Y Y Roadside, slough edge,

15% heads attacked1997

Site 2 September 1, 1995 c. 500 NS Pre Y Y Edge of field, 16% headsattacked 1997

Site 3 September 2, 1996 c. 500 NS Pre Y In ditch beside crop, 7.5%heads attacked 1997

Site 4 September 2, 1996 c. 500 NS Pre N Edge of slough, next tocaraway crop, fewplants in 1997

ishart (51°338N,103°598W)

September 1, 1995 c. 500 NS Pre Y — Waste area

ynyard (51°468N,104°118W)

August 24, 1995 c. 500 NS Pre N — Edge of wheat field, lowarea

orkton (51°138N,102°288W)

Site 1 August, 1994 c. 500 NS Pre Y — — Edge of cultivated field,no scentless chamomileat site in 1996

Site 2 Fall, 1996 c. 500 NS Pre Y Edge of wheat field

Manitoba

unnotar (50°278N,96°578W)

August, 1994 2,100 NS Pre Y Y Y Low site on edge of lagoon

rickson (50°308N,99°558W)

Site 1 August, 1992 300 NS Pre N — — — — Edge of hay field, acciden-tally mowed in 1993

Site 2 August, 1994 500 NS Pre — Y N Field edgeinnipeg Beach

(50°308N, 96°588W)July 2, 1992 57 G Pre Y — — — — Native pasture, gravelly

soil, most plants deadin 1993 due to drought

Note. All were open releases unless shown as caged under ‘‘Site description and remarks.’’a G: Germany; R: Laboratory colony at Regina, derived from Germany; NS: Nova Scotia.b Y, recovery of O. hookeri; N, site monitored but no recovery; —, site not monitored.c Sites in British Columbia were not checked in 1996 due to inclement weather.d At sites in Saskatchewan where a recovery year is shown but the percentage attack is not indicated, attack was less than 5% of seed heads

issected.

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92 MCCLAY AND DE CLERCK-FLOATE

ng the conclusions of Peschken and Sawchyn (1993)hat O. hookeri is virtually monophagous on scentlesshamomile.

xperimental Plots 1993–1996

The interpretation of results in the experimentallots was complicated by large between-plot variationnd year-to-year changes in scentless chamomile den-ity and flower production (Fig. 2). Scentless chamo-ile densities declined greatly over the 4 years of the

tudy; this was not an effect of O. hookeri but wasrimarily due to competition from other plant species,ainly smooth brome, Bromus inermis Leyss. (Poa-

eae), which progressively invaded the plots. The shad-ng effect of the screen cages on plots 3 and 4 furthereduced the vigor of scentless chamomile on these plots,eading to lower flower production and more rapidisplacement by B. inermis. In 1996, to ensure thatcentless chamomile populations would persist on the

FIG. 2. Flower head production of scentless chamomile (above)nd percentage cover of scentless chamomile and other plant species

TABLE 3

Flowering Stages of Scentless Chamomile;Modified from Freese (1991)

tage DescriptionEquivalent stages

(Freese, 1991)

1 Closed or open buds; ray flowers foldedin or erect

I–III

2 Ray flowers spread out flat; diskflowers less than 50% open; disk flat

IV–V

3 Ray flowers spread or withering; diskflowers mostly or all open butcorollas still attached, disk swelling,no ripe seed

VI–VII

4 Ray flowers withered or fallen, seedbeginning to ripen or ripe, corollas ofdisk flowers falling or fallen

VIII–X

below) in experimental plots at Vegreville, 1993–1996. V

lots, dead B. inermis top growth was hand weededrom three plots and new growth was sprayed with aelective grass-killing herbicide, Select (clethodim).O. hookeri was recovered in the experimental plots at

egreville every year from 1993 to 1997. In 1993ampling was conducted only in the caged plot in which. hookeri was released. In 1994 it became apparent

hat O. hookeri was not confined to the caged plot, sorom 1994 to 1996 all six plots were sampled for theeevil. Estimated numbers completing development

anged from 67 to 767 adults m22 (Fig. 3). In 1995,stimated O. hookeri populations were lower than in994, but rates of attack were higher (Fig. 3); this wasecause the density of scentless chamomile plants inhe plots and their flower head production had declinedue to competition from other plant species. The re-uced total population in 1995 may have been partlyue to dispersal away from the plots. In 1996, thestimated population increased slightly but the rate ofttack (weevils per head) increased sharply; this iselated to the reduced flower head production in thatear (Fig. 2).Densities of O. hookeri in stage 3 heads were usually

ower than in stage 4 heads (Fig. 4). As oviposition onlyccurs into heads in stages 1 and 2, this probably

FIG. 3. Omphalapion hookeri population (individuals per m2)nd percentage of scentless chamomile heads attacked by O. hookerin experimental plots at Vegreville, 1993–1996.

FIG. 4. Number of Omphalapion hookeri per head of scentlesshamomile in flowering stages 3 and 4 in experimental plots at

egreville, 1993–1996.

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93ESTABLISHMENT OF Omphalapion hookeri ON SCENTLESS CHAMOMILE

eflects the fact that heads which had reached stage 4y the sampling date were available for ovipositionarlier in the season than heads which had reachedtage 3, and were thus exposed to higher rates ofviposition.O. hookeri showed a clumped distribution over avail-

ble flower heads. The variance/mean ratio in theeld plots in 1996 was 3.26, consistent with the valuesound by Freese (1991). The maximum number of adult. hookeri found in a single head in the field plotsas 12.

ffects on Seed Production

In the field plots, both seed weight and seed numberhowed significant differences among plots and flower-ng stages, a highly significant positive regression oneed head volume, and a highly significant negativeegression on numbers of O. hookeri (regression coeffi-ients shown in Table 4). Heads attacked by O. hookeriherefore produced fewer seeds than would have beenxpected from unattacked heads of the same size andowering stage in the same plot. The regression coeffi-ients indicate that seed production in the field plotsas reduced by about 11.2 seeds or 0.263 mg by each. hookeri developing in a head. In the rearing cage the

ffects were less marked, although still significant;ach O. hookeri reduced seed production by 2.48 seedsr 0.101 mg. The reasons for the differences betweenhe effects in the field plots and in the rearing cage arenknown. They can be only partially explained by

arger achene size in the rearing cage; mean individualchene weight, calculated from a regression of acheneeights against numbers, was 0.0386 mg in the rearing

age and 0.0297 mg in the field plots. Possibly the

TABLE 4

Effects of Seed Head Volume and Omphalapion Infestationevel on Achene Production per Head of Scentless Chamo-ile, Vegreville, 1996

Datasource

Dependent vari-able

Regression coefficients(estimates 6 std. error) for

Seed headvolume (mm3)a

O. hookerinumbera

ieldplots Achene number 0.32 6 0.011*** 211.18 6 1.02***

Achene weight(mg) 0.0119 6 0.0003*** 20.263 6 0.027***

earingcage Achene number 0.17 6 0.02*** 22.48 6 0.79**

Achene weight(mg) 0.0076 6 0.0006*** 20.101 6 0.029**

a Superscripts indicate estimates significantly different from zero:* 0.001 , P , 0.01; *** P , 0.001.

otted plants in the rearing cage, being well watered i

nd fertilized and subject to less competition thanlants in the field, were better able to compensate foramage by O. hookeri. Both values are considerablyower than the 21 achenes per weevil reported to beeeded for complete development by an O. hookeri

arva (Freese 1991).Mean germination of seeds from the field plots was

6.5 and 52.9% in 1995 and 1996, respectively. Thereas no effect of level of O. hookeri infestation onermination in either year (analysis of covariance: 19955 0.428, 1996 P 5 0.676), indicating that larval feed-

ng by O. hookeri has no detrimental effect on theemaining seeds in the head.

ield Releases and Recoveries

O. hookeri established successfully at 74% of sites inestern Canada where it was released and subse-uently monitored (Table 2). Successful establishmentccurred throughout most of the geographic range ofcentless chamomile on the Canadian prairies (Fig. 1),rom southeastern Manitoba to Fort St. John, northeast-rn British Columbia, which was the highest latitudet which the weevil was released (56.14°N, 120.55°W).G test (Sokal and Rohlf, 1981) showed no significant

ifferences in frequency of establishment between adultseleased pre- and postdiapause (73 versus 80%, respec-ively) or between weevils originating from Germanynd from Nova Scotia (70 versus 75%, respectively).stablishment was achieved at some sites with quitemall initial releases (e.g., 38 adults at Vegreville,lberta; 57 adults at Winnipeg Beach, Manitoba). Aumber of the failures to establish were associatedith environmental changes or human activities at the

elease site, such as drought, mowing, construction,erbicide spraying, or trampling by cattle (e.g., Viking,lberta; Kelvington, Saskatchewan). Monitoring atome sites was made more difficult by the tendency ofense scentless chamomile infestations to decline ashey are replaced by perennial plant species. This wasoted in the field plots at Vegreville and at several fieldelease sites such as Sherwood Park and Nisku, Al-erta, and Yorkton, Saskatchewan (Table 2).Percentage of seed heads attacked by O. hookeri was

nitially less than 5% at most sites where the weevilstablished in Saskatchewan and Manitoba. However,eevil attack was as high as 15% one year after release

n SE Saskatchewan (Rocanville; Table 2) and up to 8eevils were found per head in this region (Rocanvillend Whitewood, site 2). At Canwood site 3 (1995elease) up to 17 adult O. hookeri were found in oneeed head in 1997. Recovery in consecutive years at aite (e.g. Balgonie; Table 2) did not always show anncrease in the number of weevils recovered. However,t other sites monitoring in consecutive years showed

ncreased rates of attack or confirmed the presence of

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94 MCCLAY AND DE CLERCK-FLOATE

. hookeri at sites at which it had not previously beenecovered.O. hookeri successfully established both from spring

eleases of postdiapause adults which had been kept inold storage over winter and from late summer or falleleases of newly emerged, prediapause adults. Sinceptimum storage conditions for reliable survival of. hookeri over winter have not been determined, itay be more advisable at present to use prediapause

dults for routine field releases.

ispersal

In early summer of 1996, in the fourth year afterelease, adult O. hookeri were found in small numbersn almost all patches of M. perforata up to 100 m fromhe Vegreville release plots. Scattered adults wereound up to 240 m away from the plots. In 1997,cattered adults were found up to 800 m from theelease point. At Terwillegar Park, Edmonton, 1 yearfter release, adults were found up to 42 m away fromhe release point, but not on two isolated patches of M.erforata about 75 m from the release point. By 2 yearsfter release, however, O. hookeri was abundant onhese two patches, and scattered individuals wereound up to 700 m from the release point. At Fort St.ohn, BC, seed head dissection data showed that withinyear of release, the weevil had dispersed more than

00 m, including about 50 m across an area devoid ofcentless chamomile. As the insect is univoltine, thesebservations indicate that some individual adults canisperse at least 350 m before ovipositing, and thatpen areas up to 50 m wide without stands of M.erforata do not seem to represent a barrier to dis-ersal. It is not known whether this dispersal occursrimarily before or after overwintering.

henology

O. hookeri is univoltine in Alberta, as was found byreese (1991) in Germany. At the field sites overwin-ered adults were seen on scentless chamomile plantsrom early May onwards. Oviposition began as soon asower buds in a suitable stage were available. In theass rearing cages, adults were found ready to emerge

rom the heads on August 5, 1994, and emerged adultsere found August 12, 1994. Assuming that the firstdults found in heads were the progeny of the six adultslaced in the cage on June 24, development from egg todult was complete in not more than 42 days. In theeld plots, adults which were probably newly emergedere seen from early August onwards.

eneral Discussion

Our results indicate that it should be possible tostablish O. hookeri throughout the areas infested by

centless chamomile in western Canada. The weevil

oes not appear to be limited to any particular habitatype, nor does climate appear to be a limiting factor forts establishment within this area. The ultimate effectsf this insect will depend on whether it can reachufficiently high densities to destroy most of the plant’seed production. In our field plots unattacked scentlesshamomile plants produced an average of 171 seeds peread in 1996. Based on the results above, a populationensity of about 15 weevils per head would be needed topproach complete seed destruction. The maximumumber of O. hookeri found in a single head in the fieldlots was 17; however, up to 30 were found in a head inhe mass rearing cages. No parasitoids were rearedrom any seed heads in the experimental plots or fieldelease sites. This contrasts with the situation inurope where five parasitoid species are recorded

Freese and Gunther, 1991) and third-instar mortality,ainly from parasitism, can be around 40% (Freese,

991). Further population monitoring should revealhether this freedom from parasitism will allow. hookeri populations in Canada to increase to a levelhich will cause significant seed destruction in theeld.

ACKNOWLEDGMENTS

We thank Robert B. Hughes, Irving Switzer, Leslie Dietz, Kimtromme, Sophie Verzosa, and Rick Weste for technical assistance;iether Peschken, Glen Sampson, Dieter Schroeder, and Andreareese for providing collections of O. hookeri; and Chuck Richardson,uss Jasman, and Christopher Saunders for arranging access to fieldites in Alberta. Thanks also to the following people for collections ofeed heads for dissection and for information on releases: Ken Nickelnd Jill Copes (BC); Eric Johnson, Barb Gradin, Doug Billett, Lenuras, Brad Thompson, Ed Tanner, James Donovan, Judy McKell,endy Schatz, Darlene Fisk, Brian Harris, Lewis Reeve, Ernieatrick, Donald Dyck, Ivan Allin, Leroy Bader, and Doug Patience

SK); and Carla Pouteau, Risa Kennedy, Rick Hnatiuk, and Neilalbraith (MB). Financial support was provided by the Canada-lberta Environmentally Sustainable Agriculture Agreement (projectES 048-93) and by Nova Gas Transmission Limited.

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lonso-Zarazaga, M. A. 1990. Revision of the supraspecific taxa in thePalaearctic Apionidae Schoenherr, 1823 (Coleoptera, Curculionoi-dea). 2. Subfamily Apioninae Schoenherr, 1823: introduction, keysand descriptions. Graellsia 46, 19–156.

owes, G. G., Spurr, D. T., Thomas, A. G., Peschken, D. P., andDouglas, D. W. 1994. Habitats occupied by scentless chamomile(Matricaria perforata Merat) in Saskatchewan. Can. J. Plant Sci.74, 383–386.

ole, D. E. 1994. ‘‘Scentless Chamomile: Biology and Control.’’Alberta Agriculture, Food and Rural Development, Edmonton,Alberta.ouglas, D. W., Thomas, A. G., Peschken, D. P., Bowes, G. G., andDerksen, D. A. 1991. Effects of summer and winter annual scent-less chamomile (Matricaria perforata Merat) interference on spring

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eschken, D. P., and Sawchyn, K. C. 1993. Host specificity andsuitability of Apion hookeri Kirby (Coleoptera: Curculionidae), acandidate for the biological control of scentless chamomile, Matri-

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eschken, D. P., Sawchyn, K. C., and Bright, D. E. 1993. First recordof Apion hookeri Kirby (Coleoptera: Curculionidae) in NorthAmerica. Can. Entomol. 125, 629–631.

eschken, D. P., Thomas, A. G., Bowes, G. G., and Douglas, D. W.1989. Scentless chamomile (Matricaria perforata)—a new targetweed for biological control. In ‘‘Proceedings of the VII InternationalSymposium on Biological Control of Weeds, March 6–11, 1988,Rome, Italy’’ (E. S. DelFosse, Ed.), pp. 411–416. Ist. Sper. Patol.Veg. (MAF). Rome.

okal, R. R., and Rohlf, F. J. 1981. ‘‘Biometry: The Principles andPractice of Statistics in Biological Research,’’ 2nd ed. Freeman,New York.oo, S. L., Thomas, A. G., Peschken, D. P., Bowes, G. G., Douglas,D. W., Harms, V. W., and McClay, A. S. 1991. The biology ofCanadian weeds. 99. Matricaria perforata Merat (Asteraceae).Can. J. Plant Sci. 71, 1101–1119.