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Agricultural and Forest Entomology (1999) 1, 209±217

Suppression of infestation by pheromone- mediated augmentation of the predatory spined soldier bug, maculiventris (Say) (: )

J. R. Aldrich1 and W. W. Cantelo2 1USDA-ARS Chemical Ecology Laboratory, Bldg. 007, Rm. 326, BARC-West, Beltsville, Maryland 20705, U.S.A. and 2USDA-ARS Vegetable Laboratory, Beltsville, Maryland 20705, U.S.A .

Abstract 1 Hardware and protocols were tested to enable individual growers and insectary operators to mass-produce predatory spined soldier bugs (SSBs), Podisus maculi- ventris (Say) (Heteroptera: Pentatomidae: ), for augmentative biological control.Using pheromone-based technology, an average of 1775 female SSBs (potentially as many as 1.6 million offspring) were captured each year during 2± 3 weeks in early spring. 2 Data for the ®rst 2 years of a 3-year project to use SSB for biological suppression of the Colorado potato beetle (CPB), Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae), veri®ed earlier research showing that augmentation of SSB (~5 nymphs/plant) can signi®cantly suppress CPB infestations.In the third year, wild SSBs were transferred directly from pheromone traps to mid-plot nursery cages having a mesh size chosen to retain the adult predators but allow their offspring to escape.Pheromone dispensers were placed peripherally to pro- mote dispersal of young predators and immigration of new wild spined soldier bug adults.Pheromone-mediated augmentation using porous nursery cages and pheromone dispensers was less labour-intensive than earlier methods, and resulted in signi®cantly improved potato yield. 3 Trapping SSB adults early in the spring protects them from parasitization by ta- chinid ¯ies and scelionid wasps that use the pheromone to facilitate host-®nding. The compatibility of pheromone-mediated predator augmentation/conservation with implementation of transgenic plants, imidacloprid insecticide, and other bio- control methods is discussed.

Keywords Biological control, conservation, natural enemy, Harmonia, Lebia, ladybird beetles, kairomone, tachinid, scelionid.

spectrum insecticide, and genetically engineered potato produ- Introduction cing Bacillus thuringiensis (Bt) proteins selectively toxic to The Colorado potato beetle (CPB), Leptinotarsa decemlineata beetles.However, cross-resistance to imidacloprid has already (Say) (Coleoptera: Chrysomelidae), quickly became the most been detected in some (Wen & Scott, 1997) and the destructive pest of potato in eastern North America after its host- ability of the CPB to evolve resistance to transgenic Bt-potato shift to cultivated potato some 150 years ago (Casagrande, has been demonstrated in the laboratory (Whalon & Wierenga, 1987).Since then, control of the beetle in eastern North America 1994). has relied almost totally on insecticides, but the beetle developed The likely evolution of resistant ®eld populations of the CPB resistance progressively faster to one insecticide after another (Olson et al., 1996) and the higher costs of new control measures, (Hare, 1990).Two new products have entered the marketplace to justi®es continued research to optimize deployment strategies of control CPB in potato: imidacloprid, a novel type of broad- new technologies, and to foster emerging non-insecticidal technologies.For transgenic potato, planting mixtures of Correspondence: Dr Jeffrey R.Aldrich.Tel: + 1 301 504 8531; susceptible and transformed potato should slow the appearance fax: + 1 301 504 6580; e-mail: [email protected] of resistant individuals (Gould, 1994), or Bt-transgenic potato

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could be planted peripherally prior to sowing a ®eld with forest at the Beltsville Agricultural Research Center-East untransformed potato to intercept colonizing CPB adults (BARC-E) at sites remote from potato plots.Each trap was (Whalon & Wierenga, 1994).Similarly, the best way to retard baited with ~350 mg of 20% pheromone in polyvinyl chloride evolution of resistance to imidacloprid by L. decemlineata, and (Aldrich et al., 1984) and rebaited every 2±4 days from mid- to reduce cost, may entail mixed-row or perimeter treatments to March to mid-May.In 1994 and 1995, 30 and 26 traps, intercept colonizing CPB adults.Nevertheless, `it is in the best respectively, were deployed at the same site; in 1996, 30 traps interest of potato growers to continue to use all available were deployed at a different BARC-E remote site.Traps were

integrated pest management approaches, such as crop rotation, to ¯ushed with CO2 to remove spined soldier bugs, at which time minimize the use of imidacloprid' (Dively et al., 1998). the sex of the trapped adults was recorded. Biological control, of course, is an important component of In 1994 and 1995, wild SSB adults were brought to the integrated pest management that can positively or negatively laboratory, grouped in half-pint paper cartons (~15/carton) affect how rapidly insects come to tolerate transgenic crops provided with a water bottle, pupae of Tenebrio molitor L. (Gould et al., 1991; Arpaia et al., 1997). (Coleoptera: Tenebrionidae) (Rainbow Mealworms, Inc., We have been pursuing a novel approach to augment and Compton, CA, U.S.A.), a fresh green bean and a piece of conserve predators for biocontrol (Aldrich, 1998).Our goal has cheesecloth for oviposition.These cartons were kept in cool been to develop hardware and protocols to enable individual growth chambers (15°C; 65% relative humidity (RH); growers, insectary operators and gardeners to mass-produce LD 14 : 10 h photoperiod) to delay oviposition, and transferred nymphs of the predatory spined soldier bug (SSB), Podisus to a warm growth chamber (26°C, 65% RH, and LD 16 : 8 h) 2± maculiventris (Say) (Heteroptera: Pentatomidae: Asopinae), 3 weeks prior to augmentation to promote oviposition. from wild adults caught in pheromone-baited traps.We have Cheesecloth pieces were collected and replaced twice a week focused our efforts on the SSB because this predator is abundant and pieces with eggs were combined in a few large containers for throughout much of North America (McPherson, 1982), SSB emergence of nymphs.In 1996, spined soldier bugs were adults and nymphs prey on all stages of a wide variety of insects harvested and collected as before, but the wild adults were and SSB males produce a chemically simple, yet powerful transferred directly to nursery cages constructed in ®eld plots as aggregation pheromone that is commercially available (Aldrich described below. et al., 1984; Aldrich, 1995). In addition, SSB nymphs are attracted to the pheromone, suggesting that the synthetic 1994 and 1995 ®eld plots pheromone can be used to disperse nymphs from points of augmentation (Sant'Ana et al., 1997). Augmentation of SSBs Nine 500 m2 plots spaced > 25 m apart were planted with has shown promise for suppression of CPB infestations, as has potatoes on 24 April 1994, at BARC-E (Solanum tuberosum augmentation of the twospotted stink bug, Perillus bioculatus `Kennebec' variety; ~1040 plants/plot; 0.92 m row spacing; (F.) (Asopinae) (Boiteau, 1988; Biever & Chauvin, 1992; 46 cm between plants).The population of CPBs was very low at Hough-Goldstein & Whalen, 1993).However, the SSB is more this site because potato had not recently been grown in this fecund than P. bioculatus and can eat at least as many CPB eggs location; therefore, overwintered CPB adults were collected at and larvae as does the twospotted stink bug (Hough-Goldstein & other locations and released in the ®eld plots at the rate of one McPherson, 1996). beetle/plant in two releases (31 May and 10 June).Treatments (3 Here we describe results of a 3-year pilot test to mass-trap SSB replicates/treatment) consisted of: (1) plots augmented with adults in overwintering habitat for augmentation of their seven 2nd±4th-instar SSB nymphs per plant, (2) plots containing offspring in potato and to attract indigenous spined soldier bugs six evenly spaced SSB pheromone dispensers per plot (Soldier to infested potato ®elds.We sought to augment and conserve Bug Attractorsq, Sterling International, Inc., Liberty Lake, WA, SSB in potato ± with the least amount of labour possible ± at a U.S.A.) and (3) untreated check plots. SSB nymphs were placed larger scale than previously achieved and to employ techniques on potato plants by hand using camel-hair brushes in two compatible with the latest technologies to control the CPB. releases; 5 nymphs/plant (2±6 June) and 2 nymphs/plant (17 June).Pheromone dispensers were deployed on 2 June and replaced on 20 June. Materials and methods In 1995, ®eld plots were planted as is in 1994 but earlier (7 April) and the same treatments were applied to each plot as in the Spring harvest of Podisus maculiventris adults previous year with the following modi®cation.Pheromone- Live male and female SSBs were harvested annually in treatment plots included a walk-in cubicle screen cage (3.7 m per pheromone-baited traps as they emerged from overwintering. side) in which cold-hardy crucifers were transplanted from cold- Traps were made of transparent cylindrical containers frames on 17 April (18 plants/variety in two rows; 20 cm (20.2 3 19.7 cm; Tri-State Molded Plastics, Inc., Dixon, between plants, 30 cm between rows): Elisa cabbage, hybrid Kentucky, U.S.A.) by cutting two holes (9 cm diameter) in broccoli, snow crown cauli¯ower, leafy Chinese cabbage, opposite sides and covering each hole with an inwardly Russian red kale, Chinese cabbage, Packman broccoli and projecting screen funnel.The containers were turned upside Bona kale.From 18±25 April, ~30 wild pierid butter¯ies were down, so that the normal top of the container became the bottom netted and released in each ®eld cage, and on 24 April one red of the trap held in place by two elastic cords hooked into the kale plant infested with laboratory-reared (L.) screen funnels.Traps were hung from branches (~1.5m from the larvae was placed in each cage in an effort to provide prey for the ground, > 30 m apart) bordering oak-dominated deciduous offspring of wild SSB adults released in the cages on 24 April

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Suppression of Colorado potato beetle infestation 211 and 11 May (two equal releases totalling ~150 adults/cage, 1 : 1 On 24 May and 6 June 1995, and on 7 and 18 June 1996, the sex ratio).On 22 May, the ®eld cages were opened by draping the stages of CPB and SSB, and adults of carabid and coccinellid screening on the top of the frame to allow SSB nymphs to escape. predators were counted on 10 randomly selected sets of plants/ Augmentation plots received seven SSB nymphs/plant, spread plot (5 plants/set).Defoliation was scored as above for 10 over six releases between 12 May and 14 June.It was randomly selected sets of plants/plot (5 plants/set) on 7 July 1995 unnecessary to supplement CPBs in 1995 because there were and 27 June 1996.Potatoes were harvested by hand (5 samples/ ample overwintered adults in the area from the previous year.By plot; 5 plants/sample) on 2 August 1995 and 7 August 1996 and the ®rst week in June all plots were being heavily defoliated by the number of tubers and grams of potatoes were recorded for CPBs, so on 7 June the plots were rescued by spraying with Bt each sample. San Diego variety (M-trakq; Ag.Chem.,Girdletree, MD, U.S.A.; 425 g AI/ha). Podisus maculiventris pheromone trap tests In 1996, the standard `Aldrich' trap used to harvest SSB adults 1996 ®eld plots was compared in the ®eld to a different type of trap, the `Mizell' trap (Mizell et al., 1996) and modi®cations thereof. The Mizell In 1996, the number of potato plots was increased to 15, planted trap consists of a yellow triangular baf¯e staked to the ground in sets of three as described above, with the ®ve replicates widely with a screen collector placed on the narrow top of the trap.In scattered over BARC (> 0.5 km between sets) such that one experiment, Aldrich traps were compared with tall (120 cm) migration between replicates was insigni®cant (Follett et al., and short (60 cm) Mizell traps.For this experiment, ®ve of each 1996).Treatments (5 replicates/treatment) consisted of: (1) kind of trap were alternated (> 30 m apart) along a powerline cut imidacloprid border treatment, (2) imidacloprid border treat- through deciduous woods at an isolated BARC-E location.The ment + mid-plot SSB nursery + pheromone dispensers (`total- traps were baited with pheromone and monitored from 25 March treatment' plots) and (3) untreated check plots.Plots consisted of to 1 August as described above.A second experiment conducted six 30-m rows planted with potato on each side of two middle at another isolated BARC-E site compared short Mizell traps rows which were left unplanted for control and insecticide- having the screen-type collector with short Mizell traps using the border treatments or planted with Siberian kale the previous fall top portion of a commercially available yellowjacket trap as the for total-treatment plots.A fall planting of Siberian kale was collector (Sterling International, Inc., Liberty Lake, WA, chosen in the hope that this winter-hardy crucifer would provide U.S.A.). Traps were arranged, baited and monitored from 30 more cover foliage and alternative prey in early spring for SSB March to 14 May in a fashion similar to that for the companion nymphs in nursery cages than the crucifers tried previously. test. Imidacloprid (Admireq 2F (¯owable), Bayer, St.Louis, MO, U.S.A.; 3 mL AI/30 m (row) was applied in the furrow over the seed pieces with a backpack sprayer to the outside two potato Statistical analyses rows and ~2.5 m at each end of inside rows. Mid-®eld nurseries Analysis of variance (ANOVA) was performed on data with the were created by stretching Shade Nettingq (Gardener's Supply MIXED procedure (SAS Institute Inc., 1997). Residuals were Co., Burlington, VT, U.S.A.; 1/8-inch mesh, 6-foot width) over examined graphically for homogeneity and normality. wire hoops to cover the two rows of kale, burying the sides and Heterogeneous variance of the residuals was addressed by ends of the netting to form an enclosure.Spring-collected SSB partitioning the variance into groups of similar variance.Least adults were released inside these enclosures as they were caught square means and their standard errors are reported.Some data in pheromone-baited traps (~300 adults/cage; 1 : 1 sex ratio). were transformed to satisfy ANOVA assumptions; back-trans- The 1/8-inch mesh size was chosen for the netting because adult formed means are reported for comparison. SSBs are too large to pass through this material, whereas their offspring could easily escape.On 3 June, six Soldier Bug Attractors were placed peripherally around the total-treatment Results plots between the Admire-treated and the untreated potato rows to promote dispersal of nymphs from the mid-plot nurseries Spring Podisus maculiventris harvest (Sant'Ana et al., 1997) and to attract newly-emerged wild SSB Overwintered SSBs are extremely responsive to pheromone- adults (Aldrich et al., 1984). baited traps just prior to the bud burst of deciduous trees (Fig.1) ± pollen shedding of red maple ( Acer rubrum)isa convenient, reliable indicator that emergence of SSB is Sampling in plots imminent (Aldrich, 1995).In 1994, a total of 4642 SSB adults On 22 June 1994, the stages of CPB and SSB were counted on 20 (1721 females and 2921 males) were captured, mostly from 2±19 randomly selected sets of plants/plot (5 plants/set).On 23 June April, in pheromone-baited traps to supply predators for and 14 July, defoliation was rated on a scale of 0±5 (0 = no augmentation.In 1995, the ®rst adult SSBs emerged on 14 damage; 5 = total defoliation) for 20 randomly selected sets of March, two weeks earlier than in 1994, yet the peak emergence in plants/plot (5 plants/set) by the same observer (WWC).Potatoes 1995 occurred on the same date as in 1994 (9 April).Essentially were harvested by hand (10 samples/plot; 5 plants/sample) on 9 the same number of adult predators were caught in 1995 (1781 and 10 August and the number of tubers and grams of potatoes females and 2855 males) as the year before (in four fewer traps), were recorded for each sample. despite the removal of adults from this location in 1994.In 1996,

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traps were monitored only on sunny, warm days; however, this beetles themselves, signi®cant treatment effects were detected more relaxed servicing regime resulted in basically the same both in augmentation plots and plots having pheromone harvest of predators (1824 females and 2502 males), with peak dispensers.Augmentation of SSB nymphs and the placement emergence occurring just four days later than the previous years. of pheromone dispensers in plots resulted in signi®cantly fewer egg masses than in control plots on 22 June and masses of de¯ated CPB eggs were found in these plots which appeared 1994 and 1995 ®eld plots identical to masses fed upon by SSB nymphs in the laboratory, Counts of the stages of CPB per ®ve potato plants are shown in but the reduced levels of eggs for the two treatments were not Table 1.In the initial year of the study when the relatively low signi®cantly different from each other.Augmentation plots had population of CPB in the area required augmentation of the signi®cantly fewer late-stage beetle larvae than plots having pheromone dispensers or untreated check plots.Surveys of spined soldier bugs on 22 June 1994, after completion of augmentation, revealed no signi®cant differences in augmenta- tion plots, pheromone dispenser plots and control plots.Visual detection of early instar SSB nymphs in the essentially intact potato canopy in 1994 was dif®cult. In 1995, the CPB reached outbreak levels requiring a rescue treatment with Bt on 7 June.Counts of the beetle stages made prior to the biopesticide treatment had more egg masses and larvae in control plots relative to pheromone-treated plots (intermediate) and predator-augmented plots (lowest numbers of these CPB stages); however, the only signi®cant difference detected was for the late-stage beetle larvae.At the outbreak population level of CPB, observations in the ®eld indicated an experimental breakdown occurred in two ways.First, defoliation of control plots and pheromone-treated/nursery-cage plots was so severe that adult beetles were observed ¯ying and walking to predator-augmented plots.Second, deer exerted continual pressure on the potato plots by browsing and, as the beetle outbreak progressed, the impact of deer became concentrated on augmentation plots. In 1995 plot surveys, signi®cantly more SSB nymphs were found in plots augmented with SSB nymphs (1.13 6 0.01/5 plants) than in pheromone-treated/nursery-cage plots (0.08 6 0.02) or control plots (0.05 6 0.01) on 6 June (P < 0.05), but not on 6 July. Counts for naturally occurring carabid and coccinellid predators ranged as high as 0.38 6 0.06 and 0.40 6 0.09 adults per ®ve plants for Lebia grandis Hentz and Harmonia axyridis (Pallas), respectively.For the carabid ( L. grandis) signi®cantly more individuals were observed in augmentation plots than in the other plot types on both sampling dates and a similar trend was observed for the coccinellids, H. Figure 1 Spring harvest of wild Podisus maculiventris adults in axyridis, Coccinella septempunctata L.and Coleomegilla pheromone-baited traps for 1994±96. maculata (De Geer), probably because the potato foliage in the

Table 1 Counts of the stages of Colorado Year Treatment Egg masses Early larvae** Late larvae Adults potato beetle per ®ve potato plants on 22 June 1994 and 24 May³ or 6 June 1995 for the 1994 SSB nymphs 3.5 6 3.4 a² 0.26 6 0.2 a 0.05 6 0.02 a 0.20 6 0.05 a following treatment plots (n = 3 per treatment): SBA 6.1 6 3.9 a² 7.6 6 2.9 a 7.3 6 2.5 b 0.22 6 0.05 a (a) augmented with seven early instar spined Control 10.9 6 4.6 b² 6.3 6 2.9 a 6.7 6 2.5 b 0.31 6 0.05 a soldier bug (SSB) nymphs per plant, (b) six 1995 SSB nymphs 8.1 6 1.2 a³ 121.1 6 14.4 a 90.4 6 16 a 5.8 6 0.9 a Soldier Bug Attractors (SBA) per plot (1994) or SBA + SSB adults 10.4 6 1.2 a³ 132.9 6 14.4 a 174.6 6 17 b 3.2 6 0.9 a six SBA + 150 caged SSB adults (1 : 1 Control 11.6 6 1.6 a³ 136.8 6 14.4 a 169.0 6 17 b 3.8 6 0.9 a male:female) per plot (1995) and (c) untreated controls*. *ab LS means within a column having an identical letters are not significantly different at the 0.05 level by LSD. ** 1st + 2nd-stage larvae = early larvae; 3rd + 4th-stage larvae = late larvae. ² back-transformed 6 95% con®dence interval; analysed after log transformation to satisfy ANOVA assumptions. ³ counted on 24 May.

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Suppression of Colorado potato beetle infestation 213

Table 2 Defoliation and potato yields in 1994 and 1995 for the following treatment plots (n = 3 per treatment): (a) augmented with seven early instar spined soldier bug (SSB) nymphs per plant, (b) six Soldier Bug Attractors (SBA) per plot (1994) or six SBA + 150 caged SSB adults per plot (1995) and (c) untreated controls; and 1996 treatment plots (n = 5 per treatment; from rows not treated with imidacloprid): (a) augmented with » 300 caged SSB adults + 4 SBA per plot + Admire in outside 2 rows, (b) Admire in outside two rows and (c) untreated controls*.

Defoliation Number of potatoes Grams of potatoes Year Treatment 6 SEM** per plant 6 SEM per plant 6 SEM

1994 & 1995 SSB nymphs 1.3 6 0.3 a 10.2 6 2.1 a 884 6 208 a SBAq('94)/SBAq + SSB adults (¢95) 2.9 6 0.3 b 9.6 6 2.1 a 664 6 208 b Control 2.7 6 0.3 b 6.7 6 2.1 b 386 6 208 c 1996 SBB adults + SBAq + Admireq 0.12 a² 13.0 a³ 851 a³ (± 2.1 6 0.9) (3.3 6 0.4) (29.2 6 4.8) Admireq 0.16 a² 9.7 b³ 640 ab³

(± 1.8 6 0.8) (3.1 6 0.4) (25.3 6 4.8) Control 0.78 b² 7.4 b 496 b³ (± 0.3 6 0.7) (2.7 6 0.4) (22.3 6 5.0)

*abc LS means within a column having an identical letter are not significantly different at the 0.05 level by LSD. ** defoliation scale from 0 to 5 (0 = none; 5 = total); recorded 14 July 1994, 7 July 1995 and 27 June 1996. ² back-transformed for comparison; analysed after ln transformation to satisfy ANOVA assumptions (transformed means and SEM in parentheses). ³ back-transformed for comparison; analysed after square-root transformation to satisfy ANOVA assumptions (transformed means and SEM in parentheses).

Table 3 Counts of the stages of Colorado potato beetle per ®ve potato plants in 1996 for the following treatment plots (n = 5 per treatment): (a) augmented with » 300 caged SSB adults + 4 SBA per plot + Admire in outside two rows, (b) Admire in outside two rows and (c) untreated controls; and dates: 7 and 18 June*.

Effect Treatment Date Egg masses Early larvae Late larvae Adults

Treatment SBB adults + SBA + Admire ± 1.3 6 0.8 a 6.1 6 4.4 a 3.9 6 1.6 a 0.46 6 0.3 a Treatment Admire ± 1.0 6 0.8 a 15.3 6 6.2 ab 7.3 6 4.2 a 0.46 6 0.3 a Treatment Control ± 3.1 6 1.6 a 23.9 6 7.8 b 28.5 6 11.6 a 1.7 6 0.6 a Date 7 June 3.4 6 1.4 a 16.8 6 5.2 a 0.0 6 1.5 a 1.4 6 0.5 a Date 18 June 0.14 6 0.07 b 13.4 6 6.0 a 26.5 6 8.2 b 0.35 6 0.3 b

*ab LS means within a column having an identical letters are not significantly different at the 0.05 level by LSD.

other plot types had been so decimated that there were fewer augmentation treatment than for the treatment involving CPB to prey upon than in augmentation plots.The multicolored pheromone dispensers, which in turn resulted in a signi®cantly Asian ladybird beetle, H. axyridis, arrived in the plots earlier greater mass of tubers than from control plants. than the seven-spotted ladybird beetle, C. septempunctata, or the pink-spotted ladybird beetle, C. maculata. 1996 ®eld plots Analysis of defoliation data for 1994 and 1995 with year as a ®xed variable showed that the same treatment pattern occurred in Counts of the stages of CPB per ®ve potato plants by treatment the two years, and that there was a signi®cantly higher CPB and by date (7 and 18 June) were more variable than comparable infestation in the second year (1994 defoliation data for 1994 and 1995 because the CPB populations in the rating 6 SEM = 1.50 6 0.27 versus 3.02 6 0.27 in 1995; various localities varied from extremely high to very low P < 0.05). In view of these results, and the fact that identical or (Table 3).The trend was for lower CPB infestations in total- similar treatments were duplicated in the same plots in 1995, the treatment plots than imidacloprid border-treatment plots, each of combined defoliation and yield data for 1994 and 1995 are which were much more protected from beetles than plants in reported (Table 2).Over this 2-year period, defoliation was untreated check plots.However, the only signi®cant differences signi®cantly lower in the plots augmented with SSB nymphs detected were for early CPB larvae (Table 3).Signi®cant than in the treatments involving pheromone dispensers in plots differences with time were seen for the numbers of CPB egg or in control plots.The numbers of potatoes per plant from plots masses, late-stage larvae and adults, re¯ecting the dynamics of receiving SSB nymphs and plots receiving pheromone dis- beetle infestation. pensers (+ SSB adults in 1995) were not signi®cantly different Total-treatment plots had 0.30 6 0.16 SSB nymphs per ®ve from each other, but plants from both these types of treatments plants on 7 June compared to values near zero for Admire-only had signi®cantly more tubers than did control plants.Finally, the plots and control plots, but these differences were not weight of tubers/plant was signi®cantly greater for the nymphal statistically signi®cant, and near-zero values of SSB nymphs

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Table 4 Performance in 1996 of different types SSB agults (mean/trap/day 6 SEM) and sizes of traps (n = 5 per treatment) in capturing live spined soldier bug (SSB) adults, Test Trap type Date Total Females Males Podisus maculiventris*.

I.A Aldrich** 25 Mar±6 May 9.82 6 2.1 ab 4.05 6 0.7 a 5.93 6 1.4 ab I.A Mizell (short)² 25 Mar±6 May 13.50 6 2.1 a 4.05 6 0.7 a 9.46 6 1.4 a I.A Mizell (tall)² 25 Mar±6 May 6.47 6 2.1 b 2.28 6 0.7 a 3.88 6 1.4 b I.B Aldrich 20 May±1 Aug. 0.44 6 0.1 a 0.27 6 0.06 a 0.16 6 0.05 a I.B Mizell (short) 20 May±1 Aug. 0.83 6 0.1 b 0.47 6 0.07 b 0.37 6 0.07 b I.B Mizell (tall) 20 May±1 Aug. 0.87 6 0.1 b 0.53 6 0.06 b 0.35 6 0.05 b II Mizell/screen top 30 Mar±14 May 6.07 6 1.0 a 2.34 6 0.4 a 3.73 6 0.7 a II Mizell/YJ top³ 30 Mar±14 May 5.40 6 0.8 a 2.47 6 0.4 a 2.95 6 0.5 a

*ab LS means for a test within a column having an identical letters are not significantly different at the 0.05 level by LSD. ** cylindrical-style trap described in Aldrich et al. (1984). ² baf¯e-style trap described in Mizell et al. (1996); 60 cm (short) and 120 cm (tall), each with a screen top as the collector. ³ Sterling International, Inc. (http://www.rescue.com) commercial yellowjacket trap (with the bottom removed) used as the collector.

Defoliation of plants from imidacloprid border-treatment plots and total-treatment plots did not differ signi®cantly, but plants from both of these types of treatments were signi®cantly less damaged than plants from control plots (Table 2).The number of potato tubers per plant was signi®cantly greater for plants from total-treatment plots than for plants from plots treated only with Admire and plants from control plots.The weight of potatoes/plant for plants from Admire-only plots was not signi®cantly different from values for plants from total- treatment plots and control plots and the mean of 851 g of potatoes from total-treatment plants was signi®cantly higher than the mean of 496 g from control plants.

Podisus maculiventris pheromone trap tests Data for Aldrich- versus Mizell-type traps are presented in two sections corresponding to the occurrence of overwintered SSB adults (Table 4, 1.A, late March to early May) and newly emerged adults (Table 4, 1.B, late May to July). Numbers of SSB adults caught in pheromone traps was at least an order of magnitude greater for overwintered adults in the spring (I.A) than for newly emerged summer adults (I.B). Mizell traps performed as well as or better than Aldrich traps in the spring, Figure 2 Counts (mean 6 SEM) of ladybird beetle adults (Coleoptera: and signi®cantly better than Aldrich traps in the summer.In the Coccinellidae) for the four most abundant species in all potato plots on spring, short Mizell traps caught more SSB adults than did tall 6 and 18 June 1996 (ab LS means within a species having an identical Mizell traps, but this difference was due mainly to higher capture letters are not signi®cantly different at the 0.05 level by LSD). of males.The test comparing different types of collectors on short Mizell traps (Table 4, 2) showed that the cumbersome screen collector could be replaced with the top portion of a were recorded in all the plots for the later sampling date. commercially available yellowjacket trap with no loss in Practically no L. grandis adults were observed in plots in 1996, trapping ef®ciency. but the pattern of ladybird beetles in the plots was more interesting (Fig.2).The exotic ladybird species, H. axyridis and Discussion C. septempunctata, were much more abundant than the native species, Hippodamia convergens GueÂrin-MeÂneville, and C. Most research on predator augmentation for Colorado potato maculata. Harmonia adults were ®rst to colonize the potato plots beetle (CPB) control has focused on the twospotted stink bug, and then their numbers declined signi®cantly as C. septempunc- Perillus bioculatus (F.) (Asopinae), because this predator is tata adults arrived. virtually host-speci®c on the beetle (e.g. Hough-Goldstein &

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Suppression of Colorado potato beetle infestation 215

Whalen, 1993; Cloutier & Bauduin, 1995; Drummond & control plots.Our results are comparable to those from the Maine Groden, 1996).Prey speci®city notwithstanding, spined soldier Potato Ecosystem Project, where Bt-treatment combined with bugs (SSB) and P. bioculatus are similar in their abilities to prey inoculation of fungal spores from Beauveria bassiana and upon the CPB (Hough-Goldstein & McPherson, 1996), but under releases of Perillus nymphs provided progressively better CPB natural conditions neither predator arrives in potato ®elds early control (Drummond & Groden, 1996). enough, or develops large enough populations, to prevent beetle In the third year of the pilot test, the goal was to reduce the outbreaks (Drummond & Groden, 1996; Aldrich, 1998).Small- amount of labour required to implement pheromone-mediated scale augmentation experiments indicate that releases of about SSB augmentation and to combine this biocontrol strategy with ®ve P. bioculatus or SSB nymphs per plant in early season potato imidacloprid insecticide treatment.Data from this experiment can signi®cantly protect the crop from CPB infestations (Biever were highly variable, re¯ecting widely ranging population levels & Chauvin, 1992; Hough-Goldstein & McPherson, 1996); of CPBs in the vicinity of different sets of plots.In addition, the however, this level of predator release translates to 100 000 size of plots was smaller than desirable for tests involving border nymphs per hectare.SSBs are now being sold for biological treatments and patchy infestations of the , control ± $25 per 100 4th and 5th-instar nymphs (Koppert B.V., Ostrinia nubilalis (HuÈbner) (Lepidoptera: Pyralidae), con- The Netherlands) and $60 per 100 adults (ARBICO, Inc., founded statistical analysis of the data.Nonetheless, there were Tucson, AZ, U.S.A.) ± but at these prices SSBs are commercially signi®cantly fewer early CPB larvae in total-treatment plots useful only for high-value crops such as in glasshouse operations (imidacloprid/augmentation/pheromone) relative to untreated where certain pests are Bt-resistant (De Clercq et al., 1998a). It control plots, and defoliation of plants in the total-treatment plots seems unlikely that suf®cient numbers of either asopine can be and imidacloprid border-treatment plots was signi®cantly mass-reared for commercially feasible augmentation in potato. reduced relative to control plants (but not signi®cantly different The twospotted stink bug only occurs east of the Rocky between treatments).Yields were the best evidence that Mountains due to range expansion with the Colorado potato pheromone-mediated enhancement of SSB signi®cantly added beetle (Knight, 1923) and is relatively uncommon throughout its to protection against CPB infestation; the number of potatoes present range.The suspected pheromone of P. bioculatus is was higher for total-treatment plants than for either imidaclo- stereochemically complex and the available racemate failed to prid-treated or untreated plants and the weight of potatoes from attract the bugs in Maryland (Aldrich et al., 1986; Aldrich total-treatment plants was signi®cantly higher than untreated unpublished data).Even if an active pheromone were available control plants. for Perillus, the population of this species is probably too low to To date, there is no indication that removal of 1000±2000 attract substantial numbers of wild adults (Aldrich, 1998).Using pheromone-trapped SSB females from 3±5 ha islands of pheromone-based technology, however, we captured an average deciduous forest adversely affects the annual populations of of 1775 female SSBs each year during 2±3 weeks in early spring, this predator (Fig.1, 1995 and 1996; Aldrich, unpublished data, with the potential to produce up to 1.6 million young predators 1997 and 1998).What is clear is that pheromone-calling SSB based on fecundity and survival estimates for P. maculiventris males subject themselves and their mates to intense parasitism (De Clercq et al., 1998c). We believe that empowering pressure from tachinid ¯ies and scelionid wasps exploiting the individual growers and insectary operators with this type of pheromone as a host-®nding kairomone (Aldrich et al., 1984; pheromone-based technology is the most realistic means to Aldrich, 1995).At least 10 times more SSB adults can be trapped produce enough SSBs for widespread applications. in early spring than in summer (Table 4) and capturing the adult Data for the ®rst 2 years of our study verify earlier research predators early in the spring effectively protects them from showing that augmentation of SSB nymphs can signi®cantly parasitoids, which only attack after most SSBs have emerged. suppress CPB infestations (Boiteau, 1988; Biever & Chauvin, The risk of intraguild predation ± a major problem in some 1992; Hough-Goldstein & McPherson, 1996).In the initial year agroecosystems (Rosenheim et al., 1995) ± at this point appears of the pilot test when pressure from the beetle was low, negligible for P. maculiventris because SSBs are ineffective pheromone dispensers alone attracted enough wild SSB adults predators of ladybird beetles such as Harmonia axyridis (Hough- from the surrounding natural habitat to reduce the numbers of Goldstein et al., 1996). Indeed, the predator guild itself has CPB egg masses signi®cantly, leading to increased yield.The shifted; exotic ladybird species are now more abundant in second year of the experiment was a much more realistic test Maryland (Fig.2) and other parts of the country (Drummond & because the resident CPB population was comparable to levels Groden, 1996) than are native species such as C. maculata, encountered by commercial potato growers.Under these which were once the dominant ladybirds in potato (refs.in conditions, by early June even plots where predators were Arpaia et al., 1997). added were so overwhelmed by the beetle that it was decided to Pheromone-mediated augmentation using porous nursery check the outbreak with a treatment of Bt-biopesticide.The 1995 cages and pheromone dispensers to promote dispersal of young experiment also suffered from the effects of adult beetles moving predators and immigration of new wild SSB adults is much more from decimated control plots to augmentation plots and from practical than the labour-intensive methods employed in the ®rst deer browsing.In addition, despite our efforts to establish pierid 2 years of the study.The ease of transferring wild SSBs from butter¯ies inside the walk-in ®eld cages, we observed few larvae pheromone traps to nurseries could be further reduced by using on any but the laboratory-infested plants.Nevertheless, the same Mizell-style traps with a collector that can be conveniently treatment pattern occurred in 1995 as in 1994 and, over the two- exchanged with a fresh pheromone-baited collector when year period, augmentation and pheromone treatments resulted in trapped predators are transported to nurseries.Encapsulated signi®cantly better yields than those obtained from untreated diets for asopine predators will eventually be available (e.g. De

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Clercq et al., 1998b), which will be useful to improve the Plants (ed.by R.J.Hardie and A.K.Minks), pp.357±381.CAB survival and fecundity of wild SSB females in nursery cages, as International, Wallingford, U.K. well as providing a mechanism for commercial insectaries to Aldrich, J.R., Kochansky, J.P. & Abrams, C.B. (1984) Attractant for a reduce the cost of rearing this predator.SSBs are practically bene®cial insect and its parasitoids: pheromone of the predatory immune to Bt endotoxins (Boyd & Boethel, 1998), but the spined soldier bug, Podisus maculiventris (: Pentatomi- dae). Environmental Entomology, 13, 1031±1036. predators are susceptible to contact with imidacloprid (less so to Aldrich, J.R., Oliver, J.E., Lusby, W.R. & Kochansky, J.P. (1986) exposure via ingestion) (De Cock et al., 1996; Boyd & Boethel, Identi®cation of male-speci®c exocrine secretion from predatory 1998).More research is needed to determine the best mulches stink bugs (Hemiptera, Pentatomidae). Archives of Insect Biochem- (e.g. Brust, 1994) or cover crops to use with porous predator istry and Physiology, 3, 1±12. nurseries, and how best to integrate this augmentation practice Arpaia, S., Gould, F. & Kennedy, G.G. (1997) Potential impact of with existing insecticidal and transgenic control measures.A Coleomegilla maculata predation on adaptation of Leptinotarsa combination of cultural, physical and biological suppression decemlineata to Bt-transgenic potatoes. Entomologia Experimentalis tactics will continue to be crucial for preserving insecticidal et Applicata, 82, 91±100. controls against a pest as intractable as the CPB (Weber & Ferro, Biever, K.D. & Chauvin, R.L. (1992) Suppression of the Colorado 1995; Dively et al., 1998). potato beetle (Coleoptera: Chrysomelidae) with augmentative Harnessing the pheromone of SSB, we believe, offers an releases of predaceous stinkbugs (Hemiptera: Pentatomidae). opportunity to enhance the ef®cacy of this predator.This Journal of Economic Entomology, 85, 720±726. Boiteau, G.(1988) Control of the Colorado potato beetle Leptinotarsa opportunity for semiochemical husbandry, however, seems decemlineata (Say): learning from the Soviet experience. Bulletin of unlikely to be unique (Glinwood et al., 1998; Aldrich, 1999). the Entomological Society of Canada, 20, 9±14. State-of-the art research on deployment of Bt-transgenic cotton Boyd, M.L. & Boethel, D.J. (1998) Susceptibility of predaceous in Australia, for example, still emphasizes conservation of hemipteran species to selected insecticides on soybean in Louisiana. natural enemies by intercropping with alfalfa (Fitt & Wilson, Journal of Economic Entomology, 91, 401±409. 2000), possibly in the future combined with nutritional sprays to Brust, G.E. (1994) Natural enemies in straw-mulch reduce Colorado lure predators into the cotton crop (Mensah, 1997).Trap- potato beetle populations and damage in potato. Biological Control, cropping [even with transgenics (Whalon & Wierenga, 1994)] is 4, 163±169. increasingly accepted as a means to concentrate pests where they Casagrande, R.A. (1987) The Colorado potato beetle: 125 years of can be destroyed more conservatively than eventually would be mismanagement. Bulletin of the Entomological Society of America, required.There is an emerging science of `farmscaping', `beetle 33, 142±150. banking' and planting `insectary hedgerows' to provide refuges Cloutier, C.& Bauduin, F.(1995) Biological control of the Colorado potato beetle Leptinotarsa decemlineata (Coleoptera: Chrysomeli- in agroecosystems for bene®cials (Pickett & Bugg, 1998). dae) in Quebec by augmentation releases of the two-spotted stinkbug Attractants for key biocontrol agents could improve the linkage Perillus bioculatus (Hemiptera: Pentatomidae). Canadian Entomol- between these and yet to be imagined innovative approaches to ogist, 127, 195±212. natural enemy augmentation and conservation. De Clercq, P., Merlevede, F., Mestdagh, I., Vandendurpel, K., Mohaghegh, J.& Degheele, D.(1998a) Predation on the tomato looper Chrysodeixis chalcites (Esper) (Lep., Noctuidae) by Podisus Acknowledgements maculiventris (Say) and Podisus nigrispinus (Dallas) (Het., We thank Dr Russell F.Mizell, III (University of Florida, North Pentatomidae). Journal of Applied Entomology, 122, 93±98. Florida Research & Education Center, Monticello) for providing De Clercq, P., Merlevede, F. & Tirry, L. (1998b) Unnatural prey and arti®cial diets for rearing Podisus maculiventris (Heteroptera: traps, and Mr Rod G.Schneidmiller (President, Sterling Pentatomidae). Biological Control, 12, 137±142. International, Inc., Liberty Lake, WA) for providing yellow- De Clercq, P., Vandewalle, M. & Tirry, L. (1998c) Impact of jacket traps and Soldier Bug Attractors.We thank Drs Mizell and inbreeding on performance of the predator Podisus maculiventris. Joseph Dickens (USDA-ARS Vegetable Laboratory, Beltsville) Biocontrol, 43, 299±310. for reviewing the manuscript.We are also grateful to the many De Cock, A., De Clercq, P., Tirry, L. & Degheele, D. (1996) Toxicity student workers and colleagues in the ICEL who helped with this of diafenthiuron and imidacloprid to the predatory bug Podisus project.Mention of commercial products does not constitute an maculiventris (Heteroptera: Pentatomidae). Environmental Ento- endorsement by the U.S.Department of Agriculture. mology, 25, 476±480. Dively, G.P., Follett, P.A., Lindusda, J.J. & Roderick, G.K. (1998) Use of imidacloprid-treated row mixtures for Colorado potato beetle References (Coleoptera: Chrysomelidae) management. Journal of Economic Entomology, 91, 376±387. Aldrich, J.R. (1995) Chemical communication in true bugs and Drummond, F.A., Groden, E. (1996) Insect pests and natural enemies. exploitation by parasitoids and commensals. 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