Hexane extracts of spruce budworm, Choristoneura fumiferana, moth scales, applied at 0.04 moth-gram equivalents/branch and at 0.06 moth-gram equivalents/tree, failed to increase parasitism rates of Trichogramma spp. in two cutover spruce-fir stands in Maine. Releasing  Maine-strain  T. minutum apparently increased parasitism rates about 20-fold. However, application of kairomone extracts to whole branches and to upper crowns of small trees may have interfered with host-searching behaviors of Trichogramma parasitoids

Jennings, Daniel T

Jones, Richard L

English

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Field Tests of Kairomones to Increase Parasitism of Spruce Budworm (Lepidoptera: Tortricidae) Eggs by \u3ci\u3eTrichogramma\u3c/i\u3e Spp. (Hymenoptera: Trichogrammatidae)

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The Great Lakes Entomologist Volume 19 Number 3 - Fall 1986 Number 3 - Fall 1986 Article 9 October 1986 Field Tests of Kairomones to Increase Parasitism of Spruce Budworm (Lepidoptera: Tortricidae) Eggs by Trichogramma Spp. (Hymenoptera: Trichogrammatidae) Daniel T. Jennings University of Maine Richard L. Jones University of Minnesota Follow this and additional works at: https://scholar.valpo.edu/tgle  Part of the Entomology Commons Recommended Citation Jennings, Daniel T. and Jones, Richard L. 1986. "Field Tests of Kairomones to Increase Parasitism of Spruce Budworm (Lepidoptera: Tortricidae) Eggs by Trichogramma Spp. (Hymenoptera: Trichogrammatidae)," The Great Lakes Entomologist, vol 19 (3) Available at: https://scholar.valpo.edu/tgle/vol19/iss3/9 This Peer-Review Article is brought to you for free and open access by the Department of Biology at ValpoScholar. It has been accepted for inclusion in The Great Lakes Entomologist by an authorized administrator of ValpoScholar. For more information, please contact a ValpoScholar staff member at scholar@valpo.edu. 1986 THE GREAT LAKES ENTOMOLOGIST 185 FIELD TESTS OF KAIROMONES TO INCREASE PARASITISM OF SPRUCE BUDWORM (LEPIDOPTERA: TORTRICIDAE) EGGS BY TRICHOGRAMMA SPP. (HYMENOPTERA: TRICHOGRAMMATIDAE) Daniel T. Jennings! and Riehard L. Jones2 ABSTRACT Hexane extracts of spruce budworm, Choristoneura fumiferana, moth scales, applied at 0.04 moth-gram equivalents/branch and at 0.06 moth-gram equivalents/tree, failed to increase parasitism rates of Trichogramma spp. in two cutover spruce-fir stands in Maine. Releasing "Maine-strain" T. minutum apparently increased parasitism rates about 20-fold. However, application of kairomone extracts to whole branches and to upper crowns of small trees may have interfered with host-searching behaviors of Trichogramma parasitoids. Numerous studies have demonstrated the importance of kairomones for stimulating host-searching behavior of entomophagous parasitoids (Jones et al. 1973; Lewis et al. 1971; Lewis et al. 1975a, 1975b). Kairomones not only stimulate host-seeking behavior but also may help retain released parasitoids within a targeted area (Gross et al. 1975). Most kairomone studies have dealt with field crop pests. However, kairomones also have potential for increasing parasitism of forest insect pests including eggs of the spruce budwonn, Choristoneura fumiferana (Clemens). The polyphagous egg parasitoid Trichogramma minutum Riley parasitizes eggs of the spruce budwonn in northeastern spruce-fir forests. Parasitism of spruce budwonn eggs by T, minutum may be as high as 77% (Anderson 1976), but is usually less than 15%, and varies by locality nd year (Miller 1953, 1963; Neilson 1963; Thomas 1966). Efforts to increase parasitism rates by aerial-broadcast releases of T. minutum have been moderately successful (Houseweart et al. 1984), but not sufficient to suppress epidemic spruce budworm popUlations. In a preliminary laboratory bioassay (W. J. Lewis, USDA ARS, Tifton, GA) of "Maine-strain" T. minutum, hexane extracts of spruce budwonn moth scales applied to Heliothis sp. egg substratum, increased parasitism from 34% (controls) to 54% (treated). This paper reports results of field tests to detennine (a) if kairomones sprayed on host-tree foliage increase parasitism of spruce budwonn eggs by native, wild Trichogramma spp., and (b) if kairomones sprayed on host-tree foliage in the presence of released "Maine-strain" T. minutum, plus native Trichogramma spp., increase parasitism of spruce budwonn eggs. INortheastern Forest Experiment Station, USDA Building, University of Maine, Orono, ME 04469. 2Department of Entomology, Hodson Hall, University of Minnesota, St. Paul, MN 55108. 1Jennings and Jones: Field Tests of Kairomones to Increase Parasitism of Spruce BudworPublished by ValpoScholar, 1986186 THE GREAT LAKES ENTOMOLOGIST Vol. 19, No.3 METHODS Kairomone Extracts. More than 8000 spruce budworru moths were killed by cooling and then shipped in dry ice from the Great Lakes Forest Research Centre, Canadian Forestry Service, Sault Ste, Marie, Ontario, to the Department of Entomology. University of Minnesota, St. Paul, Minnesota. Hexane extracts of budworm moth scales were forruulated according to the procedure described by Jones et aL (1973). Extracts were concentrated to 10 moth-grams (I moth equivalent) per milliliter and refrigerated (5°C) until used in the field. Study Areas. Two study areas were located in a spruce-fir forest heavily infested with spruce budwornl; both areas were in Number 14 Plantation, Washington County, Maine, about 16.0 km west of Dennysville and 17.6 km north f East Machias. Area A was 2.4 km northwest of Patrick Lake; area B was 1 km southof area A. Both study areas were in cutover spruce-fir stands with abundant small-tree regeneration of balsam fir, A ie  balsamea (L) MilL, and spruces, Picea spp. In area A, 100 balsam fir trees from 1.6 to 4.8 m in height were chosen for study. These small trees were clumped in two openings with a total area of about 0.20 ha. The openings were surrounded by spruce-fir overstory about 15 m in height. Overstory trees were heavily defoliated by the spruce budworru. In area B, 50 balsam fir trees were chosen and paired in shape and height with 50 nearby trees of the same species. Selected trees were small, ranging from I. I to 3 7 m in height, and were densely clumped in a clearing about 0.04 ha. Surrounding overstory spruce, fir, and pine, Pinus strobus L., were large; estimated overstory tree heights were 15-20111 for both spluce and fir and 30 m for pines. Paired Branches. We chose two branches, one treated branch and one control branch. on each selected tree in area A, yielding a total f 200 branches. Chosen branches were in the upper and middle crowns of selected trees with each pair member at the same crown level and usually the same whorl. A I: 1000 ml dilution of moth-scale extract: hexane was prepared and applied by pressurized-can sprayer. About 400 ml of hexane, containing 4-.0 moth-gram equivalents, were sprayed on the 100 treated branches, yielding O.D-t. moth-gram equivalentslbranch. During spray application. each control branch was shielded with a large paper bag. Treated branches were sprayed between 1330 and 1500 h Eastern Daylight Time, (EDT), 11 July 1979. This date corresponded with peak egg-laying by spruce budworru moths (Houseweart et aL 1982); fresh, green egg masses were present on some balsam-fir trees in area A.Paired Trees. In area B, 50 trees were treated and paired with 50 control trees. For treated trees, the upper 113 (30--60 cm) of each tree was sprayed with 6 mI of the moth-scale extract:hexane dilution, yielding about 0.06 moth-gram equivalents tree. Nearby paired-control trees were shielded uring spray application. The moth-scale extract: hexane dilution was applied by pressurized-can sprayer between 16(Xl and 1800 h EDT, II July 1979; fresh, green egg masses were present on some small balsam- fIr trees in area B. Parasite Releases. To supplement native Trichogramma. we released lab-reared parasitoids in area B shortly « 30 min) after applying kairomone to treated trees. !'ath'e "Maine-strain" T. minutum were sent earlier to Rincon Vitm'a Insectaries Inc .. Oak View, California, for mass production in Sitotroga cerea/ella (Oliyief} host eggs. For field releases, host-egg cards with unemerged parasitoids were placed in two carton sizes: 0.47 1 ice-cream carton with 16 squares/carton and 0.18 I hot cold drinking cup with 10 squares/cup. Each container was sprayed with I ml ((J.OI moth-gram equiyalentl of scale extract prior to loading with host-egg cards. Four cartons and two cups were hung from upper-crown branches of small trees: deployment sites were distributed uniformly throughout the O.04-ha area. Egg Densities. Foliage samples were collected from both study areas 7 days after treatment. Paired treated and control branches were pruned from selected trees in area A. Foliated branch lengths and widths were measured (cm) and branch surface areas 2The Great Lakes Entomologist, Vol. 19, No. 3 [1986], Art. 9https://scholar.valpo.edu/tgle/vol19/iss3/9---------~------~~----~-.--~~ 1986 187 THE GREAT LAKES ENTOMOLOGIST calculated by the fonnula L x W/2 (Sanders 1980). Branches were then individually and transported o the laboratory for foliage examination. For treated and control trees in area B, the entire upper 1/3 of each tree was removed, bagged, and transported to the laboratory. This destructive sampling helped to thin some of the dense, overstocked regeneration in area B. Following the procedures outlined by Dixon et al. (1978), trained examiners inspected the foliage in the laboratory and removed all needles bearing egg masses. masses were then examined microscopically and categorized as new or old, on the descriptions of egg-mass age given by Morris (1955). The length of each new egg mass was measured (0.01 mm) with an ocular micrometer, and the number of egg rows counted. Regression equations of Leonard et al. (1973) were used to estimate eggs/mass, except eggs in 1- and 1.5 row masses were counted individually. Al  parasitized and nonviable eggs were counted individually. Egg densities were expressed as ggs/m2 of branch foliage area or eggsll/3-tree erown. Data Analyses. Means and standard errors were calculated for tree heights in both study areas. A paired (-test (P 0.01) was used to compare tree heights of treated and control trees in area B. Egg-density data were subjected to Hartley's test for homogenity of variances; transfonnations were not required. However, arcsine transformations were made on all percentages prior to statistical tests. Analysis of variance (ANOV A) was used to evaluate differences between egg densities by treatment (treated, control) and differences among percentages for each egg category (eclosed, parasitized, nonviable). Regression analyses were used to detennine relationships between tree heights and combined (treated and control) egg densities for each experiment. RESULTS Tree Heights. Trees. in area A were distributed about equally among five height classes: 1.5-2.1, 2.2-2.6, 2.7-3.0, 3.1-3.5, and 3.6-4.8 m. Overall mean height was 2.86 ± 0.07 m for the 100 paired branch trees in area A. For the 50 paired trees in area B, paired (-test indicated treated trees were signifieantly (P < 0.01) taller than control trees; however, the mean difference was < 0.5 m. Mean heights were 1.97 0.07 m for treated trees and 1.54 ± 0.09 m for control trees in area B. Paired Branches, An analysis of variance indicated no significant difference between egg densities for treated (x 487.66 eggs/m2) and control (x 495.53 eggs/m2) branches (P > 0.95). Percentages of eggs in each category (hatched, parasitized, nonviable) were also not significantly different between treated and control branches (Table 1). Parasitism by native Trichogramma spp. was extremely low « Table I) in area A. More were parasitized by Trichogramma spp. on control than on treated branches. the mean percentages were not significantly different. Table I Comparison of 100 paired treated and control branches by egg category. area A. Washington County, Maine, with native Trichogramma spp. as parasites. Percentage of eggs" Variable Hatched Parasitized Nonviable Treated 85.91 0.09 14.00 Control 89.07 0.23 10.70 F-value ([»1> I.90 (0.17) 0.09 (0.76) 1.98 (0.16) aArcsine transfonnation of percentages before analysis. bDiffercnces not significant. 3Jennings and Jones: Field Tests of Kairomones to Increase Parasitism of Spruce BudworPublished by ValpoScholar, 1986188 THE GREAT LAKES ENTOMOLOGIST Vol. 19, No.3 Regression analysis indicated virtually no relationship (il 0.05) between tree height and egg density (eggs/m2) for the 100 paired branch trees in area A. Paired Trees. Mean egg densities for treated (x 52.16 eggsi1l3-tree crown) and control (x = 59.80 eggs/ l/3-tree crown) trees in area B were not significantly different (ANOVA, P = 0.44). Percentages of eggs in each category (hatched, parasitized. nonviable) were also not significantly different for the paired trees Cfable 2). Parasitism rates of 3.66% (treated) and 4.66% (control) were not significantly different; however. again more eggs were parasitized on control branches than on treated branches. Regression analysis indicated a weak relationship (il 0.24) between tree height and egg density for the 50 paired trees in area B. Parasite Releases. We estimated ca. 287,000 "Maine strain" T. minutum emerged and dispersed from the host egg cards deployed in area B. Subsamples of host egg cards indicated release densities of reared parasitoids were 67,497 for small cups and 219,581 for large cartons. We have no data on the retention of released parasitoids in area B, However, the increased rates of parasitism in area B compared to area A indicate some treatment effect due to parasitoid releases, County, Maine. with native « 5,OOO,000lha) as parasites. Table 2, Comparison of 50 paiTrichogramma red treated nd spp, contrand ol trees by category"Maine strain" T, , area B, Washington minutum Percentage of eggsfl Variable Hatched Parasitized Nonviable Treated 83.53 3,66 12,81 Control 81.23 4.66 14,]1 F-value (p)b 0,67 (0.42) 0,27 (0,60) 0,311O.58l a Arcsine transformation of percentages before analysis. bDifferences not significant. CONCLUSION We found no evidence that (a) spruce budworm moth-scale extracts sprayed on host-tree foliage increased parasitization of budworm eggs by native, wild Trichogramma spp., or (b) spruce budworm moth-scale extracts sprayed on host-tree foliage in the presence of released "Maine-strain" T. minutum parasitoids increased parasitization of budworm eggs. Comparing parasitism rates between experimental areas indicates that releasing "Maine-strain" T. mimltum apparently increased parasitism of spruce budworm eggs . about 20-fold. However, the observed low parasitism rates, combined with the low parasitoid release rate « 5,000,000 Trichogramma/ha), also indicates that most parasitoids either (a) left the area in spite of kairomone present in the rele3-<.e container. (b) died, or (c) failed to search for spruce budworm Chiri and Legner (1983) concluded that complete coverage of host food plant~ with extracted kairomones might lead to a significant loss in parasitoid searching time. Total coverage applications may "mask" naturally occurring cues and cause early dispersal of par sitoids from treated plots, Although our observed parasitism rates were low, the data in both field tests may reflect a lowered searching efficiency of Trichogramma on individually treated branches and small tree crowns of balsam tir. Much more research is needed to elucidate important relationships between Trichogramma spp, and the spruce budworm. Particularly important arc laboratory 4The Great Lakes Entomologist, Vol. 19, No. 3 [1986], Art. 9https://scholar.valpo.edu/tgle/vol19/iss3/91986 THE GREAT LAKES ENTOMOLOGIST 189 studies to quantify response-area curves of T. minutum to varying concentrations of kairomone extracts. The quest to improve parasitoid searching efficiencies via appropriate distribution of moth-scale extracts on host-tree foliage remains unresolved. LITERATURE CITED Anderson, J. F. 1976. Egg parasitoids of forest defoliating Lepidoptera. pp. 233-249 inJ. F. Anderson and Harry K. Kaya (eds.). Perspectives in forest entomology, Academic Press, NY. 428 pp. Chiri, A. A., and E. F. Legner, 1983. Field applications of host-searching kairomones to enhance parasitization of the pink bollworm (Lepidoptera: Gelechiidae). J. Econ. Entomol. 76: 254--255. Dixon, W. M., M. W. Houseweart, and D. T. Jennings. 1978. How to examine branches for spruce budworm egg masses. CANUSAJCFRU Publ. 18 pp. Gross, H. R., Jr., W. J. Lewis, R. L. Jones, and D. A. Nordlund. 1975. Kairomones and their use for management of entomophagous insects: III. Stimulation of Trichogramma achaeae, T. pretiosum, and Microplitis croceipes with host-seeking stimuli at time of release to improve their efficiency. J. Chern. Ecol. 1:431-438. Houseweart, M. W., S. G. Southard, and D. T. Jennings. 1982. Availability and acceptability of spruce budworm eggs to parasitism by the egg parasitoid. Trichogramma minutum (Hymenoptera: Trichogrammatidae). Canadian Entomol. 114:657-666. Houseweart, M. W.• D. T. Jennings, and R. K. Lawrence. 1984. Field releases of Trichogramma minutum (Hymenoptera: Trichogrammatidae) for suppression of epi­demic spruce budworm, Choristoneura fumiferana (Lepidoptera; Tortricidae), egg populations in Maine. Canadian Entomol. 116:1357-1366. Jones, R. L., W. J. Lewis, M. Beroza, B. A. Bieri, and A. N. Sparks. 1973. Host-seeking stimulants (kairomones) for the egg parasite Trichogramma evanescens. Environ. Entomol. 2:593-596. Leonard, D. E .• G. A. Simmons, and G. K. vanDerwerker. 1973. Spruce budworm: techniques to improve counting of eggs. J. Econ. Entomol. 66:992. Lewis, W. J., A. N. Sparks, and L. M. Redlinger. 1971. A method f host-finding by Trichogramma evanescens. J. Econ. Entomol. 64:557-558. Lewis, W. J., R. L. Jones, D. A. Nordlund, and A. N. Sparks. 1975a. Kairomones and their use for management of entomophagous insects: I. Evaluation for increasing rates of parasitization by Trichogramma spp. in the field. J. Chern. Ecol. 1:343-347. Lewis, W. J., R. L. Jones, D. A. Nordlund, and H. R Gross, Jr. 1975b. Kairomones and their use for management of entomophagous insects: II. Mechanisms causing increase in rate of parasitization by Trichogramma spp. J. Chern. Ecol. 3:349-360. Miller, C. A. 1953. Parasitism of spruce budworm eggs by Trichogramma minutum. Canadian Dept. Agric. Sci. Serv., Div. For. BioI., Bi-mon. Progr. Rep. 9(4):1. 1963. Parasites and the spruce budworm. pp. 228-244 in R. F. Morris (ed.). The dynamics of epidemic spruce budworm popUlations. Mem. Entomol. Soc. Canada 31. 332 pp. Morris, R. F. 1955. The development of sampling techniques for forest insect defoliators, with particular reference to the spruce budworm. Canadian J. Zoo!. 33:225-294. Neilson, M. M. 1963. The analysis of egg survival in the unsprayed area. pp. 37-41 in R. F. Morris (ed.). The dynamics of epidemic spruce bud worm populations. Mem. Entomo!. Soc. Canada 31. 332 pp. Sanders, C. J. 1980. A summary of current techniques used for sampling spruce budworm populations and estimating defoliation in eastern Canada. Canadian For. Serv., Sault Ste. Marie, Ont. Rep. O-X-306, 33 pp. + ap endix. Thomas, H. A. 1966. Parasitism by Trichogramma minutum (Hymenoptera: Trichogram­matidae) in the spruce budworm outbreak in Maine. Ann. Entomo!. Soc. Amer. 59:723-725. 5Jennings and Jones: Field Tests of Kairomones to Increase Parasitism of Spruce BudworPublished by ValpoScholar, 1986

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Field Tests of Kairomones to Increase Parasitism of Spruce Budworm (Lepidoptera: Tortricidae) Eggs by \u3ci\u3eTrichogramma\u3c/i\u3e Spp. (Hymenoptera: Trichogrammatidae)

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