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1983 The elr ation of wild parsnip, Pastinaca sativa L., to parasitoid populations associated with soybean pests in central Iowa Linda Anne Buntin Iowa State University

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Buntin, Linda Anne

THE RELATION OF WILD PARSNIP, PASTINACA SATIVA L., TO PARASITOID POPULATIONS ASSOCIATED WITH SOYBEAN PESTS IN CENTRAL IOWA

Iowa State University PH.D. 1983

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Copyright 1983 by Buntin, Linda Anne All Rights Reserved

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University Microfilms International

The relation of wild parsnip, Pastinaca sativa L.,

to parasitoid populations associated

with soybean pests in central Iowa

by

Linda Anne Buntin

A Dissertation Submitted to the

Graduate Faculty in Partial Fulfillment of the

Requirements for the Degree of

DOCTOR OF PHILOSOPHY'

Major: Entomology

Approved: Members of the Committee: Signature was redacted for privacy. Signature was redacted for privacy. ïn Charge of Major Work

Signature was redacted for privacy.

epartment

Signature was redacted for privacy. rate College

Iowa State University Ames, Iowa

1983

Copyright @ Linda Anne Buntin, 1983. All rights reserved. il

TABLE OF CONTENTS PAGE

INTRODUCTION 1

LITERATURE REVIEW 2

Habitat Diversity 2 Importance of habitat diversity 2 Benefits and detriments of diversity 3

Fencerows 6

Nutrition Supplied by Flowering Plants 9

Positive Impact of Weeds in Agroecosystems 11 Weed retention in pest suppression programs 11 Applications in agriculture 12 Vegetables 12 Corn 13 Cotton and alfalfa 14 Soybeans 15 Sugarcane 15 Orchards 16 Vineyards 17 Ornamentals and forests 17

Green Cloverworm 20 Biology of green cloverworm 20 Natural enemies of green cloverworm 21

Wild Parsnip 25 Biology of wild parsnip 25 Insect associates of wild parsnip 27

Trapping Methods 28

Faunal Lists 32

MATERIALS AND METHODS 34

Field Procedures 34 Soybean studies 34 Parsnip studies 36

Laboratory Procedures 37 Rearing studies 37 Feeding studies 37

Statistical Analyses 38 iii

RESULTS AND DISCUSSION 41

Soybean Studies 41

Wild Parsnip Studies 64 Diptera 64 Hymenoptera-Braconidae 83 Hymenoptera-Ichneumonidae 105 Hymenoptera-Parasitica 113 Hymenoptera-Aculeata 137

Laboratory Studies 142

CONCLUSIONS 145

LITERATURE CITED 150

APPENDIX 179

Description of plots 179

ACKNOWLEDGEMENT 181 iv

LIST OF TABLES

PAGE

TABLE 1. Species of larval lepidopterans collected from soybean fields in central Iowa during 1979 41

TABLE 2. Mean seasonal totals (Y+SE) per field and apparent paras itization rates of minor larval lepidopterans collected in 1979 from central Iowa soybean fields .... 43

TABLE 3. Mean seasonal totals (X±SE) per field and apparent parasitization rates of minor larval lepidopterans collected in 1979 from two locations in central Iowa soybean fields 44

TABLE 4. Mean seasonal totals (X±SE) per field of larval green cloverworms collected in 1979 from central Iowa soybean fields with and without wild parsnip borders 46

TABLE 5. Mean seasonal totals (%±SE) per field of green cloverworm larval stages collected in 1980 from central Iowa soybeans with and without wild parsnip borders 47

TABLE 6. Mean seasonal totals (%±SE) per field of green cloverworm larval stages collected in 1980 from two locations in central Iowa soybean fields 48

TABLE 7. Mean (±SE) apparent seasonal mortality (%) per field in 1979 caused by natural enemies of green cloverworm larvae collected from central Iowa soybean fields with and without wild parsnip borders 53

TABLE 8. Mean apparent seasonal mortality (%) per field in 1979 caused by natural enemies of green cloverworm larvae collected from two locations in central Iowa soybean fields 54

TABLE 9. Mean (±SE) apparent seasonal mortality (%) per field in 1980 caused by natural enemies of green cloverworm larvae collected from central Iowa soybean fields with and without wild parsnip borders 56

TABLE 10. Mean (±SE) apparent seasonal mortality (%) per field in 1980 caused by natural enemies of green cloverworm larvae collected from two locations in central Iowa soybean fields 57 V

TABLE 11. Mean (±SE) seasonal parasitization (%) per field of green cloverworm instars respectively susceptible to three parasitoid species and collected from central Iowa soybean fields in 1980 58

TABLE 12. Mean (-SE) seasonal parasitization (%) per field of green cloverworm instars respectively susceptible to three parasitoid species from two locations in central Iowa soybean fields in 1980 60

TABLE 13. Mean (-SE) seasonal parasitization (%) per field in 1980 of green cloverworm larval stages collected from central Iowa soybean fields with and without wild parsnip borders ... 61

TABLE 14. Mean (±SE) seasonal parasitization (%) per field of green cloverworm larval stages collected in 1980 from two locations in central Iowa soybean fields with and without parsnip borders 63

TABLE 15. Species list of identified Diptera trapped among wild parsnip in central Iowa during 1979 and 1980 66

TABLE 16. Mean seasonal totals (X^SE) per plot of Tachinidae (Diptera) trapped among wild parsnip in central Iowa during 1979 and 1980 67

TABLE 17. Mean seasonal totals (%±SE) per plot of males and females of selected tachinids trapped among wild parsnip in central Iowa during 1979 and 1980 72

TABLE 18. Mean seasonal totals (X±SE) of Diptera other than Tachinidae trapped among wild parsnip in central Iowa during 1979 and 1980 81

TABLE 19. Species of Braconidae (Hymenoptera) trapped among wild parsnip in-central Iowa during 1979 and 1980 84

TABLE 20. Mean seasonal totals (X±SE) per plot of Microgastrinae (Hymenoptera: Braconidae) trapped among wild parsnip in central Iowa during 1979 and 1980 85

TABLE 21. Mean seasonal totals (X±SE) per plot of braconid species (excluding Microgastrinae) trapped among wild parsnip in central Iowa during 1979 and 1980 94

TABLE 22. Ichneumonid taxa known as green cloverworm associates and trapped among wild parsnip in central Iowa during 1979 and 1980 105

TABLE 23. Mean seasonal totals (X±SE) of ichneumonid taxa trapped per vi

plot among wild parsnip in central Iowa during 1979 and 1980 107

TABLE 24. Taxa of Hymenoptera-Parasitica (excluding Ichneumonoidea) trapped among wild parsnip in central Iowa during 1979 and 1980 114

TABLE 25. Mean seasonal totals (X±SE) of Ghalcidoidea (Hyraenoptera) trapped per plot among wild parsnip in central Iowa during 1979 and 1980 116

TABLE 26. Mean seasonal totals (ITiSE) of Hymenoptera-Parasitica other than Ichneumonoidea and Ghalcidoidea trapped per plot among wild parsnip in central Iowa during 1979 and 1980 .... 118

TABLE 27. Taxa of Hymenoptera-Aculeata trapped among wild parsnip in central Iowa during 1979 and 1980 140

TABLE 28. Mean seasonal totals (X±SE) of Bethyloidea (Hymenoptera) trapped per plot among wild parsnip in central Iowa during 1979 and 1980 141

TABLE 29. Mean longevity (days) of parasitoids held individually in the presence of wild parsnip flowers, soybean leaves, wild parsnip with soybeans, or a check with neither 143 vii

LIST OF FIGURES

PAGE

FIGURE 1. Location of sites from which samples were collected during 1979 and 1980 35

FIGURE 2. Mean weekly totals per field of green cloverworm larvae collected in 1979 and 1980 from central Iowa soybean fields with and without wild parsnip borders 50

FIGURE 3. Mean weekly totals per plot of Archvtas apicifer (Diptera: Tachinidae) trapped among wild parsnip in central Iowa during 1979 and 1980 69

FIGURE 4. Mean weekly totals per plot of Winthemia rufopicta (Diptera: Tachinidae) trapped among wild parsnip in central Iowa during 1979 and 1980 70

FIGURE 5. Mean weekly totals per plot of Blondelia hvphantriae (Diptera: Tachinidae) trapped among wild parsnip in central Iowa during 1979 and 1980 74

FIGURE 6. Mean weekly totals per plot of Lespesia archippivora (Diptera: Tachinidae) trapped among wild parsnip in central Iowa during 1979 and 1980 76

FIGURE 7. Mean weekly totals per plot of Oswaldia assimilis (Diptera: Tachinidae) trapped among wild parsnip in central Iowa during 1979 and 1980 77

FIGURE 8. Mean weekly totals per plot of Winthemia quadripustulata (Diptera: Tachinidae) trapped among wild parsnip in central Iowa during 1979 and 1980 78

FIGURE 9. Mean weekly totals per plot of Winthemia sinuata (Diptera: Tachinidae) trapped among wild parsnip in central Iowa during 1979 and 1980 79

FIGURE 10. Mean weekly totals of Cotesia flaviconchae (Hymenoptera: Braconidae) trapped per plot among wild parsnip in central Iowa during 1979 and 1980 88

FIGURE 11. Mean weekly totals of Cotesia mareiniventris (Hymenoptera: Braconidae) trapped per plot among wild parsnip in central Iowa during 1979 and 1980 89 viii

FIGURE 12. Mean weekly totals of Glyptapanteles militaris (Hymenoptera: Braconidae) trapped per plot among wild parsnip in central Iowa during 1979 and 1980 91

FIGURE 13. Mean weekly totals of Protomicroplitis facetosa (Hymenoptera; Braconidae) trapped per plot among wild parsnip in central Iowa during 1979 and 1980 93

FIGURE 14. Mean weekly totals of Macrocentrus grandii (Hymenoptera: Braconidae) trapped per plot among wild parsnip in central Iowa during 1979 and 1980 98

FIGURE 15. Mean weekly totals of selected Blacinae (Hymenoptera: Braconidae) trapped per plot among wild parsnip in central Iowa during 1979 and 1980 100

FIGURE 16. Mean weekly totals of Meteorus autographae (Hymenoptera: Braconidae) trapped per plot among wild parsnip in central Iowa during 1979 and 1980 101

FIGURE 17. Mean weekly totals of Meteorus rubens (Hymenoptera: Braconidae) trapped per plot among wild parsnip in central Iowa during 1979 and 1980 103

FIGURE 18. Mean weekly totals of Vulgichneumon brevicinctor (Hymenoptera: Ichneumonidae) trapped per plot among wild parsnip in central Iowa during 1979 and 1980 109

FIGURE 19. Mean weekly totals of Mesochorinae (Hymenoptera: Ichneumonidae) trapped per plot among wild parsnip in central Iowa during 1979 and 1980 110

FIGURE 20. Mean weekly totals of Cryptinae (Hymenoptera: Ichneumonidae) trapped per plot among wild parsnip in central Iowa during 1979 and 1980 Ill

FIGURE 21. Mean weekly totals of Campopleginae (Hymenoptera: Ichneumonidae) trapped per plot among wild parsnip in central Iowa during 1979 and 1980 112

FIGURE 22. Mean weekly totals of Perilampus fulvicornis (Hymenoptera: Pteromalidae: Perilampinae) trapped per plot among wild parsnip in central Iowa during 1979 and 1980 120

FIGURE 23. Mean weekly totals of Perilampus hyalinus (Hymenoptera: Pteromalidae: Perilampinae) trapped per plot among wild parsnip in central Iowa during 1979 and 1980 121

FIGURE 24. Mean weekly totals of Pteromalidae (Hymenoptera; excluding ix

Perilampinae) trapped per plot among wild parsnip in central Iowa during 1979 and 1980 123

FIGURE 25. Mean weekly totals of Eurytoma sp. A (Hymenoptera; Eurytomidae) trapped per plot among wild parsnip in central Iowa during 1979 and 1980 124

FIGURE 26. Mean weekly totals of Encyrtidae trapped per plot among wild parsnip in central Iowa during 1979 and 1980 . . . 125

FIGURE 27. Mean weekly totals of Tetrastichus spp. (Hymenoptera: Eulophidae) trapped per plot among wild parsnip in central Iowa during 1979 and 1980 127

FIGURE 28. Mean weekly totals of Horismenus spp. (Hymenoptera: Eulophidae) trapped per plot among wild parsnip in central Iowa during 1979 and 1980 128

FIGURE 29. Mean weekly totals of Polynema spp. (Hymenoptera: Mymaridae) trapped per plot among wild parsnip in central Iowa during 1979 and 1980 129

FIGURE 30. Mean weekly totals per plot of Cynipoidea(Hymenoptera) trapped among wild parsnip in central Iowa during 1979 and 1980 131

FIGURE 31. Mean weekly totals per plot of Hyptia thoracica (Hymenoptera: Evaniidae) trapped among wild parsnip in central Iowa during 1979 and 1980 132

FIGURE 32. Mean weekly totals per plot of Diapriidae (Hymenoptera) trapped among wild parsnip in central Iowa during 1979 and 1980 134

FIGURE 33. Mean weekly totals per plot of Trissolcus spp. (Hymenoptera: Scelionidae) trapped among wild parsnip in central Iowa during 1979 and 1980 135

FIGURE 34. Mean weekly totals per plot of Scelionidae excluding Trissolcus spp. (Hymenoptera) trapped among wild parsnip in central Iowa during 1979 and 1980 136

FIGURE 35. Mean weekly totals per plot of Platygastridae (Hymenoptera) trapped among wild parsnip in central Iowa during 1979 and 1980 138

FIGURE 36. Mean weekly totals per plot of Ceraphronidae (Hymenoptera) trapped among wild parsnip in central Iowa during 1979 and 1980 139 1

INTRODUCTION

The retention of fencerows has been shown to encourage parasitoids that attack crop pests. Fencerow weeds may act as alternative food sources or diet supplements for natural enemies. Wild parsnip,

Pastinaca sativa L., is a common biennial found in fencerows and disturbed habitats, and the attractiveness of its flowers to Diptera and

Hymenoptera is documented by many researchers. In this study, the relation of wild parsnip to parasitoid populations associated with soybean pests in central Iowa was examined. The objectives of the study were as follows:

1. Determination of larval lepidopterous fauna present and their

natural enemies and parasitization rates in soybean fields

with and without wild parsnip borders,

2. Determination of relative abundance and seasonal occurrence

of insect fauna associated with wild parsnip,

3. Determination of wild parsnip effect on adult parasitoid

longevity.

The combined results of this investigation were used to establish the role of wild parsnip in the soybean ecosystem. 2

LITERATURE REVIEW

Habitat Diversity

Importance of habitat diversity

Superfluous vegetation surrounding and within an agricultural crop has demonstrated importance. Farming regions with diverse agriculture usually face less severe pest problems than do areas with limited monocultures (Bishop et al., 1979). On a smaller scale, weedy fields are less likely to experience pest outbreaks than are cleanculture fields (Altieri, 1981). Planting monocultures is still the favored practice in modern agriculture, particularly for annual crops, even though the practice limits the application of classical biological control and reduces the effect of biotic agents of natural control

(Hagen and Hale, 1974; Stehr, 1974; Zandstra and Motooka, 1978).

Habitat diversity may increase the effectiveness of natural enemies and, thus, is an effective technique in biological control programs (DeLoach, 1970; Perrin, 1980). Altieri and Whitcomb (1979a) found that manipulating the abundance and composition of crop-associated weed populations enhanced the activity and survival of the beneficial insects that attacked pests of the crop. Stehr (1974) recommended maintaining diversity, especially when the nutritional requirements of the beneficial species are unknown.

Increased diversity is not always associated with or necessary for increased stability or decreased pest outbreaks (Way, 1979). Suitable natural control occasionally may be achieved simply by varying crop 3 density. Davis (1966) investigated the effects of various densities of oats, Avena sativa L., on the natural enemies of four grain aphid species. Of the nine combinations of different planting densities and various row widths, fields with the lowest densities exhibited the highest ratio of parasitoids to hosts. This example illustrates that each crop system is unique and must be evaluated independently.

Benefits and detriments of diversity

Way (1979) summarized the benefits and detriments of diversity, claiming that mixed vegetation may disguise the crop, making it less visible to pests, or that the vegetation may serve as a barrier or repellent to pests. In addition, alternative vegetation may attract pests away from the crop. Superfluous plants among the crop plants or near the crop may provide food sources or refuge for beneficial organisms. However, decreased diversity may be beneficial when it deprives pests of alternative hosts, reduces weed competition with the crop, or decreases the area to be searched by natural enemies of the pest.

To assess the detrimental aspects of adjacent vegetation, van

Emden (1965b) searched and found in the 1939-1965 literature, about 450 separate accounts of pests harbored in wild hosts adjacent to crop fields. Some pest infestations surely arise from these weeds, and destruction of such alternative hosts sometimes may be endorsed as a crop protection method (van Emden, 1965b).

Occasionally, even the usually beneficial organisms associated with fencerows may be detrimental to the crop. Formica neoclara Emery, 4 a common ant of fencerows and irrigation canals, reduced the numbers of lepidopterous defoliators in the adjacent sugar beet crop but also was responsibile for an increased population of bean aphids, Aphis fabae

Scopoli (Capinera and Roltsch, 1981). The ants tended and protected homopterous pests in the crop, stimulating their growth and reproduction. The resulting abundant aphid and membracid populations reduced sugar beet sucrose production (Capinera and Roltsch, 1981).

The benefits and detriments of environmental plant diversity may differ from crop to crop. Diversity studies with collards, Brassica oleracea L., showed that flea beetles, Phyllotreta cruciferae (Goeze), infested plants grown in an extensive monoculture more often than collards planted adjacent to natural vegetation (Tahvanainen and Root,

1972). The diversity had no apparent effect on natural enemies, including the chrysomelid's primary parasitoid Microctonus vittatae

Muesebeck. Although the impact of natural enemies on flea beetle populations was unaffected, the diversity of natural vegetation exerted a direct influence on the phytophagous species and reduced its outbreaks. Perhaps chemical emanations from the adjacent vegetation somehow interfered with the ability of P. cruciferae to find and feed on the host plant, resulting in reduced infestation and damage (Tahvanainen and Root, 1972). Collards in monoculture were colonized more rapidly and sustained greater feeding damage, even though Root (1973) later demonstrated that the diversity of natural enemies actually was higher in pure stands of collards than in weedy stands.

Pest populations may be affected by weeds within fields, and 5 levels of certain pest infestations may be altered by cultivating the field or allowing the weeds to remain (Cromartie, 1975). Pimentel

(1961) and Horn (1981) demonstrated that collard monocultures experienced pest outbreaks, but collards grown with mixed vegetation had none. Pimentel found that, contrary to Root's (1973) results, coccinellids and syrphids were the only numerous bénéficiais in pure stands of collards. Collards with mixed vegetation had a balanced assortment of spiders, predatory insects, and parasitoids, suggesting that plant diversity prevented pest outbreaks by encouraging natural enemies, and, therefore, that plant diversity itself should be encouraged (Pimentel, 1961).

The negative effects of extensive habitat destruction become highly visible in alfalfa. Bishop et al. (1979) explained that when extensive areas of alfalfa are harvested within a short period of time, resident populations of natural enemies are disrupted, especially if suitable habitats surrounding the crop are lacking. Strip cutting of alfalfa is a cultural method that retains habitat réfugia and provides environmental stability to preserve populations of natural enemies

(Bishop et al., 1979). Strip harvests also benefit the farm economy when harvested for feed or when sold (Laster, 1974). Occasionally, however, strip cutting may be detrimental by encouraging alfalfa pests whose damage outweighs the benefits provided by the protected natural enemies (Andaloro and Peters, 1978).

Depending upon the specific type of diversification, there may be a positive or negative effect on the incidence of crop disease. 6

Priestley and Wolfe (1977) recommended the combined planting of at least three small grain cultivars to avoid disease problems. In this case, genetic diversification protected barley and wheat from barley mildew, caused by Erysiphe graminis De Condole ex Merat fils ssp, hordei, and wheat yellow rust, caused by Puccinia striiformis West. Diversification of species, however, may present a crop risk because weedy vegetation may provide alternate hosts for plant pathogens (National Research

Council, 1969).

Fencerows

Although research often has demonstrated the possible benefits of habitat diversity as a practical method for reducing pest problems, actual implementation in practice has been infrequent, and present diversity derives primarily from existing vegetation in fencerows (Rabb et al., 1976).

Traditionally, the presence of fencerows has been considered detrimental to farming practices. Fencerows not only occupy valuable land that could be put into crop production, but yields of adjacent crops possibly are reduced because of shading and root competition by the hedgerow vegetation (Wunz, 1952). Fencerows also may harbor insects, weeds, and other pests that are injurious to the crop (Allen,

1941; Bendixen et al., 1979, 1981; Ben-Saad and Bishop, 1969; Chmiel and

Wilson, 1978; Cinereski and Chiang, 1968; Dambach, 1948; Fye, 1980;

Katanyukul and Thurston, 1979; Messina and Root, 1980; Tahvanainen,

1972; van Emden, 1965a; Wunz, 1952). Tall vegetation in hedgerows 7

creates a special problem along highways because it reduces visibility

and continually, encroaches onto the road (Jennings et al., 1977;

National Research Council, 1968; van Emden, 1962a, 1965b).

A similar situation exists along railroad right-of-ways. Weed control is mandatory in the 1- to 3-m zone on each side of the rail bed.

The zone of weed control serves as a firebreak to protect adjacent properties from sparks created by the rail cars. Weeds that grow over the tracks reduce traction for braking, shorten the life of wooden railroad ties, reduce water drainage, interfere with ballast structure, and obstruct the foot path for train crews. Cleaning tracks may become a frequent and costly operation if vegetation is excessive (National

Research Council, 1968).

Some scientific studies refute certain negative attitudes toward

fencerow retention. Elton (1958) discussed the merits of maintaining hedgerows and roadside verges in Great Britain. Allen (1941) described

fencerow destruction as a futile attempt to kill crop pests, especially

because most injurious insect pests do not overwinter in fencerows.

Fencerow devastation only removed the feeding habitats and nesting areas of numerous small mammals, birds, and beneficial insects that were

responsible for reducing population levels of crop pests. After

studying the insect fauna of hedgerows in Great Britain, van Emden

(1962a) concluded that the vegetation harbored greater numbers of

predators and parasitoids than the adjacent crops, and that unmanaged

fencerows supported more bénéficiais than managed fencerows. When the

requirements of resident natural enemies are known to include resources 8 from hedgerows, the local ratio of cultivated to uncultivated land becomes particularly significant (Rabb et al., 1976).

Large numbers of beneficial invertebrates have been found in grassy fencerows, in fencerows with mixed vegetation, and in woody fencerows. Allen (1941) recorded the species of vegetation that occurred in fencerows in Ohio. Wunz (1952) observed fencerows in

Pennsylvania and discovered that those with brushy vegetation presented less of a crop risk because they harbored fewer weed species and lower populations of pest insects and small mammals than other fencerow types.

Brushy fencerows also provided shelter for desirable wildlife and were associated with increased growth of adjacent field crops. Dambach

(1948) found that fencerows were less likely to become a potential source of insect pests if the border vegetation was not in the same taxonomic group as the crop plants. Fencerows of grass and forage harbored more insect species injurious to small grains and forage crops than did brushy or woody fencerows. Conversely, brushy and woody hedgerows harbored more pest species of vegetable crops and orchards, respectively, than did grassy hedgerows (Dambach, 1948).

Altieri and Whitcorab (1979a) suggested that the presence of certain weeds early in the season allowed for the maintenance of natural enemy populations before pest outbreaks occurred. Perrin (1975) stated that weeds in fencerows determine to a considerable extent what predators are present in the adjacent crop.

Often, the importance of fencerow réfugia is recognized only after they are removed. For example, a noticeable local decline in the number 9 of tachinid parasitoids of the New Guinea sugarcane weevil, Rhabdoscelus obscurus (Boisduval), was observed when weeds surrounding sugarcane fields were treated with herbicides (Deeper, 1974; Topham and Beardsley,

1975). Similarly, in orchards, when weeds beneath the trees were mowed, resident beneficial organisms died from lack of food and refuge. This event reduced the natural control of potential pests, allowing them to become economic problems for the first time (Flint and van den Bosch,

1981).

Nutrition Supplied by Flowering Plants

The requirements of natural enemies for survival, development, and reproduction are varied and complex. All predators and parasitoids require resources in addition to the prey or host (National Research

Council, 1969). Messenger et al. (1976) identified some of the general factors that affect natural enemies. These include favorable climate, synchrony with the host, various innate characteristics of the host, presence of alternate hosts, food sources for parasitoid adults, competition with or hyperparasitism by other insects, and the use of toxic chemicals or other agronomic measures on the crop.

Stehr (1974) discussed the specific requirements of parasitoids.

Some adult parasitoids require proteins, sugars, and moisture for survival and egg production. Some obtain these through host feeding, but most do not. Nectar, pollen, and insect prey from flowering plants constitute the food supplements important to beneficial insects.

Unfortunately, supplementary foods frequently are in limited local 10

supply or totally absent (National Research Council, 1969;

Shchepetilnikova, 1958). Absence of food, moisture, and shelter in

areas of parasitoid introductions may be one reason for release failures

(Stehr, 1974). Those species dependent upon supplementary foods not

only must find them within a short time after emergence, but also within

a short flight distance from the next insect host (National Research

Council, 1969).

The attraction of natural enemies and pollinators to nectar-

bearing plants has been observed for at least a century. Trelease

(1881) observed various bénéficiais collecting nectar from flowers of

aspen, Populus sp. The most numerous visitors were ants and

ichneumonids, but Augochlora g. pura (Say) and Halictus sp.

(Halictidae), Monophadnoides geniculatus Hartig (Tenthredinidae),

Microgaster sp. (Braconidae), and Coccinella sp. (Coccinellidae), also

were observed.

Nectar may be especially important to natural enemies with life

cycles that do not coincide with that of the host. Aphytis proclia

(Walker) (Encyrtidae), which emerges with only partially developed

ovaries, requires nectar to complete ovarial development and prolong

life. Cotesia glomerata (L.) (Braconidae), a species with fully

developed ovaries, requires the nectar supplement for maintenance only

while its insect host is absent (Shchepetilnikova, 1958). 11

Positive Impact of Weeds in Agroecosystems

Weed retention in pest suppression programs

Encouraging parasitoids in agricultural areas through environmental manipulation is a strongly endorsed pest management (PM) strategy (Barfield and Stimac, 1980; Fye, 1972). Provision of supplementary foods has potential value in PM, especially where naturally occurring beneficial organisms require manipulation or augmentation for successful effect (Hagen and Bishop, 1979).

Alternatively, PM specialists have recognized the usefulness of fencerows and vegetation among crop plants in maintaining natural enemies. Maximizing the positive impact of such vegetation and understanding the complexity of its effects have been important aspects of many on-going PM programs.

Most phytophagous species in undisturbed habitats exist at relatively low population levels because of a complex system of natural controls (Rabb et al., 1974). In disturbed (i.e., manipulated) agricultural ecosystems the controlling processes also must be intentionally manipulated to lower and stabilize the populations of phytophagous species that suddenly are defined as pests. This has made the preservation and encouragement of natural enemy species an important component of pest management practices (Rabb et al., 1974).

Fye (1972) specified four basic requirements that must be met before a PM program should rely on bénéficiais dependent upon alternate vegetation or a second crop. First, the subject crop must have some degree of tolerance to the target insect pests. Second, the secondary 12 crop or vegetation must be able to sustain the natural enemies. Third, the maturity of the alternate plants must occur at a time that permits or encourages the shift of bénéficiais when the host on the primary crop is susceptible to attack. Finally, the secondary vegetation must be located in proximity to the crop for convenient dispersal by the natural enemies.

Altieri and Whitcomb (1979a) suggested five steps for developing

PM stategies to incorporate weeds. These include determining the insect fauna in the crop and the fencerows, selecting the weed species with most potential for increasing beneficial insect populations, determining practical methods for managing the desired weeds, assessing the impact of the weeds on insect pest populations, and applying the results to experimental field studies.

Applications in agriculture

Corbet (1974) summarized the management practices and cultural manipulations that enhance natural pest control in field crops, forests, greenhouses, orchards, pastures, and vegetables in Canada. Beirne

(1974) compiled a list of biological control programs where conservation and habitat management were used to benefit the existing natural enemies. Specific examples of programs in various crops and ornamentals follow.

Vegetables When Cotesia glomerata, a parasitoid of Artogeia spp., had access to mustard flower nectar, it lived longer and deposited more eggs. When quick-flowering mustards were planted intentionally in the area of the cabbage crop, paras itization rates of Artogeia spp. 13 increased from 10% to 60% (National Research Council, 1969).

Plantings of parsnip, caraway, dill, parsley, and wild umbellifers have been recommended because they increase the parasitization of vegetable pests. When the umbellifers were planted near cole crops in area ratios of 1:400, 94% of cabbage noctuid moths, Barathra brassica

L., were parasitized by Ernestia consobrina Meigen and Exetastes cinctipes Meigen (Kopvillem, 1960; Serebrovsky et al., 1948).

Smith (1963) experimented with the effect of weeds within the crop. In one study, Brussels sprouts were grown under two cultural methods: clean culture, where bare soil was maintained between crop plants, versus periodic mowing, where naturally occurring weeds were allowed to grow within the crop but were mowed to six inches to reduce competition with the crop. The naturally occurring species included fat hen, Chenopodium album L.; spurry, Spurgula arvensis L.; white charlock,

Rhaphanus raphanistrum L.; yellow charlock, Sinapis arvensis L.; and heart's-ease, Polygonum persicaria L. The presence of these weeds significantly increased the numbers of predators and dramatically reduced the population of cabbage aphids, Brevicoryne brassicae L. The most abundant predator was the anthocorid bug Anthocoris nemorum (L.).

Smith (1963) hypothesized that interfering with the contrasting pattern of green plants against brown soil camouflaged the crop, which prevented the aphids from locating the host, but encouraged the colonization by predators.

Corn An advantage of maintaining hedgerows and woodlands in the area of corn crops was studied by Hsaio and Holdaway (1966). The 14 parasitic tachinid Lydella thompsoni Herting, and its primary host,

European corn borer, Ostrinia nubilalis (HÎibner), were poorly synchronized in Minnesota. When corn borers were scarce, the tachinid populations were maintained on an alternative host, the stalk borer,

Papaipema nebris (Guenee). The favored host plant of P. nebris is giant ragweed. Ambrosia trifida L., a common component of fencerows in the area. The intentional planting of ragweed was not recommended, but the preservation of hedgerows in which the plant occurred was encouraged.

In Florida corn fields, Mexican tea, Chenopodium ambrosiodes L., serves as an alternative hunting site for predaceous insects and spiders. About 40% of the predatory species collected from Mexican tea also were collected in the adjacent corn fields. These 33 species of predators were sustained on Mexican tea until corn pest populations increased later in the season (Altieri and Whitcomb, 1979b).

Cotton and alfalfa Stern (1969) developed a unique management practice for cotton in the southern U.S. Cotton is affected by numerous pests. Lygus bug, a severe pest, leaves alfalfa hay in the spring to invade cotton. Pesticides applied early to kill Lygus often destroyed cotton-dwelling predators and parasitoids that suppressed the other potential pests of cotton. Cotton bollworm, Heliothis zea Boddie, cabbage looper, Trichoplusia ni (Hubner), and beet armyworm, Spodoptera exigua (Hubner), were among the pests whose populations were released from natural controls. Instead of growing the crops separately, alfalfa was interplanted with cotton in an attempt to manipulate the pests and natural enemies. The interplanted field never required a chemical 15 treatment for either Lygus or the lepidopterans. Both crops had higher yields than check fields. The alfalfa served as a trap crop for Lygus hesperus Knight and L. elisus Van Duzee (Sevacherian and Stern, 1974), and a refuge for the adult predators and parasitoids that later dispersed to the adjacent cotton and attacked lepidopterous eggs and larvae (Stern, 1969). For example, the introduced braconid, Peristenus stygicus Loan, would feed on nectar and aphid honeydew, and suppress

Lygus in alfalfa (van Steenwyk and Stern, 1976). Alfalfa also acts as a trap crop for the stink bug Euschistus cinspersus Uhler, another cotton pest (Toscano and Stern, 1976).

Soybeans Several benefits derive from weeds associated with soybeans. In Florida, rattle-box, Crotalaria usaramoensis Baker, can serve not only as trap plants for southern green stink bug, Nezara viridula (L.), but also as a nectar source for the pest's tachinid parasitoids, Trichopoda pennipes (F.) and T. lanipes (F.) (Drake, 1920).

The pods of rattle-box attract N. viridula from adjacent soybeans, whereas the trap plant flowers increase parasitoid activity. Higher parasitization of corn earworm eggs by Trichogramma spp. occurs in soybeans when the crop is associated with the weeds, Desmodium sp. or

Croton sp., than occurs in pure soybean stands (Altieri, 1981).

Sugarcane Nutrients required by adults of Lixophaga spenophori

(Villeneuve), tachinid parasitoids of the New Guinea sugarcane weevil,

Rhabdoscelus obscurus (Boisduval)^ derive primarily from certain weeds

(Leeper, 1974). The availability of castor bean, Ricinus communis L., and the euphorbs, Euphorbia hirta L., E. glomerifera (Millspaugh) L. C. 16

Wheeler, and Phyllonthus niruri L., all of which commonly occur in irrigation ditches and uncultivated areas adjacent to sugarcane fields, is important in promoting the effectiveness of the tachinids (Deeper,

1974; Topham and Beardsley, 1975).

Orchards Some of the same weeds useful to field crops are included in orchard pest suppression programs. For example, planting rattle-box may benefit parasitoids in Hawaiian orchards (Leeper, 1974).

Crotalaria usaramoensis in macadamia nut orchards lures stink bugs from the trees while providing the same nutritional benefit to T. pennipes that it does in mainland soybeans.

In the eastern U. S., weedy ground cover retained in orchards provides food and refuge for egg parasitoids, Trichogramma spp. As a result, codling moth, Cydia pomonella (L.), levels may be lower in weedy orchards than in clean cultivated ones (Driggers and Pepper, 1936).

Experiments in Ontario found that parasitjLzation of codling moth nearly doubled in weedy orchards (Leius, 1967a). Egg and pupal parasitization of eastern tent caterpillar, Malacosoma americanum (F.), in the orchards also increased. The primary flowering plants benefiting parasitoids during the summer were wild parsnip, Pastinaca sativa and wild carrot,

Daucus carota L. (Leius, 1967a).

Russian orchardists plant Phalcelia spp. (Hydrophyllaceae) as dietary supplements for the encyrtid, Aphytis proclia, a parasitoid of

San Jose scale, Quadraspidiotus perniciosus (Comstock). The decline of scale populations is correlated with the presence of Phalcelia (National

Research Council, 1969). 17

Vineyards In the California Central Valley, a grape leafhopper,

Erythroneura elegantula Osborn, can damage grape leaves and affect fruit quality. Eggs of the leafhopper are parasitized and populations can be held below economic levels by a mymarid, Anagrus epos Girault (Doutt and

Nakata, 1965). In the winter, when E. elegantula populations plummet, the mymarid survives by parasitizing eggs of a blackberry leafhopper,

Dikrella cruentata Gillette. Anagrus epos migrates back to grapes in the spring and keeps E. elegantula populations low from the beginning of the season. Vineyards without nearby blackberry bushes (Rubus spp.) lack acceptable levels of natural control. When the role of blackberry was discovered by the grape growers, they began planting the shrubs in areas near their vineyards to enhance the activity of A. epos (Doutt and

Nakata, 1965; Flint and van den Bosch, 1981; Hagen and Hale, 1974).

The California Division of Highways and the University of

California also are convinced of the value of fencerows to agriculture.

In a new program, roadside hedgerows no longer are mowed but are permitted to flower throughout the year. Maintenance of the hedgerows may provide a higher level of predator and parasitoid activity for the surrounding crops (Flint and van den Bosch, 1981).

Ornamentals and forests Supplementary plants also find use near ornamentals and forest trees. European pine shoot moth, Rhyacionia

buoliana (Denis & Schiffermuller), populations in California were not sufficiently suppressed by their introduced parasitoids (Corbet, 1974).

It was discovered that adults of the parasitic braconid, Orgilus

obscurator (Nees), feed at wild carrot flowers. The plant increases the 18 braconid's longevity and effectiveness, and now it is cultivated in pine plantations to increase the possibility of parasitoid attack on R. buoliana.

Syme (1966) discussed the importance of wild carrot to 0. obscurator in southern Ontario. Daucus carota is the only abundant umbellifer whose flowering period coincides with flights of 0. obscurator. Unfortunately, the plant was considered a noxious weed according to the Ontario Weed Control Act, and legally it could not be encouraged or permitted to flower. Seemingly, a review of the plant's benefits by authorities, has changed the law. Syme (1975) conducted feeding studies with two other Canadian parasitoids of R. buoliana: the ichneumonid, Exeristes comstockii (Cresson), and the eulophid, Hyssopus thymus Girault. About 35 different plants were tested, but wild parsnip was not included. Exeristes comstockii was particularly attracted to common milkweed, Asclepias syriaca L., and wild carrot. Apple, Pyrus malus L., and several other plants increased longevity and fecundity of

H. thymus. Syme examined the seasonal phenology of plant bloom so recommendations for plant encouragement could be based on the coincidence of bloom period and adult parasitoid activity. Some of these beneficial plants also were designated as noxious weeds (Syme,

1975).

In the central Caucasus Mountains in Europe, 0. obscurator and the ichneumonid, Limneria ramidula Brischke, are the predominant parasitoids of R. buoliana. When the importance of certain flowering plants as food sources for the parasitoids was discovered, auxiliary planting in pine 19 plantations was encouraged. The important nectar sources are parsnip,

Pastinaca intermedia Fischer & Meyer; cherry Cerasus avium L.; and two spurges, Euphorbia villosa Waldst & Kit and E. macroceras Fischer &

Meyer (Guly, 1963).

Other researchers experimented with additional methods of food provisioning in ornamentals. "Artificial honeydew" offered at yellow feeding stations attracted and successfully sustained four parasitoid species of R. buoliana: Temelucha interruptor (Gravenhorst), Pristomerus orbitalis Holmgren, 0. obscurator. and Campoplex sp. (Koehler and Kolk,

1969).

In the Soviet Union, the urabellifer Ligusticum discolor Ledebour is maintained in the Academy of Sciences Botanical Gardens as a food source for the tachinid, Ernestia consobrina (Zetterstedt), a parasitoid of lepidopterous pests on the botanical displays (Serebrovsky et al.,

1948).

Fleming (1968) suggests that the success of parasitoids of

Japanese beetle, Popillia japonica Newman, a serious pest of ornamentals, is influenced by wild flowers in the area. Establishment and survival of the five most important parasitoids depend upon the abundance of P. japonica grubs and the presence of flowering wild carrot and other weeds. The adult tiphiid, Tiphia popilliavora Rohwer, prefers

D. carota. Tiphia vernalis Rowher and the adult tachinids, Hyperecteina aldrichi Mesnil and Dexilla ventralis (Aldrich), feed only on honeydew

and D. carota nectar; however, another tachinid, Prosena siberita (F.), was observed feeding at various flowers (Fleming, 1968). 20

In Haiti J large populations of T. popilliavora fed upon wild parsnip and suppressed white grubs, but in Puerto Rico, where wild parsnip was scarce, parasitoid populations were low and failed to suppress Japanese beetle (Wolcott, 1942).

The feeding habits of T. vernalis were more closely observed by

Gordner (1938). The wasps fed exclusively on honeydew produced by aphids that were associated with cherry, elm, and maple. More Japanese beetle grubs were present in areas where parasitoid food sources were limited. Superparasitism occurred frequently when honeydew was limited, possibly because female wasps failed to disperse from feeding sites.

Tiphia vernalis failed to become established when released where honeydew sources were lacking.

All these examples illustrate Pimentel's (1961) conclusion that complex species diversity is essential to the stability of agroecosystems. In each case, the addition or manipulation of secondary vegetation increased the activity of natural enemies and reduced the economic impact of the primary pests.

Green Cloverworm

Biology of green cloverworm

In the Midwest, the green cloverworm (GCW), Plathypena scabra (F.) is one of the insects included in the complex of major soybean pests

(Kogan, 1981, Pedigo et al., 1981). The most commonly collected caterpillars in Illinois soybean fields are: GCW; celery looper,

Anagrapha falcifera (Kirby); variegated cutworm, Peridroma saucia 21

(Hubner); alfalfa caterpillar, Colias eurytheme Boisduval; and forage looper, Caenurgina erechtea (Cramer) (Zewadski, 1979b).

Although GCW is considered the most destructive insect pest of midwest soybeans (Anon., 1980; Kogan, 1981; Mueller and Kunnalaca,

1979), it is only an occasional or sporadic pest, because it is not present in large enough numbers to cause economic injury every year

(DeWitt et al., 1978; Mueller and Kunnalaca, 1979).

The habits and life stages of GCW in soybeans were described by

Sherman (1920); its general biology was examined and summarized by

Pedigo et al. (1973, 1977). GCW growth and development at different temperatures were studied by Hammond et al. (1979), who also prepared a thermal unit development model from the result^.

Natural enemies of green cloverworm

The usual low population levels of GCW seem to be maintained by a complex of predators, parasitoids, and pathogens. There are, however, few published studies of GCW predators. The most complete studies in

Iowa (Pedigo et al., 1973; Bechinski and Pedigo 1981) found that damsel bugs, Nabis spp., and minute pirate bugs, Orius insidiosus (Say), are important GCW predators. These articles should be consulted for a list of additional potential predators of GCW in soybeans.

Numerous species of parasitoids have been reported to attack GCW.

Of these, only two GCW egg parasitoids are known. Sherman (1920) reared

Trichogramma pretiosum Riley from GCW eggs in North Carolina. In Iowa, only a scelionid, Telenomus sp., has been reared (Lentz and Pedigo,

1975). 22

The best known natural enemies of GCW are larval parasitoids. Ten species have been reared from GCW collected in Iowa alfalfa and soybeans

(Lentz and Pedigo, 1975). The most prevalent parasitoid, Rogas

nolophanae Ashmead (Braconidae), parasitizes about 18% of the collected

GCW, but parasitism occurs about twice as often in northern Iowa as in

southern Iowa. Mean seasonal rate of parasitization in the Ames area is

17.5% (Lentz and Pedigo, 1975). In 1970, R. nolophanae was reared

primarily from third, fourth and fifth instars of GCW and at the

following respective rates of parasitization: 19.3, 50.0, and 29.5%.

Winthemia sinuata Reinhard (Tachinidae) is the second most

prevalent parasitoid (Lentz and Pedigo, 1975). In 1970, it was reared

from about 10% of the collected GCW, but it occurred about four times

more often in southern Iowa than in northern Iowa. Winthemia sinuata

was reared only from fifth and sixth instars, at parasitization rates of

6% and 94%, respectively.

Other primary parasitoids were the tachinids, Oswaldia assimilis

(Townsend), Blondelia hyphantriae (Tothill), and Lespesia archippivora

(Riley); the braconids, Cotesia marginiventris (Cresson), C.

flaviconchae (Riley), Meteorus hyphantriae Riley, and Protomicroplit is

facetosa (Weed); and the ichneumonid, Sinophorus validus (Cresson).

Annual parasitization rates for all larval parasitoids combined were

calculated at about 30% in 1970 and 36% in 1971 (Lentz and Pedigo,

1975).

Lentz and Pedigo (1974) studied the two most common GCW

parasitoids in Iowa, R, nolophanae and W. sinuata, under laboratory 23 conditions. Third instar GCW were preferred by ovipositing R. nolophanae females. Second instars sometimes were parasitized, but fourth, fifth, and sixth instars rarely were. The paras itization rate of susceptible instars was 13.6%. About 80% of W. sinuata oviposition occurred on sixth instar GCW, and 20% on fifth instars. The parasitization rate was about 12% (Lentz and Fedigo, 1974).

Several additional parasitoid species attack GCW elsewhere. These include, from North Carolina, the tachinids, Euphorocera claripennis

(Macquart), Eusisyropa boarmiae (Coquillett), Lespesia aletiae (Riley), and Euphorocera floridensis Townsend; the bombyliid. Villa lateralis

(Say); the sarcophagid, Boettcheria cimbicis (Townsend).; and an unidentified ichneumonid species of the tribe Campoplegini (Sherman,

1920). McCutcheon and Turnipseed (1981) also reared a number of parasitoids from GCW in North Carolina. These include the phorids,

Dohrniphora cornuta (Bigot) and Megaselia sp.; the tachinids, Archytas sp., Chaetophlepsis plathypenae Sabrosky, C. townsendi (Smith),

Eusisyropa blanda (Osten Sacken), E. boarmiae, L. aletiae, Prophryno parviteres (Aldrich and Webber), Euphorocera spp., E. floridensis. and

W. sinuata;the braconids, C. marginiventris, P. facetosa, and R. nolophanae and the ichneumonids, Campoletis flavicincta (Ashmead), and

Venturia nigriscapus (Viereck). In some regions of South Carolina, the tachinid C. plathypenae was the most common parasitoid of GCW. Cotesia marginiventris, however, was the predominant parasitoid statewide on

GCW, Heliothis zea, and Pseudoplusia includens (Walker) (McCutcheon and

Turnipseed, 1981). 24

Many of the same parasitoids were reared from GCW in Delaware

(Whiteside et al., 1967). A parasitization rate of 20% was achieved by the combined effects of the braconids, R. nolophanae, C. marginiventris,

P. facetosa, and Meteorus autographae Muesebeck; the ichneumonids,

Isdromas lycaenae (Howard), and Charops annulipes Ashmead; the sarcophagid, Helicobia rapax (Walker); and the tachinids, W. sinuata,

Chaetophlepsis sp., E. floridensis, and Compsilura concinnata (Meigen).

In Missouri, Barry (1970) reared eight species of parasitoids from

GCW. These include the tachinids, Chaetophlepsis sp., W. sinuata, and

Copecrypta ruficauda (Wulp); and the braconids, C. marginiventris, P. facetosa, R. nolophanae, Meteorus sp., and M. autographae. The seasonal parasitization rates were computed for the four predominant parasitoids at 6.4% for R. nolophanae, 5.0% for P. facetosa. 3.3% for W. sinuata, and 2.7% for C. marginiventris.

Two hyperparasitoids of GCW also are known (Barry, 1970). The ichneumonid, Mesochorus discitergus (Say), emerged from both R. nolophanae and P. facetosa, whereas the chalcidid, Ceratosmicra meteori

Burks, was reared only from R. nolophanae.

Parasitization rates varied among regions and also changed seasonally. In Illinois, populations of GCW and nine other common lepidopterous defoliators of soybeans are suppressed, at least to some degree, by parasitoids (Zewadski, 1979b). The total seasonal rate of

GCW parasitization in South Carolina was about 10% (McCutcheon and

Turnipseed, 1981). In Missouri, parasitization rates were highest in

June, at about 30%, but dropped to about 12% by September, with a 25 seasonal average of 12-15% (Barry, 1970). The combination of parasitoids and pathogens in Iowa may kill 30% of the GCW larval population, reducing it significantly in only a few days (DeWitt et al.,

1978).

Wild Parsnip

Biology of wild parsnip

Wild parsnip, Pastinaca sativa (Umbelliferae: Peucedaceae), is characterized as a tall, glabrous, yellow-flowered biennial with pinnately compound leaves. The generic name is derived from the Latin

"pastus," which means food (Fernald, 1950). Pastinaca sativa is cultivated for its edible root, but originally it may have been grown for medicinal purposes, as well. The plant is an emmenagogue, and the fruits act as a carminative (French, 1971). Pastinaca sativa is of additional medical importance because its oils are noted for evoking human phytophotodermatitis, a blistering of the skin similar to that caused by poison ivy (Gunsolus, 1978; Mitchell and Rook, 1979).

Additional chemicals in P. sativa and other umbellifers also have been examined. These tests have isolated coumarins, falcarinone, and acetylenes (Bohlmann, 1971; Nielson, 1971). Fluctuations in chemical composition of the plants may be responsible for the changing .diversity of insect fauna attracted to the flowers (Lawton, 1978). Some chemical analyses are useful in plant systematics, and P. sativa is one of several umbellifers subjected to serological tests to determine its taxanomic relationship to similar botanical groups (Pickering and 26

Fairbrothers, 1971).

Pastinaca sativa originated in western Europe but has been introduced to many temperate countries (French, 1971). The plant frequently escapes cultivation and often occurs along roadsides and in fencerows. It occasionally becomes a severe weed problem by competing with and eventually dominating desirable vegetation (French, 1971;

Gunsolus, 1978; Jennings et al., 1977),

Bell (1971) worked extensively with the flowers of Umbelliferae and described their unique structure. These flowers bear a stylopodium, which is a swollen, colorful style that secretes nectar. Although P. sativa flowers are anatomically similar to several other umbellifers

(Theobald, 1971), it was the only species studied whose stylopodial color changed as the plant matured. During the bud stage, the petals are positioned in a manner that leaves the stylopodium uncovered and the nectar exposed. The flower structure permits pollination by a large number of unspecialized pollinators (Bell, 1971; Judd, 1970; Spradbery,

1973). All umbelliferous plants have exposed nectaries, and so they have evolved as the family of plants most favored by nectar-feeding insects with short mouthparts (Gyorfi, 1945). The flower structure allows pollinators to visit the nectaries at a time of early floral development (Bell, 1971), and it offers ready accessibility to the nectar (Leius, 1967a). Sugar concentrations of floral nectar also vary, not only between species, but among flowers on the same plant and florets of the same umbel (Park, 1930). However, the sugar content of this nectar is not constant throughout the day. 27

Insect associates of wild parsnip

Numerous insects are attracted to and harbored by P. sativa. The principal herbivores of P. sativa in North America are the parsnip webworms, Depressaria spp. (Lepidoptera; Oecophoridae), which infest and feed on the flower heads, destroy the seed, and tunnel through the stem

(Bethune, 1869; Brittain and Gooderham, 1916; Gorder, 1983; Harrison,

1913; Riley, 1888). Depressaria pastinacella (Duponchel) is the most frequently encountered species in North America, but D. cinerecostella

Clemens is another species that might be collected in the Midwest

(Bethune, 1869; Clarke, 1952; Hodges, 1974; Riley, 1889). Depressaria spp. are relatively host specific when compared with those in

Agonopterix, a related genus whose members attack a wide variety of

Umbelliferae (Clarke, 1952).

Natural enemies seem to have only a minor role in parsnip webworm population dynamics in Iowa (Gorder, 1983). Gorder reared only two parasitoids, which were Apanteles depressariae (Muesebeck) and an unidentified dipteran. Depressaria is parasitized by several hymenopterans in Europe, although Riley (1889) failed to rear any from webworms in this country. Southwick (1892), however, found a parasitic dipteran, an ichneumonid (Limneria sp.), and a bacterial pathogen.

Harrison (1913) identified several ichneumonids that parasitized D. pastinacella, but the paras itization rate was less than 1.0%. The hairy woodpecker, Dendrocopus villosus (L.), may be an effective predator of

larvae and pupae (Bethune, 1869). A potter wasp, Eumenes fraternus Say, was described as a predator of webworm larvae (Southwick, 1892). 28

Harrison (1913) claimed that earwigs were significant predators of webworm pupae, but rather than rely on any of the natural enemies, he recommended that infested flowers be removed by hand and that alternative host plants near cultivated parsnip be destroyed.

Other herbivorous insects of P. sativa include the agromyzid leaf miner flies and swallowtail butterflies. Allen (1956) observed agromyzid larv?-> and adults on wild parsnip in Great Britian. A taxonomic key and description of the flies, larvae, and mines collected from Pastinaca, Angelica. Heracleum, and Laspitium in North America is available (Griffiths, 1973).

The majority of pollinators of Umbelliferae are flies, thrips, and unspecialized hymenopterans such as bees, wasps, and ants (Bell, 1971).

Specialized bees and lepidopterans make up only a small percentage of the pollinators. Bell speculated that other relatively unspecialized groups, such as Coleoptera and Hemiptera also might be attracted in high numbers to Umbelliferae, but the oils characteristic of these plants repel chewing and sucking insects. Other observers document the abundance of Diptera and Hymenoptera at P. sativa flowers (Allen, 1956;

Gottsche, 1976; Southwick, 1892; Spradbery, 1973).

Trapping Methods

An assortment of trap types and sampling methods are useful for monitoring pest populations, assessing insect dispersal, evaluating insect color preferences, and attracting and capturing pests for population reduction. 29

Roberts et al. (1978) used traps to observe the movements of alfalfa weevil, Hypera postica (Gyllenhal), between alfalfa fields and surrounding woodlots. In an effort to develop pest management recommendations, Pausch et al. (1980) used emergence, flight, and pitfall traps, sweep net, and square-foot samples to observe the dispersal of three weevils: alfalfa weevil; clover leaf weevil, H. punctata (F.); and clover root curculio, Sitona hispidulus (F.).

Traps can assess the presence and movement of natural enemies.

Reardon et al. (1977) compared the effectiveness of Malaise, McPhail, and sticky tube traps in collecting parasitoids of gypsy moth, Lymantria dispar (L.). Malaise traps captured 99% of the Hymenoptera taken and

100% of the braconids and ichneumonids (Reardon et al., 1977). Haack et al. (1981) successfully used polyethylene bands coated with Tree

Tanglefoot to monitor the movements of Phasgonophora sulcata Westwood, a chalcidid parasitoid of the twolined chestnut borer, Agrilus bilineatus (Weber), on oak trees. The movements of predators that feed on green peach aphid, Myzus persicae (Sulzer), were readily observed using vertically aligned clear plastic sticky traps placed 5 cm above soil level in potato fields (Mack and Smilowitz, 1977).

Insects often are attracted to traps that resemble their food source in color and/or shape. Kring (1968) was able to attract and capture adult seed corn maggots, Delia platura (Meigen), on sticky white or yellow stakes more often than on any other colors. The yellow stakes may stimulate a feeding response, because the flies feed at yellow and yellow-orange flowers in May and June (Kring, 1968). Prokopy (1967) 30

reached a similar conclusion from tests with yellow panels and adult

apple maggots, Rhagoletis pomonella (Walsh). Repetition of the

Rhagoletis preference tests using 8-cm diam red wooden spheres showed

that Stickem®-coated spheres captured more flies than Stickem^-coated

red 'Winesap' apples of similar size (Prokopy, 1968a, 1968b). Moore

(1969) confirmed these findings but noted that the spheres also

attracted and removed from the orchard beneficial and non-target

species.

Gottsche (1976) developed traps especially attractive to insect

visitors of P. sativa. She found that food searching by the torymid,

Megastigmus bipunctatus (Swederus) is directed mainly by color signals

(Gottsche, 1977). The reaction of M. bipunctatus toward green and

yellow is dependent on the wasp's state of nutrition. Initially, wasps

prefer green to yellow, but later, yellow is more attractive than green.

Although P. sativa flowers were more attractive to M. bipunctatus than

those of 41 other plant species tested, vertically placed 8 x 16-cm

yellow rhomboids were more attractive than P. sativa.

Yellow is consistently the most attractive color in tests of

representatives from the major insect orders. Trials with cereal leaf

beetle, Oulema melanopus (L.), and meadow spittlebug, Philaenus

spumarius (L.), showed that more individuals were taken on yellow traps

than on any other color (Wilson and Shade, 1967). The preference for

yellow by the greenhouse whitefly, Trialeurodes vaporariorum (Westwood)

is exploited by erecting yellow sticky boards to protect greenhouse

crops (Berberich, 1979). The attraction of aphids to yellow is well- 31 known and is incorporated in the design of sticky traps and water pan traps for monitoring the alate stage of these pests (Adlerz, 1976;

Broadbent, 1948; Johnson et al., 1967; Lange et al., 1978). Yellow feeding stations containing supplementary food sources and erected in pine plantations attracted parasitoids (Koehler and Kolk, 1969).

Capinera and Walrasley (1978) showed that yellow and orange water-pan and sticky traps capture the highest numbers of sugar beet insects, including palestriped flea beetle, Systena blanda Melsheimer, and assorted leaf hoppers. Yellow traps designed to capture Japanese beetles also are highly attractive to bumble bees (Hamilton et al.,

1971). Yellow traps intended to attract the tachind parasitoids of gypsy moth attracted a sufficient variety of flies to expand the study to all parasitic tachinids in the forest (Weseloh, 1981). Yellow traps developed to monitor populations of R. pomonella in orchards also trapped large numbers of tachinids, and varying numbers of anthorayiids,

dolichopodids, muscids, otitids, and pipunculids (Moore, 1969).

When cherry fruit flies, Rhagoletis cingulata (Loew), were offered

a choice of 27 different colors of painted traps, yellow or dark yellow

tints were preferred to any other color (Prokopy and Boiler, 1971).

Prokopy and Boiler (1971) were intrigued by this preference for yellow

and investigated the optical properties of yellow and other colors based

on measurements of spectral reflectance. They found that green, orange,

and yellow all reflected considerable energy, but yellow was the most

intensely reflective color. However, when offered a choice between

rectangles painted with yellow or with more energetic daylight- 32 fluorescent yellow enamels, the flies most often selected the former, indicating that the response is one of true color discrimination and positive attraction to yellow (Prokopy and Boiler, 1971). A second fly species, R. pomonella, also was highly responsive to visual stimuli, including color, shape, and size of the test objects. It displayed a significant preference for yellow, which Prokopy (1968b) attributed to true color discrimination and not to a response primarily based on reflective intensity.

Faunal Lists

References to the insect faunas of the habitats observed in this study are limited, although several authors record the insect faunas associated with various wild flowering plants (Altieri and Whitcomb,

1979b, 1980; Frost, 1977, 1979; Futuyma and Gould, 1979; Grensted,

1946b; Kevan, 1973; Messina, 1978; Messina and Root, 1980; Root, 1973;

Root and Tahvanainen, 1969). A faunal list of insects of Iowa prairies was prepared by Hendrickson (1929).

Literature on the fauna of wild parsnip is limited. Allen (1954,

1956) and Griffiths (1973) listed the species of agromyzid flies attracted to wild parsnip. Insect faunal listings for the related wild carrot and cow parsnip also are incomplete (Grensted, 1946a; Judd,

1970).

A greater wealth of documentation exists for fauna of soybean fields, including lists of predators in Iowa soybean fields, and Iowa green cloverworm parasitoids (Bechinski and Pedigo, 1981; Culin and 33

Yeargan, 1983a, 1983b; Dietz et al., 1976; Harper and Garner, 1973;

Ignoffo et al., 1975a, 1975b; Kogan, 1981; Lentz, 1973; Lentz and

Pedigo, 1972; McCutcheon and Turnipseed, 1981; Pedigo et al., 1981). 34

MATERIALS AND METHODS

This study was conducted in the field and laboratory between June

1 and August 31 in 1979 and 1980. Plot locations are indicated in

Figure 1, and described in the Appendix.

Field Procedures

Soybean studies

In 1979, seven soybean fields were chosen for study. Each of five

fields bordered on one side by wild parsnip was sampled once per week

for foliage-dwelling larval insects. Each of two check fields without wild parsnip borders was sampled twice per week. Similarly, in 1980,

four soybean fields were selected, and each was sampled twice per week.

Two fields were bordered on one side with wild parsnip. Two others without wild parsnip served as checks.

On each sampling date, five random samples were taken in each

soybean field within 150 m of the field margin. In parsnip-bordered

fields, the margin adjacent to the wild parsnip was sampled. Five

samples also were taken at random sites beyond 150 m from the margin.

Sampling was done for 30 sec at each random site by vigorously shaking

the soybean plants in two adjacent rows over a square meter white drop

cloth laid on the ground between the rows. This is a preferred sampling

procedure for soybean canopy-dwelling arthropods (Dietz et al., 1976;

Hammond and Pedigo, 1976; Kogan and Pitre, 1980; Pedigo, 1980). Larvae

collected from 60 cm of row (30 cm on each side of the cloth)

constituted a sample. All lepidopterous larvae were counted, their 35

GENERAL HIGHWAY AND TRANSPORTATION MAP

IOWA DEPARTMENT"OF 'TRANSPORTATION DIVISION or PLANNING AND RESEARCH OFFICE Of TRANSPORTATION INVENTORY MONi (*!*) m-im # •N COAMUNON KITH UNITED STATES DEPARTMENT OF TRANSPORTATION FEDERAL MIOHWAY ADMINISTRATION

FIGURE 1. Location of sites from which samples were collected during 1979 and 1980 36 numbers recorded, and they were returned to the laboratory for further study.

Parsnip studies

To sample the insect fauna attracted to wild parsnip flowers, sticky traps resembling flowering parsnip stalks were placed in stands of wild parsnip. In 1979, five stands adjacent to soybean fields and five plots of wild parsnip located in old fields not immediately adjacent to soybeans were sampled. Two stands of each type were sampled in 1980.

Trap plate size was based on the mean diameter of 50 wild parsnip terminal umbels. Plywood discs 5-mm thick were cut to represent that average diameter. The discs were painted to resemble the flowering 'D umbels of wild parsnip using Diamond Vogel gloss enamel in federal yellow (No. AZ-3404) above and limerick green (No. DF-1503 formulation

3-9-1) below. Each disc was glued yellow side up and 3 cm from the end of a 1-m-long, 6-mm-diam green wooden stake. The clear, sticky compound

Tack-Trap was spread on the insides of 150-mm-diam clear plastic petri

bottoms. A 7-mm-diam hole was made in the center of each plate. The

petri plates without their tops were placed over the painted discs and were held in place by small pieces of yellow modeling clay. Ten traps, spaced 5 m apart, were placed in a line parallel to the field edge in

the center of each fencerow, and in a line through the center of each wild parsnip plot. Petri plates were replaced every other day, and the

collected plates topped with their covers were returned to the

laboratory. Trapped insects were identified to family or superfamily. 37 counted, and their numbers were recorded. Specimens of groups with parasitic behavior were identified as specifically as possible with existing keys. Specimens that were difficult to identify were compared with specimens in the Iowa State University Insect Collection and/or confirmed by Dr. J. W. Mertins, Biological Control Project, Iowa State

University. Most specimens of the families Tathinidae and Braconidae, and individuals suspected of being GCW parasitoids were identified to species. Suspected GCW parasitoids were compared with the GCW parasitoid collections of G. L. Lentz and E. J. Bechinski, which are incorporated in the reference collections of the Soybean Pest Management

Research Unit at Iowa State University. Information on trapped species was recorded by date and locality of collection.

Laboratory Procedures

Rearing studies

All lepidopterous larvae collected by shake sampling were returned to the laboratory, identified, and reared separately in cylindrical 30 x

25-mm or 50 x 35-mm clear plastic containers (zipper cases). Larvae were fed fresh soybean leaves daily. Parasitism, disease, or adult emergence was recorded for each individual. Species and numbers of reared parasitoids of GCW also were recorded.

Feeding studies

To assess the effect of wild parsnip on the longevity of adult parasitoids, groups of representative parasitoid species were held either in the presence or absence of wild parsnip flowers. Adult 38 parasitoids that emerged from field-collected GCW were placed individually in separate, screen-topped, 1-pint ice cream cartons. Each carton contained a 1-dram shell vial filled with wetted cotton to provide moisture to the parasitoid. Cartons were fitted with sprigs of wild parsnip flowers and soybean leaves, with soybean leaves alone, or with neither. Plant stems were inserted in Aquapics®, water-filled plastic tubes, to keep the plants from desiccating. Plants were replaced with fresh sprigs and/or leaves daily. Cartons were held in an environmental chamber at 27°C, 70% RH, and 16 hr photophase, and the longevity of each parasitoid was recorded.

Statistical Analyses

Estimates of parasitization and pathogen-induced mortality were computed by two methods (Marston, 1980; Shephard et al., 1983).

Apparent mortality caused by a single species per year was calculated with the following equation:

PHx

X 100

TH - THD where

PHx = total number of natural enemy x reared from host H

TH = total number of host H

THD = total number of host deaths not attributed to natural enemies 39

The resulting percentage, therefore, is based on mortality of all host larval stages collected.

This measure of mortality, however, probably underestimates parasitization and may not express the true potential of a parasitoid

(Marston, 1980; Shephard et al., 1983). A more accurate measure is the parasitism sustained only by instars susceptible to attack. In 1980, data were recorded by GCW instar to more accurately evaluate parasitization. Percent parasitization for a particular parasitoid was calculated with the following equation:

Px + Py + ... Pn

X 100

(GCWx + GCWy + ... GCWn) - (Dx + Dy + ... Dn) where

Px,y..,n = total number of parasitoid sp. P reared from

susceptible host instars x,y...n

GCWx,y...n = total GCW collected in instars x,y...n

Dx,y...n = total GCW deaths in instars x,y...n not attributed

to parasitism

For example, C. marginiventris is known to attack only GCW instars I,

II, and III (Lentz and Pedigo, 1975), and only those instars were used to estimate parasitization. Parasitization by R. nolophanae was calculated using information on GCW instars II, III, and IV.

Calculations for parasitization by W. sinuata required data on GCW 40 instars V and VI. The resulting percentage provides the estimated impact of species P on only the portion of the GCW population susceptible to attack by species P at the time of collection.

Treatment (i.e., soybean fields with and without wild parsnip borders) differences for species discussed in this study were examined by analysis of variance. Estimates of GCW larval numbers and parasitization also were analyzed with a split-plot design according to distance of the sampling site from the fencerow. Split-plot significance was estimated with a t-test and whole plot significance was expressed in an F-test.

To standardize the numbers of collected GCW and trapped parasitoids for graphs of seasonal trends, sample tallies were summed within fields and averaged across fields by week to produce a mean weekly total. For example, points plotted on July 1 represent the average total number of the selected species collected per field, during the week beginning on July 1. The mean represents the weekly total for the week beginning July 1, and not just the mean of samples taken on that single sampling date. Averages for insects trapped at wild parsnip also were calculated from weekly totals per plot. 41

RESULTS AND DISCUSSION

Soybean Studies

The nine species of lepidopterous larvae collected from soybean fields in 1979 are listed in Table 1. Six families were represented, but the most common species were noctuids. The listing is consistent with previous work (Pedigo et al., 1981). GCW accounted for more than

99% of the lepidopterous larvae sampled from fields in 1979.

TABLE 1. Species of larval lepidopterans collected from soybean fields in central Iowa during 1979

Tortricidae Arctiidae Choristoneura rosaceana (Harris) Diacrisia virginica (F.) Xenotemna pallorana (Robinson) Noctuidae Pyralidae Caenurgina erechtea (Cramer) Achvra rantalis (Guenee) Plathvpena scabra (F.) Geometridae Trichoplusia ni (Hubner) Anavitrinella pampinaria (Guenee) Pieridae Colias eurytheme Boisduval

The mean seasonal larval totals per field and parasitization rates of lepidopterans other than GCW are shown in Tables 2 and 3. More species of larval lepidopterans were collected in soybeans associated with wild parsnip than in those without wild parsnip. Furthermore, at least some level of parasitoid attack also was more likely when wild parsnip was present. Parasitization rates ranged form 0 to 100%, and 42 all collected specimens of A. rantalis collected in parsnip-bordered fields were parasitized. No parasitoids were reared from A. pampinaria,

D. virginica, C. erechtea, or the tortricids. Statistical analysis of possible differences in parasitization rates between bordered and unbordered fields were not performed because of the low population densities for minor species. F-tests on such small sample sizes would not have been valid.

In Table 3, the mean seasonal larval totals were separated according to distance of the sampling site from the fencerow. The diversity of lepidopterous species was greatest toward the field center in soybeans without wild parsnip, whereas the species diversity of lepidopterans in parsnip-bordered soybeans seemed somewhat more uniform throughout the field. Once again, F-tests were not performed on the seasonal totals due to the small number of insects collected.

In 1979, GCW larvae were collected approximately 50% more often from fields of soybeans without wild parsnip than from soybean fields associated with wild parsnip (Table 4). Although the difference in seasonal totals between the two field types was not significant at the

0.05 level, it approached that statistical standard of significance (P =

0.08). There were fewer larvae near the field edges than near the field centers in both kinds of fields, but there was no significant difference between field types.

Because the species other than GCW composed such a minor portion of the lepidopterous fauna of soybean fields in 1979, they were not included in the 1980 tallies. Therefore, the second year's results 43

TABLE 2. Mean seasonal totals (X±SE) per field and apparent parasitization rates of minor larval lepidopterans collected in 1979 from central Iowa soybean fields

Species Soybeans alone Soybeans with Parsnip (2 fields) (5 fields) 1 0 - o o 0 Tortricidae 1.,50 ± 0,,50 0, 4 ,37 7o parasitized^ 0.00 0.00 Pyralidae A. rantalis 1.,00 ± 0,,00 0,.40 ± 0.,25 7o parasitized 50.00 100.00 Pieridae C. eurytheme 1,,00 ± 1,,00 0,,80 ± 0,,37 % parasitized 0.00 75.00

Geometridae 1 + o o A. pampinaria 0, O ,00 0,.20 ± 0.,20 7o parasitized 0.00 0.00 Actiidae D. virginica 0,.00 ± 0..00 0 .60 ± 0,.25 7o parasitized 0.00 0.00 Noctuidae C. erechtea 1.,00 ± 1,,00 0,.00 ± 0,,00 % parasitized 0.00 0.00 14- o O T. ni 0, O .00 0 .40 ± 0,,40 7o parasitized 0.00 50.00

aparasitization rates based on total number of larvae per species collected from all fields 44

TABLE 3. Mean seasonal totals (X±SE) per field and apparent parasitization rates of minor larval lepidopterans collected in 1979 from two locations in central Iowa soybean fields

Soybeans alone Soybeans with Parsnip (2 fields) (5 fields)

Species < 150m^ > 150m < 150m > 150m

Tortricidae 0.00 ± 0.00 1.50 ±0.50 0.00 ± 0.00 0.80±0.37 % parasitized^ 0.00 0.00 0.00 0.00 Pyralidae A. rantalis 0.00 ± 0.00 1.00 ± 1.00 0.20 ± 0.20 0.20± 0.20 7o parasitized 0.00 50.00 100.00 100.00 Pieridae Ç. eurvtheme 0.00 ± 0.00 1.00 ± 1.00 6.20± 0.20 0.60±0.20 % parasitized 0.00 0,00 100.00 100.00 Geometridae _A. pampinaria 0.00 ± 0.00 0.00 ±0.00 0.00± 0.00 0.20±0.20 7o parasitized 0.00 0.00 0.00 0.00 Arctiidae D. virginica 0.00 ± 0.00 0.00 ± 0.00 0.20± 0.20 0.40± 0.40 7o parasitized 0.00 0.00 0.00 0.00 Noctuidae £. erechtea 0.50 ± 0.50 0.50 ± 0.50 0.00± 0.00 0.00 ±0.00 % parasitized 0.00 0.00 0.00 0.00 T. ni 0.00 ± 0.00 0.00 ± 0.00 0.00± 0.00 0.40 ±0.40 % parasitized 0.00 0.00 0.00 50.00

^locations were separated according to distance of sampling site from the fencerow

^parasitization rates based on total number of larvae per species collected from all fields 45 include only data on GCW.

The average seasonal totals of GCW instars collected per field in

1980 are listed in the upper part of Table 5. The effect of wild parsnip presence on seasonal totals separated by larval size appears in the lower part of the table. Instars I and II were combined as "small larvae" in the test. Medium larvae comprised instars III and IV, and large larvae included instars V and VI. First instars were collected the least often, and third instars were collected the most often. The apparent lack of first instars probably is due to the difficulty of sampling and seeing this stage in the field. The presence of wild parsnip had no statistically significant effect on population densities of any particular instar, or larval size. Neither was there a significant difference between types of fields for the GCW populations as a whole, even though, as in 1979, fewer larvae were collected from soybeans associated with wild parsnip.

Statistical analysis failed to establish the existence of an edge effect for GCW due to the presence of wild parsnip (Table 6). Distance from the fencerow had no statistically detectable effect on the mean seasonal incidence of GCW instars, sizes, or the population as a whole, even though more total larvae were collected near the edge in both types of fields.

The mean weekly totals of GCW collected per field in 1979 are illustrated in the upper portion of Figure 2. In fields with wild parsnip borders, the first GCW appeared in the last week of June. The population peaked in the last week of July. GCW still was present in 46

TABLE 4. Mean seasonal totals (X±SE) per field of larval green cloverworras collected in 1979 from central Iowa soybean fields with and without wild parsnip borders

Location Soybeans alone Soybeans with Parsnip P > F (2 fields) (5 fields)

entire field 329.50 ±18.50 171.00± 50.50 0.08

< 150m 159.50 ± 6.50 72.00 + 12.32 0.01

> 150m 170.00 ±25.00 99.80 ± 22.60 0.04

P > t 0.72 0.31 47

TABLE 5. Mean seasonal totals (X±SE) per field of green cloverworm larval stages collected in 1980 from central Iowa soybeans with and without wild parsnip borders

Stage Soybeans alone Soybeans with Parsnip P > F (2 fields) (2 fields)

I 1,,50 ± 0,,50 7,.50 ± 4,.50 0,.32 II 30..00 ± 5,.00 28,.50 ±13,.50 0,,92 III 52,.00 ±17,,00 42,.50 ±23,,50 0,,77 IV 20,.00 ± 5,.00 23 .00 ± 13,.00 0,.84 V 33,.00 ±10,.00 23,.00 ± 5,,00 0,.47 VI 32,.00 ± 9,.00 23,.50 ± 15,,50 0,.68

small 31,.50 ± 4,.50 36 .00 ± 18,.00 0,.83 medium 72,.00 ±22,.00 65,.50 ±36,.50 0,.89 large 65,.00 ±19,.00 46,.50 ±20,.50 0 .57

total 168,.50 ±45,.50 152,.00 ±79,.00 0,.87 TABLE 6. Mean seasonal totals (X±SE) per field of green cloverworm larval stages collected in 1980 from two locations in central Iowa soybean fields

Soybeans alone Soybeans with Parsnip (2 fields) (2 fields)

Stage < 150m& > 150m P>t < 150m > 150m P>t

I 0,,50 ± 0,.50 1,.00 ±0,,00 0.42 5.00± 3,.00 2.50 ± 1,.50 0.53 II 17,.50 ± 5,,50 12,.50 ±0.,50 0.46 13.50±10, .50 15 .00 ±3,.00 0.90 III 30,.00 ± 9..00 22,.00 ±8.,00 0.57 23.00±12, .00 19 .50±11,.50 0.85 IV 10,.50 ± 1..50 9,.50 ±3.,50 0.82 13.50± 6,.50 9.50 16,.50 0.71 V 16,.00 ± 6,,00 17,.00 ±4.,00 0.90 11.50+0, .50 11.50 ±5,.50 1.00 VI 16,.50 ± 6,,50 15,.50 ±2.,50 0.90 12.50± 9,.50 11.00 1 6,.00 0.91 1 o o o small 18 + .00 13 .50 ±0,.50 0.47 18.50113 .50 17.50 14,.50 0.95 medium 40,.50±10, .50 31,.50+11, .50 0.62 36.50+18 .50 29 .00118,.00 0.80 large 32,.50112, .50 32,.50 ±6,.50 1.00 24.001 9 .00 22.50111, .50 0.93

Total 91,.00+28 .00 77,.50117, .50 0.72 83.00+45 .00 69 .00134,.00 0.82

®locations were separated according to distance of sampling site from the fencerow 49 fields without wild parsnip in the last week of August, when sampling ended. GCW did not appear in fields without wild parsnip until the first week of July, but populations peaked earlier (in the third week) than in parsnip-bordered fields. Populations declined to zero by the last week in August. GCW populations reached economic threshold levels in both types of fields in 1979. This type of population trend was termed an outbreak population configuration (Pedigo et al., 1983).

Based on that model, peak populations presumably occurred during the GCW first generation in 1979, with a smaller second generation occurring later in the season.

The-mean seasonal totals of collected GCW plotted by week in 1980

(Figure 2) indicate that two generations occurred. The first generation, in the second week of July, was smaller than the second generation. GCW densities failed to reach economic proportions during either generation. This type of population trend was termed endemic by

Pedigo et al. (1983). GCW larval population trends in soybeans with and without wild parsnip borders generally were similar. Larvae were present in parsnip-bordered fields when sampling commenced, but the first larvae were not collected in fields without wild parsnip until two weeks later. GCW larval populations remained low in both field types through July. The second generation occurred in August with peak populations occurring in the second week of August in fields without parsnip, and the third week of August in fields with parsnip borders. A few larvae were collected in both field types on the last sampling date.

Consequently, seasonal trends in 1980 were much different from trends in 50

soybeans and parsnip (N=5) 1979 —soybeans alone (N=2)

80.0 +

60.0 +

40.0 +

20.0 +

0.0

-4-- - - -+- -H —I— - - -4— - - -4 -4-- - - —I Jul 1 Aug 1

soybeans and parsnip (N=5) 1980 soybeans alone (N=2)

40.0 4-

30.0 4-

20.0 4-

10.0 4-

0.0 4-

-4-- - - -4-- -4- 4- 4- 4- 4- 4" . Jul 1 Aug 1

FIGURE 2. Mean weekly totals per field of green cloverworm larvae collected in 1979 and 1980 from central Iowa soybean fields with and without wild parsnip borders 51

1979. Peak populations were larger and occurred about 3 weeks earlier in 1979 as compared to 1980.

Four species of parasitoids were reared from GCW larvae in 1979.

These were R. nolophanae, C. marginiventris, W. sinuata, and M. autographae. The mean rates of paras itization per field for GCW larvae collected in fields with and without wild parsnip borders are shown in

Table 7. R. nolophanae was the most commonly reared parasitoid. C. marginiventris was second, W. sinuata was third, and M. autographae was the least common. The presence or absence of wild parsnip did not significantly affect the level of parasitiztion by either R. nolophanae or W. sinuata. Parasitization rates by C. marginiventris were highly variable. It parasitized about twice the number of GCW in the presence of wild parsnip as in its absence. This difference, however, was not significant because of the high level of variablilty. Although M. autographae was the least common of the reared parasitoids, a significant difference (P = 0.04) existed between treatments. This probably is not a valid difference, however, because M. autographae

population levels were low, thus making accurate estimates of

parasitization difficult. When the combined effects of the Hymenoptera

and Diptera-Hymenoptera complex were examined, parasitoid-induced

mortalities were about 20% higher in the presence of wild parsnip as in

its absence. These differences were statistically significant at the

0.05 level for both parasitoid groups. The higher rates of

parasitization in fields with wild parsnip primarily were the result of

increased parasitization rates by C. marginiventris in these fields and, 52 therefore, they were of questionable significance.

GCW larvae also were infected by pathogens. The fungus Nomuraea rileyi (Farlow) Sampson accounted for about 90% of the pathogen-related mortality. The remaining 10% was caused by unidentified fungal pathogens. The presence of wild parsnip had no significant effect on the degree of pathogen-related mortality. When pathogen mortality is added to that caused by parasitoids, GCW mortality was slightly higher when wild parsnip was present. This difference, however, was not large enough to be statistically significant.

The mean seasonal incidences per field of parasitism and pathogen- induced mortality near the field edge and near the field center are shown in Table 8. With the exception of M. autographae, the rates of parasitoid- and pathogen-induced mortality generally were greater near the field edge than near the center. However, statistical tests for edge effect demonstrated no significant differences for any of the parasitoids or pathogens in 1979.

The natural enemies that attacked GCW collected in 1980 are listed in Table 9. As in 1979, R. nolophanae was the most commonly reared parasitoid. W. sinuata, however, was the second most commonly reared parasitoid in 1980. C. marginiventris ranked third, and no specimens of

M. autographae were reared. Unlike 1979, the incidence of pathogen- induced mortality was very low in 1980. Furthermore, all pathogen- induced death in 1980 was caused by N. rileyi. The presence of wild parsnip in fencerows resulted in no significant differences for any of the parasitoid or pathogen categories, even though mortality from each 53

TABLE 7. Mean (±SE) apparent seasonal mortality (%) per field in 1979 caused by natural enemies of green cloverworm larvae collected from central Iowa soybean fields with and without wild parsnip borders

Species Soybeans alone Soybeans with Parsnip P > F (2 fields) (5 fields)

C. marginiventris 7.,57 ± 1,,19 17.,43 + 2. 13 0.,23

M. autoeraphae 0,,87 + 0,,51 0,,11 + 0.,11 0,,04

R. nolophanae 27,,71 + 1,,61 25,,57 + 3,,62 0,,79

W. sinuata 2.,52 + 0,,43 2.,70 + 0.,81 0,,60

Total Hymenoptera 36,,15 + 1,,76 43,, 11 + 3., 46 0,,04

Total parasitoids 38,.68 + 1..85 45,.81 ± 3,,00 0.,03

N. rileyi 16,,50 ± 2,,40 13..89 + 2,,13 0,,64

Other pathogens 1,.07 + 0,.43 0,.61 ± 0.,27 0..25

Total pathogens 17,.67 + 2,.23 14,50 + 1,.95 0 .60

Total natural enemies 56,.35 + 1,.93 60,.31 + 3,.77 0,.40 TABLE 8. Mean apparent seasonal mortality (%) per field in 1979 caused by natural enemies of green cloverworm larvae collected from two locations in central Iowa soybean fields

Soybeans alone Soybeans with Parsnip (2 fields) (5 fields)

Species < ISOm* > 150m P>t < 150m > 150m P>t

C. marginiventris 8,,96 ± 0,,20 6,,18 ±2,.15 0 .33 18,,32 ± 2,.36 16,.55± 3,,82 0,,70

M. autographae 0..73 + 0.,73 1,,01 ± 1,.01 0,.84 0,,00+0, .00 0,.22± 0,,22 0,,34

R. nolophanae 28,.25 ± 2.,41 27,,18 ±3,.02 0,.81 27.,75 ± 5,.56 23,.39± 5,,06 0,,58

W. sinuata 3,.13 ± 0..21 1,.92 ±0,.58 0 .19 2,,04± 1,.40 3 .35± 0 .88 0,.45

Total Hymenoptera 37..94 ± 2..94 34,.37 ± 1,.87 0 .41 46,, 06 ± 6,.18 40 .16± 3,.34 0,.43

Total parasitoids 41,.06 ±2,.73 36,.29 ±1,.29 0,.26 48,,11 ± 5,.27 43 .51± 3,.20 0,.48

N. rileyi 16,.72 ±5,.78 16,.47 ± 1,.03 0,.97 15,.89 ± 2,.43 11,.89 + 3,.54 0,.38

Other pathogens 1,.15 ±0,.31 1,.01 ±1,.01 0,.91 0,.28 ± 0,.28 0,.95± 0,.43 0. 23

Total pathogens 17,.87 ±5,.46 17,.47 ±0,.03 0,.95 16,.17 ± 2,.31 12,.83± 3,,25 0.,42

Total natural enemies 58,,94 ±2,.73 53,.77 ±1,.27 0..23 64,,28+5, .17 56..35± 5,,41 0, 32

^locations were separated according to distance of sampling site from fencerow 55 species was slightly higher and the combined impact of all natural enemies was substantially higher in soybeans without wild parsnip. The trend is contrary to results observed in 1979.

Mortality rates for GCW larvae collected from sites less than and greater than 150 m from the fencerow in 1980 are shown in Table 10.

Only the total Hymenoptera in soybeans with wild parsnip showed a significant (P = 0.05) edge effect, with parasitization higher at the field edge. No other parasitoid or pathogen exhibited a significant edge effect in 1980, although the rate of paras itization by W. sinuata was greatest near the field center regardless of the presence or absence of wild parsnip. In soybeans with wild parsnip, C. marginiventris provided substantially greater parasitization near the center of the field; however, this comparison was not significant.

Because parasitism was recorded by instar in 1980, it was possible to calculate GCW parasitism based upon the stages that are susceptible to attack. In this study, R. nolophanae was reared primarily from instar II through IV. C. marginiventris and W. sinuata were reared from instars I through III and instars V and VI, respectively. The parasitization rates based on susceptible stages (Table 11) demonstrate a greater impact by parasitoids on the GCW population than do the apparent parasitization rates based on the total number of larvae collected in the season. This trend was most evident with W. sinuata.

This species parasitized 23.4% of the eligible GCW instars, but only

9.6% of the total larvae (c.f.. Table 9) collected in fields with wild parsnip. The 23.4% rate still was half the parasitization rate reported 56

TABLE 9. Mean (±SE) apparent seasonal mortality (%) per field in 1980 caused by natural enemies of green cloverworm larvae collected from central Iowa soybean fields with and without wild parsnip borders

Species Soybeans alone Soybeans with Parsnip P > F (2 fields) (2 fields)

C. marginiventris 3,,96 + 1,,58 3,,11 ± 1.,94 0,.70

R. nolophanae 22,,00 + 4.,59 13.,09 ± 1.,72 0,.28

W. sinuata 12..32 ± 1,,64 9,,55 + 1,,46 0,,36

Total Hymenoptera 25,,97 ± 4,,93 16,,20 + 1,,37 0,,32

Total parasitoids 38,,30 ± 4.,12 25.,75 + 1,,82 0,,22

N. rileyi 2,.34 + 0,,90 1,,09 + 1.,09 0.,37

Other pathogens 0,,00 + 0,,00 0.,00 + 0.,00

Total pathogens 2,,34 ± 0.,90 1,,09 + 1,,09 0,,37

Total natural enemies 40,.63 ± 3,,95 26.,84 ± 2.,81 0,,20 TABLE 10. Mean (±SE) apparent seasonal mortality (%) per field in 1980 caused by natural enemies of green cloverworm larvae collected from two locations in central Iowa soybean fields

Soybeans alone Soybeans with Parsnip (2 fields) (2 fields)

Species < 150m& > 150m P>t < 150m > 150m P>t

C. marginiventris 5..47 + 3..22 2.,45 ± 0.,33 0.,45 0.,57 + 0,.57 5,,65 ± 3,,05 0..23

R. nolophanae 23,, 19± 0.,72 20.,82±11. ,10 0. 85 13.,39± 0 .89 12,,79 ± 4.,10 0..90

W. sinuata 9..93 + 0,.94 14. 72+ 1.,95 0.,16 9,,33 + 1 .38 9..77 ± 3.,27 0..91

Total Hymenoptera 28 .66± 3.,94 23.,27+10. ,77 0. 68 13.,96± 0 .32 18,.44 ± 1.,04 0..05

Total parasitoids 38,.59 + 4..89 37. 99+ 8..82 0.,9.6 23..30 + 1 .70 28..20 + 2..23 0.22

N. rileyi 3,.30 + 1,.05 1, 39+ 1..39 0.,39 0..00± 0.00 2..17 ± 2,.17 0.42

Other pathogens 0 .00 + 0..00 0.,00+ 0,.00 0,.00± 0.00 0,.00 ± 0,.00

Total pathogens 3.30± 1 .05 1..39 ± 1.39 0..39 0.Q0± 0.00 2.17 ± 2 .17 0.42

Total natural enemies 41.89± 5,.94 39.38± 7 .43 0..81 23.30± 1.70 30.39 ±4,.40 0.27

^locations were separated according to distance of sampling site from the fencerow 58 in laboratory studies by Lentz and Pedigo (1974). R. nolophane parasitized more than 40% of the three susceptible GCW instars as compared with 22.0% for all larvae in soybeans without wild parsnip

(c.f., Table 9). Examination by this measure of the impact of wild parsnip indicates that higher parasitization of susceptible instars by all parasitoids occurred in the absence of wild parsnip; however, there still was no significant difference that could be attributed to the wild parsnip.

TABLE 11. Mean (±SE) seasonal parasitization (%) per field of green cloverworm instars respectively susceptible to three parasitoid species and collected from central Iowa soybean fields in 1980

Species Soybeans alone Soybeans with Parsnip P > F (2 fields) (2 fields)

Ç. marginiventris 10.10 ± 4.10 6.44 ± 4.06 0.49

R. nolophanae 40.55 ± 8.42 21.66 ± 2.28 0.20

W. sinuata 25.30 ± 2.14 23.38 ± 3.22 0.50

Parasitization rates based on susceptible stages generally were higher near the field edge than near the center in both types of fields

(Table 12). The exception was for C. marginiventris, which parasitized

more frequently in the field center when wild parsnip was present. T-

tests, however, demonstrated that wild parsnip produced no significant 59 edge effect for any parasitoid. Although the means seem to show differences between sampling locations within fields, statistical tests indicate that parasitization rates were similar throughout the field.

Parasitism during 1980 also was calculated for each GCW instar and larval size to establish if wild parsnip enhanced parasitism for any particular instar or size. These parasitization rates are shown in

Table 13. With the exception of instar I, wild parsnip had no significant effect on parasitization rates in any particular instar or larval size. The significant difference observed for instar I is questionable, however, because very few first instars were collected in the field without wild parsnip in 1980. An accurate estimate of instar

I parasitization, thus could not be obtained for these fields.

The test for an edge effect (Table-14) indicates that some significant differences in parasitization rates occurred for instar I and VI. Parasitization of GCW larvae grouped by size was not significantly affected by presence of parsnip. The differences for instar I parasitization are questionable for reasons that already have been discussed. Parasitization of instar VI occurred more frequently at the field center regardless of the presence or absence of wild parsnip in the field margin. Because W. sinuata is the major parasitoid of sixth instars (Lentz and Pedigo, 1975), this result suggests that the rate of W. sinuata parasitization may be lower near the field edge in

1980 regardless of the presence of wild parsnip. Winthemia sinuata parasitization based on total GCW larvae collected also shows this pattern (Table 10), although not with significance, and suggests that TABLE 12. Mean (±SE) seasonal parasitization (%) per field of green cloverworm instars respectively susceptible to three parasitoid species from two locations in central Iowa soybean fields in 1980

Soybeans alone Soybeans with Parsnip (2 fields) (2 fields)

Species < ISOma > 150m P>t < 150m > 150m P>t

Ç. marginiventris 13.81 ±8.41 6.38 ± 1.62 0.48 1.16 + 1.16 11.72 ±6.46 0.25

R. nolophanae 41.65 ±0.91 39.46±20.54 0.92 21.98 ± 3.02 21.33 ±4.67 0.92

W. sinuata 22.68 ± 3.63 27.92 ± 0.65 0.22 28.41 ± 3.45 18.35 ±0.17 0.09

®locations were separated according to distance of sampling site from the fencerow 61

TABLE 13. Mean (±SE) seasonal parasitization (%) per field in 1980 of green cloverworm larval stages collected from central Iowa soybean fields with and without wild parsnip borders

Stage Soybeans alone Soybeans with Parsnip P > F (2 fields) (2 fields)

I 0,.00 ± 0,.00 20,.83 t12,.50 0,,04 II 57,,84 ±11,.58 39,,24 ±6,.05 0,,44 III 61,,25 ± 8,.31 20,,55 ± 8,,03 0,,12 IV 15.,69 ± 3,,43 33.,33 ± 22.,57 0.,56 V 13,.33 ± 2..97 5,,56 ± 5,.56 0,.34 VI 36,,50 ± 4,.70 36,,28 ± 1,,73 0,,80

small 57.,84 ±11,.58 39,,78 ±6,,41 0,,47 medium 44,,30 ± 7,.34 16,.06 ± 6,.46 0,.15 large 25,,30 ± 2,.14 23,.38 ± 3,.22 0..50 M total 38, C ± 4,.12 25,,75 ± 1,.82 0,.65 62 the effectiveness of W. sinuata may be lower at the edge of soybean fields regardless of the presence of wild parsnip. This possibility, however, is not conclusively demonstrated by the results of this study.

The results of the soybean studies demonstrate that six families and nine species of larval lepidopterans were present in central Iowa soybeans in 1979, but that GCW made up 99% of the larval lepidopteran fauna. Nearly 50% fewer GCW were collected from fields associated with wild parsnip than from soybeans without wild parsnip. Although the difference between treatments in 1979 was not significant at the 0.05 level, F-tests produced a value approaching that standard (P = 0.08).

In 1980, 10% fewer GCW were collected from parsnip-associated soybeans than soybeans alone. The difference between treatments was not significant. The consistently higher GCW population densities in the absence of wild parsnip suggests that the plant may either enhance GCW mortality through some unknown means or negatively influence oviposition by GCW moths in adj acent soybeans.

The comparisons for GCW parasitism in the two field types revealed that, in general, parasitization rates were unaffected by the presence of wild parsnip. With the exception of M. autographae, there were no significant differences in parasitization by any particular species in either year. In 1979, significant differences in parasitization by M. autographae were questionable because of the very small sample size and unstable population levels. In 1979, the significant differences between treatments in two measures of parasitization were due primarily to the high variability in parasitization rates by Ç. marginiventris. TABLE 14. Mean (±SE) seasonal parasitization (%) per field of green cloverworm larval stages collected in 1980 from two locations in central Iowa soybean fields with and without parsnip borders

Soybeans alone Soybeans with Parsnip (2 fields) (2 fields)

Instar < 150m a > 150m P>t < 150m > 150m P>t 1 o o o I 0 .00± 0.00 0,.00 ± 0..00 41.67± 8..33 0, + .00 0..04 II 62..50±12 .50 53,.17±24. .60 0. 77 34.52+ 1..19 43,.95113. .19 0..55 III 69,.72± 8.85 52,,78±13. .89 0.41 21.54± 1,.54 19,.56119. .56 0..93 IV 10,,56± 0.56 20,.83 ± 4,.17 0. 13 8.33± 8..33 58,.33+41, .67 0,.36 V 16,.11± 6 .11 10,.56 ± 0,.56 0.46 11. 11±11..11 0,.00 ± 0..00 0,.42 VI 28,.63± 1 .36 44.,36 ± 2,.70 0.04 33.33± 0..00 39,.23 ± 0..77 0,.02

small 62,.50±12 .50 63,.17+24, .60 0. 76 37.65 ± 2..35 41,.90115, ,24 0,.81 medium 48,.81± 3.36 39.,79±16, .45 0.64 16.41± 1..77 15,.71115. .71 0..97 large 22 .68± 3.63 27..92+0, .65 0. 29 28.41± 3,.41 18,.35 1 0,.71 0,.10

Total 91,.00+28 .00 77..50+17. .50 0. 72 83.00+45, .00 69,.00±34. .00 0,.82

^locations were separated according to distance of sampling site from the fencerow 64

In 1980, no significant differences were observed except for parasitization sustained by GCW instars I and VI. Significance for instar I may be due to the high variability of data or to sampling difficulty rather than a true treatment effect. Although no other significant differences occurred in comparisons of GCW instars between treatments, there were significant differences for instar VI in tests with regard to distance from the fencerow in fields with and without wild parsnip. Because instar VI is attacked almost exclusively by W. sinuata, this trend indicates that parasitization by W. sinuata was higher near the field center than near the field edge. A possible explanation may concern the attractiveness of the fencerow; flies may be attracted out of the field if wild parsnip is nearby. The attractiveness of wild parsnip itself cannot have been the sole reason because a similar edge effect occurred even in soybeans where wild parsnip was absent. In general, however, in both years, the parasitization comparisons calculated for GCW instars and larval sizes demonstrated no consistently significant differences between treatments for any particular instar, larval size, or for the GCW population as a whole.

Wild Parsnip Studies

Diptera

The families and species of Diptera trapped at wild parsnip in

1979 and 1980 are listed in Table 15. The family Tachinidae contains

the largest number of potentially beneficial species of Diptera trapped 65 at wild parsnip. Although W. sinuata was the only dipterous species reared from GCW during this study, six additional species that were trapped at wild parsnip are reported as parasitoids of GCW (Arnaud,

1978; Lentz and Pedigo, 1975). Likewise, several other tachinids have been reported as parasitoids of the minor lepidopterans collected in soybean fields in 1979, but none of these parasitoids was reared during this study.

The seasonal averages of Tachinidae trapped among wild parsnip

(Table 16) indicate that the most common tachinids in 1979, in descending order, were W. rufopicta, A. apicifer, and W. sinuata. In

1980, W. sinuata was the most common identified taxon. In general, higher numbers of tachinids were trapped among wild parsnip associated with soybeans than at wild parsnip alone. In 1979, all tachinid species, except 0. assimilis, were more abundant among wild parsnip associated with soybeans than among wild parsnip alone. Almost twice as many specimens of tachinids (218.0 vs. 114.5) were collected per plot in soybean-associated wild parsnip than in wild parsnip alone. The trend also was true in 1980, with eight of twelve taxa being more common in soybean-associated wild parsnip plots. 0. assimilis was the only tachinid that occurred more frequently in both years in parsnip alone.

With the exception of Linnaemya tessellata (Brooks) in 1979, there were no significant differences in the number of individuals of any taxon of tachinids collected in wild parsnip alone as compared with the number in wild parsnip with soybeans.

There were large year-to-year differences in the trap catches of TABLE 15. Species list of identified Diptera trapped among wild parsnip in central Iowa during 1979 and 1980

Asilidae Tachinidae Culicidae Archytas apicifer (Walker) Therevidae A. aterrimus (Robineau-Desvoidy) Thereva spp. A. metallicus (Robineau-Desvoidy)^ Stratiomyidae Blondelia hyphantriae (Tothill)^ Qdontomvia spp. Chaetoplagia atripennis Coquillet Sargus spp. Cylindromyia spp. Stratiomys normula Loew Dinera spp. Do1ichopodidae Euphorocera claripennis (Macquart)^ Syrphidae Euthera tentatrix Loew Chrysotoxum radiosum Shannon Gymnosoma spp. Eristalis arbustorum (L.) Hemyda aurata Robineau-Desvoidy o\ bardus (Say) Lespesia archippivora (Riley)^ a\ E. tenax (L.) Linnaemva tessellata (Brooks) Metasyrphus americanus (Weidemann) Microphthalma spp. Microdon fuscipennis (Macquart) Oswaldia assimilis (Townsend)^ Spherophoria spp. Periscepsia laevigata (Wulp) Xylota spp. Tachinomyia spp. Tephritidae Winthemia quadripustulata (F.)^ Muscidae W. rufopicta (Bigot) Calliphoridae W. sinuata Reinhard^ Lucilia illustris (Meigen) Sarcophagidae Bufolucilia silvarum (Meigen) Metopia argyrocephala (Meigen) Calliphora vicina Robineau-Desvoidy Phormia regina (Meigen)

^parasitoid of Plathypena scabra TABLE 16. Mean seasonal totals (X±SE) per plot of Tachinidae (Diptera) trapped among wild parsnip in central Iowa during 1979 and 1980

1979 1980

Parsnip Parsnip Taxon with Parsnip P>t with Parsnip P>t Soybeans alone Soybeans alone (5 plots) (5 plots) (2 plots) (2 plots)

A. apicifer 51..60±28. .41 33..6Ci!;12. .99 0,.58 5,.50± 5,.50 3..00± 2..00 0..71 B. hvphantriae 2..20 ± 1,.02 0..20 ±0..20 0,,09 2..00 ± 1,,00 4..00± 4..00 0,.68 Cylindromyia spp. 3,.00 ± 1..79 0..00 ± 0,.00 0..13 2,.00 ± 0..00 0..50± 0.,50 0..10 H. aurata 4,.60 i 2..14 0..00 ±0..00 0..06 7..00+ 7.,00 3..00± 0.,00 0,,63 L. archippivora 1..60 ± 1..22 0 .00 ±0..00 0,.19 0..00 ± 0,,00 0..00± 0,,00 L. tessellata 8,.00 ± 1..41 0..00 ±0,.00 0..01 5..50± 4,,50 5..50± 3.,50 1,,00 0. assimilis 9..20 ± 1,.98 18.. 20 ±12..79 0,.51 6..50± 2.,50 12..50± 9,,50 0,,60 Tachinomyia spp. 0 .00 ± 0..00 0 .00 ±0..00 2..50 ± 2..50 5,.00± 3..00 0..59 W. quadripustulata 5..80 ± 2,.58 1..20 ±1..20 0,.14 0..50 ± 0..50 0..00+ 0..00 0..42 W. rufopicta 81 .20±20,.12 35..60±21. .33 0..16 5..50 ± 0,.50 4..50+ 2..50 0,.73 W. sinuata 36,.40± 6..87 17..00±11. .48 0,.19 72..00 ± 4..00 25 .50±13..50 0..08 Other tachinids® 14.40± 2,.89 17 .80 ±5,.88 0..50 5 .50 ± 2..50 8 .00± 3..00 0..59

^includes seasonal totals of A. aterrimus. A. metallicus, Ç. atripennis. Dinera spp., E. claripennis, E. tentatrix, Gymnosoma spp., Microphthalma spp., and P. laevigata 68

A. apicifer and W. rufopicta. These differences may be explained by the presence or absence of large populations of a mutual host, the armyworm.

An armyworm outbreak in 1979 (DeWitt, 1979a) might have been responsible for the high concurrent populations of A. apicifer and W. rufopicta.

Armyworm populations were small in 1980 (Stockdale, 1980a), which probably contributed to a corresponding population decline in mean weekly totals collected per field for A. apicifer (Figure 3) and W. rufopicta (Figure 4). These seasonal trends illustrate the association of the increased tachinid populations with the presumed armyworm presence during early July in 1979 and August of 1980.

Other tachinids known as parasitoids of armyworm are Cylindromyia spp., E. claripennis, L. archippovora, P. laevigata, and W. quadripustulata (Arnaud, 1980). These tachinids did not seem to respond numerically to armyworm population changes with the dramatic magnitude of A. apicifer and W. rufopicta. Additionally, even though most of the collected tachinids known to be parasitoids of GCW were more abundant in

1979 than in 1980, none seemed to be dramatically more numerous during the GCW outbreak in 1979.

Several other tachinid species were collected in very low numbers.

These were A. aterrimus, A. metallicus, Dinera spp., E. claripennis, E. tentatrix, Gymnosoma spp., Microphthalma spp., and P. laevigata. The seasonal means of these species were combined to form 'Other tachinids' in Table 16. The collection of E. tentatrix, Gymnosoma spp., and H. aurata may be attributed to the presence of their pentatomid hosts,

Euschistus spp., and Podisus maculiventris (Say) in soybeans. 69

— parsnip and soybeans (N=5) 1979 -- wild parsnip alone (N=5)

40.0 + I I 30.0 + I I 4J 0 20.0 + iH CL I 0)U I PL 10.0 + T) 0) a a 0.0 + w2 en -+ + + + + + + + + +- - c Jul 1 Aug 1 I 1o

0.0 +•

Jul 1

FIGURE 3. Mean weekly totals per plot of Archvtas apicifer (Diptera: Tachinidae) trapped among wild parsnip in central Iowa during 1979 and 1980 70

— parsnip and soybeans (N=5) I 1979 -- wild parsnip alone (N=5) I 50.0 + I I + I I 25.0 + I M I Q) a + Tî I

+ I I 0.0 +

-+- - - -+- - - —h- -+ + +• Jul 1 Aug 1

FIGURE 4. Mean weekly totals per plot of Winthemia rufopicta (Diptera: Tachinidae) trapped among wild parsnip in central Iowa during 1979 and 1980 71

The mean weekly totals collected per plot for Tachinidae reported as parasitic on GCW (Arnaud, 1978; Harper et al., 1983; Lentz and

Pedigo, 1975) are listed according to sex in Table 17. Specimens whose sex could not be distinguished were grouped as 'unsexed.' In 1979, more flies generally were trapped in wild parsnip associated with soybeans than in parsnip alone, but the difference was statistically significant only for males of B. hyphantriae, W. rufopicta, and W. sinuata. In

1980, a greater number of species was trapped at soybean-associated wild parsnip, but the only group with a significant difference between treatments (P = 0.05) was unsexed W. sinuata. Unsexed specimens made up the majority of the W. sinuata in 1980. The seasonal averages in 1979 indicate that more A. apicifer males than females were trapped in wild parsnip, but more W. rufopicta females than males were trapped in wild parsnip. All groups of the other tachinid species were trapped in relatively equal sex ratios in both years.

The five common tachinid species parasitic on GCW exhibited 1979 population peaks that corresponded to the presence of first generation

GCW in July. When these tachinids were present in 1980, their population peaks were correlated with the high second generation GCW densities in August.

The mean weekly totals per plot for B. hyphantriae (Figure 5) show that, although populations were very low, the highest incidences were correlated in both years with the peak GCW densities (c.f.. Figure 2).

No specimens of L. archippovora were trapped in 1980, but the few trapped in 1979 (Figure 6) occurred only during the first GCW generation TABLE 17. Mean seasonal totals (X±SE) per plot of males and females of selected tachinids trapped among wild parsnip in central Iowa during 1979 and 1980

1979 1980

Parsnip Parsnip Species with Parsnip P>t with Parsnip P>t Soybeans alone Soybeans alone (5 plots) (5 plots) (2 plots) (2 plots)

A. apicifer males 31,,40 ±12,.48 0.51 1.00± 1.00 0.,50± 0.50 0. 70 females 5.60 ± 3.41 2..20 ±1 .40 0.39 1.00± 1.00 0,.50± 0.50 0.70 unsexed 25.80±15.29 0..00 ± 0,.00 0.13 3.50± 3.50 2,.00± 1.00 0. 72 B. hyphantriae

males 1.20 ± 0.49 0. o o ± 0,.00 0.04 0.50± 0.50 0..50± 0.50 1.00 females 1.00± 0.55 0..20 ± 0.20 0.21 1.50± 0.50 3,.00± 3.00 0.67

unsexed 0.00 ± 0.00 0..00 ± 0 .00 - 0.00± 0.00 0,.50± 0.50 0.42 0. assimilis males 2.40± 0.75 3,.80 ± 3 .80 0.72 0.00± 0.00 2.,00± 2.00 0.42 females 5.00± 1.14 12..40 ± 7 .06 0.33 5.00 + 2.00 8,.50± 5 .50 0.61 unsexed 1.80± 0.73 2,.00 ± 2.00 0.93 1.50 + 0.50 2,.00± 2.00 0.83 W. quadripustulata males 0.40± 0.40 0.24 ± 0.00 0.14 0.00 ±0.00 0.00± 0.00 females 4.40± 2.32 0.00 ± 0.00 0.09 0.50 ±0.50 0.00± 0.00 0.42 unsexed 1.00± 0.32 1.20 ±1.20 0.87 0.00 ±0.00 0.00± 0.00 W. tufopicta males 11.80± 2.58 3.20 ±1.69 0.02 2.50 ±0.50 0.00± 0.00 0.42 females 62.20±19.69 12.80+12.30 0.07 0.00 ±0.00 1.50± 1.50 0.42 unsexed 7.20+ 2.15 0.00 + 0.00 0.01 3.00 ±0.00 1.00± 1.00 0.18 W. sinuata males 17.40+ 4.23 1.00 ±0.63 0.01 12.00 ±3.00 4.00± 2.00 0.16 females 13.60± 2.94 15.40±11.44 0.88 6.50 ±2.50 2.00± 2.00 0.30 unsexed 5.40± 2.18 0.60±0.60 0.07 53.50 ±3.50 19.50± 9.50 0.05

w-vj 74

— parsnip and soybeans (N=5) 1979 -- wild parsnip alone (N=5)

2.0 +

1.5 +

u o 1.0 +

0)u a 0.5 + 'O 0)p- a 03 0.0 + u

CO Jul 1 Aug 1

Ia o parsnip and soybeans (N=2) a- to 1980 wild parsnip alone (N=2)

0 2.0 + % 1 g

Jul 1 Aug 1

FIGURE 5. Mean weekly totals per plot of Blondelia hvphantriae (Diptera: Tachinidae) trapped among wild parsnip in central Iowa during 1979 and 1980 75 in July (Figure 2).

The mean weekly totals for 0, assimilis are plotted in Figure 7.

Although populations peaked in 1979 and 1980 in the same weeks that GCW populations peaked, the tachinid's incidence did not fluctuate greatly.

Oswaldia assimilis populations may have been affected by the noctuid

Parallelia bistriaris Hubner, its only known host other than GCW

(ArnaudJ 1978).

No specimens of W. quadripustulata were trapped in 1980, but the mean weekly totals plotted for 1979 (Figure 8) illustrate a coincidence of the tachinid population peaks with the highest densities of GCW

(Figure 2).

The mean weekly totals for W. sinuata trapped in 1979 and 1980 are plotted in Figure 9. In 1979, the highest densities occurred during the

GCW first generation in July. In 1980, W. sinuata populations rose during both GCW generations, but they were the highest in August.

The seasonal totals of Diptera other than Tachinidae are recorded in Table 18. Dolichopodidae was the most commonly collected identifiable family. In 1979, significantly more tephritids, B. silvarum, and unidentified calliphorids were trapped among soybean- associated wild parsnip than among wild parsnip alone, but significantly more muscids and L. illustris were trapped among wild parsnip alone. In

1980, at the family level, Tephritidae exhibited a significant preference for soybean-associated wild parsnip. The calliphorids, L. illustris and C. vicina, were the only other dipterans with significant differences between treatments in 1980. The reason for these 76

— parsnip and soybeans (N=5) 1979 -- wild parsnip alone (N=5)

2.0 +

1.5 +

1.0 +

0.5 +

0.0 +

Jul 1 Aug 1

parsnip and soybeans (N=2) 1980 wild parsnip alone (N=2)

2.0 +

1.5 +

1.0 +

0.5 +

0.0 + I

Jul 1 Aug 1

FIGURE 6. Mean weekly totals per plot of Lespesia archippivora (Diptera; Tachinidae) trapped among wild parsnip in central Iowa during 1979 and 1980 77

— parsnip and soybeans (N=5) 1979 -- wild parsnip alone (N=5)

4.0 +

3.0 + I I 4J o 2.0 + rH O- I u I CLd) 1.0 + n3 I Q) Çu I a 0.0 + 2 10

IO 0 parsnip and soybeans (N=2) Cu wild parsnip alone (N=2) CO

(Uu 1 s s

Jul 1 Aug 1

FIGURE 7. Mean weekly totals per plot of Oswaldia assimilis (Diptera: Tachinidae) trapped among wild parsnip in central Iowa during 1979 and 1980 78

-parsnip and soybeans (N=5) 1979 -- wild parsnip alone (N=5)

3.0 +

1.5 +

0.0 +

Jul 1 Aug 1

parsnip and soybeans (N=2) 1980 wild parsnip alone (N=2)

3.0

1.5 +

0.0 +

Jul 1 Aug 1

FIGURE 8. Mean weekly totals per plot of Winthemia guadripustulata (Diptera; Tachinidae) trapped among wild parsnip in central Iowa during 1979 and 1980 79

— parsnip and soybeans (N=5) 1979 -- wild parsnip alone (N=5)

15.0 +

7.5 +

0.0 +

-+- -+- 1 - - -H -4 I h- Jul 1 Aug 1

parsnip and soybeans (N=2) 1980 wild parsnip alone (N=2)

15.0 +

7.5 +

0.0 + I • -+ - - Jul 1 Aug 1

FIGURE 9. Mean weekly totals per plot of Winthemia sinuata (Diptera: Tachinidae) trapped among wild parsnip in central Iowa during 1979 and 1980 80

differences is unknown.

In summary, the results of the wild parsnip trapping studies show that 11 families and more than 35 species of Diptera were present in the wild parsnip trap samples (Table 15). An abundance of parasitic Diptera was present in soybean-associated wild parsnip. The largest number of

parasitic Diptera collected among wild parsnip were representatives of

Tachinidae, and the most common tachinid species in 1979 were W.

rufopicta, A. apicifer. and W. sinuata. In 1980, W. sinuata was the

most common tachinid. The substantial abundance of A. apicifer and W. rufopicta in 1979, as compared with the numbers in 1980, may have been

due to the presence of armyworm hosts at outbreak levels in the former year. More tachinids were trapped among soybean-associated wild parsnip than in wild parsnip alone. However, there were no significant

differences between treatments in the numbers of Tachinidae collected

among wild parsnip.

Seven species of tachinid parasitoids known to attack GCW were

trapped among wild parsnip during the study. Although higher numbers of

these were present at wild parsnip associated with soybeans, no

significant differences between parsnip plots could be demonstrated. In

1979, more individual male B. hyphantriae, W. rufopicta, and W. sinuata

were trapped in wild parsnip with soybeans than in wild parsnip alone.

The remaining sexed species in 1979 and all sexed groups in 1980 were

trapped in relatively equal sex ratios when compared across treatments.

Population peaks of GCW parasitoids in 1979 corresponded with the high

numbers of first generation GCW in July. In 1980, the parasitoid TABLE 18. Mean seasonal totals (1(±SE) of Diptera other than Tachinidae trapped among wild parsnip in central Iowa during 1979 and 1980

1979 1980

Parsnip Parsnip Taxon with Parsnip P>t with Parsnip P>t Soybeans alone Soybeans alone (5 plots) (5 plots) (2 plots) (2 plots)

Stratiomyidae Odontomvia spp. 0 .00 ± 0,,00 0..00 + 0,.00 0,.50 ± 0..50 3..50 ± 0,.50 0..36 Sargus spp. 0 .00 ± 0,,00 0 .00 + 0.,00 5,.00 ± 5..00 2..50 ± 0..50 0..67 S. normula 0 .00 ± 0.,00 1..20 + 1..20 0..35 8..50 ± 5..50 12.. 00 ±10..00 0..79 Other stratiomyids 5 .80 ± 1,,02 12 .40 + 4..67 0,.21 1,.50 ± 1,.50 3..00 ± 3..00 0..70 Dolichopodidae 663 .20 ± 84.,78 997,.00 ±461..97 0..50 2820,.00+587. .00 2160..00±623. .50 0..52 Syrphidae E. arbustorum 0.00 ± 0,,00 0 .00 + 0.,00 104.00+ 60..00 122..50 ±73.,50 0..86 E. bardus 0 .00 ± 0.,00 0 .00 + 0.,00 4,.00 ±3..00 5..00 ± 1..00 0..78 E. tenax 3 .80 ± 2,,90 0 .00 + 0..00 0..23 26,.50 ±4,.50 18 .50 ± 6,.50 0..42 M. americanus 0.00 ± 0,,00 0,.40 + 0..40 0..35 8 .00 ±4..00 11..00 ± 4..00 0..65 Spherophoria spp. 0.00 ± 0.,00 0 .00 + 0.,00 13 .50 ±8..50 8..50 ± 6..50 0..69 Other syrphids 67 .80 ± 24.,14 108 .40 + 37..84 0,.39 6 .50 + 0,.50 5 .00 ± 4..00 0..74 Tephritidae 3.60 ± 1.60 0.00 + 0..00 0.05 54.50 ± 5.50 21.00 ± 5.00 0.05 Muscidae 4.00 ± 1.54 77.80 + 22..11 0.01 73.00 ± 49.00 128.00 ±30.00 0.44 Calliphoridae ]L. illustris 37.80 ± 7.66 93.80 + 5..31 0.01 208.50 ± 8.50 170.50 ± 3.50 0.05 B. silvarum 2.20 ± 0.58 0.00 + 0,.00 0.01 36.00 ± 7.00 36.50 ± 6.50 0.96 C_. vicina 0.00 ± 0.00 0.00 + 0,.00 9.00 ± 2.00 26.50 ± 1.50 0.02 P. regina 0.00 ± 0.00 0.00 + 0..00 70.50 ±12.50 71.00 ± 7.00 0.97 Other o O +

calliphorids 9.20 ± 2.80 0 0. o o 0.01 0.00 ± 0.00 0.00 ± 0.00 Other Calyptratae 1359.40+140.78 1790.00^221.81 0.14 1772.00±307.00 1542.00±629.00 0.72 Other Diptera 106.40 ±14.89 72.40 ±53.26 0.56 19.00 ± 1.00 9.00 ± 1.00 0.02 Total Diptera^ 1816.40+160.78 2280.00±315.54 0.23 2835.00±288.00 2267.50±761.50 0.77

00

^seasonal averages include Tachinidae 83 population peaks corresponded to the high densities of the second GCW generation during August. With few exceptions, there were no significant differences between the numbers or between the species of

Diptera trapped in the two types of wild parsnip plots.

Hymenoptera-Braconidae

The identified species of Braconidae trapped among wild parsnip in

1979 and 1980 are listed in Table 19. More than thirty taxa representing nine subfamilies were trapped during the two year study.

Microgastrinae and Euphorinae were the two subfamilies with the greatest number of species represented. Five of the trapped braconid species are known as parasitoids of GCW (Krombein et al., 1979).

The seasonal averages of Microgastrinae trapped among wild parsnip in 1979 and 1980 are listed in Table 20. Very few microgastrine specimens were trapped among wild parsnip without soybeans in 1979, but all the species, except A. depressariae. were represented in trap catches among soybean-associated wild parsnip. Significant differences between treatments occurred for Cotesia flaviconchae and Glyptapanteles militaris (Walsh). Glyptapanteles militaris was the most common microgastrine and occurred about forty times more often than the average of all the other species combined.

In 1980, roicrogastrines were trapped in relatively equal numbers

in both types of wild parsnip plots. There were no significant

differences between plot types for any of the species trapped in 1980,

and mean totals for Cotesia marginiventris were identical.

Glyptapanteles militaris was, again, the most commonly trapped TABLE 19. Species of Braconidae (Hymenoptera) trapped among wild parsnip in central Iowa during 1979 and 1980

Braconinae Microgastrinae Bracon spp. Apanteles depressariae (Muesebeck) Rogadinae A. forbesi Viereck Rogas nolophanae Ashmead® A. polvchrosidis Viereck Macrocentrinae A. pseudoglossae Muesebeck Macrocentrus grandii Goidanich Cotesia flaviconchae (Riley)a Opiinae Ç. junoniae (Riley) Euopius spp. Ç.. lunata (Packard) Alysiinae Ç. marginiventris (Cresson)a Chaenusa bergi (Riegel) C^. nemoriae (Ashmead) Coelinidea spp. Glyptapanteles militaris (Walsh) Dacnusa spp. Microgaster brittoni Viereck Cheloninae Protomicroplitis facetosa (Weed)® Ascogaster argentifrons (Provancher) Euphorinae A. quadridentata Wesmael Meteorus autographae Muesbeck® Chelonus spp. M. dimidiatus (Cresson) Blacinae M. rubens (Nees) Blacus spp. Perilitus coccinellae (Schrank) Aliolus spp. Schizoprymnus spp. Urosigalphus spp.

^parasitoid of Plathvpena scabra TABLE 20. Mean seasonal totals (X±SE) per plot of Microgastrinae (Hymenoptera: Braconidae) trapped among wild parsnip in central Iowa during 1979 and 1980

1979 1980

Parsnip Parsnip Taxon with Parsnip P>t with Parsnip P>t Soybeans alone Soybeans alone (5 plots) (5 plots) (2 plots) (2 plots)

A. depressariae 0..00 ±0,,00 0..00 + 0..00 3,,00 + 0..00 4,,50 ± 3,.50 0..71 A. forbesi 4,.20 ±0,,37 3,.60± 3..60 0,,87 1,,50 + 1.,50 0.,50 t 0,,50 0,.59 A. polychrosidis 0.,40 ±0,,40 0..00± 0,.00 0.,35 1.,00 ± 0,,00 0,,50 + 0.,50 0,.42 A. pseudoglossae 0,.80 ±0.,58 0,.00 + 0,.00 0,,20 1,,00 + 1,,00 0.,50 ± 0.,50 0,.70 + o O C. flaviconchae 1.,20 ±0,,49 0. 1+ 0,,00 0.,04 2.,50 1.,50 2,,00 ± 2.,00 0..86 C. iunoniae 0,,40 ±0.,40 0,.00± 0.,00 0.,35 0,,00 + 0,,00 0,,00 ± 0..00 C. lunata 0,,80 ±0,,58 0,.00 + 0.,00 0,.20 0.,50 + 0 .50 0,.00 ± 0,,00 0..42 C. marginiventris 3..40 ±1,.60 0..80± 0,.80 0..18 2.,50 + 0 .50 2 .50 ±0.,50 1,.00 C. nemoriae 1..00 ±0,.77 0,.00± 0,.00 0..23 3,,50 + 0 .50 2 .50 ± 0.,50 0,.29 G. militaris 40,.40 ±11,.20 0..00 + 0,.00 0..01 11.,50 + 3,,50 7,.00 ± 0.,00 0..32 M. brittoni 0..60 ±0,.40 0.,00± 0,.00 0,,17 0.,50 + 0.,50 1 .50 ±0,,50 0.,29 Microgaster spp. ±0, .00 + + 0..60 .22 1. 1 0,.63 0.,37 7.,00 1.,00 5 .00 ± 1,.50 0,,65 o o P. facetosa 0..20 ±0,,20 0. + 0,.00 0,,35 0,,00 + 0.,00 0,.50 ±0,,50 0,,42 + '+ o Other microgastrines 2..00 ±0,,63 0. O 0..00 0.,01 0,,00 0.,00 0..00 ±0.,00 ! 1 1 86 microgastrine, but it was trapped at lower frequencies in 1980 than in the previous year.

The fluctuations in microgastrine populations may be partly explained by the abundance and location of potential host populations.

All the taxa of Microgastrinae that were trapped among wild parsnip are reported as parasitoids of Lepidoptera (Krombein et al., 1979).

Apanteles depressariae was captured only in 1980. Densities were approximately the same in both types of wild parsnip plots. The reason for the absence of this species in 1979 is unknown, but the similarity in numbers between wild parsnip plots was expected because A. depressariae is a parasitoid of the parsnip webworm (Krombein et al.,

1979). Apanteles forbesi Viereck is noted as a parasitoid of armyworm and several cutworm species (Krombein et al., 1979). Similar trap catches in each plot type probably were due to the presence of noctuid hosts in associated grassy fencerow vegetation. The hosts of Apanteles polychrosidis Viereck are leaf rollers and leaf miners on woody plants

(Holland, 1968; Krombein et al., 1979). The parasitoid's similar seasonal averages between treatments suggest that the hosts may have been present in shrubby fencerow vegetation. Apanteles pseudoglossae

Muesebeck is specific to the noctuid Idia lubricalis (Geyer) (Krombein et al., 1979). The host generally inhabits fencerows or old fields

(Holland, 1968). The similar numbers of A. pseudoglossae between treatments suggest that the hosts were present in or near each type of wild parsnip plot.

Two of the collected species of Cotesia, C. flaviconchae and C. 87 marginiventris, are reported as parasitoids of GCW (Krombein et al.,

1979). They also attack Colias eurytheme and Trichoplusia ni, respectively. All three of these lepidopterans were collected in soybeans during the study, but the latter two generally were not abundant. Although reported as a parasitoid of GCW, C. flaviconchae was not reared from any of the GCW larvae collected during this study.

Cotesia flaviconchae was captured only in plots associated with soybeans in 1979. In 1980, however, its numbers were nearly identical in both types of wild parsnip plots. Mean weekly totals trapped per plot for C. flaviconchae revealed very low populations that fluctuated between 0 and

1 throughout the season (Figure 10).

Although C. marginiventris parasitized a substantial percentage of

GCW larvae collected in both years, seasonal trap collection totals did not show a distinct relationship to the presence of hosts in soybeans.

Seasonal peaks in late July of both years (Figure 11) further illustrate that C. marginiventris did not respond directly to GCW population increases (c.f.. Figure 2). This might be expected because the parasitoid is reported to attack at least 20 hosts other than GCW, many of which occupy fencerows as well as crop land.

The other three species of Cotesia trapped among wild parsnip are not associated with hosts that were collected in adjacent soybean fields. Cotesia iunoniae (Riley) is specific to the buckeye butterfly,

Junonia coenia (Hiibner) (Krombein et al., 1979), which feeds on several fencerow plants (Howe, 1979). Populations of C. iunoniae were very low in 1979, and absent in 1980. The hosts of Cotesia lunata (Packard) are 88

— parsnip and soybeans (N=5) 1979 -- wild parsnip alone (N=5)

1.0 + I

4J O 0.5

(Uu I a + TJ (U P4 a 0.0 4 u

CO a Jul 1 Aug 1 I Io 0) I parsnip and soybeans (N=2) ÇU CO I 1980 wild parsnip alone (N=2) I 1.0 + k (L) I I I + § 0.5

0.0 + I

Jul 1 Aug 1

FIGURE 10. Mean weekly totals of Cotesia flaviconchae (Hymenoptera: Braconidae) trapped per plot among wild parsnip in central Iowa during 1979 and 1980 89

—parsnip and soybeans (N=5) 1979 -- wild parsnip alone (N=5)

2.0 +

1.5 +

u o 1.0 +

u 0 a 0.5 + TD Q) (24 (QOu 0.0 + u u cn 1 Jul 1 Aug 1 d)a parsnip and soybeans (N=2) a M 1980 wild parsnip alone (N=2)

2.0 + 0) 1 1.5 + S 1.0 +

0.5 + \

0.0 + I - + - - Jul 1 Aug 1

FIGURE 11. Mean weekly totals of Cotesia marginiventris (Hymenoptera: Braconidae) trapped per plot among wild parsnip in central Iowa during 1979 and 1980 90 swallowtail butterflies, including the black swallowtail, or parsleywortn, Papilio polyxenes asterias Stoll (Krombein et al., 1979).

This host is found on numerous species of Urabelliferae, including wild parsnip (Howe, 1979; Lewis, 1980a). Populations of C. lunata were very low, and there were no statistically significant differences between wild parsnip plots. Cotesia nemoriae (Ashmead) parasitizes several geometrid pests, including cankerworm, Alsophila pometaria (Harris), and linden looper, Erannis tiliaria (Harris) (Krombein et al., 1979). The hosts inhabit fencerows and old fields (Holland, 1968). The densities of C. nemoriae indicate the presence of hosts in or near each type of wild parsnip plot in 1979 and 1980.

Glyptapanteles militaris was the microgastrine most commonly trapped in both years. The mean weekly totals per plot (Figure 12) illustrate the great variability of the parasitoid's population between years. The variable catches of G. militaris might be associated with the outbreaks of armyworm in 1979 (DeWitt, 1979a), and reduced presence of armyworm in 1980 (Stockdale, 1980a).

The catches of the rest of the Microgastrinae were very low.

Hosts of Microgaster brittoni Viereck are unknown, but hosts of other

Microgaster species include several species of Microlepidoptera.

Protomicroplit is facetosa is a GCW parasitoid, but other hosts include additional noctuids (Krombein et al., 1979). No P. facetosa, however, were reared from any of the GCW collected in this study.

Protomicroplitis facetosa adults were present in both types of parsnip plots, so the parasitoid was not solely associated with the presence of 91

— parsnip and soybeans (N=5) 1979 -- wild parsnip alone (N'=5)

30.0 +

15.0 +

0.0 +

Jul 1 Aug 1

parsnip and soybeans (N=2) 1980 wild parsnip alone (N=2)

30.0 +

15.0 +

0.0 +

-+ + + + +- -+ + + + +- Jul 1 Aug 1

FIGURE 12. Mean weekly totals of Glvptapanteles militaris (Hymenoptera: Braconidae) trapped per plot among wild parsnip in central Iowa during 1979 and 1980 92 hosts in soybeans. This also is suggested by the mean weekly totals

(Figure 13), in that the occurrence of trapped specimens did not coincide with peak GCW populations.

The seasonal average incidences per plot for species from the braconid subfamilies other than Microgastrinae are listed in Table 21.

The most common taxa in both years were Ascogaster quadridentata

Wesmael, Chaenusa bergi (Riegel), and unidentified Blacinae. In 1979, more specimens of every taxon, except C. bergi. were trapped among soybean-associated wild parsnip than in wild parsnip alone. Significant differences occurred for Macrocentrus grandii Goidanich, and the group

"other Blacinae." Furthermore, five times the average number of braconids (all taxa combined) were trapped among wild parsnip with soybeans than in wild parsnip alone. This difference between treatments was significant at the 0.01 level. In 1980, Bracon spp. and

Urosigalphus spp. were the only two collected species trapped in greater numbers in wild parsnip alone than among wild parsnip with soybeans.

All other trapped species in Table 21, except Perilitus coccinellae

(Schrank), were more common at soybean-associated wild parsnip.

Although none of the individual species showed significant differences between treatments in 1980, the mean seasonal total of braconids (all taxa combined) trapped among soybean-associated wild parsnip was about

2.5 times greater than that among wild parsnip alone. This difference between treatments was significant at the 0.03 level.

As suggested for Microgastrinae, fluctuations of braconid populations within and between years may be attributed to the varying 93

— parsnip and soybeans (N=5) 1979 -- wild parsnip alone (N=5)

1.0 +

4J 0 0.5 + iH a (Uu a 'O0) a o* 0.0 + 4J2 U) c Jul 1 Aug 1

1o 0) parsnip and soybeans (N=2) a w 1980 wild parsnip alone (N=2)

1.0 + M Q) 1 § IE 0.5 + A / \ / \ / \ / \ / \ / \ / \ / \ / \ 0.0 + _l \_ I

Jul 1 Aug 1

FIGURE 13. Mean weekly totals of Protomicroplitis facetosa (Hymenoptera: Braconidae) trapped per plot among wild parsnip in central Iowa during 1979 and 1980 TABLE 21. Mean seasonal totals (X±SE) per plot of braconid species (excluding Microgastrinae) trapped among wild parsnip in central Iowa during 1979 and 1980

1979 1980

Parsnip Parsnip Subfamily- with Parsnip P>t with Parsnip P>t Soybeans alone Soybeans alone (5 plots). (5 plots) (2 plots) (2 plots)

Braconinae Bracon spp. 1.20 ±0.73 0.00 i 0.00 0.14 0.00 ±0.00 0.50 ± 0.50 0.42 Rogadinae R. nolophanae 0.20 ±0.20 0.00 ± 0.00 0.35 0.00 ±0.00 0.00 ±0.00 Macrocentrinae grandii 3.40 ± 1.08 0.00 ± 0.00 0.01 0.50 ±0.50 0.00 ±0.00 0.42 Opiinae Euopius spp. 0.40 ±0.24 0.00 ± 0.00 0.14 1.50 ± 1.50 0.50 ±0.50 0.59 Alysiinae C^. bergi 7.60 ± 2.04 10.40 ± 3.59 0.51 9.00 ±3.00 5.50 ±2.50 0,64 Coelinidea spp. 0.40 ±0.40 0.00 ±0.00 0.35 0.00 ±0.00 0.00 ±0.00 Dacnusa spp. 0.00 ±0.00 0.00 ±0.00 4.50 ±2.50 0.00 ±0.00 0.21 Cheloninae o A. argentifrons 0,.20 ± 0,,20 0..00 ± 0 00 0. 35 0..50+ 0..50 0.00 ±0 O 0.42 o 00 A. quadridentata 4,,00 ± 1,,22 1..60 ± 03 0. 17 14, 1+ .50 4.50 ±3.50 0.39 1 1 o o o Chelonus spp. 0..20 ± 0.,20 0,.00 ± 0 00 0.35 0. + ,00 0.00 ±0.00 Blacinae Blacus spp. 0,,80 ± 0,,58 0..00 ± 0 00 0.21 0,.50 + 0..50 0.00 ±0.00 0.42 Aliolus spp. 0. 04 + 0.,04 0..00 ± 0 00 0. 34 0,.00 ± 0..00 0.00 ±0.00 1 Urosigalphus spp. 0..00 ± 0.,00 0,.00 ± 0 00 0,.00 ± 0..00 2.00 ±20 .00 0.42 — 1 o o 0 t other Blacinae 10..00 ± 4.,26 0..00 ± 0 00 0.04 115..50±23. .50 31. + .00 0.10 Euphorinae M. autographae 0,.80± 0,,49 0..00 ± 0 00 0. 14 0,.50± 0,.50 0.00 ±0.00 0.42 M. dimidiatus 0.. 60 ± 0,,60 0..00 ± 0 00 0.35 5..00 ± 4,.00 0.50 ±0.50 0.38 M. rubens 1, 80± 0,,92 0,.00 ± 0 00 0.08 5, 50± 1..50 0.50 ±0.50 0.08 P. coccinellae 0..40± 0.,40 0..00 ± 0 00 0.35 2,.50+0. .50 2.50 ±2.50 1.00 other Euphorinae 0..20± 0,.20 0,.00 ± 0 00 0. 35 7..50± 1,.50 1.00 + 1.00 0.07 Other braconids 11,.80± 3,,10 3,.40 ± 2 68 0.07 16..50± 2..50 36.50 ±0.50 0.04 Total Braconidae^ 101, 00± 8,.26 20,.80 ± 9 97 0.01 278..50±20. .50 112.0±20 .00 0.03

^includes Micfogastrinae 96

abundance and location of host populations. The only identified trapped species of Rogadinae, and the most important parasitoid of GCW collected

in the soybean fields during this study, was R. nolophanae. This

parasitoid is specific to two hosts; GCW and the noctuid. Balsa malana

(Fitch) (Krombein et al., 1979). Balsa malana occurs in the eastern

U.S. and Canada, west to Kansas, and its host is apple (Forbes, 1954).

Few apple trees were located in the immediate area of the plots,

therefore, the populations of R. nolophanae probably were responding

primarily to GCW. Only a single specimen of R. nolophanae was trapped

among wild parsnip during either year. This specimen was trapped during

the GCW outbreak in 1979. The lack of R. nolophanae was unexpected,

especially among wild parsnip associated with soybeans, because large numbers of Rogas adults were present in adjacent soybean fields. The

trapping results may be due to the adult behavior of this species.

Rogas nolophanae is reported as a host-fluid feeder and not a nectar

feeder (Lentz and Pedigo, 1974). Thus, it may not visit flowers in

general or wild parsnip in particular. The paucity of captured

specimens supports this contention.

A small number of specimens of the subfamily Braconinae were

captured among wild parsnip. All were Bracon spp., which are noted as

parasitoids of numerous larval Coleoptera and Lepidoptera (Krombein et

al., 1979). The populations were very low and no significant

differences were detected between plots.

The only identified species of Macrocentrinae captured among wild

parsnip was M. grandii. It is specific to European corn borer (Krombein 97 et al., 1979) and attacks second and third instar larvae (Clausen,

1956). The higher catches among soybean-associated wild parsnip probably were due to the proximity of corn fields near the soybeans, or perhaps to rotation between the two crops in the same fields. The absence of M. grandii among wild parsnip alone confirms its host dependency, because these plots were isolated and located some distance from either corn or soybeans. Mean weekly totals per plot for M. grandii (Figure 14) illustrate that densities peaked during the first week in July in 1979 and during the last week of June in 1980. These peaks corresponded with the presence of first generation European corn borer larvae in each year (Stockdale, 1979a, 1980b, 1980c).

Euopius spp. are recorded as parasitoids of various grass- inhabiting Diptera. Similar low densities in the two types of wild parsnip plots indicate the presence of hosts in or near both types of plots. C. bergi, Coelinidea spp., and Dacnusa spp. are parasitoids of agromyzid leaf miners, some of which commonly are found on wild parsnip and related umbellifers (Griffiths, 1973). The insignificant effect of soybean presence on Alysiinae incidence suggests that these parasitoids probably are attacking hosts in the fencerows.

The Blacinae are known as parasitoids of Coleoptera. Populations of Blacus spp., Aliolus spp., and Urosigalphus spp. were low among soybean-associated wild parsnip, and these braconids, except the last mentioned, were absent from wild parsnip alone. The group "other

Blacinae" was the most commonly collected taxon of Braconidae in both years. Catches were extremely high in 1980, and populations peaked 98

— parsnip and soybeans (N=5) 1979 -- wild parsnip alone (N=5)

2.0 +

1.5 + I I 4J O 1.0 + iH CU U Q) CX 0.5 + TJ 0) Cu s- 0.0 + u U I w -+•-----+- +- Jul 1 Aug 1 I I0

0.5 + I

0.0 + I -+"• -- -+- - - -+ + +- Jul 1 Aug 1

FIGURE 14. Mean weekly totals of Macrocentrus grandii (Hymenoptera: Braconidae) trapped per plot among wild parsnip in central Iowa during 1979 and 1980 99 during the third week in July in both years (Figure 15). Although this group was composed of a number of blacines, most of the specimens collected were suspected as Schizoprymnus spp. A common species of this genus in midwest is S. phillipsi Viereck. Its known host is the mordellid beetle Mordellistena andrae ustulata LeConte, which is generally distributed throughout the United States (Arnett, 1960).

Numerous mordellids were collected in trap catches, especially in 1980, but these were not identified to species.

Five taxa of Euphorinae were trapped among wild parsnip. Meteorus

autographae Muesebeck is noted as a parasitoid of GCW, armyworm, T. ni and various species of cutworms (Krombein et al., 1979). M. autographae was present only among soybean-associated wild parsnip. Furthermore,

this parasitoid seemed to respond to the presence of GCW, because it was trapped only during peak GCW levels in both years (Figure 16). This relationship is supported by the fact that M. autographae was reared

from collected GCW during this same time. As with R. nolophanae, very

few specimens were collected, but the captures coincided with the GCW outbreak in 1979.

No specimens of M. hyphantriae, the only species of Meteorus

reared from GCW by Lentz and Pedigo (1975), were captured on the traps.

M,. autographae is the species associated with GCW in several surrounding

states (Harper et al., 1983), whereas M. hyphantriae has been identified

only from Iowa.

Meteorus dimidiatus (Cresson), a parasitoid of several leaf

rollers, a pyralid and a noctuid (Krombein et al., 1979), was present. 100

— parsnip and soybeans (N=5) 1979 -- wild parsnip alone (N=5) I 4.0 +

3.0 + I I 2.0 + I w m 1 cx 1.0 + XI

CO -4------+- Aug 1

Ia Q) parsnip and soybeans (N=2) (Xw wild parsnip alone (N=2) iw o 40 k 0 1 30

20

10

Jul 1 Aug 1

FIGURE 15. Mean weekly totals of selected Blacinae (Hymenoptera: Braconidae) trapped per plot among wild parsnip in central Iowa during 1979 and 1980 101

—parsnip and soybeans (N=5) 1979 -- wild parsnip alone (N=5)

1.0 +

0.5 +

0.0 +

-+ + + + + + + +- Jul 1 Aug 1

parsnip and soybeans (N=2) 1980 wild parsnip alone (N=2)

1.0 +

0.5 +

0.0 +

Jul 1 Aug 1

FIGURE 16. Mean weekly totals of Meteorus autographae (Hymenoptera: Braconidae) trapped per plot among wild parsnip in central Iowa during 1979 and 1980 102 in both types of wild parsnip plots. Although two species of tortricid leaf rollers were collected from adjacent soybean fields, M. dimidiatus is reported to attack only the uncommon Xenotemna pallorana. Meteorus rubens (Nees) populations were not significantly different at the 0.05 level between plot types, but approached that statistical standard (P =

0.08) in both years. The recorded hosts of M. rubens include numerous noctuids, including cutworms, some of them associated with corn

(Krombein et al., 1979), and so the presence of M. rubens may be due to the proximity of corn fields, rather than soybeans. The mean catch weekly totals per plot of M. rubens are shown in Figure 17. The parasitoid was present in trap catches in July and August of 1979. In

1980, specimens were absent until the second week of July, but were present through the end of the season. Two peaks of activity seemed to occur in each year.

Perilitus coccinellae (Schrank), a parasitoid of Coccinellidae, was present in both types of wild parsnip plots. Four of its known hosts

(Krombein et al., 1979), Coccinella septempunctata L., Coleomegilla maculata Timberlake, Cycloneda sp., and Hippodamia convergens Guerin-

Meneville, also were among the trap catches at wild parsnip plots.

In summary, the results of the trapping studies indicate that numerous braconids were trapped among wild parsnip. Nine subfamilies and more than 30 lesser taxa were represented. The Microgastrinae and

Euphorinae contained the most species. In each year, the total number of trapped braconids was significantly greater in soybean-associated wild parsnip than in wild parsnip alone. Significant differences 103

— parsnip and soybeans (N=5) 1979 -- wild parsnip alone (N=5)

3.0 +

4Jo 1.5 + 1-4 eu u

1c

1.5 +

0.0 + I .

Jul 1 Aug 1

FIGURE 17. Mean weekly totals of Meteorus rubens (Hymenoptera: Braconidae) trapped per plot among wild parsnip in central Iowa during 1979 and 1980 104

between plot types occurred in 1979 for catches of C. flaviconchae. G.

militaris, M. grandii, and unidentified Blacinae. No significant

differences were found for the remaining species in 1979 or for any of

the species in 1980. Populations of the commonly trapped braconids were

highly variable between years, possibly because of numeric variation in

host populations. In most cases, these braconids could have been

parasitoids of corn pests and might have responded to changes in their

respective host populations. Apanteleg forbesi, G. militaris, M.

grandii, and M. rubens are four important parasitoids of lepidopterous

corn pests that were trapped among wild parsnip. Corn fields were

nearby but not immediately adjacent to the fencerows where trapping was

conducted.

Five species known to attack GCW were among trap catches, but all

were present in relatively low numbers. The incidence of M. autographae

and R. nolophanae, however, did coincide with population peaks of GCW.

The levels of C. flaviconchae. C. marginiventris, and P. facetosa did

not coincide with GCW peaks, possibly because these braconids may have

been associated with any of a number of hosts other than GCW. Cotesia

flaviconchae in 1979 was the only potential GCW parasitoid that occurred

in significantly different numbers between parsnip plot types. In

general, wild parsnip had no effect on populations of GCW braconid

parasitoids. 105

Hymenoptera-Ichneumonidae

Because of the difficulty of ichneumonid identification, trapped specimens not suspected as GCW parasitoids were keyed only to subfamily

(Townes, 1969). The four taxa of trapped Ichneumonidae that are known as GCW parasitoids are listed in Table 22. Vulgichneumon brevicinctor

(Say) and Mesochorus spp. are recorded as .a parasitoid and hyperparasitoid of GCW, respectively (Krombein et al., 1979). The trapped Coccygomimus spp., however, were not Coccygomimus aequalis

(Provancher) or C. annulipes (Brulle), two species that are known as GCW pupal parasitoids (Bechinski and Pedigo, 1983).

TABLE 22. Ichneumonid taxa known as green cloverworm associates and trapped among wild parsnip in central Iowa during 1979 and 1980

Pimplinae Itoplectis conquisitor (Say) Coccygomimus spp. Ichneumoninae Vulgichneumon brevicinctor (Say) Mesochorinae Mesochorus spp.

The seasonal average numbers of the various ichneumonid subfamilies and species trapped per plot are listed in Table 23. The most common groups were Cryptinae and Campopleginae. In 1979, they each occurred among soybean-associated wild parsnip about ten times more frequently than did any of the other subfamilies. With the exception of 106

Labeninae, Ichneumoninae, and Metopiinae, ichneumonids were trapped among wild parsnip with soybeans in greater numbers than among wild parsnip alone. Significantly larger numbers of Coccygomimus spp.,

Cryptinae and Ophioninae occurred among soybean-associated wild parsnip.

About twice the number of total ichneumonids were trapped among wild parsnip with soybeans as among wild parsnip alone, but the means per plot were not significantly different.

About 50% of the ichneumonid groups present in 1979 were absent in

1980. Again in 1980, Cryptinae was the most commonly identified subfamily. With the exception of Ichneumoninae, Banchinae and

Mesochorinae, more ichneumonids of each taxon were trapped among wild parsnip associated with soybeans than among wild parsnip alone. A significant difference occurred between treatments only for Banchinae.

Although season-long nearly twice as many ichneumonids were collected among soybean-associated wild parsnip as among parsnip alone, there was no statistical difference between the treatment means.

Itoplectis conquisitor (Say) was present only at soybean-associated wild parsnip in 1979. This species is known as a parasitoid of about 75 hosts (Krombein et al., 1979), but no specimens of the parasitoid were reared during this study. Therefore, the parasitoid probably was not associating specifically with hosts in soybeans.

Hosts of V. brevicinctor include GCW, T. n_i, armyworm, and 0. nubilalis (Krombein et al., 1979). The parasitoid was absent from plots of wild parsnip alone, but the numbers trapped in the other plots were so low that a significant difference between treatments was not TABLE 23. Mean seasonal totals (X±SE) of ichneumonid taxa trapped per plot among wild parsnip in central Iowa during 1979 and 1980

1979 1980

Parsnip Parsnip Taxon with Parsnip P>t with Parsnip P>t Soybeans alone Soybeans alone (5 plots) (5 plots) (2 plots) (2 plots)

Pimplinae I. conquisitor 1,.00 + 0..77 0 .00 + 0..00 0..23 0,,00± 0,.00 0,.00 ±0,.00 Coccvgomimus spp. 1.,40 + 0,.50 0 .00 + 0,.00 0,.03 0.,50± 0,.50 0,.00 ±0..00 0..42 Labeninae 0..20 + 0..20 0.40 + 0..40 0,.67 0,,00± 0,.00 0 .00 ±0,.00 Tryphoninae 0,.20 + 0,.20 0..00 + 0..00 0..34 0..00 + 0,.00 0,.00 ±0,.00 Cryptinae 14,.40 + 2,.58 3 .20 + 1..98 0..01 11.,00± 2 .00 3..50 ±0..50 0,.06 Ichneumoninae 1..40 + 0..74 2,.80 + 2..80 0,.65 0, 00± 0 .00 0,.50 ±0,.50 0,.42 V. brevicinctor 0..20 + 0..20 0 .00 + 0..00 0..35 1.,50± 1,.50 0,.00 ±0,.00 0,.42 Metopiinae 2..00 ± 1..00 4.40 + 2..69 0,.43 1,,50± 1,.50 0..00 ±0..00 0..42 Banchinae 1,.80 + 0..73 1,.60 + 1,.60 0..91 0.,00± 0,.00 2,.50 ±0,.50 0..04 Ctenopelmatinae 0..20 ± 0..20 0 .00 + 0,,00 0..34 0.,00± 0,.00 0..00 ±0,.00 C ampop1eginae 13..20 + 5..90 4,.60 + 1..94 0.,20 2.,00± 2,.00 2,.00 ±1,.00 1..00 Cremastinae 3,.00 + 1..84 0 .00 + 0,,00 0..14 4.,00± 3..00 1,.00 ±0..00 0,.42 Ophioninae 0..80 + 0..20 0 .00 + 0,,00 0,,01 0,,00± 0,.00 0,.00 ±0..00 Mesochorinae Mesochorus spp. 1,,60 ± 0,.40 0 ,80± 0,,80 0,,39 0,,50± 0..50 1..00 ±0.00 0..42 Diplazontinae 0,,20+0, .20 0.,00± 0,,00 0,,35 0.,00 + 0..00 0..00 ±0.00 Oxytorinae 0.,80± 0,.58 0..00± 0,,00 0.,21 0.,00 + 0..00 0..00 ±0.00 Other ichneumonids 3,,40± 1..32 2..60 + 2,,60 0.,79 1.,50± 0..50 2..50 ± 1.50 0..59 Total ichneumonids 45.,80±10, .55 20..40± 8.,35 0.,10 22..50 ± 0..50 13..00 ±3.00 0..09 108 detected. Mean weekly totals plotted in Figure 18 demonstrate that capture of the single specimen in 1979 coincided with the high GCW populations. Parasitoid catches in 1980 were not correlated with high

GCW population levels.

All known species of Mesochorinae are hyperparasitoids (Krombein et al., 1979). The genus Mesochorus is large with worldwide distribution. Some of the common known hosts are Apanteles spp.,

Cotesia spp., Meterous spp., and Microgaster spp. (Krombein et al.,

1979). Mean weekly catches (Figure 19) were low in 1979 and 1980.

Cryptinae is the largest ichneumonid subfamily, and the greatest number of collected ichneumonids in each year were representatives of this group. Mean weekly totals of Cryptinae per plot (Figure 20) illustrate population peaks during the first week of July in 1979, but peaks occurred during June and July of 1980.

Campopleginae includes the second largest group of trapped ichneumonids. Although the GCW parasitoid Sinophorus validus (Cresson) is classified in this group, its presence among the trap catches is unconfirmed because the representatives of this group were not identified to species. The mean weekly totals per plot in Figure 21 illustrate a population peak that may correspond to the armyworm outbreak in 1979. Populations were much lower in 1980.

The other ichneumonid subfamilies were trapped among wild parsnip in low numbers. Trends and differences among these groups, therefore, are difficult to demonstrate.

The results of the trapping study demonstrate that fourteen 109

— parsnip and soybeans (N=5) 1979 -- wild parsnip alone (N=5)

1.0 +

0.5 +

(Uu CL TJ (U a a CO 0.0 + •uu (A d Jul 1 Aug 1 .1 a o> parsnip and soybeans (N=2) a- 1980 wild parsnip alone (N=2) CO

1.0 + M 0) I c ta r 0.5 +

0.0 + I -+ + + + + + + + +- Jul 1 Aug 1

FIGURE 18. Mean weekly totals of Vuleichneumon brevicinctor (Hymenoptera: Ichneumonidae) trapped per plot among wild parsnip in central Iowa during 1979 and 1980 110

-parsnip and soybeans (N=5) 1979 -- wild parsnip alone (N=5)

1.0 +

4JO 0.5 + rHqu 0)u CL

CO d Jul 1 Aug 1 Io 0) parsnip and soybeans (N=2) a 1980 wild parsnip alone (N=2) CO M-l 0 1.0 + V u Q) 1 + \ 5 X 0.5 + »

0.0 +

Jul 1 Aug 1

FIGURE 19. Mean weekly totals of Mesochorinae (Hymenoptera: Ichneumonidae) trapped per plot among wild parsnip in central Iowa during 1979 and 1980 Ill

-parsnip and soybeans (N=5) I 1979 -- wild parsnip alone (N=5)

5.0 + I I + I I 4Jo 2.5 + I uOJ a T) Q) Gu CX to 0.0 + ' U

CO I Jul 1 Aug 1 0)ÇJ parsnip and soybeans (N=2) a CO 1980 wild parsnip alone (N=2) iw o 5.0 + Ï-4 QJ I rO I + g S 2.5

0.0 +

Jul 1 Aug 1

FIGURE 20. Mean weekly totals of Cryptinae (Hymenoptera: Ichneumonidae) trapped per plot among wild parsnip in central Iowa during 1979 and 1980 112

— parsnip and soybeans (N=5) I 1979 -- wild parsnip alone (N=5) I 10.0 +

4J O 5.0

u

0 1.0 U Q) 1 C § IS 0.5

0.0

Jul 1 Aug 1

FIGURE 21. Mean weekly totals of Campopleginae (Hymenoptera: Ichneumonidae) trapped per plot among wild parsnip in central Iowa during 1979 and 1980 113 subfamilies of Ichneumonidae were represented in the trap catches, but that V. brevicinctor was the only definitive GCW parasitoid. In general, more ichneumonids, taxon by taxon, were trapped among soybean- associated wild parsnip than among wild parsnip alone. The total number of total ichneumonids trapped among wild parsnip with soybeans was nearly twice that among wild parsnip alone. In 1979, Cryptinae and

Campopleginae were the most common groups, but in 1980, only Cryptinae had high populations. Only Cryptinae exhibited consistently significant or near significant differences in both years in mean catches between plot types. The significant differences that occurred for other subfamilies are questionable because of the small sample sizes.

Hymenoptera-Parasitica

The families and identified species of Hymenoptera-Parasitica

(excluding Ichneumonoidea) trapped among wild parsnip in 1979 and 1980

are listed in Table 24. None of the identified Parasitica are known

parasitoids or hyperparasitoids of GCW.

The mean seasonal totals of Chalcidoidea trapped per plot among wild parsnip in 1979 and 1980 are listed in Table 25. In 1979, the most

common family was Eulophidae, of which Tetrastichus spp. composed the

most common taxon. More families of chalcidoids were trapped among wild

parsnip associated with soybeans than among wild parsnip alone.

Significant differences between treatments occurred for pteromalids,

some perilampines, a eurytomid sp., some eulophids, and some mymarids.

In 1980, Eulophidae, Perilampinae, and Eurytomidae were the most common

taxa. Although more specimens of each taxon were trapped among soybean- TABLE 24. Taxa of Hymenoptera-Parasitica (excluding Ichneumonoidea) trapped among wild parsnip in central Iowa during 1979 and 1980

Chalcidoidea Cynipoidea Torymidae Evanioidea Pteromalidae Evaniidae Perilampus fulvicornis Ashmead Hyptia thoracica (Blandard) P. hyalinus Say Gasteruptiidae Eurytomidae Proctotrupoidea Eurytoma spp. Proctotrupidae Chalcididae Diapriidae Brachymeria spp. Psilus colon Say Eupelmidae Scelionidae Encyrtidae Trissolcus spp. Ooencyrtus spp. Platygastridae Pentacnemus bucculatricis Howard Inostemma spp. Eulophidae Platygaster spp. Tetrastichus spp. Ceraphronoidea Horismenus spp. Ceraphronidae Mymaridae Ceraphron spp. Polynema spp. Megaspilidae Trichogrammatidae Megaspilus spp. 115 associated wild parsnip than among parsnip alone, a preference was demonstrated statistically only for Pteromalidae and the eulophid

Tetrastichus spp. Of the four species groups tallied by sex, only

Eurytoma sp. A had fewer females trapped than males. Tetrastichus spp.,

Horismenus spp., and Polynema spp. had more females than males trapped among wild parsnip.

The mean seasonal totals of Parasitica (excluding Ichneumonoidea and Chalcidoidea) trapped per plot among wild parsnip in 1979 and 1980 are listed in Table 26. In 1979, Scelionidae was the most commonly trapped family. Although Trissolcus spp. were commonly trapped identifiable scelionids, the high total number for the family was due to the unidentified scelionid species. Every family and species except

Proctotrupidae was more commonly trapped among soybean-associated wild parsnip than among wild parsnip alone. Significant differences were observed only for Scelionidae, Platygastridae, and Ceraphronidae. In

1979, more than three times the number of Hymenoptera-Parasitica

(excluding Ichneumonoidea) were trapped among wild parsnip associated with soybeans as among wild parsnip alone. The treatment difference was not significant at the 0.05 level, but it approached that statistical standard (P = 0.06).

In 1980, Scelionidae, Evaniidae, and Cynipoidea were the most common groups. Every family and species except Platygaster spp. occurred more often (or as often) among wild parsnip associated with soybeans than among wild parsnip alone; however, none of the catches differed statistically between the two treatments. The total seasonal TABLE 25. Mean seasonal totals (l(iSE) of Chalcidoidea (Hymenoptera) trapped per plot among wild parsnip in central Iowa during 1979 and 1980

1979 1980

Parsnip Parsnip Species with Parsnip P>t with Parsnip P>t Soybeans alone Soybeans alone (5 plots) (5 plots) (2 plots) (2 plots)

Torymidae 1,.40 + 0..08 0..00 + 0..00 0..07 1 .00 ± 1..00 0,.00± 0..00 0..42 Pteromalidae^ 29.,60 + 10.• .12 1..80 + 1..80 0..03 68.00 ± 0..00 21 .50± 4..50 0..01 Perilampinae 12..80 + 3..84 0..00 + 0..00 0..11 203 .50± 67..50 16..00±11. .00 0..39 P. fulvicornis 1..00 + 0,.77 0..00 + 0..00 0..23 195 .00+ 61..00 13..50+10. .50 0..10 P. hvalinus 9..80 + 2.,44 0..00 + 0..00 0..01 2 .50 ± 1..50 1..50± 0..50 0..59 other perilampines 2,.00 + 0..63 0..00 + 0..00 0..01 6 .00 ± 5..00 2..00± 0..00 0..50 Eurytomidae 34..40 + 9.,06 12..20 + 5.,78 0,.07 118 .00± 55..00 20..50± 0..50 0..21 Eurvtoma sp. A 24..40 + 7.,35 11.,20 + 5,,00 0..17 102 .50± 48..50 14..50± 0..50 0..21 males 14..80 + 3.,61 9.,20 ± 3.,97 0..33 48,.00+ 25..00 8..50± 0..50 0..25 females 8.,20 + 3,,75 2,,00 + 1.,38 0..16 40 .50+ 11,.50 6..00+0. .00 0..10 unsexed 1,,40 + 1..67 0..00 ± 0,,00 0..26 14.00± 12..00 0..00+0. .00 0..37 Eurvtoma sp. B 10..00 + 2..17 1..00 + 1.,00 0..01 15 .50 ± 6..50 6 .00 ± 1..00 0..29 Chalcididae 0..40 + 0..24 0..00 + 0..00 0..14 3 .00 ±3..00 1 .00+0..00 0..57 Brachvmeria spp. 0..20 + 0..20 0..00 + 0..00 0..35 0.00 ± 0..00 1..00 ± 0..00 other chalcidids 0..20 ± 0..20 0..00 + 0..00 0..35 3 .00 ± 3..00 0 .00 ± 0..00 0..42 iiu^elinidae 2 .20 ' 1 .20 .00 • 2.00 0 .'J 3 0.50 1 0. 50 0.,50 + 0.50 1..00 Encyrtidae 42,.20 ±16,.36 75,.60 ±51. 00 0,.55 17.50 + 6.50 17. 00±10 .00 0..97 Eulophidae 331 .80^tl37. .64 47,.80 ±33.65 0.08 458.50±147. 50 50. 00 ±9 .00 0..11 Tetrastichus spp. 296..20±120, .44 45..60 ±31.46 0,.08 442.00±142. 00 44. 00 ±6.00 0..01 males 87 .80 ±45,.04 20,.00 ± 10. 61 0,.18 123.00 +32. 00 15. 00 ±2.00 0..08 females 202..40 ±79..06 24..60 ±20. 22 0..06 317.50±110. 50 29.00 ±4.00 0.. 12 unsexed 6..00 ± 1..30 1,.00 ± 1. 00 0,.02 7.50 + 0.50 0.00 ±0.00 0.. 10 Horismenus spp. 27..60 ±18..63 2..20 ± 2. 20 0..21 9 .00 + 4.00 5. 00 ±2.00 0..47 males 9..20 ± 6..48 2..20 ± 2. 20 0..34 1.00 + 1.00 1. 00 ±1.00 1..00 females 12..40 ± 7..68 0..00 ± 0.00 0..15 3.00 + 1.00 2.50 ±0.50 0..69 unsexed 6..00 ± 4..50 0..00 ± 0. 00 0..22 5 .00 + 2.00 1.50 ±1.50 0..30 other eulophids 8..00 ± 1..51 0..00 ± 0. 00 0..01 7.50 + 1. 50 1.00 ± 1.00 0..07 Mymaridae 12..60 ± 2..36 5..20 ± 3. 22 0..10 15 .50 + 3.50 9.00 ±5 .00 0.,40 Polynema spp. 8,.20 ± 2..26 1,.20 ± 0.97 0..02 4.00 + 1.00 4.50 ± 2.50 0..87 males 1..20 ± 0..59 0..40 ± 0.40 0..29 2.00 + 0.00 0. 50 ± 0.50 0.. 10 females 6,.60 ± 2..25 0..60 ± 0.40 0..03 2.00 + 1.00 4.00 ± 2.00 0..47 unsexed 0..40 ± 0..24 0..20 ± 0.20 0..54 0.00 + 0.00 0.00 ± 0.00 other mymarids 4,.40 ± 1..25 4..00 ± 2.39 0,.89 11 .50 + 2.50 4.50 ± 2.50 0..19 Trichogrammatidae 1..20 ± 0..37 3..20 ± 1. 59 0..26 0.50 + 0.50 0.50 ± 0.50 1..00

^excluding Perilampinae TABLE 26. Mean seasonal totals (Î(±SE) of Hymenoptera-Parasitica other than Ichneumonoidea and Chalcidoidea trapped per plot among wild parsnip in central Iowa during 1979 and 1980

1979 1980

Parsnip Parsnip Species with Parsnip P>t with Parsnip P>t Soybeans alone Soybeans alone (5 plots) (5 plots) (2 plots) (2 plots)

Cynipoidea 36,,80 + 7,,06 17 .80 + 8.68 0. 13 74.50 ± 24.50 34,.00±12, .00 0,.28 Evaniidae H. thoracica 6.,80 + 4.,35 0.00 + 0.00 0. 15 120 .00:ill? .50 2,.00 ±2,.00 0,.42 Proctotrupidae 0,,40 + 0.,24 0.60 + 0.60 0. 77 2.00 ± 1.00 2,.00 ±2,.00 1,.00 Diapriidae 10,.20 + 1..32 4.20 + 2.94 0. 10 17.50 ± 6 .50 9,.50 ±5,.50 0 .45 Scelionidae 71,.00 + 11..10 17 .80 + 9.35 0.01 182.00 ± 41.00 47,.00±14, .00 0 .09 Trissolcus spp. 26,.60 + 9,.26 6 .40 + 3. 14 0.07 39 .00 ± 1.0.00 12,.50 ±5,.50 0 .15 other scelionids 44,,40 + 10. 38 11.40 + 6.28 0.03 143.00 ± 31.00 34,,50 ±8,.50 0,.08 Platygastridae 34.,80 + 6,.03 5.60 + 5.60 0.01 29 .50 ± 3 .50 33,.00±16, .00 0..85 Inostemma spp. 2,,00 + 1,.26 0.00 + 0.00 0. 15 1.00 ± 1.00 0,.00 ±0,.00 0 .42 Platveaster spp. 32,.80 + 5..74 5.60 + 5.60 0.01 28.50 ± 4.50 33,.00^16, .00 0 .81 females 17,.20 + 3,.38 2.60 + 2.60 0.01 20.00 ± 4.00 13,.50 ±5,.50 0 .44 unsexed 15..60 + 3.,35 3.00 + 3.00 0.02 8.50 ± 0.50 19,,50±10, .50 0,.40 Ceraphronidae Ceraphron spp. 10,.40 + 3,.12 1.00 + 0. 77 0.02 8.00 ± 2.00 6,,50 ±3,.50 0,.75 males 3,.40 + 1,.20 0.20 ± 0. 20 0.03 2.00 ± 2 .00 1,,00 ± 1,.00 0,.70 females 6..00 + 2,.02 0.80 + 0.80 0.04 5 .50 ± 3 .50 5,,00+4 .00 0,.93 unsexed 1,.00 + 0,.31 0.00 + 0.00 0.01 0.50 ± 0.50 0,,50 ±0,.50 1,.00 Other Hymenoptera 7,.20 + 2,.63 0.00 + 0.00 0.03 1.50 ± 0 .50 1,,50 + 1,.50 1,.00 Total Parasitica^ 649,.80: 1:170, .38 198.00+123. 99 0.06 1229 .001343 .00 293,,50+71. .50 0.. 12

^includes Chalcidoidea (Table 25) and Bethyloidea (Table 28) 119 average of Hymenoptera-Parasitica (excluding Ichneumonoidea) trapped per plot among soybean-associated wild parsnip was about four times greater than that among wild parsnip alone, but the seasonal averages were not statistically different.

As suggested for parasitic Diptera, great fluctuations of parasitic Hymenoptera populations between years might be associated with the presence or absence of large host populations. For example, the perilampine, Perilampus fulvicornis Ashmead is known as a parasitoid of numerous Braconidae, including Apanteles spp., Ascogaster spp., Cotesia spp., and Meteorus spp. (Krombein et al., 1979). Perilampus hyalinus

Say is known as a parasitoid of Lespesia spp., Apanteles spp., Cotesia spp., and Meteorus spp. Many of these hosts were present in the field in 1979 and 1980, and so it is possible that the changing incidences of the perilampines were tied to the changing availabilities of their corresponding hosts. The seasonal trends in Figure 22 illustrate that the highest P. fulvicornis populations occurred in August 1980.

As shown in Figure 23, P. hyalinus exhibited its greatest numbers in

July of both years.

The complete absence of Torymidae among wild parsnip alone and the significantly higher numbers of Pteromalidae (excluding Perilampinae)

trapped among soybean-associated wild parsnip indicate that these

parasitoids may have had hosts associated with soybean fields. The mean

weekly totals of Pteromalidae (excluding Perilampinae) trapped per plot

(Figure 24) graphically show the higher abundance of this group in

soybean-associated wild parsnip. The highest incidence of pteromalids 120

— parsnip and soybeans (N=5) 1979 -- wild parsnip alone (N=5)

5.0 + I I +

•P o 2.5 + r—j I u I P.Q) + T) I Q) tx I P. CO 0 + u 4J I -+- - + - - - - }-- « g Aug 1 ao Q) parsnip and soybeans (N=2) a CO wild parsnip alone (N=2)

100 % "i

: s 50

0 +

-+- -+ + +- -+ + +- Jul 1 Aug 1

FIGURE 22. Mean weekly totals of Perilampus fulvicornis (Hymenoptera: Pteromalidae: Perilampinae) trapped per plot among wild parsnip in central Iowa during 1979 and 1980 121

—parsnip and soybeans (N=5) 1979 -- wild parsnip alone (N=5)

5.0 +

+

2.5 +

0.0 +

+ + + + + + + + +- - Jul 1 Aug 1

parsnip and soybeans (N=2) 1980 wild parsnip alone (N=2)

5.0 +

2.5 +

0.0 + '

Jul 1 Aug 1

FIGURE 23. Mean weekly totals of Perilampus hvalinus (Hymenoptera: Pteromalidae: Perilampinae) trapped per plot among wild parsnip in central Iowa during 1979 and 1980 122 occurred during the last week of June in 1980. Mean seasonal totals were lower in 1979.

Although eurytotnids were more abundant among soybean-associated wild parsnip, they were present in both types of plots, and so were not exclusively associated with soybean-inhabiting hosts. Populations of

Eurytoma sp. A were lower in 1979 than in 1980, but catches peaked in early July in each year (Figure 25).

Trap catches of Chalcididae and Eupelmidae were too low for valid statistical tests. Although the genus Brachymeria was represented in trap catches, the species collected in this study was not Brachymeria ovata (Say), a known parasitoid of GCW pupae (Bechinski and Pedigo,

1983).

Encyrtids occurred with nearly equal frequency regardless of the treatment. The hosts listed for Qoencyrtus spp. and P. bucculatricis include lepidopterans that ordinarily might inhabit fencerow vegetation

(Holland, 1968; Krombein et al., 1979). Therefore, the encyrtid populations probably were unaffected by the presence of soybeans.

Seasonal trends of encyrtid captures (Figure 26) also were similar in both types of wild parsnip plots. Populations in both treatments peaked

in July in both years.

Populations of the eulophids Tetrastichus spp. were significantly

higher among soybean-associated wild parsnip than among parsnip alone.

Species native to Iowa attack a wide range of hosts (Krombein et al.,

1979). Although the highest numbers were in wild parsnip associated

with soybeans, the marked presence of Tetrastichus in wild parsnip alone 123

— parsnip and soybeans (N=5) 1979 -- wild parsnip alone (N=5)

15.0 +

7.5 + p. S A T) m ft o. CO 0.0 + M -+- -+ + + + + + + +- Jul 1 Aug 1 Iu OJ parsnip and soybeans (N=2) o. w 1980 wild parsnip alone (N=2) iw 0 15.0 + 0)u 1 g IT 7.5 +

0.0 + I -+- - - -+- - - -4"- - - Jul 1 Aug 1

FIGURE 24. Mean weekly totals of Pteromalidae (Hymenoptera; excluding Perilampinae) trapped per plot among wild parsnip in central Iowa during 1979 and 1980 124

-parsnip and soybeans (N=5) 1979 -- wild parsnip alone (N=5)

30.0 +

+ I

15.0 + I M 0) I Cu + T3 OJ I O. I a + 2 0.0

CO Jul 1 Aug 1

Io parsnip and soybeans (N=2) acu CO 1980 wild parsnip alone (N=2) M-4 I 0 30.0 + U (U I I 1 + g I I 15.0 + I I +

0.0 +

Jul 1 Aug 1

FIGURE 25. Mean weekly totals of Eurvtoma sp. A (Hymenoptera: Eurytomidae) trapped per plot among wild parsnip in central Iowa during 1979 and 1980 125

—parsnip and soybeans (N=5) 1979 -- wild parsnip alone (N=5)

30.0

+ I I 15.0 + I k I OJ & + TJ I OJ cx n)O- 0.0 M -+----4 --H --H—---4 tn IC Jul 1 Aug 1 0)o parsnip and soybeans (N=2) cx CO I 1980 wild parsnip alone (N=2) iw 0 30.0 uQ) I 1 + c I tfl I :s 15.0 4

4- I I 0.0 4- I - - -+- - - —f - - - -4------4-- Jul 1 Aug 1

FIGURE 26. Mean weekly totals of Encyrtidae trapped per plot among wild parsnip in central Iowa during 1979 and 1980 126

might be associated with hosts in fencerow and old field vegetation.

Mean weekly catches of Tetrastichus per plot (Figure 27) show that the

populations were highest in early July.

Species of a second eulophid genus, Horistnenus spp. also attack

hosts present in soybeans, old fields, or fencerows. Some species of

Tetrastichus and Horismenus are hyperparasitoids (Krombein et al.,

1979). Trends of weekly catches of Horismenus spp. (Figure 28) were

similar to those of Tetrastichus, in that populations peaked in July in

1979. Catches of Tetrastichus, however, were much larger than those of

Horismenus.

Most of the trapped specimens of Mymaridae belong to the genus

Polynema. Of the Polynema species likely to occur in Iowa, most inhabit

grassy vegetation or attack homopterous and hemipterous eggs in such a

habitat (Krombein et al., 1979). Because the population levels of

Polynema spp. were similar in both types of wild parsnip plots, these

species probably were not attacking hosts present only in soybeans. The

mean weekly catches (Figure 29) show low, but relatively stable

occurrence in each year.

The wide range of available hosts in both soybeans and fencerows

(and the polyphagous nature of the parasitoids) may explain why trap

catches of Trichogrammatidae were statistically similar in both parsnip

treatments.

Most species of Cynipoidea are exclusively associated with plant

galls, either as inquilines in the galls of other species, or as gall-

makers themselves (Krombein et al., 1979). As expected, their Incidence 127

— parsnip and soybeans (N=5) 1979 -- wild parsnip alone (N=5) I 150 + I I + I I 75 + I I uo a + I CLQ) I CU + 2 « -+------+- - - -+------4-- - g Jul 1 Aug 1

0)O parsnip and soybeans (N=2) a 1980 wild parsnip alone (N=2) CO M-t I 0 150 + M 0) I 1 + 1 I § :g 75

I +

^ — **4*" " " «•B M —— = —— Jul 1 Aug 1

FIGURE 27. Mean weekly totals of Tetrastichus spp. (Hymenoptera: Eulophidae) trapped per plot among wild parsnip in central Iowa during 1979 and 1980 128

•parsnip and soybeans (N=5) 1979 -- wild parsnip alone (N=5)

10.0

5.0

0.0

Jul 1 Aug 1

parsnip and soybeans (N=2) 1980 wild parsnip alone (N=2)

10.0

5.0 +

Jul 1 Aug 1

FIGURE 28. Mean weekly totals of Horismenus spp. (Hymenoptera: Eulophidae) trapped per plot among wild parsnip in central Iowa during 1979 and 1980 129

—parsnip and soybeans (N=5) 1979 -- wild parsnip alone (N=5)

4.0 +

3.0 +

2.0 + cx 0)u CL 1.0 + 13 I 0) a I a 0,0 + s •u I

FIGURE 29. Mean weekly totals of Polvnetna spp. (Hymenoptera: Mymaridae) trapped per plot among wild parsnip in central Iowa during 1979 and 1980 130 in the traps was not affected by the presence of soybeans. Although higher numbers were trapped among soybean-associated wild parsnip, t- tests demonstrated no significant difference between treatments. The highest cynipoid populations were present in July (Figure 30).

The evaniid Hyptia thoracica (Blandard) was present in substantial numbers among soybean-associated wild parsnip in 1980. Great variability between the two soybean-associated parsnip plots in the numbers of H. thoracica trapped, however, led to a lack of significant difference between the seasonal treatment means. Hyptia thoracica is an eggcase parasitoid of wood cockroaches, Parcoblatta spp. (Krombein et al., 1979). Both parasitoid and host were trapped most often in the two soybean-associated parsnip plots adjacent to railroad lines.

Presumably, Parcoblatta was inhabiting the wooden railroad ties. The weekly catches of H. thoracica, shown in Figure 31, indicate that the population peaked in mid-July in each year.

Proctotrupids were present in relatively equal numbers in both types of wild parsnip plots, indicating that the most hosts were not primarily associated with soybean fields. Host records include larval

Coleoptera that could be present in either soybean or fencerow habitats

(Krombein et al., 1979).

The hosts of Diapriidae are relatively unknown. The few records list host families in the Hymenoptera (Dryinidae) and Diptera (several families) (Krombein et al., 1979), many of which might be present in fencerows. The lack of significantly different catches between wild parsnip plot types indicates the availability of hosts regardless of the 131

-parsnip and soybeans (N=5) 1979 -- wild parsnip alone (N=5)

15.0 +

o 7.5 +

0)M P- t) (U A 0.0 + u

CO Jul 1 Aug 1 Io (U parsnip and soybeans (N=2) Ou CO 1980 wild parsnip alone (N=2) iw 0 15.0 + u Q) 1 g 7.5 +

0.0 +

Jul 1 Aug 1

FIGURE 30. Mean weekly totals per plot of Cynipoidea(Hymenoptera) trapped among wild parsnip in central Iowa during 1979 and 1980 132

— parsnip and soybeans (N=5) 1979 -- wild parsnip alone (N=5)

3.0 +

1.5 +

M 0) ex + I a(u a I (0 0.0 + k •| (0 Jul 1 Aug 1 Io 0) parsnip and soybeans (N=2) COA 1980 wild parsnip alone (N=2) iw 0 30.0 + OJM I 1 s I s 15.0 +

+ I I 0.0 +

Jul 1 Aug 1

FIGURE 31. Mean weekly totals per plot of Hvptia thoracica (Hymenoptera: Evaniidae) trapped among wild parsnip in central Iowa during 1979 and 1980 133 presence of soybeans. The highest incidence of diapriids occurred during the latter part of July in each year (Figure 32).

The scelionids Trissolcus spp. are parasitic only on Hemiptera eggs, especially those of stinkbugs (Krombein et al., 1979). Host species include the soybean-inhabiting Euschistus spp., and Podisus spp.

Although differences between trap catches in the two types of wild parsnip plots were not significant at the 0.05 level, the t-test values did approach that standard (P = 0.07) in 1979. Mean weekly catches per plot (Figure 33) illustrate that Trissolcus populations were stable until August in both years.

In 1979, significant differences existed between plot types for the combined catches of other Scelionidae. It is likely that many of the specimens in this group were Telenomus, a large genus with numerous parasitoids of Lepidoptera on woody vegetation and Pentatomidae that might occur on soybeans (Krombein et al., 1979). The mean weekly catches of scelionids other than Trissolcus trapped per plot are shown in Figure 34. Telenomus sp., a potential GCW egg parasitoid (Lentz and

Pedigo, 1975), may be among the trapped scelionid species, because small, but distinct population peaks occurred during the GCW first generation in 1979 and during the GCW second generation in 1980 (c.f..

Figure 2).

Except for Inostemma spp. in 1979, trap catches of Platygastridae were significantly different between treatments. The statistically similar seasonal means per plot between plot types in 1980 probably are more typical because the known hosts of Inostemma and Platygaster 134

— parsnip and soybeans (N=5) I 1979 -- wild parsnip alone (N=5) I 10.0 + I + I I 5.0 + I M

MH I O 10.0 + U

Ic c I 0)CO I 5.0 +

+ I I 0.0 +

Jul 1 Aug 1

FIGURE 32. Mean weekly totals per plot of Diapriidae (Hymenoptera) trapped among wild parsnip in central Iowa during 1979 and 1980 135

I I —parsnip and soybeans (N=5) I 1979 -- wild parsnip alone (N=5) I 10.0 + I

+ I I U o 5.0 +

u

Jul 1

FIGURE 33. Mean weekly totals per plot of Trissolcus spp. (Hyinenoptera: Scelionidae) trapped among wild parsnip in central Iowa during 1979 and 1980 136

•parsnip and soybeans (N=5) 1979 -- wild parsnip alone (N=5) I 40 +

I 30 +

o 20 + 1-4 a I u I Q) CX 10 + I

Iu Q) parsnip and soybeans (N=2) a 1980 wild parsnip alone (N=2) CO iw I 0 40 + 0)u 30 + 1c c I CO I S 20 + I I 10 +

Jul 1 Aug 1

FIGURE 34. Mean weekly totals per plot of Scelionidae excluding Trissolcus spp. (Hymenoptera) trapped among wild parsnip in central Iowa during 1979 and 1980 137 generally are cecidomyiid gall flies likely to inhabit fencerow vegetation (Krombein et al., 1979). The greatest numbers of platygastrids consistently were trapped in late July of both years

(Figure 35).

The t-tests for Ceraphronidae showed a significant difference between plot types only in 1979 trap catches. Even though host species are little known (Krombein et al., 1979), the higher populations among soybean-associated wild parsnip indicate that the parasitoids may be attacking soybean-inhabiting hosts. The graphs of mean weekly catches of all trapped ceraphronid species (Figure 36) show that 1979 populations declined after mid-July, but that incidence in 1980 did not decline until the last week of trapping.

Hymenoptera-Aculeata

The Aculeata trapped among wild parsnip in 1979 and 1980 are listed in Table 27. Although many specimens of higher Hymenoptera were collected among wild parsnip, only the parasitic groups in the

Bethyloidea were identified beyond the level of family.

Mean seasonal catches (Table 28) were very low in 1979, but more bethyloids were present among soybean-associated wild parsnip than among wild parsnip alone. Only Dryinidae catches exhibited a significant difference between treatments. In 1980, the seasonal average catches

per plot were higher for all taxa in all plots, and Dryinidae and

Bethylidae were the most common bethyloid families. Bethylids and

chrysidids were trapped more often among wild parsnip alone, but

dryinids again were trapped more frequently among wild parsnip with 138

—parsnip and soybeans (N=5) 1979 -- wild parsnip alone (N=5)

15.0 +

I +

7.5 + I

0)u a -o I cu p. 0.0 + I 4Ju Jul 1 Aug 1 CO c I I parsnip and soybeans (N=2) Io OJ I 1980 wild parsnip alone (N=2)

CO V-l 15.0 + o (Uu Xi

0.0 +

Jul 1 Aug 1

FIGURE 35. Mean weekly totals per plot of Platygastridae (Hymenoptera) trapped among wild parsnip in central Iowa during 1979 and 1980 139

•parsnip and soybeans (N=5) 1979 •- wild parsnip alone (N=5) I 5.0 + I I + I I 2.5 + I I ueu a + TD I 0) ÇU I a cd 0.0 + w I -+ + +- ,+ + + + CO Jul 1 Aug 1

Iu 0) parsnip and soybeans (N=2) a w 1980 wild parsnip alone (N=2) iw I 0 5.0 + k 0) I 1 + g 2.5 + 1 I +

0.0 +

Jul 1 Aug 1

FIGURE 36. Mean weekly totals per plot of Ceraphronidae (Hymenoptera) trapped among wild parsnip in central Iowa during 1979 and 1980 140

TABLE 27. Taxa of Hymenoptera-Aculeata trapped among wild parsnip in central Iowa during 1979 and 1980

Bethyloidea Formicoidea Bethylidae Formicidae Chrysididae Eumenidae Chrvsis sdd. Vespidae Trichrvsis sdd. Pompilidae Dryinidae Sphecoidea Phorbas sdd. Sphecidae Drvinus sdd. Apoidea Scolioidea Colletidae Tiphiidae Andrenidae Mutillidae Halictidae Megachilidae Apidae

soybeans. The seasonal mean catch was significantly different between treatments only for Chrysididae. The lack of consistently significant trends in these data makes meaningful interpretation difficult.

Less than twenty families of Parasitica (excluding Ichneumonoidea) were represented in trap catches, but no identified species parasitic on

GCW were captured during this study. Overall, more Parasitica were collected among soybean-associated wild parsnip than among wild parsnip alone, but significant 'Ifferences in catches could be demonstrated for less than ten taxa in both years combined. Several of these statistical values probably are questionable because of low population densities.

Great fluctuations in Parasitica populations between years may be associated with the presence or absence of large host populations and those hosts need not necessarily occur in soybeans. Although there were 141

TABLE 28. Mean seasonal totals (X±SE) of Bethyloidea (Hymenoptera) trapped per plot among wild parsnip in central Iowa during 1979 and 1980

1979 1980

Parsnip Parsnip Family with Parsnip P>t with Parsnip P>t Soybeans alone Soybeans alone (5 plots) (5 plots) (2 plots) (2 plots)

Bethylidae 1.00± 0.32 0.80 ±0.80 0.82 3.50±0.50 8.00 ± 5.00 0.46

Chrysididae 1.40± 0.51 1.00 ±0.77 0.68 2.00± 1.00 7.00 ± 0.00 0.04

Dryinidae 1.80± 0.37 0.00 ±0.00 0.01 9.00±5.00 2.50± 1.50 0.34 142 substantial differences between treatments in catches of Parasitica

(excluding Ichneumonoidea), significance could not be demonstrated statistically in either year.

Laboratory Studies

Longevity information for adult parasitoids held in the presence or absence of wild parsnip is given in Table 29. Of the three tested

GCW parasitoids, only R. nolophanae consistently exhibited increased longevity in the presence of wild parsnip. Mean survival time was highest on wild parsnip alone, followed by wild parsnip with soybeans.

The shortest longevity occurred in the check.

Winthemia sinuata had the best (and equal) mean survival time on wild parsnip alone and soybeans alone. The combination of wild parsnip and soybeans provided a shorter survival time than soybeans alone. The shortest longevity occurred for flies held in the check.

Cotesia marginiventris experienced maximal mean survival time in the check. Mean survivorship on wild parsnip alone equaled the mean duration on soybeans alone. Specimens held in the presence of both plants expired sooner than those in the other treatments. The small sample size assigned to each treatment makes the validity of the statistical tests on longevity for this species questionable. To further study braconid longevity, tests were conducted with the related

C. congregatus (Say) reared from larval catalpa sphinx, Ceratomia catalpae (Boisduval), because numerous specimens of this parasitoid were readily available in 1980 (Lewis, 1980b). The test results for this TABLE 29. Mean longevity (days) of parasitoids held individually in.the presence of wild parsnip flowers, soybean leaves, wild parsnip with soybeans, or a check with neither

Treatment^ R. nolophanae W. s inuata C^. marginiventris Ç. congregatus

N % N X N X N X

Check 21 2.00 7 2.67 2 1.50 41 1.39

Wild parsnip 21 2.62 8 3.50 3 1.33 40 1.58

Soybeans 21 2.38 8 3.50 3 1.33 41 1.61

Wild parsnip 22 2.41 8 2.80 4 1.25 41 1.51 and Soybeans

® containers fitted with shell vial of wetted cotton to supply moisture number of specimens assigned to treatment 144 second species may offer an indication of potential longevity in C. marginiventris. Mean longevities in tested C. congregatus were not very much different from those in C. marginiventris. Maximal mean longevity occurred on soybeans alone, followed by wild parsnip alone. The poorest survivorship was in specimens held in the check.

The laboratory longevity trials show that W. sinuata sustained the greatest longevities of the species tested, and C. marginiventris had the shortest. An analysis of variance and subsequent Duncan's multiple range test revealed no significant differences between treatments for any of the species. The presence of wild parsnip either alone or in combination with soybeans did not significantly enhance survivorship for any of the species tested. 145

CONCLUSIONS

The effect of wild parsnip on parasitoids of soybean pests in central Iowa was investigated in three components: assessment of the possible impact of wild parsnip on nearby pest populations in the crop field, confirmation of parasitoid visitation at wild parsnip flowers, and assessment of the possible contribution of wild parsnip flowers to parasitoid longevity.

The combined results of the soybean studies' indicate that at least six families and nine species of larval lepidopterans are present in central Iowa soybean fields. GCW accounted for 99% of the lepidopterous foliage feeders. GCW populations were 10-50% higher in soybeans without nearby wild parsnip than in parsnip-bordered soybeans, but statistical analyses could show no significant difference between the numbers of insects in the two field types. This study did not find any provable effect of wild parsnip on parasitoids or pathogens. If the 10-50% difference in GCW numbers between field types is associated with wild parsnip, then it is due to an untested effect, such as predator response, or a change in GCW moth ovipositional behavior. In general, presence of wild parsnip produced no significant effect on parasitization rates by the parasitoids examined. Wild parsnip failed to enhance parasitization in any particular GCW instar, larval size, or population as a whole in either 1979 or 1980. Neither was there a significant effect on pathogen incidence. Comparisons of parsitoid activity in soybeans according to distance of the sampling site from the fencerow containing parsnip demonstrated no edge effect. 146

The results of the wild.parsnip trapping studies revealed an

abundance of parasitic Diptera. The greatest number of identifiable

trapped species were Tachinidae, of which seven species were known GCW

parasitoids. More species, and generally larger numbers, of Diptera were trapped among soybean-associated wild parsnip than among parsnip

alone. Except for a few instances, the proximity of soybeans

produced no statistically demonstrable effect on trap catches of

Diptera. In general, there were no significant differences between the numbers or between the species of flies trapped in the two types of wild

parsnip plots. The yearly fluctuations in tachinid populations might be

tied to changing populations of hosts not necessarily found in soybeans.

An armyworm outbreak in 1979 was associated with an abundance of A.

apicifer and W. rufopicta, but those tachinids were relatively uncommon

in 1980 when the armyworm populations were substantially lower.

Populations of non-parasitic Diptera were variable between years.

Seasonal population levels of collected GCW tachinid parasitoids were

highest in the GCW outbreak year (1979). In addition, weekly trap-catch

data reflected changes in host densities. All trapped tachinid species known to attack GCW had populations that peaked during the high first

generation of GCW in 1979, but they peaked in 1980 during the high

second GCW generation. Because many tachinids and other Diptera were

trapped among wild parsnip, the plant may be useful as a nectar source;

however, statistical analysis does not support any important role.

Numerous parasitic Hymenoptera were trapped among wild parsnip,

with the greatest numbers generally captured from soybean-associated 147 plots. Five species of braconid GCW parasitoids were present, but trap catches of these were extremely low, and no significant differences in numbers caught were detectable between plot types. Of particular note is the near absence of R. nolophanae from trap catches, even though it was the braconid most commonly reared from field-collected GCW. This suggests that R. nolophanae probably derives no benefit from wild parsnip. The observation is consistent with the findings of others that

R. nolophanae is a host-fluid feeder, and it is supported by laboratory longevity tests, in which wild parsnip flowers did not significantly increase survivorship of R. nolophanae.

Cotesia marginiventris was trapped more frequently than R. nolophanae, but populations did not coincide well with GCW population changes. Braconid parasitoids often associated with certain corn pests were present in significantly greater numbers (or nearly so) among crop- associated wild parsnip. This suggests that wild parsnip may play a more beneficial role in the population dynamics of parasitoids associated with pests of corn than it does for parasitoids associated with soybean pests.

Although at least 14 subfamilies of Ichneumonidae were present, V. brevicinctor was the only trapped species of ichneumonid known to attack

GCW. Cryptinae and Campopleginae were the most commonly trapped subfamilies. The total number of ichneumonid individuals trapped among soybean-associated wild parsnip was nearly twice that trapped among parsnip alone, but this difference was statistically insignificant. In general, trap-catch differences between parsnip plot types were not 148 significant for most of the analyzed components of this ichneumonid fauna, as well.

More than 20 families of Hymenoptera-Parasitica (excluding

Ichneumonoidea) were represented in trap catches, but no species parasitic on GCW was captured during this study. More taxa and more individual insects were trapped among soybean-associated wild parsnip than among wild parsnip alone, but significant differences in numbers caught could be demonstrated for only a few groups. Great fluctuations observed in parasitoid populations between years might be associated with changes in host populations. Once again, substantial differences between wild parsnip plot types existed for trap catches of Hymenoptera-

Parasitica (excluding Ichneumonoidea), but statistical significance could not be demonstrated.

The laboratory longevity tests revealed that W. sinuata sustained the greatest longevity in the presence of wild parsnip, followed by R. nolophanae, apd, finally, by C. marginiventris. Statistical analysis of data for each species showed no significant differences between treatments. The presence of wild parsnip, either alone or in combination with soybeans, did not significantly enhance survivorship in any of the species tested.

In summary, although measurably higher GCW populations were present in soybeans alone as opposed to parsnip-bordered soybeans, the presence of wild parsnip had no statistically significant effect on insect defoliator populations in soybean fields. Numerous species of

Diptera and Hymenoptera parasitic on GCW were trapped in all wild 149

parsnip plots, but significant differences in populations between treatments could not be demonstrated. The presence of wild parsnip in

laboratory longevity trials failed to significantly enhance survivorship in any of the GCW parasitoids tested. These combined results suggest that wild parsnip fulfills a minor role in maintaining GCW parasitoids, and, therefore, weed management practices directed at wild parsnip in soybean fencerows should not have a significant impact on natural control of GCW populations exerted by parasitoids. 150

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APPENDIX

Description of plots

Field sampling was conducted at twelve different sites during the two years of the study. Except as noted, all plots were in Story

County, Iowa, and were located within a 15-km radius of Ames. Five plots of wild parsnip alone were chosen as trapping sites. Site 1 was on the property of the Minnesota Mining and Manufacturing Co. in the NW corner of Section (Sec) 6, Grant Township (Twp). Site 2 was on the property of M. C. Haynes, immediately W of 1003 E Lincoln Way in the SW corner of Sec 1, Washington Twp. Both of these plots were sampled in

1979 and 1980. Site 3 was on the W side of Elwood Drive, S of the

Mortensen Pkwy-Elwood Dr intersection. Sec 16, Washington Twp. Site 4 was on the property of F. lasevoli, S Dakota Avenue, Sec 17, Washington

Twp. Plot 5 was on the H. Watts property, adjacent to the W side of

Interstate 35, Sec 31, Grant Twp. These 3 plots were sampled only in

1979.

Two check fields of soybeans without parsnip borders were sampled in 1979 and 1980. Check 1 was on the R. V. Ross farm in Sec 15,

Franklin Twp. Check 2 was on the Iowa State University Alumni

Association property in the SE corner of Sec 21, Washington Twp.

Five soybean fields bordered on at least one side by wild parsnip were selected for both shake sampling and trapping studies. Plot 1 was on the C. Brown farm and bordered the Chicago Northwestern Railroad Line in the NE corner of Sec 6, Colfax Twp., Boone County. Plot 2 was at 180

Matson Farms, Inc., and it bordered the Chicago Northwestern Railroad

Line, in the SW corner of Sec 15, Washington Twp. Both of these sites were sampled in 1979 and 1980. Plot 3 was on the property of D. C.

Christofferson, and it bordered the Chicago Northwestern Railroad Line in the NE corner of Sec 21, Washington Twp. Plot 4, which was bordered on two sides by wild parsnip, was on the Lunde farm, E of Interstate 35 in the SE corner of Sec 6, Union Twp. Plot 5 was on the Stensland farm,

W of Interstate 35 in Sec 7, Union Twp. These 3 sites were sampled only in 1979. 181

ACKNOWLEDGEMENT

Dedicated to him who provided the love, inspiration, encouragement and support.

In him and this work I am fulfilled.