AN ABSTRACT OF THE THESIS OF
Sarote Panasahatham for the degree of Doctor of Philosophy in Ecology presented on October 18. 2000. Title: Biology. Ecology, and Management of Scaptornyza apicalis Hardy (Diptera: Drosophilidae) on Meadowfoam. Limnanthes alba Benth. in Western Oregon. Redacted for Privacy Abstract approved: i. Fisher
Biology of Scaptomyza apicalis Hardy (Diptera: Drosophilidae) was studied in relation to its host, meadowfoam, Limnanthes a/ba, a recent oil seed crop grown in the
Willamette Valley, Oregon. Populations of flies and larvae were monitored weekly over three consecutive crop-years beginning in 1996. Yellow sticky traps gave relative population estimates of adults. Absolute estimates of larval populations were derived using Berlese funnels to extract immatures from whole plant samples.
Weather and crop phenology are key factors in population regulation.
Meadowfoams, Limnanthes species, were the only observed hosts for S. apicalis in this study. This has four to five overlapping generations per year. Adults of a small founder population colonize commercial fields coincident with fall rains and seedling emergence.
Females deposit eggs in or on plant tissue. Larvae mine leaves and stems. They also bore into crown tissue and flower buds later in the season. Second generation flies arising from the larvae of the founder population first appear in late winter. Successive generations peak during the rapid vegetative growth stage of meadowfoam (mid-April).
A steady decline in adult and larval numbers occurs as daily temperatures rise and plants develop flower buds. Last flies are detected in early July when meadowfoam is harvested.
Temperatures belowØOCelsius during December were a key mortality factor for
S. apicalisin 1998.
Three often major weather components analyzed, accounted for up to 60 percent of the trap count variability. These components were temperature, solar radiation and relative humidity.
S. apicalis larvae fed only on plants within theLimnanthesin feeding studies.
They accepted nine native meadowfoams but with varying survival rates. The commercial meadowfoam cultivar, Floral, was the most suitable larval host.
An increase in supplemental nitrogen fertilizer rates generally resulted in increased infestations of S. api ca/is and decreased seed yields. BIOLOGY, ECOLOGY AND MANAGEMENT OF SCAPTOMYZA APICALIS HARDY (DIPTERA: DROSOPHILIDAE) ON MEADOWFOAM, LIMNANTHESALBA BENTH. IN WESTERN OREGON
by
Sarote Panasahatham
A THESIS
Submitted to
Oregon State University
In partial fulfillment of the requirements for the degree of
Doctor of Philosophy
Presented: October 18, 2000 Commencement: June 2001 Doctor of Philosophy thesis of Sarote Panasahatham presented on October 18, 2000
APPROVED:
Redacted for Privacy Major Professor,
Redacted for Privacy
Chair of Department
Redacted for Privacy Dean of Graduate
I understand that my thesis will become part of the permanent collection of Oregon State University libraries. My signature below authorizes release of my thesis to any reader upon request.
Redacted for Privacy Sarote Panasahatham, Author ACKNOWLEDGEMENTS
I would like to thank Dr. Glenn C. Fisher, my major professor, for his guidance, encouragement, understanding, and financial support from the beginning of my MS through the completion of my Ph.D. program. There is absolutely no perfect word that allows me to express how much I feel indebted to him. I sincerely thank Drs. Paul C.
Jepson and Marcos Kogan, who represented my major department, Dr. Russell S. Karow from department of Crop and Soil Science who represented the minor department, Dr.
Gary F. Merrill from department of Biochemistry and Biophysics who represented
Graduate School, for serving on my committee, assisting the development of my research proposal and revising my thesis.
I especially thank Dr. D. Michael Burgett and Ms. Deanna Watkins for their concern, encouragement, and support that helped me overcome all troubles during my stay. I would like to express my appreciation to Joe DeFrancesco and Daryl Ehrensing who assisted me throughout the study. My sincere appreciation also goes to Dr. Lynn
Royce who assisted me with photography. I thank Drs. Hans Luh and Phil Henegan who patiently tutored me in computer science.
I thank the Board of Directors and the Managing Directors of Thailand Tobacco
Monopoly for funding my graduate studies.
I thank my three children; Ahm, Aim, and Ohm; for their good behavior during my long stay in the US. I want them to know how much I love them. Lastly, I would like to express my deepest gratitude to my parents, brothers, and sisters for all their love, concern, support, and encouragement that inspired me to pursue graduate degrees. CONTRIBUTION OF AUTHORS
This thesis has been benefited from advice, suggestion, and funding kindly offered by Dr. Glenn C. Fisher, my major professor and adviser. Many people assisted me in the field. Thanks go to Mr. Joseph T. DeFrancesco and Mr. Daryl T. Ebrensing who helped me with most field experiments. I am grateful to Anthony Hitz, Brandy
Rush, and Stephanie Moore who helped me sample for adults and larvae. TABLE OF CONTENTS
Page
CHAPTER 1 INTRODUCTION AND LITERATURE REVIEW
THE MEADOWFOAM PLANT...... 1
MEADOWFOAM AS A NEW OILSEED CROP...... 3
MEADOWFOAM ANI) POLLiNATORS...... 5
MEADOWFOAM AND ITS ASSOCIATED iNSECT PESTS...... 7
RESEARCH OBJECT D/ES...... 10
REFERENCES CITED...... 11
CHAPTER 2. SEASONAL DEVELOPMENT AND iNFLUENCE OF WEATHER ON NATURAL POPULATIONS OF Scaptomyza apicalis HARDY (DIPTERA: DROSOPHILIDAE) IN COMMERCIAL MEADOWFOAM FIELDS...... 15
ABSTRACT...... 16
INTRODUCTION...... 18
MATERIALS AND METHODS...... 21
FIELD BIOLOGY AND SEASONAL DEVELOPMENT OF FLIES AND LARVAE...... 23 ASSOCIATION OF MFF NATURAL POPULATIONS AND WEATHER...... 28
RESULTS...... 30
FIELD BIOLOGY AND SEASONAL DEVELOPMENT OF FLIES AND LARVAE...... 30 ASSOCIATION OF MFF NATURAL POPULATIONS AND WEATHER...... 41
DISCUSSION...... 43 TABLE OF CONTENTS (continued)
Page
REFERENCES CITED...... 46
CHAPTER 3. SURVIVAL AND DEVELOPMENT OF Scaptomyza apicalis HARDY (DIPTERA: DROSOPH1LIDAE) ON SOME SELECTED HOST PLANTS AND NATIVE MEADOWFOAMS...... 50
ABSTRACT...... 51
iNTRODUCTION...... 52
MATERIALS AND METHODS...... 56
RESULTS...... 58
DISCUSSION...... 61
REFERENCES CITED...... 63
CHAPTER 4. EFFECTS OF NITROGEN FERTILIZATION AND iNSECTICIDE ON MEADOWFOAM FLY (Scaptomyza apicalis HARDY) INFESTATIONS AND MEADOWFOAM SEED YIELD COMPONENTS...... 66
ABSTRACT...... 67
iNTRODUCTION...... 68
MATERIALS AND METHODS...... 70
RESULTS...... 71
DISCUSSION...... 81
REFERENCES CITED...... 83
CHAPTER 5. CONCLUSIONS...... 85
BiBLIOGRAPHY...... 89 LIST OF FIGURES
Figure Page
2.1 Installation and position of yellow sticky traps used to monitor Scaptomyza apicalis Hardy flight activities in commercial meadowfoam fields from October 1996 to August 1999 in the Willamette Valley, Linn Co., OR...... 25
2.2 Four developmental stages, of Scaptomyza apicalis Hardy on cultivated meadowfoam, Limnanthes alba (cv. Floral)...... 27
2.3 Weekly mean temperature, mean solar radiation, mean relative humidity, and total precipitation of three meadowfoam crop-years from September 1996 to August 1999 in Linn and Benton Co., Willamette Valley, OR 32
2.4 Seasonal development of Scaptomyza apicalis Hardy in five, three, and three commercial meadowfoam fields over three crop-years, in Linn and Benton Cos., Willamette Valley, OR...... 35
2.5 Annual trends of Scaptomyza apicalis Hardy fly populations collected weekly on yellow sticky traps from commercial meadowfoam fields over three crop-years in Linn and Benton Cos., Willamette Valley, OR...... 36
2.6 Numbers of Scaptomyza apicalis Hardy larvae found in plant samples taken monthly from commercial meadowfoam fields over three crop-years in Linn and Benton Cos., Willamette Valley, OR...... 37
2.7 Adult and larval populations of Scaptomyza apicalis Hardy relative to meadowfoam development over three crop-years in Linn and Benton Cos., Willamette Valley, OR...... 38
4.1 Mean number of Scaptomyza apicalis Hardy larvae (n=4) in fertilized plots with and without insecticide (oxydemeton-methyl) applications at Oregon State University, Hyslop Field Laboratory from February to May 1998...... 75
4.2 Mean weekly numbers of Scaptomyza apicalis Hardy fly on yellow sticky traps (n =9) at Oregon State University, Hyslop Field Laboratory from October 1997 through September 1998...... 75 LIST OF FIGURES (continued)
Figure Page
4.3 Mean seed yield of meadowfoam (cv. Floral) (n4) in plots of different fertilizer rates with and without oxydemeton-methyl insecticide sprays conducted from October 1997 to July 1998 at Hyslop Field Laboratory.... 79 LIST OF TABLES
Table Page
2.1 Statistical models and their parameter estimates of weekly trap counts (log (l+y)) on yellow sticky traps of Scaptomyza apicalis Hardy and some weather components (log (x)) conducted on 3 crop-years from October 1996 to August 1999 in Linn and Benton Cos., Willamette Valley, OR...... 42
3.1 Developmental times for larvae and pupae, adult longevity, and survival rates of Scaptomyza apicalis Hardy inoculated as first instar larvae on cultivated meadowfoam (cv. Floral) in greenhouse trial...... 59
3.2 Developmental times for larvae and pupae, adult longevity, and survival rate of Scaptomyza apicalis Hardy inoculated as first instar larvae on nine native meadowfoams compared to the cultivated species, Limnanthes alba (cv. Floral) in greenhouse trial...... 60
4.1 Analysis of variance for main effects and treatment interactions of nitrogen fertilizer rate and insecticide application effects on Scaptomyza apicalis Hardy larval density, meadowfoam (cv. Floral) flower density, seed set and seed yield at Hyslop Field Laboratory from October 1997 to August1998 ...... 72
4.2 Correlation among larval density of Scaptomyza apicalis Hardy, flower density and seed yield of meadowfoam (cv.Floral) at Hyslop Field Laboratory of crop year 1997-98...... 72
4.3 Effects of nitrogen fertilizer (urea) rates on larval densities of Scaptomyza apicalis Hardy applied to meadowfoam (cv. Floral) at Hyslop Field Laboratory from February to May 1998...... 74
4.4 Comparisons of meadowfoam flower density within plots of different fertilizer rates at Hyslop Field Laboratory on June 11, 1998...... 76
4.5 Distribution and percentages of the seed set per flower of different fertilizer rates and insecticide treatments on meadowfoam, Limnanthes alba (cv. Floral) collected at Hyslop Field Laboratory on June 28, 1998.. 78
4.6 Mean seed yield of meadowfoam, Limnanthes alba (cv. Floral) in plots of different fertilizer rates, with and without oxydemeton-methyl insecticide sprays conducted from October 1997 to July 1998 at Hyslop Field Laboratory...... 80 DEDICATION
This thesis is dedicated to my parents, Amnuay and Jintana Panasahatham, and
Pra Kru Nimmankarasophol (Luang Por Soi Kantisaro). BIOLOGY, ECOLOGY, AND MANAGEMENT OF Scaptomyza apicalis HARDY (DIPTERA: DROSOPHIL[DAE) ON MEADOWFOAM, Limnanthes a/ba BENTH. IN WESTERN OREGON
CHAPTER 1
iNTRODUCTION AND LITERATURE REVIEW
The meadowfoam plant
Meadowfoams, Limnanthes spp. (F. Limnanthaceae), are native plants of western
North America occurring from coastal Southern California north to Vancouver Island,
British Columbia (Mason, 1952). They are low-growing, herbaceous, winter-spring
annuals adapted to the Mediterranean climate of the Pacific Coast of North America.
The scientific name, Limnanthes (marshflower), is appropriate, as native plants
commonly are found around vernal poois, moist depressions, and along riverbanks (Jam
et al., 1977; Jolliff, 1989). Plants are quite tolerant of wet or poorly drained soils (Jolliff
et al., 1981). The common name "meadowfoam" was given to L. a/ba a/ba because its
dense, white flowers at full bloom resemble a field covered with foam. Meadowfoam
seeds germinate in the fall. The plant grows as a rosette during winter. Meadowfoam
produces perfect flowers, self-compatible but protandrous (pollen is shed before the
stigmata are receptive); therefore, cross-pollination is required for seed set (Norberg et
al., 1993). Each flower potentially produces five seeds or nutlets. Native meadowfoams
are pollinated by oligolectic bees, Andrena (Hesperandrena) limnanthis L. and Osmia
/ignariapropinqua Cresson (Megachilidae) (Thorp, 1990). 2
Meadowfoam seed typically contains about 30 percent oil. This oil consists almost entirely of long-chain fatty acids of which more than 95 percent areC20andC22 long-chain fatty acids (Miwa and Wolff, 1962). This oil is a most promising substitute for the uses of sperm whale oil, which has been banned for U.S. import by the
Endangered Species Conservation Act of 1969 (Cook, 1971; Jamet al., 1977). TheC20 eicosenoic acid that contains two double bonds accounts for 65 percent of the acids, which is the highest for any known oil from plants. There are two isomers ofC22(erucic acid), A13 isomer and L5 isomer, which correspond in the double bond locations. These two forms ofC22make up another 30 percent of the meadowfoam oil composition.
Because of the high oil content in the seed and the unique long-chain fatty acids, there is great potential to use it as the raw material for many products including cosmetics, surfactants, plasticizers, lubricants, printing dye, wood finishes as well as rubber, and detergent additives. Currently most commercial oil use is in the Japanese cosmetic market (Ebrensing, 1997).
Meadowfoam seed also contains potent biocidal compounds. These include glucosinolate glucolimnanthin and its degradation products, isothiocyanates, (3- methoxyphenyl) acetonitrile and 3-methoxyphenyl isothiocyanate (Lewis and Papavizas,
1971; Brown et al., 1991; Brown and Mona, 1995). The primary enzyme mediated hydrolysis product of glucolimnathin, 3-methoxybenzyl isothiocyanate (3MBITC), was reported to be highly toxic to larvae offal! armyworm, Spodopterafrugiperda (J.E.
Smith) and European corn borer,Ostrinia nub!lalis (Hubner), when crude meal was incorporated into an artificial diet at a 3 percent rate (Bartelt and Mikolajczak, 1989).
The degradation product of glucolimnanthin is phytotoxic. Vaughn et al. (1996) reported that (3-methoxyphenyl) acetonitrile (3MPAN) from ethyl ether and ethanol extracts inhibited radical elongation of velvetleaf (Abutilon theophrasti Medicus) and wheat
(Triticum aestivum L).
Meadowfoam as a new oilseed crop
Meadowfoam was found to be well adapted to poorly drained soil, and therefore it is an attractive rotational crop for producers of cool-season grass seed in the Willamette
Valley, Oregon (Jolliff, 1981; Young and Youngberg, 1996a). Its growing season and harvest period are similar to winter grains and grass seed crops in the western U.S. It is adapted to a wide range of soils and climates (Jolliff 1981; Ehrensing et al., 1997).
Meadowfoam research at Oregon State University dates back to 1966. Initial research at Oregon State University focused on domestication, agronomy, variety development, and initial processes of commercialization (Calhoun, 1975; Jolliff, 1989;
Jolliffet al., 1981; Pearson and Jolliff, 1986; Karow et al., 1986).
With the use of selective herbicides, meadowfoam can be rotated with grass species grown for seed. This rotation makes possible the effective control of grassy weeds extremely difficult in grass seed monocultures (Ehrensing et al., 1996; Young and
Youngberg, 1996b). Meadowfoam can be grown and harvested using conventional grass seed production equipment, management of postharvest residue is simple as dry plant matter is minimal and easily incorporated into the soil. This is significant as open field burns already have become expensive and greatly restricted in western Oregon (Jolliff,
1981; Ehrensing et al., 1996; Young and Youngberg, 1996a; Young and Youngberg,
I 996b). The first commercial variety of cultivated meadowfoam(L. a/ba a/ba),Foamore,
was released in 1975. This variety was developed in 1970 from a single plant, the
accession P1238-704 by the Oregon Agricultural Experiment Station. The canopy height
varied from 25 to 30 cm. It had an upright growth habit, and yielded from 1,000 to 1,500
kg/ha of clean seed in research plots (Jolliff, 1989). A second variety, Mermaid, was
released in 1984, also from a single plant selection from line P1 283-703(L. a/ba alba)
made in Corvallis, Oregon. According to Pearson and Jolliff (1986), Mermaid showed
better seed retention than Foamore. Floral was the third cultivar released by Oregon
State University. It is currently the primary commercial variety. During development
and testing, Floral was designated as 0RL85-765, and is a half-sib of the interspecific
hybrid betweenL. floccosa grandifloraandL. a/ba a/ba.Floral exceeded previously
released varieties in seed yield, oil yield, and resistance both to lodging and embryo
abortion (Fiez et aL, 1991; Franz et al., 1991). However, clean seed yields of Floral can
be quite variable ranging from 400 to 1,700 kg/ha in commercial fields. Damage from
insects and poor pollination have been considered factors contributing to this variation
(Jolliffet al 1993; Ebrensing et al, 1997).
Under current cultural practices, meadowfoam is seeded at from 25 to 35 kg/ha on
15-cm row spacing during the first 2 weeks of October. Timing of the seeding is crucial for seed germination because soil temperatures are below 15.6° C in the Willamette
Valley at this time. Seed planted in warmer soil can develop a secondary dormancy, which leads to poor stand establishment.
Meadowfoam is relatively insensitive to supplemental N fertilizer compared to other field crops (Ehrensing, 1996). Applications of nitrogen fertilizer do not consistently increase seed yields (Pearson and Jolliff, 1986; Jolliff et al., 1981; Jolliff et
al., 1993; Ebrensing et al., 1996). Jolliffet al. (1993) reported that a late February
topdressing of N actually decreased seed yield, seed oil content, and oil yield. Increasing
N fertilizer sharply increased lodging and decreased harvest index. Interestingly, flower
densities increased when N fertilizer was applied up to 80 kg N/ha. Excessive N
applications prolong vegetative growth, increase incidence of lodging, increase incidence
of insect damage, and make meadowfoam more vulnerable to gray mold (Botrytis
cinerea) (Jolliff et al, 1993; Ehrensing 1996).
Meadowfoam typically is swathed during the last week of June, when seed
moisture content is about 42 percent. Windrows can be combined and threshed within 7
to 10 days after swathing. At that point, seed moisture content is generally below 12
percent. Chaff and stems are pulverized finely by the combining process. Very little
residue is left for management. Seed is cleaned to remove stems and dirt prior to oil
extraction (Ebrensing et al., 1997).
Meadowfoam and pollinators
Meadowfoam flowers are self-compatible, protandrous, and entomophilous
(Devine and Johnson, 1978; Jahn and Jolliff, 1990; Jahns et al., 1997). In their natural
habitat, native meadowfoam species mostly are pollinated by an oligolectic bee, Andrena
(Hesperandrena) limnanthis L. (Thorp, 1990). Another bee species, Osmia lignaria propin qua Cresson (Megachilidae), is also a potential pollinator for meadowfoam (Jahns
and Jolliff, 1991a, b). 6
Despite abundant flowering, cultivated meadowfoam rarely sets more than two out of five potential seeds per flower (Franz and Jolliff, 1989). The non-synchronous development of male pollen before female stigmata becomes receptive and the stickiness of pollen inhibits self- and wind-pollination. Therefore, insect pollinators are required for optimum seed set. The honeybee (Apis mellfera L.) is the primary pollinator of cultivated meadowfoam. Honeybees forage on meadowfoam flowers for pollen and nectar. When stigmata are receptive, both nectar and pollen foragers are capable of successful pollination. Floral variety requires five honeybee hives per hectare for adequate pollination (Jahns et al, 1997). Norberg et al. (1993) reported a significant positive linear relationship between flower density and bee density on the numbers of seed per unit area. Jahns and Jolliff (1990) reported that 1, 6, and 11 honeybee visits to receptive flowers produced an average of 1.6, 2.3, and 3.3 seeds per flower, respectively.
This suggests that meadowfoam seed set can be enhanced by increasing numbers of hives per unit area.
Availability of hives may be a significant limitation for large-scale production of meadowfoam (Burgett, 1976; Burgett et al., 1984; Pearson and Jolliff, 1986). Embryo abortion is another factor that determines seed set of meadowfoam. At least 20 percent of seed set may be lost to temperature-related pre- or post-fertilization embryo abortion
(Franz and Jolliff, 1989). Substantial weather risk is associated with honeybee pollination due to windy, rainy weather and cold temperatures that prelude honeybee flight. 7
Meadowfoam and its associated insect pests
Relatively few insect species have been reported in association with
meadowfoam. Lattin and West (1979) reported four potential pest species collected in
meadowfoam fields. None of them were causing damage at the time. The species were:
the western spotted cucumber beetle (Diabrotica undecimpunctata var. undecimpunctata
Mannerheim); a Nitidulid beetle (Meligethes seminulum); the seed bug (Nysius niger);
and a seed-feeding carabid beetle (Acupalpus meridianus).
Fiez et al. (1991) was the first to report damage to meadowfoam by S. apicalis,
while they were studying yield components of meadowfoam breeding lines in 1988. It
was Marshall R. Wheeler who tentatively identified this insect as Scaptomyza sp. in 1990.
David A. Grimaldi subsequently identified the fly as Scaptomyza apicalis Hardy in 1997.
He based his identification on characteristics of wing length, wing venation and structure
of male and female phallic organs reported by Maca (1972). Ehrensing et al. (1990) and
Jolliffet al. (1993) observed that this insect seemed to be differentially attracted to plots
with higher rates of fall-applied nitrogen based on plant damage by larvae. These authors
observed damage to leaves, stems, flower buds, and flowers by larvae.
Scaptomyza apicalis Hardy has been recorded under various names. Hardy
(1849) first elevated it to species status, Scaptomyza apicalis Hardy from specimens previously named Drosophilaflava Fallen (Hendel, 1926), collected in Scotland from white turnip. The name was changed to Notiphilafiaveola Meigen in 1830 and later changed to Scaptomyzafiaveola by A.H. Holiday in 1856. Basden (1954) examined the entire complement of palaearctic Drosophilids and adopted S. apicalis as the species and relegated S. flaveola to synonymy. In 1966, Wheeler and Takada proposed the name Scaptomyza montana Wheeler for the nearctic forms and used the name Scaptomyza apicalis Hardy only for palaearctic forms, being unable to compare European and
American specimens.
Maca (1972) examined and compared the external morphology and internal male genitalia of the European S. apicalis and American S. montana. Based on these studies, he synonymized S. montana under S apicalis. Maca also provided a comprehensive review of the life history, host plant range, and natural enemies of S. apicalis in Europe.
S. apicalis larvae reportedly mine in leaves. Developmental periods for larvae at
18°C were 2 to 3 days in the 1instar, 3 to 4 days in the 2'' instar, 8 days in the 3 instar. Adults emerged from puparia in about 12 days with oviposition occurring about
10 days after emergence. Under "insufficient humidity," larvae and puparia were observed to enter quiescence for up to 300 days (Maca, 1972).
According to Maca (1972), adult coloration could vary from yellow, light brown, gray brown, to dark gray. However, there are no morphological differences between light and dark forms. He speculated that the differences in adult coloration might depend on temperatures experienced during larval development.
According to the European records, this insect exploits a wide range of host plants, most of which are in family Brassicaceae which most of them contain high levels of thioglycosides (Basden, 1954; Maca, 1972). Basden (1954) reported that in Scotland, the larvae of S. apicalis mined leaves of white and yellow turnip (Brassica rapa); garden pea (Pisum sativum); broccoli (Brassica oleracea); cabbage (Brassica oleracea); and various kales (Brassica oleracea) from May to August. Larvae also were reported mining leaves of Scurvy grass (Cochlearia officinalis) and Lady's fingers (Anthyllis vulneraria) on the coast of Scotland in late October (Basden,1954). Maca (1972)
reported seven plant families in Czechoslovakia as hosts for the fly. However, only five
species from four families were detailed. His reported hosts include: Brassicaceae: field
pennycress (Thiaspi arvense), garden radish (Raphanus sativus), and turnip (Brassica
rapa), Resedaceae: Caylusea abyssinica; Viciaceae: garden pea (Pisum sativum);
Asteraceae: Rhodanthe manglesii; Capparidaceae; Tropaeolaceae; and Papaveraceae.
She also mentioned that artificially transferred larvae can develop on plants of certain
other families as well, but she failed to mention specific plants.
Records of S. apicalis in North America are quite different from those in Europe.
According to Wheeler (1952) and Wheeler and Takada (1986) adults (recorded under S.
montana) were commonly associated with watercress (Nasturtium officinale) in southern
California and along the Rogue River near Gold Beach, Oregon. However, he was
unable to successfully rear adults from this host.
Interestingly, a congeneric species, S. nigrita, has been found on glucosinolate-
containing plants in the Brassicaceae, B. oleracea (broccoli); and the Cruciferae,
Cardamine cordfloria (bittercress) in Colorado (Free and Williams, 1979; Collinge and
Lauda, 1988; Collinge and Lauda, 1989a; Collinge and Lauda, 1989b).
Adults of two species of parasitoids in the Braconidae and Eulophidae has been reared from puparia of S. apicalis. Parasitization rates as high as 50 percent by the braconid, Dacnusa (Pachysema) temula Haliday, have been recorded in Europe (Maca,
1972). Maca also mentioned an unidentified Eulophid that emerged from puparia about
10 days before D. temura. It was, however, believed to be a hyperparasite. 10
Research objectives
To date, the Scaptomyzid identified as S. apicalis is the only insect pest observed to cause substantial injury and stand loss in commercial fields of meadowfoam.
Infestations of S. apicalis are observed consistently in both experimental plots and commercially grown fields in the Willamette Valley. The extent and severity of meadowfoam damage varies widely from year to year and field to field. In general, the heavier infestations were observed consistently in fields seeded to meadowfoam for second and third years. As meadowfoam acreage increases, S. apicalis poses a serious problem for commercial production. A better understanding of the fly biology and host range, the interactions between insect and plant and how cultural practices influence fly infestations and meadowfoam seed yield are essential to the development of effective, economical methods of controls.
Specific objectives of this study were to:
1.Describe the biology, seasonal development, and factors regulating populations of S.
apicalis in commercial meadowfoam fields of Willamette Valley, Oregon.
2.Determine the suitability of plants common to the Willamette Valley and previously
in reported European literatures as larval hosts of palearetic populations of S. apicalis.
3.Determine the host range of S. apicalis within native population ofLimnanthes spp.
4.Determine how nitrogen fertilizer rates and insecticide use affect S. apicalis
infestations, meadowfoam yield components and seed production. 11
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Fiez, T.E., O.S. Norberg, and G.D. Jolliff. 1991. Yield components in three meadowfoam lines. Agon. J. 83: 598-602.
Franz, R.E., and G.D. JoIliff. 1989. Temperature effects on megagametophytic development in meadowfoam. Crop Sci. 29: 133-14 1.
Franz, R.E., G.D. Jolliff, and M. Siddigh. 1991. Embryo abortion in three meadowfoam lines. Crop Sci. 3 1:1651-1654.
Free, J.B., and I. Williams. 1979. The distribution of insect pests on oil seed rape (Brassicanapus)and the damage they cause. J. Agri. Sci. 92: 139-149.
Hardy, J. 1849. Notes on the remedies for the turnip-fly amongst the ancients, and on the turnip-fly of New Holland, with a notice of a new genus and species of Diptera. Berwickshire Nat. Club, Hist. (1842-1849)2: 3 59-362.
Jahns, T.R., and G.D. Jolliff. 1990. Pollen deposition rates effects on seed set in meadowfoam. Crop Sci. 30: 850-853.
Jahns, T.R. and G.D. Jolliff. 1991. Osmia lignariapropinqua Cresson: an alternative pollinator for meadowfoam in cages. Crop Sci. 31: 1,274-1,279.
Jahns, T.R., and (iD. Jolliff 1991. Survival rate and reproductive success of Osmia lignariapropinqua Cresson (Hymenoptera: Megachilidae) in caged meadowfoam, Limnanthes a/ba Hartw. Ex Benth. (Limnanthaceae). J. Kansas Ent. Soc. 64: 95- 106.
Jahns, T.R., D.M. Burgett, and GD. Jolliff. 1997. Pollination and seed set of meadowfoam. Oregon State Univ. Ext. Ser. EM 8666. 4p.
Jam, S.K., R.O. Pierce, and H. Hauptli. 1977. Meadowfoam: potential new oil crop. 18- 20.InCalifornia Agri. California Agri. Exp. Stn., Univ. of California, Davis, CA. 31: 18-20.
Jolliff, G.D. 1981. Development and production of meadowfoam (Limnanthes a/ba). 269- 285.InE.H. Pryde, L.H. Princen and K.D. Mukherjee (eds.). New sources of fats and oils. Am. Oil Chem. Soc., Monogr. No. 9. Champaign, IL. 255 p.
Jolliff, GD., I.J. Tinsley, W. Calhoun, and J.M. Crane. 1981. Meadowfoam (Limnanthes alba): Its research and development as a potential new oilseed crop for the Willamette Valley of Oregon. Station Bulletin 648. Oregon State University. 17p. 13
Jolliff, G.D. 1989. Meadowfoam domestication in Oregon: A chronological histoty. 53- 65. In L.L. Hardman and L. Waters, Jr. (eds.). Strategies for alternative crop development: Case histories. Proc. of Nat.Sym. Univ.ofMinn. 253 p.
Jolliff, G.D., M. Seddigh, and M.L. McGahuey. 1993. Nitrogen rate and timing effects on meadowfoam oil yield and oil-yield components. Field Crops Res. 31:111-119.
Jolliff, G.D., M. Seddigh, OS. Norberg, and T.E. Fiez. 1993. Seeding rate, nitrogen fertilization, and irrigation effects on floral meadowfoam oil yield. Agron. J. 85(2): 188-193.
Karow, R., G.D. Jolliff, and M. Stoltz. 1986. Growing meadowfoam in the Willamette Valley. Ext. Cir. 1237, Oregon State Univ., Corvallis, OR 97331.
Lattin, J.D., and K. West. 1979. Insects associated with meadowfoam. In GD. Jolliff (ed.). The production and development of meadowfoam Limnanthes alba as a renewable source of critically needed raw materials for industrial utilization. Part VI. Pacific Northwest Regional Commission Grant No. 10890022. Final report. December 1979.
Lewis, J.A., and G.C. Papavizas. 1971. Effect of sulfur-containing volatile compounds and vapors from cabbage decomposition on Aphanomyces euteiches. Phytopathology. 61:208-214.
Maca, J. 1972. Czechoslovak species of the genus Scaptomyza Hardy (Diptera, Drosophilidae) and their bionomics. Acta Entomologica Bohemoslovaca. 69(2): 128-130.
Mason, C.T., Jr. 1952. A systematic study of the genus Limnanthes R. Br. In Univ. of Calif. Publication in Bot. 25(6): 455-507, Univ. of California Press, Berkeley and Los Angeles.
Miwa, T.K. and IA. Wolff. 1962. Fatty acids, fatty alcohols, and wax esters from Limnanthes douglasii (meadowfoam) seed oil. J. Am. Oil Chem. Soc. 39: 320- 322.
Norberg, 0.S., M. Seddigh, G.D. Jolliff, and T.E. Fiez. 1993. Flower production and honey bee density effectsonmeadowfoam seed yield. Crop Sci. 33:108-112.
Pearson, C.H., and G.D. Jolliff. 1986. Nitrogen fertilizer effects on growth, flowering, oil yield, and yield components in meadowfoam. Agron. J. 78: 1,030-1,034.
Thorp, R.W. 1990. Vernal pool flowers and host-specific bees. 109-122. In D.H. Ikeda and R.W. Schlising (eds.) Vernal pool plants: their habitat and biology. Proc. 14
Pacific Section, Botanical Soc. of Am., and the Pacific Division, Am. Assoc. for the Adv. Of Sci., 8th, Chico, California State Univ..
Vaughn, S.F., R.A. Boydston, and CA. Mallory-Smith. 1996. Isolation and identification of(3-methoxyphenyl) acetonitril as a phytotoxin from meadowfoam(Limnanthes a/ba)seedmeal. J. Chem. Ecol. 22(10): 1,939-1,949.
Wheeler, M.R. 1952. The drosophilidae of the Nearctic region, exclusive of genus Drosophila.Univ. Tex. Publ. 5024: 162-218.
Wheeler, M.R. and H. Takada. 1966. The Nearctic and Neotropical species of Scaptomyza Hardy (Diptera: drosophilidae). Univ. Tex. Publ. 6615: 37-78.
Young, W.C., ifi, and H.W. Youngberg. 1996. Cropping systems for perennial ryegrass seed production: I. Minimum tillage establishment of rotation crops in stubble without burning. Agron. J. 88: 73-77.
Young, W.C., ifi, and H.W. Youngberg. 1996. Cropping systems for perennial ryegrass seed production: H. Minimum tillage systems for changing cultivars in certified seed production. Agron. J. 88: 78-82. 15
CHAPTER 2
SEASONAL DEVELOPMENT AND INFLUENCE OF WEATHER ON NATURAL POPULATIONS OF Scaptomyza apicalis HARDY (DIPTERA: DROSOPHILIDAE) IN COMMERCIAL MEADOWFOAM FIELDS
Sarote Panasahatham, Glenn C. Fisher, Joseph T. DeFrancesco, and Daryl T. Ehrensing 16
Abstract
Field biology, seasonal development, and association of its natural population
development with key weather components of Scaptomyza apicalis Hardy (Diptera:
Drosophilidae) were studied in commercially grown meadowfoam fields for 3 crop-
years from September 1996 to August 1999. Relative populations of the fly were
monitored with yellow sticky traps at weekly intervals from September to August of
each crop-year. Absolute larval densities were obtained by sampling plants at monthly
interval and extracting larvae in Berlese fimnels. Each year, population development of
S. apicalis coincided closely with seasonal weather change and developmental stages of
meadowfoam crop.
Both insect and plant responded to rainfall as the environmental cue that initiate their annual cycles in the early fall. S. apicalis adults colonize newly emergent
seedlings. Females insert or simply place eggs on leaves or petioles. The larvae mine
leaf parenchyma and meristemic tissues of the crown during the plants vegetative stage.
Pupae are attached to plant stems or are found on soil surface and debris.Flies constantly fed on free moisture in the plant canopy and were active on warm, sunny days. Numbers of adults and larvae were low from October through late January. Then populations grew exponentially peaking in early March. Populations gradually declined as meadowfoam plants approached the reproductive stage. At this time larval feeding sites shifted to flower buds, flowers, and young seed pods. No adults or larvae were detected in meadowfoam fields at harvest in late June. Temperature, solar radiation, 17 and relative humidity were the most influential weather components affecting the adult and accounted for nearly 60 percent of trap count variability. 18
Introduction
Meadowfoam, Limnanthes alba Hartweg ex. Bentham (Limnanthaceae), is a
low-growing winter annual plant native to northern California and southern Oregon. It
is well adapted to the mild winters and warm, dry summers of the Pacific Northwest. It
also grows well on the poorly drained and heavy soils generally suitable only for grass
seed production in the Willamette Valley. Meadowfoam can be grown and harvested
with the same farm machinery used for grass seed production. Meadowfoam has the
potential to be an economic rotational crop for grass seed in the Willamette Valley. It
has been cultivated and commercialized for its oil, which has many potential uses as
industrial lubricants to base formulations for cosmetics (Calhoun, 1975; Jolliff, 1981;
hrensing et al., 1997).
Three cultivars, Foamore, Mermaid and Floral, have been released for commercial production since 1975 (Jolliff, 1989; Jolliff, 1991; Ehrensing et al., 1997).
Floral has been the cultivar produced commercially because of its superior agronomic characteristics and seed and oil yields over previously released varieties. As a result of increased commercial interest, meadowfoam acreage in the Willamette Valley has expanded dramatically from nearly 320 hectares in 1992 to over 3,600 hectares in 1996
(Ehrensing et al., 1997).
Relatively few species of insects has been collected from commercial meadowfoam in the Willamette Valley. A field survey made by Lattin and West in
1979 reported four potential pest species associated with meadowfoam. There were the western spotted cucumber beetle (Diabrotica undercimpunctata var undecimpunctata 19
Mannerheim); a nitidulid beetle(Meligethes seminulum);the seed bug(Nysius niger);
and a seed-feeding carabid beetle (Acupalpus meridianus). However, none of them
were noted damaging meadowfoam at the time.
Reference will be made to Scaptomyza apicalis Hardy (Diptera: Drosophilidae)
as the "meadowfoam fly" (MFF). It is an unofficial common name. MFF was first
reported damaging leaves, petioles, crown tissues, and flower buds of meadowfoam in
experimental plots at the Hyslop Field Laboratory in 1988 (Jolliff, 1989; Fiez et al.,
1991; Ehrensing et al., 1997). It was observed that flies were apparently attracted to
plots with higher nitrogen fertilizer rates and that greater infestations were associated
with lower seed yields (Jolliffet aL, 1993). Since then, this insect has consistently
infested research plots and commercial meadowfoam fields in the Willamette Valley.
The seventy of infestations increases where meadowfoam is grown successively for 2 to
3 years.
Perusal of scientific literature revealed that & apicalis occurs throughout the
Holarctic region of both northern hemispheres (Wheeler, 1952; Wheeler and Takeda,
1966). However, details on its biology and host plants only appear in the European
literature. This insect has been recorded under various names, such as Scaptomyza apicalis Hardy, Drosophila flava Fallen, Notzjhilaflaveola Meigen, and Scaptomyza flaveola Holiday (Hendel, 1926; Hardy, 1984; Basden, 1954; Maca, 1972). In Europe,
larvae of this insect are leafininers and found on a wide range of host plants in the
Brassicaceae, Resedaceae, Viciaceae, Asteraceae, Capparidaceae, Tropaeolceae, and
Papaveraceae. It has been most commonly reported from Brassicaceae, especially on common vegetables such as broccoli, cabbage, kale, and turnip. Most of these reported 20
host plants are characterized by having large concentrations of glucosinolates or
thioglycosides (Basden, 1954; Maca, 1972). Developmental periods for first, second
and third instar larvae at 18°C were 2 to 3, 3 to 4 and 8 days, respectively. Duration of
the pupal stage was about 12 days. Adult longevity and female oviposition periods
were similar in length and averaged about 10 days. Adult coloration was reported to be
variable, ranging from dark gray, yellow brown and pale yellow morphs. The variation
was thought to possibly be due to the effect of temperature regimes during the immature
stages (Maca, 1972).
In the United States, this insect identified asScaptomyza montanaWheeler. The
first specimen was collected from Glacier National Park, Montana in 1949 (Wheeler,
1952). Its cited geographical range includes Nova Scotia, Connecticut, New York,
District of Columbia, Tennessee and Maryland, on the East Coast. Indiana, and Illinois
in the central states and Alaska, Montana, Idaho, Washington, Oregon and California in
the west (Wheeler, 1952; Wheeler and Takeda, 1966). The first mention of this insect's
collection in Oregon was along the Rogue River near Gold Beach (Wheeler, 1952).
Wheeler (1952) indicated that S.montanawas common in southern California. Adult
and larvae could be found on watercress(Nasturtium officinale).However, he was
unable to rear them on this host in the laboratory.
Understanding the biology of an insect pest and how its populations are
regulated are fundamental to the development of effective management techniques.
This insect has never been the subject of study on meadowfoam. Yet, damage to meadowfoam has been consistently observed in Willamette Valley meadowfoam fields for at least the last 10 years. As meadowfoam acreage increases, S. apicalis likely will 21
continue to be a serious problem for commercial producers, hence, the impetus to
document the biology and develop management techniques for this pest.
Materials and Methods
Studies on the seasonal development of larvae and adults, field biology and
influence of weather on natural populations of MFF were conducted on cultivated
meadowfoam (cv. Floral) during 3 consecutive growing seasons in 11 commercial fields
from October 1996 to August 1999. Study sites numbered five, three and three in the
Willamette Valley in the crop-year 1996-97, 1997-98, and 1998-99 crop-years,
respectively. All study sites were located in Linn and Benton Counties, Oregon.
Study sites and agronomic practices In the 1996-97 season, five commercially
grown meadowfoam fields were selected as primary study sites: Smiths', Pughs',
Pimm's, Harrys' and Glaser's; of 45.5, 30.5, 65.0, 54.5, and 37.6 hectares, respectively.
Crops were produced under standard agronomic practices, as follows: fields were
prepared during the first half of September and seeded with meadowfoam (cv. Floral) at rates of 25 to 30 kgfhectare on 15-cm row spacings during the first 2 weeks of October.
Plants generally germinated in late October when the soil moisture contentwas
sufficient, a result of rainfall. Plants grew slowly during fall and late winter until the rosette stage. Urea was applied once in late February or early March at 40 to 60 kg/ha.
Water requirements were met entirely by rainfall. Honeybees were placed in or near borders of fields at bloom. Four to five hive per hectare are suggested (Jahns et al.,
1997). Plants were swathed at about 42 percent seed moisture during the last week of
June. Windrows were formed and left in the fields for about 2 weeks until seed 22 moisture content approached 12 percent. The crop was threshed with conventional grass seed combines during the second week of July. Meadowfoam seed was subsequently cleaned to remove stems and dirt prior to oil extraction (Jolliff et al., 1981;
Ehrensing et al., 1997).
In 1997-98, three different commercial fields were chosen: Smiths,' Pughs,' and
Van Leeuwen's, at 36.5, 45.1, and 35.5 hectares, respectively. These fields were located in Linn County, Oregon. Agronomic practices were followed in all fields as described in 1996-97, except Pughs,' where seed left in the field from the previous season's harvest germinated to provide the new stand. Here, plant density was generally comparable to that of newly seeded fields, which was about 300 to 400 plants/meter. Meadowfoam plants in this field emerged 2 weeks earlier than direct seeded plants in the other two fields.
In 1998-99, a third set of meadowfoam fields (0.34, 31.6 and 41.5 hectares) were studied. The first field was established at Oregon State University's Hyslop Field
Laboratory, near Corvallis. The second and third fields were the commercial fields referred to as Reynold's and Pughs' in Benton and Linn Counties, Oregon, respectively.
General agronomic practices as described in 1996-97 were used to produce the seed crops.
Crop phenology Meadowfoam is classified as a winter annual. In the
Willamette Valley, seed germinates in late October, usually two weeks after seeding, and after the first heavy rains post-seeding. Plants grow slowly during fall and winter.
Vegetative growth and tissue differentiation occurs after late January. Stem elongation is evident in early March. Plants enter the reproductive stage in late April. 23
Vernalization and anthesis occur in early May, at which time hives of honeybees are placed in fields for pollination. Full bloom occurs during the second half of May. Each flower, which has the potential for producing five seeds, requires multiple visits from honeybees for optimum seed set. Seed set and maturation occurs from May to June.
Seed harvest is initiated by swathing fields and leaving plants to desiccate in windrows during last week of June. Windrows are threshed with conventional grass seed combines 2 weeks after swathing (Jolliff, 1989; Jolliff, 1991; Ehrensing et al., 1997).
Field biolo2y and seasonal develoDment of flies and larvae
Understanding the factors governing the seasonal development and abundance of insect populations are essential to optimization of pest management practices
(Pedigo, 1994; Pedigo and Zeiss, 1996). Because insects are poikilotherms, environmental conditions are important factors governing insect development, behavior, and interactions with their host plants. Temperature is generally considered the most important factor in determining the rate of insect development (Lamb and Gerber,
1985). Populations of a given species occur within a fairly defined, species-specific range of temperatures (Wagner et al., 1984; Fan et al., 1992). The lowest temperature at which growth and development occurs within the range is referred to as developmental threshold. Developmental rates rise as temperature increase. The duration of development can be described as a function of heat unit summation. (Bodenheimer,
1951; Arnold, 1959; Campbell et al., 1974). Common models that describe insect developmental rates are non-linear at both the high and low temperature extremes and linear at intermediate temperatures (Wagner Ct al., 1984; Judd et al., 1991; Fan et al., 24
1992). This heat accumulation, often described in terms of degree-days, is assumed to be fairly constant and species-specific (Baskerville and Emin, 1969). The degree-day approach is used widely in describing insect development and phenology. It has significant implications for applying pest management tactics, especially the timing of the insecticide use (Baskerville and Emin, 1969; Abrami, 1972; Wagner et al., 1984;
Petitt eta!,1991; Fan et al., 1992; Pedigo and Zeiss, 1996).
Life histoiy, seasonality of populations and conditions influencing population growth and development were studied in 3 consecutive crop-years from September
1996 to August 1999. Yellow sticky traps were used to monitor adults as reported by previous authors (Fiez et al., 1991; Jolliffet al., 1993; Ehrensing et al., 1997). Nine yellow traps of23x28 cm with an 18x23-cm sticky surface (Pherocon 1C®) were used to detect and monitor fly flight activity of MFF in each field. Traps were placed randomly within fields and were at least 100 m apart. Each trap was attached to a 2-cm- diameter, 120-cm-long metal pole and secured with a metal clip. Traps were positioned on the pole so that lower edges of the traps were at least 30 cm from the ground or were even with the top of plant canopy (Figure 2.1). These traps were used to monitor flies for 48 consecutive weeks in each crop-year, which began from the first week of
September through first week of August. Traps were collected and replaced with new traps as necessary at the end of each week. When collected, traps were covered with clear plastic wrap and transported to the laboratory. The numbers of flies on each trap were counted with stereomicroscope and recorded. In this manner, weekly average numbers of flies per trap were documented for each study site. 41
Figure 2.1 Installation and position of yellow sticky traps used to monitor Scaptomyza apicalis Hardy flight activities in commercial meadowfoam fields from October 1996 to August 1999 in the Willamette Valley, Linn Co., OR. 26
Larvae were detected in plant samples, which taken at monthly intervals from
December until June, about 2 weeks prior to harvests in the three cropping seasons.
Ten samples often meadowfoam plants each were taken from each study site on each collection date. Samples were taken randomly and spaced at least 100 m apart from one another. Samples were cut at ground level, placed in labeled bags, and transported to the laboratory. Larvae were extracted from each individual sample by Berlese funnels with 25 to 40 watt light bulbs, according to plant size (Southwood, 1978; Pedigo, 1989).
Samples remained in the funnels for 3 to 5 days until they were sufficiently dry and larvae had exited the host materials. Extracted larvae fell into jars filled with 75 percent alcohol and were transferred to Petri's disc for quantification under a stereomicroscope.
Numbers of larvae in each sample were recorded by date of sample collection.
Seasonal occurrence and larval populations according to meadowfoam developmental stage were determined throughout the 3 crop-years.
Weather data for Linn and Benton County, Oregon from 1996 to 1999 were obtained from Oregon Climate Service (www.ocs.orst.edu), College of Oceanic and
Atmospheric Sciences, at Oregon State University, Corvallis, Oregon.
Phenology of MFF was determined and analyzed in relation to weather conditions in each crop-year. Weekly mean numbers of flies and larval densities of
MFF within the same crop-year were pooled and averaged to calculate the secular, annual trend. Weather data including weekly mean temperature, relative humidity, solar radiation, and total precipitation were analyzed for effect on occurrence, size, and distribution pattern of MFF field populations. Emphasis was placed on the relationship between winter temperatures and magnitude of fly populations in the February through 27
March time period, as well as the time period from April through June of each crop- year. The number of generations in each crop-year was derived from the number of peaks obtained from pooled field data. Life stages of MFF are shown in Figure 2.2
Figure 2.2. Four developmental stages of Scapomyza apicalis Hardy on cultivated meadowfoam, Limnanthes alba (cv. Floral). 28
Association of MFF natural populations and weather
Interestingly, predation and parasitization of MFF were not observed in any of the 3 crop-years of field survey. Seasonal population development was analyzed in relation to weather over three seasons. Begon et al. (1996) concluded that in absence of natural enemies, insects are heavily regulated by weather throughout the year.
Variation in the trap counts of MFF seen in meadowfoam commercial fields could be ascribed to three major components, namely, (a) natural population growth; (b) weather conditions just prior to collection of sticky traps; and (c) variable due to random variation or residual.
Davidson and Andhewartha (1948a, b) studied the natural population fluctuation of apple blossom thrips (Thrips imaginis Bagnall) on roses from 1932 to 1946. They employed a partial regression analysis to associate daily trap counts with certain weather components. They concluded that two weather components, namely temperature and rainfall, accounted for 84 percent of the total variance of the fluctuation of the thrips populations.
Relationships of the annual trends of MFF populations, which were the means of pooled trap counts of all study sites within the same crop-year, were determined in the multiple regression analysis with 10 major weather components. Of the total variability noted among the 48 weekly trap counts from the first week of September to the first week of August of each crop-year (1996-97, 1997-98, and 1998-99) of all 11 study sites, only data from January to June from each crop-year were considered in these analyses. Data before this range, during which time flies were largely absent, were set aside because of the slow development of the immature stages during late fall and 29 winter. Data after this range also were omitted due to host plant unavailability (the crops were harvested), with the expectation that they might enter a different course of development as Maca (1972) indicated. Average weekly catches of flies were used as the response variable, and 10 major weather components were employed as explanatoiy variables.
Ten weather components were selected as independent variables. They were referenced by the following symbols:
AMX = weekly average of daily maximum temperature of the trapping week (°C)
AMX1 = weekly average of daily maximum temperature 1 week prior to the trapping
week (°C)
AMX2 = weekly average of daily maximum temperature 2 weeks prior to the trapping
week (°C)
AMM = weekly average of mean daily temperature of the trapping week (°C)
AMMIweekly average of mean daily temperature 1 week prior to trapping (°C)
AtvDvI2 = weekly average of mean daily temperature 2 weeks prior to trapping (°C)
APPweekly average of daily precipitation (mm)
TPP = total weekly precipitation (mm)
ASR = weekly average of daily mean solar radiation (Langley)
ATA = weekly average of daily mean relative humidity (percent)
Because data from trap counts and weather records violated normal distribution expectation for statistical analysis, all variables were transformed into the logarithmic scale. The weekly trap counts were transfonned into log (y+l) scale, while the selected weather component variables were transformed by log (x). In addition, autoregressive 30 of lag-I (Yule-Walker procedure) was adjusted to the trap count observations because they were collected over a series of time intervals to meet the assumption of independence for statistical analysis (Bence, 1995; Ramsey and Schafer, 1997).
Multiple regression analyses of the least square estimate were carried out to associate the trap count observations to weather components by using the SAS ver 7.0 statistical package (SAS, 1998). A stepwise procedure was employed for the selection of significant weather component variables at 0.05 critical level for variable entry and removal criteria (Ramsey and Schafer, 1997, Sharov, 1997). Quadratic terms of all weather component variables and their interaction terms also were included in the model selection process. Analyses were not carried beyond the second degree, because residual analysis did not suggest the significance of those terms (Ramsey and Schafer,
1997).
Results
Field bioloEv and seasonal development of flies and larvae
Flies appeared to remain in meadowfoam fields throughout their lives, where mating and oviposition took place. Adults constantly fed on available moisture present on plants or on the ground. They readily flew short distances within fields on warm, sunny days. Flies were relatively inactive and remained within the canopy or on the ground on cold, cloudy days. Dark gray forms commonly were found throughout the year, but some light brown forms were also found late in the season in June and early
July, just prior to harvest. Females inserted eggs within leaf tissue of meadowfoam 31
during the early season while population densities were generally low. As adult
populations increased, females also deposited eggs on the surface of leaves and stems,
especially during February and April. Eggs are white and elliptical with shiny chorions.
Early instar larvae were strictly miners in leaves and stems. Larger larvae were
observed to feed externally on tissue of the crown. Oviposition sites shifted to flower
buds, and bloom when present. Hatching larvae fed primarily inside flower buds,
primarily on ovaries and on young seed as formed. Pupae were dark brown. Pupation
occurred under the plant canopy on the ground or on the plants (Figure 2.2).
Development of MFF populations (Figure 2.4, 2.5, 2.6, and 2.7) followed
seasonal weather changes (Figure 2.3) and meadowfoam developmental stages.
Developmental patterns were similar in the 1996-97 and 1997-98 crop-years, but quite
different in 1998-99. In 1996-97 and 1997-98, the first MFF adult was detected in early
September, following rains. A small peak was detected in early September; after that, numbers of flies caught on traps declined through early January. There were six distinct peaks detected from January to June, with an average of one peak per month (Figure
2.5). Populations grew rapidly after January, and the first peak was detected in early
February. The second peak, which was consistently greatest in all 3 crop-years (about double the size of that of February) were detected in March. There were another three other distinct peaks in April, May, and June, respectively, which populations fluctuated widely and gradually declined as plants began producing flower buds. 32
Figure 2.3. Weekly mean temperature, mean solar radiation, mean relative humidity, and total precipitation of three meadowfoam crop-years from September 1996 to August 1999 in Linn and Benton Co., Willamette Valley, OR.
Temperature (C) 1996-97 40
Sour Radiation (Langley) 1996-97
20
S 0 N D 0 J F M A M JJ A
RH(%) 1996-97
Recipation (ninlw eek) 1996-97 250
200
150
ON! D JFMAMJJ A Continued on next page 33
Figure 2.3. (Continued)
Teneratiae (C 1997-98 40
Solar dlatuon (Langley) 1997-98
20 SONDDJFMAMJJA
RH(%) 1997-98
Fecipaation (nmlweek) 1987-98 250
200
150
' J J A
Continued on next page 34
Figure 2.3. (Continued)
Teniperatire (C) 1998-99
4O
Solar Fdtion (Langley) 1998-99
0 S 0 N DD J F M A M J J A
1998-99 100
ecation (rr,nM'eek) 1998-99 250
200
150
100
S 0 N DD J J A 35
Figure 2.4. Seasonal development of Scaptomyza apicalis Hardy in five, three, and three commercial meadowfoam fields over three crop-years in Linn and Benton Cos., Willamette Valley, OR.
Fvan number of fliesflraplweek 1996-97
250 200
150
100
50
0 S 0 N D J F MM A MJ J A
-.- Srrths-a--Righs-h--Am -.-- I-rrys -*--. Glaser
Mean number of fhesrap/w eek 1997-98 250
200
150
100
50
0 S 0 N D J F M M A M JJ A
.o---Sniths--a-Righss---Van Leeuw en
Mean number of fIiesrap/week 1998-99
250
200
150
100
50
0 S 0 N DD J F M A M J J A
o 1-tyslop-o-Reynold s--Righs 36
Figure 2.5. Annual trends of Scaptomyza apicalis Hardy fly populations collected weekly on yellow sticky traps from commercial meadowfoam fields over three crop- years in Linn and Benton Cos., Willamette Valley, OR.
Mean nunter of fhesftrap/w eek 1996-97
250
200
150 'C 100
50
0 S 0 N D J F M A M JJ A
L Sniths Righs £ Atw x brrys Glaser ..Annual
Mean nunter of fbesftraplw eek 1997-98 250
200
150
100
50 0 upu.----ui.au d $ 0 N DD J F M A M J J A
. Sniths u Pughs AVan Leeuw en ,pannual trenj
Mean nunther of fliesftrap/week 1998-99 250
200
150
100
50 0 ..... S 0 N D 0 J F M A M J J A
Hyslop Reynold Righs Nannual tre 37
Figure 2.6. Numbers of Scaptomyza apicalis Hardy larvae found in plant samples taken monthly from commercial meadowfoam fields over three crop-years in Linn and Benton Cos., Willamette Valley, OR.
F'&iner of larvae/10 plants 1996-97
250
200 DJFMAMJJ uSrrhs Pughs aAm o Harrys Glaser
F'kjrther of larvae/I 0 plants 1997-96 250
D J F M A MJJ
aSnths PUghs 0Van Leeuwen
N&imber of larvae/I 0 plants 1998-99
250
200
150
100
50
D J F M A M J
aHyslop Reynoldci Pughs 38
Figure 2.7. Adult and larval populations of Scaptomyza apicalis Hardy relative to meadowfoam development over three crop-years in Linn and Benton Cos., Willamette Valley, OR.
Mean number of fliesftraplw eek 1996-97 Mimber of larvae/i 0 plants
250 500
200 400
150 300
100 200 SONDD ...... -r.wr gatath 'reproductie---'
Mean number of fliesftraplw eek 1997-98 Minte of larvaeli 0 plants
250 500
200 400
150 300
100 200
50 100
0 ,, , 1,0,1,1,1 0 S 0 N D J F MM A M J J A
getath 'reproducti'we'
Mean number of fliesitraplweek 1998-99 Mintier of larvae/i0 plants
250 500
200 400
150 300
100 200
50 100 0 _ Jjj,JLj 0 S 0 ND 0 J FM A M J J A vegatathe 'reproductne--' 39
Flies were no longer detected in fields beginning in early July, with the
disappearance of plant hosts and the onset of the dry season.
In the 1998-99 crop-year, fly populations were much lower than those of 1996-
97 and 1997-98. There were sub-zero temperatures for 1 week in late December 1998,
which reduced winter survival. First and second peaks were still detected in February
and March, but they were much smaller than those of the 2 previous years. Populations
gradually declined after March with no distinct peaks detected at any sites through June.
Results are shown in Figures 2.4 and 2.5. In Figure 2.4, the curves were drawn from the
original counts. Figure 2.5 shows the weekly moving averages, which smooth out the
weekly fluctuations and eliminate short term, local oscillations, thereby bringing out
more clearly the secular trend of the populations.
Larval populations in general were comparable to those of the adults in the
1996-97 and 1997-98 crop-years, and different in 1998-99 (Figure 2.6). Larvae were
generally detected in plant samples beginning in early January. The exception was in
Pughs' field, in which a few larvae were detected in December 1997. As mentioned
earlier, this particular field was established from volunteer plant from seed left in the
field from the previous crop-year. Plant development was about 2 weeks more
advanced relative to other fields in the same crop-year.
Larval densities gradually increased and peaked in April. This was consistent in
all study sites for the 3 year study. Densities declined in April to undetectable in early
May. The exception was in 1998 that a few larvae were detected in early June.
Development of fly populations also coincided with plant development.
Populations generally grew exponentially during the plant vegetative stage and 40
gradually declined during the plant reproductive stage (Figure 2.7). Temperatures
delayed population growth during November and December, but allowed rapid growth
after January and through early April. The gradual reduction of acceptable larval
feeding sites as plants advanced into the reproductive stage is also a key factor in
population decline.
Virtually no flies were detected from July to the end August in all 3 years of the
study (Figures 2.4 and 2.5). Reports from Czechoslovakia and Scotland indicated that
S. apicalis oversummers as puparia, surviving for up to 300 days in this stage before
adult emergence. (Maca, 1972). However, virtually no puparia were found in
meadowfoam debris and soil samples from July to August for the 3 consecutive crop- years. Only three non-viable pupae were found attached to dry stems after plants were
harvested in late July 1998. It is speculated that only small fractions of the late June larvae entered pupal stage and heavy mortality occurred in larval populations as host plants matured.
No flies or larvae were found in the Willamette Valley on alternate hosts reported in European literatures.
Development of MFF populations is influenced by weather and host plant.
Meadowfoam is an acceptable host during plant's vegetative and early reproductive stages. Larvae tunnel into all succulent tissues. Larval feeding sites shift to flower buds and immature seed pods as plant mature and vegetative sites become unsuitable.
Ambient temperature controls population growth during the crop season. It is a major mortality factor during winter. Rainfall is thought to be the main environmental cue 41 that is associated with adult occurrence in early fall. Temperature and day-length along with suitable of host plant are associated with MFF disappearance in harvested fields.
Association of MFF natural populations and weather
Autoregressive coefficient of lag-i (ri) of the weekly-moving average trap counts for 1996-97, 1997-98, and 1998-99 were equal to 0.6250 (SE0.1704, t =
3.67, df= 47), -0.5888 (SE = 0.1764, t3.34, df= 47), and 0.8216 (SE = 0.1215, t =
6.76, df= 47), respectively. Multiple regression models revealed that the weather components that most associated with the trap counts of MFF natural populations were quite different for each of the 3 years of data (Table 2.1). Regression models derived from 1996-97 and 1998-99 data indicated that the weekly average of mean daily temperature 2 weeks prior to trap inspections (AMM2), weekly average of daily mean solar radiation (ASR), and weekly average of daily mean relative humidity (ATA) significantly influenced the trap catch of fly. But, only AMM2 and ATA were significant in 1997-98 crop-year. Judging from partial R2, ASR was the factor most influential in trap catches, which explained 33 percent of the trap count variability in
1996-97 and 1998-99 seasons. In 1997-98, only AMM2 and ATA were significant factors. ATA accounted for 32 percent of the variation in number of flies on traps.
Weather accounted for nearly 50 percent or greater of the variation observed in mean weekly trap catches over the 3 year study (Table 2.1). Table 2.1. Statistical models and their parameter estimates of weekly trap counts (log (1 +y)) on yellow sticky traps of Scaptomyza apicalis Hardy and some weather components (log (x)) conducted on 3 crop-years from October 1996 to August 1999 in Linn and Benton Cos., Willamette Valley, OR.
Crop No. of yeara study site Regression models" (R2 )' (Cp)d
1996-97 5 log (y+l) = 26.0040+0.9322 log (AMM2)-1 .6951 log (ASR)-4.6515 log (ATA) 0.6189 2.19160.0180 (partial R2) (0.086 1) (0.3282) (0.1264)
1997-98 3 log(y+1)=-28.6081+1.58201og(AMIM2)+5.33701og(ATA) 0.51862.98780.0114 (partialR2) (0.2305) (0.3186)
1998-99 3 log (y+l) = -28.3629+0.6374 log (AMM2)-1.4297 log (ASR)+1.2639 log (ATA)0.48955.55440.0212 (partial R2) (0.0901) (0.3259) (0.0798) a, Meadowfoam was seeded in early October and harvested during the first half of July. b, y = weekly-moving average of trap counts (n9); AMM2 = weekly average of mean daily temperature 2 weeks prior to the trapping week (°C); ASR = weekly average of daily mean solar radiation (Langley); ATA weekly average of daily mean relative humidity (%). c, Coefficient of determination d, Mallows' Cp statistic. e, Significant levels of the regression models. f, Partial correlation of each weather component to the weekly trap count. 43
Discussion
Phenology of MFF and population development is highly synchronized with
meadowfoam phenology and weather in the Willamette Valley. Occurrences of flies in
the early fall coincide well with meadowfoam seed germination and seedling
emergence. Both plant and insect respond to rainfall and subsequent soil moisture as
their environmental cue to start their new annual cycle. Rain pattern of the Willamette
Valley seems to favor fly survival by providing necessary moisture for adult sustenance
from October through June.
Adult longevity was significantly shorter in the absence of moisture. In fact,
laboratory studies showed flies could live only from 2 to 3 days in the absence of water.
They survived at least 2 weeks when water was provided. Water that accumulated on
soil or plants served as moisture sources for adults.
Flies detected in September and October served as the "founder generation"
establishing on meadowfoam seedlings. The two events are highly synchronized. A
clearer view could be seen from the field in which a crop was allowed to establish from volunteer seed in 1997-98; these plants also germinated soon after the rain, about 2 weeks after the first appearance of MFF.
Disappearance of flies in fields in late fall reflects mortality of founder generation after mating and oviposition. Weather particularly favors MFF development from late January to March during this study as average daily temperatures approached
10 degrees Celsius. This time period also coincides with the abundance of the larval food resource, as meadowfoam plants are in a lush vegetative stage. Fly populations increased exponentially during this period that 3 peaks were notes. The greatest 44 numbers of adults occurred in late February and early March. In all three crop-years, weather conditions and crop physiology were optimal for MFF development during this period of the crop-cycle.
Soon after the flowering stems elongated and flower buds formed, oviposition
and larval feeding sites shifted to the newly formed reproductive structures. MFF populations gradually declined beginning with bloom in late April. No stages were
detected after harvest in July. Larvae could develop flowering structures of meadowfoam up early seed set. Feeding sites were mainly in the carpel structure inside the unopened flowers and on tender, young seed. Severely damaged flower buds usually did not open.
As seed of the crop gradually hardened, larvae disappeared from plant samples from late April through June. Larvae did not feed on hard seed. Also, the warming temperatures beginning in April might not have favor larval development as much as those of the cooler months February and March.
It was not possible to separate effects of the onset of the thy season from maturity of the crop in reducing MFF populations. It is believed that an extremely small survives through the summer. This is probably accomplished by puparia.
Attempts were made to confirm this speculation after crops were harvested during July and August of1998and1999.Only three individual puparia were found attached to dry stems of meadowfoam and collected from soil samples in1998and1999.No adults emerged from the 3 puparia. Field surveys for adults and larvae using methods in commercial fields were unable to detect flies or larvae from other potential hosts. 45
S. apicalis andLimnanthes a/balife cycles are highly synchronized. This suggests that fly and plant may have a very close relationship having evolved together in a long period of time to this region, as indicated by Wheeler (1952) and Wheeler and
Takada (1966).
Virtually no other insects were found exploiting this plant other than MFF.
MFF is the only insect adapted to meadowfoam. It has successfully overcome chemical defenses of meadowfoam, the glucosinolates that are anti-feedant and even lethal poisons to most herbivores. (Bartelt and Mikolajczak, 1989; Vaughn, et al., 1996).
European literatures states that MFF exploits a wide range of host plants. Surprisingly, most of these reported plants also contain glucosinolates or related compounds.
Evolved tolerance mechanisms to these products could facilitate the colonization by
MIFF of meadowfoam as a host. Certainly the meadowfoam populations of S. apicalis have "escaped from the interspecific competition" as well as "enemy-free space,"
(Kogan, 1986;Begonetal., 1996). 46
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CHAPTER 3
SURVIVAL AND DEVELOPMENT OF Scaptomyza apicalis HARDY (DIPTERA: DROSOPI{[LIDAE) ON SELECTED HOST PLANTS AND NATIVE MEADOWFOAMS,LIMNANTHES SPP.
Sarote Panasahatham, Glenn C. Fisher, Joseph T. DeFrancesco, and Daryl T. Ehrensing 51
Abstract
Seven vegetables and nine native meadowfoams (Limnanthes spp.) were evaluated in comparison to a commercial hybrid meadowfoam for suitability as larval hosts for Scaptomyza apicalis Hardy. Survival rates and developmental times of larvae, pupae and adults reared from first instar larvae on the different hosts varied significantly.
Larvae of North American S. apicalis populations found in commercial meadowfoam fields feed and develop only on Limnanthes spp. Cultivated meadowfoam, a commercial hybrid, L alba (cv. Floral) resulting from the interspecific cross of L. grac4flora and L. alba was the best larval host of all Limnanthes spp. evaluated.
Survivorship was significantly greater (80%) and developmental times were significantly shorter for larvae on the hybrid, Floral, than for larvae on the native
Limnanthes spp. When held under the same environmental conditions, flies reared from larvae on the meadowfoam hybrid lived significantly longer than flies reared from larvae on the native meadowfoam. 52
Introduction
Scaptomyza apicalis Hardy, unofficially referenced here as the "meadowfoam
fly" (MFF) is a small drosophilid fly that occurs throughout the Holarctic (Basden,
1954; Wheeler and Takada, 1966; Maca, 1972). Hardy (1849) first reported finding the
leaf-mining larvae of this insect on yellow and white turnip (Brassica rapa) and pea
(Pisum sativum) in Scotland. Basden (1954) indicated that this species could also be
found on Scurvy grass (Cocklearia officinalis) and Lady's-fingers (Anthyllis
vulneraria) during summer near the east coast of Scotland. In North America, Wheeler
(1952) listed a possible single host plant, watercress (Nasturtium officinale), in his
"World Catalog of Drosophilidae." Interestingly though, his attempts to rear the larvae
on watercress failed.
Maca (1972) comprehensively reviewed literatures pertaining to the taxonomy,
bionomics and plant host associations of Scaptomyza species group in the Northern
Hemisphere. Less than a dozen plant species in the UK and Scandinavian countries are
cited as actual or probable hosts of S. apicalis. In addition to the plants noted above, broccoli, cabbage, kale, turnip and radish are also included as hosts. Most of the
Brassica host plants are characterized by usually having relatively large concentrations
of mustard oil, glucosinolates and/or thioglycosides.
Other hosts reported are field pennycress (Thiaspi arvense); Resedaceae:
(Caylusea abyssinica); Viciaceae: garden pea (Pisum sativum); Asteraceae: (Rho&znthe manglesii); Capparidaceae; Tropaeolceae; and Papaveraceae.
MFF was first reported attacking selection lines of Limnanthes alba in research plots in 1988. Flower buds were reported to be damaged (Fiez et al., 1991). Ehrensing 53
Ct al.(1990)and Jolliffet al.(1993)observed larvae mining in leaves, petioles, and
crowns during vegetative growth stage. Later they observed mining in flower buds, bloom, and immature seed pods. With the exception of a few collection records for the adults, S. apicalis was virtually unknown in Oregon until the late1980'swhen larvae were observed causing substantial injury to breeding lines ofL. a/bain the Willamette
Valley, OR. Marshall R. Wheeler tentatively identified the adults as Scaptomyza sp.
David A. Grimaldi identified a series of flies as Scaptomyza apicalis Hardy by the descriptions given by (Maca,1972).
Knowledge of an insect pest's host range can be crucial to its effective control and management. Lettuce root aphid was all but eliminated as an economic pest in head variety lettuce grown in certain areas of the Salinas Valley, CA when the identification of and role of an alternate host in the seasonal development of the aphid were determined. Elimination of a half dozen Lombady poplar trees, obligate alternate hosts of the aphid, adjacent to the lettuce fields eliminates pest populations of the aphid in these areas. At the least, alternate hosts can serve as refligia or reservoirs from which pests can emigate to infest other host plants.
Brassica vegetables and pea are S. apicalis hosts in the Palearctic. They also have been grown in the Willamette Valley commercially and in home gardens through the last century. However, only Antomyiid and Agromyzid flies have utilized these vegetables as hosts or are considered pests. Because of their presence and potential as alternate hosts for MFF, certain Brassicas and Pisum sativum were evaluated as to their fitness as alternate hosts for larvae of MW. 54
Direct feeding trials can be used to test the suitability of plants as hosts to insects (Schoonhoven et al., 1998). Acceptance of a plant and subsequent growth and development can be used to determined the suitability of a plant as a host for immature insects (Kogan, 1986; Schoonhoven et al., 1998). Acceptance normally is determined by positive and sustained feeding responses of insects to the plants provided. Non- acceptance occurs if tested subjects ignored or took but one or two bites only to abandon the plants.Performance of an immature on a plant can be described by the
survivorship and subsequent rate of development by a cohort of insects. Acceptance and performance criteria have been used to test for taxonomical differences of insects at or below species level. (Schoonhoven et al., 1998).
Variations of acceptance and performance trials have been used to evaluate host
associations for many insects, including onion maggot, Delia anliqua Meigen
(Anthomyiidae); greenbug, Schizaphis graminum (Rondani) (Aphididae); green peach
aphid, Myzuspersicae Suizer (Aphididae); brown plant hopper, Nilaparvata lugens Stal
(Delphacidae); and hessian fly, Phytophaga destructor Say (Cecidomyiidae)
(Cartwright et aL, 1946; Wu et al., 1981; Pathak and Heinrichs, 1982; Harris and Miller,
1988; Bahagiawati et al, 1989; Soni et al., 1986; Girma et aL, 1992; Ohm et al, 1997).
Ovipositing females may determine the host range of the immatures for many
species of insects. This is true where newly hatched nymphs or larvae have no options
other than host upon which the female deposited eggs (Hausmann and Miller, 1989;
Mowry et al., 1989; MomIl and Arida, 1991). Wiklund (1975) pointed out, however,
that genetic control of host selection of female for oviposition versus host selection by
feeding of larvae are different. Also many larvae are not dependent upon the female for 55 host plant location. Larvae of the omnivorous leaf-tier balloon from the bark of trees
after having hatched from eggs deposited the previous summer. Chance determines if the larvae land on or are able to locate a satisfactory host plant. Larvae of
Operophthera spp. (winter moth group) also balloon or fall from hosts and must locate
other suitable hosts to continue growth and development.
Performance can used to define host suitability. Performance considers many
parameters; survival rate, larval size, pupal size, developmental rate, and subsequent
fertility, fecundity, and longevity of the tested cohort (Kogan, 1986; Schoonhoven et al.,
1998). Host preference has been used to characterize and classify insects below species
levels (Khan and Saxena, 1988; Puterka and Peters, 1988; Mittler and Wilhoit, 1990;
Wilhoit and Mittler, 1991; Formusoh et al, 1992).
Maca (1972) used a feeding trial technique, by which larvae were reared on
potted plants to adults for confirmation plants previously cited as hosts. She confirmed
four species of plants, Thiaspi arvense, Caylussea abyssinica,Raphanussativus, and
Pisum sativum, as MFF larval hosts for S. apical/s.
A modified acceptance and performance trial was used to determine the
suitability as larval hosts the following plants, garden brassicas, radish and garden pea.
Larval acceptance and development for each host species was compared to that for
larvae on Limnanthes alba var Floral. Additional, 9 native meadowfoam species found
in Northern California, Oregon and Washington were evaluated as larval hosts by this
method. 56
Materials and Methods
These experiments were conducted in a greenhouse of the Oregon State
University campus in Corvallis from March 1 to May 25, 1998. Acceptance and performance of S. apicalis larvae on seven varieties of plants, 5 brassicas, Raphanus and Pisum compared in relation to meadowfoam, Limnanthes a/ba (cv. Floral).
Included were:
1.radish, Raphanus sativum (Brassicaceae)
2.turnip, Brassica campestris var. rapa (Brassicaceae)
3.garden pea, Pisum sativum (Viciaceae)
4.cabbage, Brassica oleracea (Brassicaceae)
5.cauliflower, Brassica oleracea (Brassicaceae)
6.broccoli, Brassica oleracea (Brassicaceae)
7.kale, Brassica oleracea (Brassicaceae)
8. meadowfoam Limnanthes a/ba (cv. Floral) (Limnanthaceae)
The experiment was arranged in a completely randomized design with 10 replications. A single first instar MIFF larva, reared from meadowfoam (cv. Floral), was transferred to the leaf of each 4-week-old plant in 10-cm diameter pot. Small punctures on leaf vessels or surfaces were made with a pin to facilitate larval penetration into leaves. Larvae were transferred to leaves using a camel-hair brush, and plants were observed until the larvae had mined completely into the leaves. Plants were then placed in 50x80x 120cm3nylon screened cages, and inspected for larvae daily. Any pupae were transferred from plants when first noticed and housed individually in 3-cm- diameter and 15-cm-long glass tubes. Moist cotton was added to tubes as a deterrent to 57
desiccation. Tubes then were capped with fine mesh, plastic screen to allow for limited
air exchange. Individual larval and pupal as well as rates of development were
recorded. Adults were allowed to emerge in the tubes and were then provided with
cotton moistened with water only. Adults were observed daily, live and dead flies were
recorded. This allowed for quantification of possible differences in longevityas a result
of larval food source.
Nine native meadowfoam species were evaluated in the above manner also
using L. alba as the reference host for comparison purposes. These testswere carried
out from April 19 to June 16, 1998 in the same greenhouse and conditions as described
for the vegetable plants. Limnanthes species investigated were
1.Limnanthes montana
2. Limnanthes douglasil rosea
3. Limnanthesfioccosa
4. Limnanthesfioccosa grandiflora
5.Limnanthesfioccosa be/lingeriana
6. Limnanthesfioccosa pumila
7. Limnanthes gracilis
8. Limnanthes gracilis gracilis
9. Limnanthes gracilis perishii
10. Limnanthes alba (cv. Floral)
Four-week- old meadowfoam seedlings in 10-cm-diameter pots were used in this trial. First instar larvae were removed from the stock culture of cultivated meadowfoam (cv. Floral) and inoculated individually on leaves of each of the native 58
meadowfoam seedlings. Plants were maintained in screened cages. They were
removed and inspected for life stages of MFF daily. Larval and pupal developmental
time, mortality, and adult longevity were recorded and compared to those observed for
MIFF on the cultivated variety. Survival rates and developmental times of MIFF were
computed according to host plant. One-way analyses of variance and mean
comparisons were performed for both experiments by using SAS (v. 7.0) statistical
analysis package (SAS, 1997).
Results
MIFF larvae rejected Brassica spp., RI sativus and P. sativum plants. None
appeared to feed and all moved away from the exudates of the pierced tissues where they were placed. All larvae were dead by the next day.
Conversely, larvae readily mined into and actively fed inside the leaves of L. a/ba cv. Floral. First instar larvae mined leaves, second and third instars tunneled down through leave petioles. Mature larvae exited petioles and fed on crown tissue. The fully mature larva attached to the plant with the cauda or simply crawled to the soil surface to pupate. Duration of larval and pupal stages averaged 12 and 12 days, respectively. Life cycle from larval stage to adult emergence of MFF on meadowfoam averaged 24 days. Adults lived an averaged of 19 days. Survival rate of MIFF on Floral cultivar meadowfoam was 70 percent. All mortality observed occurred during the larval stage. Results are shown in Table 3.1. 59
Table 3.1. Developmental times for larvae and pupae, aduft longevity, and survival rates of Scaptomyza api calls Hardy inoculated as first instar larvae on cultivated meadowfoam (cv. Floral) in greenhouse trial.
Life stage Mean developmental time (d±SD)a
Larva 12.3±1.6
Pupa 12.4±1.4
Larva to adult emergence 24.3±3.1
Adult longevity 19.3±1.6
Survival rate (Larva to adult) 7O%
a, Mean developmental time in days ± standard deviation, n = 10.
Larvae placed on native meadowfoam species initiated feeding. However, performance on these native meadowfoams, judged by survival rates, developmental times, and adult longevities, was variable. All were less suitable hosts than Floral cultivar. Mean developmental times of larvae on the native meadowfoams, which ranged from 14.2 to 17.8 days, were significantly longer than the 11.6 days recorded for the cultivar. Larvae developed most slowly on L. fioccosa grandflora; averaging 33.4 days from first instar to emergence of adult. Mean pupation times were somewhat variable, and ranged from 12.2 to 14.1 days. Flies reared from cultivated meadowfoam lived about 16 to 17 days, significantly longer than those reared from the native species.
These flies survived from 8 to 10 days. 60
Mortality occurred during the larval stages of development on plants. MFF survival rate was greatest on Floral cultivar meadowfoam of 80 percent. The lowest survival rate (20 percent) was observed for larvae reared on L. floccosa, L. floccosa pumila, L. graciiis, and L. gracillisperishii. Survival rates of 30 percent were observed on L. montana, L. doug/ash rosea, L. floccosa beiingeriana, and L. graciiis graciiis; and 40 percent on L. fioccosa grandfiora. Results are shown in Table 3.2.
Table 3.2. Developmental times for larvae and pupae, adult longevity, and survival rates of Scaptomyza apicalis Hardy inoculated as first instar larvae on nine native meadowfoams compared to the cultivated species, Limnanthes a/ba (cv. Floral) in greenhouse trial.
Dcvelo',mental time(d±SD)a Adult Survival Meadowfoam longevity rate Lalva* Pupa Lalvaadult* (d±SD) (%)
L. montana 14.2±1.6b 14. 1±1.2 28.4±3.2ab 10.6±1.6b 30
L. douglas/i rosea 16.6±1.8bc 13.2±1.2 30.6±3.8b 10.4±1.2b 30
L.floccosa 15.3±1.2bc 13.2±1.2 31.2±3.6b 10.6±1.4b 20
L.fioccosagrandiflora 17.3±1.Sc 13.4±1.6 33.4±2.8c 8.6±1.2a 40
L.fioccosabellingeriana 17.8±1.4c 13.5±1.2 31.4±2.6b 10.8±1.4b 30
L.floccosapumila 15.1±1.2bc 12.2±1.2 265±2.Sa 12.1±1.2b 20
L. gracilis 15.6±1.2bc 12.8±1.2 28.5±2.4ab 9.6±1.4ab 20
L.gracihsgracilis 15.4±1.2bc 13.4±1.4 30.6±2.6 10.6±1.2b 30
L. grad lisperi shE! 14.8±1.4b 13.3±1.2 28.6±2.6ab 10.2±1.2b 20
L.a/ba(cv. Floral) 11.6±1.2a 13.2±1.2 25.4±2.2a 16.6±1.Sb 80
a, Mean developmental times in days ± standard deviation, n = 10. Means within a column followed by the same letter are not significantly different (p = 0.05, n = 10, ANOVA-FPLSD) ns, Means within a column are not significantly different. 61
Discussion
Evidence is provided indicating that MFF has apparently restricted to
Limnanthes spp. Non-limnanthes hosts tested were uniformly rejected. The MFF population in the Willamette Valley exhibits an oligophagous dietary habit.Larvae feed and develop only in plants of the family Limnanthaceae. European populations, conversely, are polyphagous, exploiting a broader plant host range over manygenera and families. These results provide evidence for differences below species level for
European versus North American S. apicalis. It would be interesting to determine if the
European S. apicalis can useLimnanthes spp.as host plants for larvae. It can be speculated that the two exhibit biotypical differences based on the hosts. The species in
North America is defined by its hosts, restricted to Limnanthes spp. It is hard to believe gene flow has taken place between them as they are separated by a large oceanic barrier.
Interestingly, S. apicalis in both hemispheres have a common trait, in which most of their hosts contain glucosinolates. According to the chemical defense hypothesis, insects adapted to or specialized on certain plant groups use plant secondary compounds as their token stimuli for their host finding and host selection processes for feeding or oviposition (Kogan, 1986; Schoonhoven et al., 1998). The relationship between MFF and its glucosinolate-containing hosts seems to fit into this description.
Although MFF populations of both regions share the specialization on glucosinolate- rich host plants as a common trait, populations have evolved in North Americause different plant taxa under different ecological conditions.
It may be argued that an artifact of the transferring larvae, have been preconditioned on L. a/ba, would reject a different host, based on the induced feeding 62
preference principle (Schoonhoven, 1998). This principle has been demonstrated in
some insects, such as corn earworm (Heliothis zea) and cabbage butterfly (Pieris
brassicae). Larvae of both species showed a preference for food experienced in their
previous instars and refi.ised to accept other common hosts in later instars (Jermy et al.,
1968; Ma, 1972). Another example is that larvae of Bombyx hesperus, allowed to feed
on Café diable in their first two instars, though they readily accepted a different host,
Ailanthus sp., for consumption through the third instar. However, they refused to feed
and eventually died of starvation when moved back to Café diable as fourth instar larvae (Darwin, 1875). Unfortunately, in this study, there was no alternative to prepare larval stocks for the experiments, as no artificial diet or other hosts were known for
MFF.
The quality of all tested native meadowfoams as hosts for MFF larvae were substantially poorer than that of the cultivated species. It was unclear why but may involve nutritional quality or glucosinolate content, or combination of both. Regardless,
L. alba (cv. Floral), the commercial cultivar of meadowfoam is an excellent host nutritionally. This may explain in part, if not completely, on the outbreak of this insect in commercial meadowfoam fields, if other environmental conditions are favorable. 63
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Wu, R.Z., L. Zang, X. Qiu, and M. Mo. 1981. Studies on the biotype of brown planthopper, Nilaparvata lugens, in China rice varieties with different resistant genes. Acta Phytophylacica Simca. 8: 2 17-226. (Summary in English). 66
CHAPTER 4
EFFECTS OF NITROGEN FERTILIZATION AND INSECTICIDE ON MEADOWFOAM FLY (Scaptomyza apicalis HARDY) iNFESTATIONS AND MEADOWFOAM SEED YIELD COMPONENTS
Sarote Panasahatham, Glenn C. Fisher, Joseph 1. DeFrancesco, and Daryl T. Ehrensing 67
Abstract
The impacts of nitrogen fertilizer (urea) and insecticide (oxydemeton-methyl) uses in cultivated meadowfoam (cv. Floral) on meadowfoam fly (MFF), Scaptomyza apicalis Hardy (Diptera: Drosophilidae) were investigated at Hyslop Field Laboratory
from September 1997 to August 1998. Combinations of five levels of nitrogen fertilizer
(0, 22.42, 44.83, 67.25, and 89.67 kg/ha) with and without oxydemeton-methyl
applications were arranged in two-factor factorial in a randomized complete block
design with four replications. Fertilizer and insecticide were applied once in late
February and at monthly interval from late January to late April, respectively. Larval
densities, flower densities, seed set, and, seed yields were collected to measure the
impact of the treatments. Analysis of variance tests were carried out for each data set.
Proportionally more larvae are found in plots receiving high nitrogen rates compared to
low rates or no nitrogen. MFF larval density increased as its rate increased.
However, greatest fertilizer rates can significantly reduce flower density.
Monthly applications of oxydemeton-methyl from January to April reduced larval
infestation by 54 percent, but did not have significant effect on flower density. Neither fertilizer nor insecticide application effects seed set of meadowfoam. However,
interaction between nitrogen fertilizer and insecticide uses was significant on meadowfoam seed yield. High rates of nitrogen fertilizer tend to decrease meadowfoam
seed yield. Insecticide application increased seed yield at fertilizer rates of 22.42 kg/ha, but accelerated the reduction of seed yield at higher rates. 68
Introduction
To date, Scaptomyza apicalis Hardy (Drosophilidae), 'meadowfoam fly"
(MFF), is the only insect species to develop and cause appreciable injury to cultivated
meadowfoam in the Willamette Valley, OR. Plant damage is from larvae mine in the
plant crown, leaves, stem, flower buds and young seed pods. Seedling plants can be
killed, overall stand is reduced, and seed yield can be reduced. Yield reduction results
from seedling mortality, poor stand vigor and reduced seed set (Jolliff et al., 1981; Fiez
et al., 1991).
Meadowfoam is a relatively new oil seed crop. First commercial plantings were
seeded in Willamette Valley in 1983 (Pearson and Jolliff, 1986). Field trials conducted with meadowfoam parental genetic lines and accessions supported the observations that meadowfoams in general need relatively little nitrogen fertilizer for normal plant growth and seed production. Seed and oil yields in these lines were little affected by varying nitrogen rates (Calhoun and Crane, 1978; Johnson et al., 1980). However, varieties of commerce, Foamore and Mermaid, do respond positively with increased
seed yield to low and moderate levels of N fertilizers up to 50 kg N/ha. Higher rates of nitrogen, 50 to 100 kg/ha, are often associated with decreased seed yield and oil content of meadowfoam. N fertilization rates over 100 kg N/ha result in severe lodging and epidemics of gray mold(Botrylissp.) (McGahuey, 1986) Seed yields are greatly reduced (Johnson et al., 1980; Crane et al., 1981; Hart and Young, 1985; Pearson and
Jolliff, 1986).
Floral is the commercial cultivar seeded by growers in the Willamette Valley,
Oregon. It has usually produced per hectare clean seed yields averaging from 800 kg in 69
commercial fields. However, the range of yields (450 to 1,900 kg/ha) has fluctuated
substantially in these fields as well as in experimental plots (Ebrensing, 1997). Jolliff et
al. (1993) have shown that meadowfoam in experimental plots displays a negative
quadratic yield responses to N fertilizer rate. Oil yields in these plots declined as N
fertilizer applied in late winter was increased from 20 to 100 kg/ha. The highest rates of
nitrogen resulted in much greater vegetative growth and greater incidences of plant
pathogens. It also appeared that damage from the larvae of MFF was greatest in those
plants in plots receiving the greatest supplemental nitrogen (Fiez et al., 1991; Jolliff et
al., 1993).
Flower density is the only yield component of those previously studied to have a
direst, positive effect on meadowfoam seed yield (Fiez et al., 1991). However, injury
from larvae of MFF has appeared to be associated with reduced seed yields in some
commercial fields and plots containing selected breeding lines. It is interesting to note that in addition to reducing overall seed yields, plots with N fertilizer at the highest rates
also tend to have the greatest fly infestations (Jolliff et al., 1993). Increased attraction
of insects by above normal rates of nitrogen in plant tissues has been previously reported for many plants. Species diversity on a host plant is related to nitrogen levels in plant tissues. Harbaugh et al. (1983) recorded 15 species of insect pest on nitrogen fertilized chrysanthemums compared to only 6 on unfertilized chrysanthemums.
Collinge and Lauda (1988) have shown that an increase in levels of nitrogen in leaves of bittercress,Cardamine cordfoliaA. Gray, a crucifer native to North America, is accompanied by corresponding increases in the numbers of adult Scaptomyza nigrita attracted to the plants. 70
On the commercial scale, consistency of seed yield under defined conditions is crucial in determining the acceptability of meadowfoam by growers. Unfortunately, growers and researchers have experienced a wide range in meadowfoam seed production. It has been thought that MFF has contributed to this fluctuation, however supporting data has been scant. The objective of this study was to determine if nitrogen fertilizer rate and MIFF infestation alone and in combination affect meadowfoam seed yield.
Materials and Methods
Experiments were initiated in October 1997 at two locations. One was at the
Oregon State University Hyslop Field Laboratory. One was in a commercial field
(Reynolds' Farm). This second site was abandoned due to an infestation of weeds that precluded collection of significant data in the plots as well as harvest of the field.
Meadowfoam (cv. Floral) was seeded at 30-35 kg/ha with 15-cm row spacing in early
October. Plots received combinations of five levels of 46-0-0 nitrogen fertilizer (0,
22.42, 44.83, 67.25, and 89.67 kg/ha) monthly applications of oxydemeton-methyl insecticide (Metasystox-R 2EC) were interposed and plots were arranged in a two- factor factorial experiment in a randomized complete block design. Plots were 2.7x6.0 m in size. Four replications were used. Nitrogen fertilizer was topdressed at the specified rates on February 20, 1998. Oxydemeton-methyl was applied to appropriate plots at 0.56 gm ai/ha at monthly intervals from January22 to April 19, 1998 using a
CO2 charged backpack sprayer. Honeybees were placed adjacent to the plots at the equivalent of 12 hives per hectare during early bloom on May 16, 1998. 71
Nine yellow sticky traps were placed randomly in the study site to monitor and record fly activity weekly from September1997toJuly 1998.Larval infestations by plot were obtained from monthly plant samples. Samples of 10 plants each per replication were taken from plots one week after each insecticide application. Larvae were extracted from plants using Berlese ftmnels. Larval densities from the four collection dates were pooled and averaged for statistical analysis. Flower density at fill bloom was determined by counting numbers of flowers in a randomly selected 0.1m2 portion of each plot on May26, 1998.Mean numbers of seed set per flower in plots were determined as above by collecting and inspecting pods two weeks before harvest from 0.1m2portion of each plot to obtain the distribution of seeds set/pod and mean number of seeds/pod. Plots were harvested on July12, 1998.Dry, cleaned seed was weighted and recorded. Data were analyzed by two-way ANOVA in order to partition fertilizer and insecticide effects and interactions. FPLSD were used for mean separations for each data set. Correlation analyses for larval densities, flower densities and seed yields were performed. All statistical analyses were carried out by SAS v.7.0 statistical analysis package (SAS, 1998).
Results
The effects of nitrogen fertilization and insecticide application on MFF larval density, meadowfoam flower density, and seed set were independent of one another.
However, interactions did occur when seed yield was analyzed (Table 4.1).
Correlations among the response variables measured in the experiment were not 72 correlated. However, flower density and seed yield were highly correlated to each other
(r = O.52,p = 0.01, n40) (Table 4.2).
Table 4.1. Analysis of variance for main effects and treatment interactions of nitrogen fertilizer rate and insecticide application effects on Scaptomyza apicalis Hardy larval density, meadowfoam (cv. Floral) flower density, seed set and seed yield at Hyslop Field Laboratory from October1997to August1998.
Treatments Larval densityFlower densitySeed setlflowerSeed yield (no./10 plants) (0.1m2) (0.1m2) (kg/ha)
Fertilizer rates ** ** ns **
Insecticide ** ns ns ns
Interactions ns ns ns * *
**, Significant atp= 0.01, n =4; ns, not significantly different.
Table 4.2. Correlation among larval density of Scaptomyza apicalis Hardy, flower density and seed yield of meadowfoam (cv.Floral) at Hyslop Field Laboratory of crop year1997-98.
Flower density Seed yield
Larval density -0.2230 (ns) -0.0085(ns)
Flower density 0.5231 (**)
**, variableswere significantly correlated atp = 0.01 ns, variables were not significantly correlated 73
Numbers of MFF larval per plant increased only slightly within each increase in
nitrogen rate. However, larval densities for 0 kg/ha plots were significantly lower than that for the higher rates of N tested. Neither was significantly different from all
intermediate levels from 22.42 to 67.25 kg/ha (Table 4.3). Larval densities within plots treated with insecticide were significantly lower than those within the unsprayed plots.
They were not significantly different among the various fertilizer rates within thesame insecticide treatment (Figure 4.1). Overall, oxydemeton-methyl reduced larval density by 54 percent of the untreated plots.
MFF adults were first detected in this plot during early October 1997, prior to seedling emergence through harvest. Flies were trapped throughout the study andseem to display numerous peaks. Most flies were caught in February and March, with adult numbers peaking in early March. Subsequent populations of both adults and larvae of
MFF gradually declined through early July (Figure 4.2). 74
Table 4.3. Effects of nitrogen fertilizer (urea) rate on density of Scaptomyza apical/s Hardy larvae infesting meadowfoam (cv. Floral) at Oregon State University, Hyslop Field Laboratory from February to May 1998.
Fertilizer rates Larval density±SEa (kg/ha) (mean numbers/10 plants)
0 23.0±2.6 a
22.42 23.2±4.8 ab
44.83 24.3±4.1 ab
67.25 24.0±3.8ab
89.67 29.4±4.7 b
a, Mean larval density±standard error; Mean within a column followed by the same letter are not significantly different (p = 0.01, n =8, ANOVA-FPLSD). 75
Figure 4.1. Mean numbers of Scaptomyza apicalis Hardy larvae (n=4) in fertilized plots with and without insecticide (oxydemeton-methyl) applications at Oregon State University, Hyslop Field Laboratory from February to May 1998.
Mean numbers/lO plants Hyslop
60
50
40
30 20 -U- -U--- 10
0 0 22.42 44.83 67.25 89.67 fertilizer (kg/ha)
Figure 4.2. Mean weekly numbers of Scaptomyza apicalis Hardy fly on yellow sticky traps (n =9) at Oregon State University, Hyslop Field Laboratory from October 1997 through September 1998. 76
There was apparently no interaction between nitrogen fertilization and
insecticide application on flower density. Bloom density of meadowfoam in insecticide
treated plots did not produce more flowers than meadowfoam in the unsprayed plots
(Table 4.1). However, N fertilizer rate did affect meadowfoam flower production
(Table 4.1). Flower density was greatest in plots receiving no fertilizer. Mean numbers
reduced as fertilizer rates increased (Table 4.4). Unfertilized plots produced 62 percent more flowers than plots fertilized with urea at 89.67 kg/ha. Flower densities among
plots treated with the three intermediate fertilizer rates were not significantly different from one another. However, flower densities in these plots were significantly fewer than those in the unfertilized plots but significantly greater than those in the plots receiving highest fertilizer rates. Results are shown in Table 4.1 and Table 4.4.
Table 4.4. Comparisons of meadowfoam flower density within plots of different fertilizer rates at Hyslop Field Laboratory on June 11, 1998.
Fertilizer rates Flower densitya (kg/ha) (Mean numbers/O. 1m2)
0 1,311.la
22.42 1,067.3b
44.83 893.8b
67.25 907.6 b
89.67 500.6 c
a, Means within a column followed by the same letter are not significantly different (ANOVA-FPLSD,p = 0.01, LSD140.07, n = 8). 77
Number of seeds set per flower of meadowfoam plants in these plots was unaffected by nitrogen rate or insecticide application alone or in combinations (Table
4.1).All treatment combinations displayed comparable number of seeds set per flower which varied from2.11 to 2.66seeds per flower (Table4.5). Mostmeadowfoam flowers in this trial regardless of treatment produced two to four seeds, which accounting for about55percent of the seed yield. Overall, seed set averaged at2.44 seeds/flower (Table4.4).Only12percent of the meadowfoam flowers in this trial produced five or more seeds. About16percent of the pods showed no signs of seed development. Results are in Table4.5. 78
Table 4.5. Distribution and percentages of the seed set per flower of different fertilizer rates and insecticide treatments on meadowfoam,Limnanthes a/ba(cv. Floral) collected at Hyslop Field Laboratory on June 28, 1998.
Distribution of seed set/flower Treatmentsa (%) Average" (Seed! 0 1 2 3 4 5 >5 flower)
0 11.16 13.97 18.60 21.32 24.38 10.41 0.16 2.6570
OfIA 18.89 14.48 13.80 18.67 15.61 18.44 0.11 2.5339
22.42 13.99 16.65 15.08 12.78 26.66 14.84 0 2.6598
22.4211A 17.68 21.17 14.86 17.57 17.12 11.60 0 2.3007
44.83 20.03 15.18 16.23 14.53 21.33 12.70 0 2.4005
44.83/lA 13.87 15.31 20.10 22.37 19.98 8.25 0.12 2.4450
67.25 16.94 13.58 17.66 20.73 18.10 12.99 0 2.4847
67.25/IA 14.99 21.48 15.52 18.97 17.90 11.14 0 2.3675
89.67 15.97 14.93 22.05 14.24 18.05 14.76 0 2.4774
89.67/IA 21.22 16.56 21.22 19.29 14.31 7.40 0 2.1109
Average 16.47 16.33 17.51 18.05 19.35 12.25 .04 2.4437
a, Fertilizer (kg/ha)/Insecticide application (IA). ns, not significantly different (n = 4).
There was high correlation between meadowfoam flower density and seed yield
(Table 4.1). Plots with greatest flower densities consistently produced greatest seed yields. Interestingly, MIFF larval density had little effect on meadowfoam seed yield.
Although larvae were less in plots receiving oxydemeton-methyl applications densities were reduced by only a little more than 50% (Figure 4.1 and Figure 4.3). Interaction between nitrogen fertilization and insecticide application was significant on seed yield
(Table 4.1). Unfertilized plots generally produced higher seed yields than fertilizer 79 treated plots. However, seed yield was significantly increased by 10 percent when insecticide was used in plots receiving the 22.42 kg/ha fertilizer rate. In the plots receiving the highest N rate, the use of insecticide showed decreased seed yield by almost 16 percent when compared to unsprayed plots. There were no significantly different seed yields measured from the intermediate rates of fertilizer whether insecticide was used or not. Details were shown in Figure 4.3 and Table 4.6.
Figure 4.3. Mean seed yield of meadowfoam (cv. Floral) (n=4) in plots of different fertilizer rates with and without oxydemeton-methyl insecticide sprays conducted from October 1997 to July 1998 at Hyslop Field Laboratory.
Yie'd (kg/ha) Hyslop 900,
.11
Spray
0 2242 44.83 67.25 89.67 Fertilizer (kg/ha) 80
Table 4.6. Mean seed yield of meadowfoam,Limnanthes alba(cv. Floral) in plots of different fertilizer rates, with and without oxydemeton-methyl insecticide sprays conducted from October 1997 to July 1998 at Hyslop Field Laboratory.
Treatmentsa Seed yield±SE" (Fertilizer/Insecticide) (kg/ha)
0 741.2±18.7a
0/IA 691.6±25.Oab
22.42 655.1 ±22.7b
22.42/IA 729.6 ±39.7 a
44.83 674.7±36.7ab
44.83/IA 697.4±34.3 ab
67.25 660.3 ±21.7b
67.25/IA 643.9 ±20.Ob
89.67 651.1 ±29.6b
89.67/IA 548.3±26.8 c
a, Fertilizer (kg/ha)/ Insecticide applied. b, Seed yield±standard error; Means within same column followed by the same letter are not significantly different (ANOVA-FPLSD,p = 0.01, LSD = 59.808, n = 4). 81
Discussion
This trial supports results of previous research indicating that increasing nitrogen fertilizer rates can negatively affect seed yield as reported by different authors
(Calhoun and Crane, 1978; Johnson, Ct a!, 1980; MaGahuey, 1986; Fiez, et al., 1991;
Jolliff, et al., 1 993b). Meadowfoam is sensitive to excessive nitrogen fertilizer.
Excessive fertilizer rates also increase larval densities of MFF. Both are inversely correlated with seed yield. Excessive nitrogen application reduced all seed yield components. Lodging was not observed in this experiment as previously reported (Fiez et aL, 1991; and Jolliff et al., 1993b). Plants in plots with higher nitrogen rates were weak etiolate and tended to branch less compared to plants in low N rate plots.
Monthly applications of oxydemeton-methyl reduced MFF infestation rate by only 54% in this trial.It had little or no effect on flower production and seed yield in this study. Insecticide applications elevated seed yields at low nitrogen fertilizer rate
(22.42 kg/ha). Interestingly, when contrasted to unsprayed plots, the use of multiple applications of oxydemeton-methyl prior to bloom actually decreased yields in plots receiving the highest nitrogen fertilizer rate.
The significant increase in the MFF infestations at higher nitrogen rates suggests that this insect is preferentially attracted to plants high in nitrogen content.
Although larval densities were significantly different in sprayed versus unsprayed plots yields were not improved significantly (Table 4.1). This could suggest the degree of protection afforded by oxydemeton-methyl, which did not result in a significant greater number of blooms in the sprayed plots was insufficient. 82
Pollination is another important factor in meadowfoam seed yield. Jahns and
Jolliff (1990) and Jahns Ct al. (1991) reported that honeybee density was positively correlated with meadowfoam seed set and seed yield. This is particularly important because seeds set per flower in the trial was not significantly different among the treatments, indicating that differential pollination of flowers among treatments was not an influencing factor. 83
References Cited
Calhoun, W., and J.M. Crane. 1978. Seed yields of meadowfoam as influenced by N, seeding rates, and soil-water table levels. Agron. J. 70: 924-926.
Collinge, S.K., and S.M. Louda. 1988. Herbivory by leaf miners in response to experimental shading of a native crucifer. Oecologia. 75: 559-566.
Fiez, T.E., O.S. Norberg and G.D. Jolliff. 1991. Yield components in three meadowfoam lines. Agron. J. 83: 598-602.
Harbaugh, BK., J.F. Price and C.D. Stanley. 1983. Influence of leaf nitrogen on leafminer damage and yield of spray chrysanthemum. HortScience. 18: 880-881.
Hart, J., and W.C. Young ifi. 1985. Meadowfoam fertilizer trails.InH.W. Youngberg and J. Burcham (ed.). Seed Production Research at Oregon State University. USDA-ARS Cooperating, Dept. of Crop Sci., Ext./CrS. 61: 5-8.
Hart, J., and W.C. Young III. 1986. Summary of meadowfoam response to fertilizer application.InH.W. Youngberg (ed.). Seed Production Research at Oregon State University. USDA-ARS Cooperating, Dept. of Crop Sci., Ext./CrS. 68: 18- 21.
Jahns, T.R., and GD. Jolliff. 1990. Pollen deposition rate effects on seed set in meadowfoam. Crop Sci. 30: 850-853.
Jahns, T.R., D.M. Burgett, and GD. Jolliff 1991. Pollination and seed set in meadowfoam. Oregon State Univ., Ext. Cir. 1360. Corvallis.
Johnson, J.W., M.B. Devme, M.B. Kleiman and GA. White. 1980. Nitrogen fertilization of meadowfoam. Agron. J., 72: 917-919.
Jolliff, G.D., M. Seddigh. 1991. Evaluating nitrogen fertilizer rate and timing for meadowfoam seed and dry matter production. Agron. J. 72: 99-103.
Jolliff, GD., M. Seddigh and M.L. McGahuey. 1993a. Nitrogen rate and timing effects on meadowfoam oil yield and oil-yield components. Field Crop Res. 31: 111- 119.
Jolliff, G.D., M. Seddigh, OS. Norberg and I.E. Fiez. 1993b. Seeding rate, nitrogen fertilization, and irrigation effects on Floral meadowfoain oil yield. Agron. J. 85: 188-193.
Lightfoot, D.C., and W.G. Whitford. 1987. Variation in insect densities on desert creosotebush: Is nitrogen a factor?. Ecology. 68: 547-557. 84
McGahuey, M.L. 1986. Nitrogen fertilization rate and application timing effects on growth and seed-oil yield of meadowfoam. M.S. Thesis, Oregon State University. 96 p.
SAS Institute. 1998. SAS user's guide: statistics. SAS Institute, Cary, NC. 85
CHAPTER 5
Conclusions
Meadowfoam is an oil seed crop with potential for being a profitable, alternative crop on the heavy acid soils of western Oregon. It can be grown in rotation with grass seed crops and offers an economically viable alternative to annual ryegrass seed production on the heaviest and most waterlogged soils in the Willamette Valley, OR.
Nearly 3,600 hectares of the commercial variety, Floral, were harvested in 1998.
A small drosophilid fly has been the only insect observed thus far causing extensive damage in experimental plots as well as commercial fields. This fly was tentatively identified as Scaptomyza sp. by Marshall R. Wheeler in 1990. It was subsequently identified as Scaptomyza apicalis Hardy (F. Drosophilidae) by David A.
Orimaldi in 1997. The common name meadowfoam fly will be proposed.
S. apicalis larvae damage leaves, stems, crown tissue and flower buds of meadowfoam. Poor stands and low seed yields have been blamed on this fly over the last 10 years.
This research documented biology, seasonal abundance, factors regulating populations, and plants that serve as larval hosts. Effects of nitrogen fertilizer rates alone and in combination with a selective insecticide applied to meadowfoam plots were correlated to seed yield.
Factors that are most significant in regulating populations of MFF in commercial meadowfoam fields are weather and meadowfoam plant availability for oviposition and subsequent larval development. Parasitoids were not collected or reared 86
from the fields and research plots of meadowfoam. A number of carabid beetles species
were collected on the ground of meadowfoam fields. These generalist predators could
have preyed on MFF larvae and pupae, which were close to or on the ground.
However, no solid evidence was found or could be confirmed. Seasonal population
trends were synchronized highly with meadowfoain developmental stages and its annual
cycle. Fall rains appear to be the prime environmental cue initiating the new annual
cycle for both MFF and meadowfoam. Meadowfoam is seeded in early October. Seeds
germinate and seedlings emerge in the second half of October. Populations of the fly
and larvae remain low from fall until late January. Populations grew rapidly from late
January to March and gradually declined through June as plants entered and completed reproductive stages. No MFF adults were collected on traps from July until early
September. It is thought that the puparia aestivate in the soil or adults seek alternate host plants after harvest, prior to new fall seedling emergence. However, no other hosts were identified and few puparia were screened from soil samples taken after harvest from the fields.
Temperature was the weather component most influential in regulating populations of MFF. Temperature below00Celsius for a week or more in early winter accounted for a significant drop in larval and adult populations in the3Tdyear of the study. Subsequent generations of MFF in late winter and early spring remained quite low. Numbers of flies trapped on yellow sticky traps were significantly associated with temperatures 2 weeks prior to trapping, solar radiation, and relative humidity. These three weather components accounted for 50 to 60 percent of trap count variabilityas indicated in the multiple regression models. 87
Field collected MIFF would not oviposit on plants other than Limnanthes spp..
Correspondingly, larvae also rejected all non-limnanthes plants in laboratoly tests, including, radish, turnip, broccoli, cabbage, cauliflower, and kale (Brassicaceae) and
Pisum sativum (garden pea) (Viciaceae) as their hosts. This is in contrast to the
European literatures citing them as hosts. The only hosts which immatures developed on and from which adults emerged were Limnanthes spp.. Interestingly, the cultivated meadowfoam derived from L. alba (cv. Floral) proved to be the superior host for MFF larvae when compared to all other native meadowfoam species tested.
In our field trails, increasing nitrogen fertilizer rates and applications of insecticide to control MIFF did not correlate with increased seed yield. Meadowfoam was very sensitive to excessive nitrogen. Stand vigor and stem branching were significantly reduced at nitrogen fertilizer rates greater than 22.42 kg/ha. Flower densities and seed yields were also decreased at the higher nitrogen rates tested. As nitrogen rates increased, larval densities tended to increase, indicating that MFF preferred plants with high nitrogen content. Applications of oxydemeton-methyl at monthly intervals from January to April reduced larval densities by an average of 54 percent compared to untreated plots. However, these insecticide applications increased meadowfoam seed yield by only 10 percent in only one of the nitrogen rate plot (22.42 kg/ha). Higher nitrogen fertilizer rates accelerated the reduction of meadowfoam flower density and seed yield.
As mentioned earlier, weather played a significant role in regulating MIFF populations. Average temperatures between 5 and 10 degrees Celsius during December and January favored population development during late fall and early winter. This 88 allowed for rapid population increase in the following generations from late January to
March. Temperature below 0 degrees Celsius during early winter was the key mortality factor in suppressing populations of subsequent late winter and spring generations.
Reducing the density of this first fall-winter generation should be an important factor in reducing MFF damage to meadowfoam. Insecticide use in late January or early
February to suppress population may also result in the reduction of population of subsequent winter and spring generations and may, under certain conditions, benefit seed yield.
Use of nitrogen fertilizer is an important aspect of MFF management. Over fertilization results in reduced yields, increased vegetative growth, and greater injury from MFF. Meadowfoam apparently requires a very low rate of nitrogen fertilizer, 22.4 kg/ha or less. 89
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