Parasitism and Predation on Egg Masses of the Southern
Green Stink Bug, Nezara viridula (L.) (Heteroptera:
Pentatomidae), in Tomato, Okra, Cowpea,
Soybean, and Wild Radishl,2
B. M. Shepard, K. D. Elsey 3, A. E, Muckenfuss and H. D. Justo, Jr.
Clemson University, Coastal Research and Educalion Center
2865 Savannah Highway
Charleston, SC 29414 USA
J. Agric. Entomol. 11(4): 375-381 (October 1994)
ABSTRACT Predation and parasitism of eggs oCthe southern green stink
bug, Nezara uiridula (L.), were assessed by placing egg masses in tomato,
okra, cowpea, soybean, and wild radish during 1991 and 1992. Percent
parasitism and predation of N. uiridula egg masses were variable among
years and crops, but parasitism was higher than predation in tomato for both
years. Average percent parasitism and predation were approximately equal
in okra, soybean and cowpea in 1990 and in wild radish in 1991. During
1990, predation was higher than parasitism in soybean toward the end of the
growing season but parasitism was higher early in the season in okra and
cowpea. Parasitism of egg masses in wild radish reached a peak of nearly
100% during May 1991 and declined to about 30% toward the end of the
sampling period. Season long parasitism of N. uirldula egg masses in
soybean and okra was higher than predation in 1991. The major patasiic
from all crops was Trissolcus basalis (Wollaston).
KEY WORDS Nezara viridula, predation, parasitism, tomato, okra, cowpea,
soybean, wild radish. Trissolcus basalis.
The southern green stink bug, Nezara viridula (L.), is widely distributed
throughout the world and is a major pest on many fruit, vegetable, nut and grain
crops (DeWitt & Godfrey 1972, Todd & Herzog 1980). It also attacks many wild
hosts that serve as reservoirs until agricultural crops are available (Jones &
Sullivan 1982), Nezara viridula ecology and behavior were reviewed by Todd (19S9)
and reviews by Jones (1988) and Luck (1981) contained references to parasites
important in N. viridula control. The major species that attacks N. uiridula in the
United States is the egg parasite, TrissolclLs basalis (Wollaston) (Hymenoptera:
Scelionidae) Jones (1988). Nishida (1966) glued eggs of laboratory reared N.
vi.ridula to leaves of Asystasia coromandeliana Nees in Hawaii and found that
parasitism by T. basalis ranged from 14 to 55% and predation by the ant Pheidole
megacepha./a (F.) ranged from 2 to 100%. Besides this study, attacks by both
1 Accepted for publication 15 June 1994.
2 Technical contribution No. 4009 of the South Cnrolina Agricultuml Experiment Station, Clemson
University, Clemson se.
3 U. S. Vegetable Laborulory, ARS, USDA, 2875 Suvllnnnh HighwHY, Clmrlel:ltoll, South Cllrolinu 2901101.
375
376
J. AW;c. Entomol. Vol. ll, No.4 (1994)
predators and parasites on eggs of N. uiridula located in difTerent host plants
have not been measured, although Yeargan (1979) monitored the action of
parasites and predators on eggs of Acrosternum hilare (Say) and related
pentatomid species in soybean and alfalfa.
Predators have been reported as important N. uiridula mortality factors
(Kiritani 1964, Nishida 1966, Starn et al. 1987). Using an enzyme linked
immunosorbent assay (ELISA), Ragsdale et al. (1981) identified 27 species of
insects and spiders that attacked eggs and nymphs of N. ui.ridula in soybean.
In a separate study in Charleston, se, T. basalis attacked an average of
53.1 ± 1.9% of eggs per egg mass (n = 260) and predators attacked 78.0 ±
1.6% (n = 451) (H. D. Justo, personal communication). The average number
of eggs per egg mass as determined from a subs ample of the egg masses
used in this study was 73.7 ± U.8 (n = 120).
This present study was undertaken to determine the seasonal incidence of
parasitism and predation of eggs of N. uiridula in tomato, Lycopersicum
esculentum Mill.; okra, Abelmoschus esculentus (L.); cowpea, Vigna
unguiculata (L.) Walp.; soybean, Glycine max (L.) Merr.; and wild radish,
Raphanus rapha.nistrum, L., in coastal South Carolina.
Materials and Methods
Field tests were carried out at Clemson University's Coastal Research and
Education Center from 6 June to 26 October 1990 and from 10 April to 19
September 1991 to evaluate parasitism and predation on eggs of N. viridula
in tomato, okra, cowpea, soybean. Wild radish was included in 1991.
During 1990, 'Sunny' variety tomatoes were transplanted to the field on 3
August, 'Clemson Spineless' okra was planted on 30 April, 'Mississippi
Silver' cowpea was planted on 11 May, and 'Young' soybean was planted on
14 May. In 1991 the same varieties of tomato and okra as in 1990 were
planted on 19 March and 27 May, respectively. 'Carolina Cream' cowpea and
'Coker 485' soybean were planted on 9 May. Each field was approximately
0.25 ha except for the wild radish that occurred in naturally established
clumps along borders of surrounding fields.
Egg masses were obtained from a colony of N. viridula reared at the U. S.
Vegetable Laboratory, Charleston, SC. Egg masses were stored at -50·C
until ready for placement in the field. Powell & Shepard (1982) had
determined that N. viridula eggs stored at -50°C were suitable hosts for the
parasite T. basalis.
Ten freezer-stored egg masses were placed randomly in each field weekly
by gluing (Elmer's glue) the egg masses to small strips of cardboard and
stapling the strips to the undersides of leaves. At the end of each week,
missing egg masses were recorded and those remaining were removed,
placed in small plastic petri dishes and held in an insect rearing room at 24
± 5°C with a photoperiod of L:D 14:10 to allow parasites to emerge. Missing
egg masses were considered to be preyed upon. Parasitism was calculated as
a percentage of the remaining masses, either whole or partially eaten.
SHEPARD et al.: Parasitism and Pl'edation on N. uiridula Egg masses
377
Results and Discussion
1990 Tests. Predation and parasitism on N. viridula egg masses varied
widely between crops and growing seasons. More than 95% of the parasites
found in all crops during both seasons were T. basalis with Ooencyrtus
submeta.llicus (Howard) (Hymenoptera: Encyrtidae) present in low numbers.
In a crop of fall tomatoes in 1990 there was no predation on N. viridula egg
masses (n = 50) but parasitism reached 70% on two sampling dates (Fig. 1A).
Percent parasitism and predation of egg masses (n = 70) in okra are
shown in Fig. lB. Parasitism reached over 80% early in the season. During
the latter two sampling dates predators consumed about 50% of the egg
masses while T. basalis attacked from 0-20%. There was little difference in
the season-long mean levels of parasitism (37%) compared to predation (33%)
in okra.
Parasitism of egg masses (n = 50) in cowpea reached 70% in early August
but declined to zero as the season progressed (Fig. Ie). Conversely,
predation at the beginning of the season was near zero and increased to 50%
toward the end of the season. The shifts in importance between the two
natural enemy groups were evident in several of the crops and it was clear
that both parasites and predators were important in impacting natural
populations of N. uiridula.
In soybean, predators were the most important group of natural enemies
attacking egg masses (n = 70) during the last four sampling dates (Fig. 10),
but as in all crops in 1990, parasitism was highest on the first sampling
date. On 29 August, predation reached 80% but parasitism was not detected.
1991 Tests. Seasonal incidence of egg mass (n = 90) parasitism and
predation in tomato is shown in Fig. 2A. As in 1990, parasitism was higher
than predation and the latter was detected only during the last 3 wks of the
season and then at levels usually below 20%. Parasitism was low (about
10%) during the first 3 wks, peaked at 90% during mid-May and declined as
the season progressed.
Natural enemy action on N. viridula egg masses (n = 70) placed in okra
was lower than in soybean or wild radish. Parasitism was highest (about
55%) during the first sampling period (15 July) and generally declined
thereafter (Fig. 2B). Season-long average percent predation (11%) was lower
than parasitism (34%).
The action of predators and parasites on egg masses (n = 90) in soybean is
illustrated in Fig. 2C. Average seasonal parasitism (82%) was higher than
predation (41%). Parasitism increased to nearly 100% on 8 August and
remained high throughout the season. The action of predators was less
impressive but increased to about 70% toward the end of the season.
The season~long percent predation and parasitism on N. viridula egg
masses (n = 100) in wild radish are shown in Fig. 2D. The action by these
natural enemy groups on this wild host plant is about equal to that in
soybean. Parasitism reached a peak of nearly 100% during the week of 9 May
and predators took about 80% of the N. viridula egg masses during their
peak activity toward the end of May.
J. Agric. Entomol. Vol. 11, No.4 (1994)
378
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Fig. 1. Percent parasitism and predation on N. uiridula egg masses placed in
tomato (A), oha (B), cowpea (C), and soybean (D). Charleston, SC.
1990.
SHEPARD et a1.: Parasitism and Predation on N. uiridula Egg masses
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tomato (A), okra (B), soybean (C), and wild radish (D), Charleston, SC,
1991.
380
J. Agric. Entomol. Vol. 11, No.4 (994)
In summary, there were shifts in the importance of parasites and
predators during the season and between crops. In many cases, as the action
of predators increased, action by parasites declined. Obviously, predator
attacks may have masked the impact of parasites because predators
probably consumed the parasitized egg masses. Also, removal of egg mass by
predators probably prevented parasitism in many cases. The most striking
example of a clear preference by a natural enemy group was in tomato where
parasites dominated and the action of predators was almost absent.
OUf results indicate that both predators and parasites may play an
important role in regulating populations of N. viridula. The combined action
by these groups of natural enemies often attacked 100% of the egg masses
placed in some crops. Other research (H. D. Justo, personal communication)
has shown that if an egg mass is attacked by natural enemies 53 - 78% of
eggs will be destroyed.
Acknowledgment
We express our sincere appreciation to Dr. Walker A. Jones, USDA-ARS, Biocontrol
of Insects Research Unit, Weslaco, Texas, and to Dr. David Tonkyn, Biological
Sciences Department, Clemson University, Clemson, South Carolina for their helpful
comments.
We extend our thanks to Mr. Max DuBose and Ms. Louise Cauthen for their
assistance with this study. Dr. P. M. Marsh confirmed our parasite identifications. We
thank him for this.
References Cited
DeWitt, N. B. & G. L. Godfrey. 1972. The literature of arthropods associated with
soybean. II. A bibliography of the southern green stink bug, Nezara uiridula (L.).
Illinois Nat. Hist. Surv. BioI. Notes 78, 23 pp.
Jones, W. A. ]988. A world review of the parasitoids of the southern green stink bug,
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273.
Jones, W. A. & M. J. Sullivan. 1982. Role of host plants in population dynamics of
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Kiritani, K. 1964. Natural control of populations of the southern green stink bug,
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381
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273-292.
Todd. J. W. & D. C. Herzog. 1980. Sampling phytophagous Pentatomidae on
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