X?

SEASONAL ABUNDANCE OF THE GREENBUG
AND ITS NATURAL ENEMIES
IN GRAIN SORGHUM IN THE TEXAS HIGH PLAINS

George L. Teetes, Ector G. Lopez and Curtis A. Schaefer*

LSUMMARY

,_ Based on population studies during 1971, 1972, and 1973,
(biotype C greenbug, Schizaphis graminum (Rondani), tended
Etoward highest seasonal abundance in grain sorghum during mid-
gin late July. Predators showed a similar trend, but peak popula-
'0ns occurred shortly after greenbug populations began to

cline. The proportion of the greenbug population parasitized
creased to a peak in early August as the total greenbug popu-
“tion was declining rapidly. L ysiphlebus testaceipes (Cresson)

 s the most abundant primary parasite of the greenbug. Other

amary parasites reared from mummies were Diaeretiella rapae

  
  
  

q ’ Intosh) and Aphelinum nigritus (Howard). Hyperparasites
 rasites of parasites) reared from mummies were Charips sp.,

1 hyneuron siphonophorae (Ashmead), Asaphes lucens

C‘ ovancher), and Aphidencyrtus aphidivorus (Mayr). Charips sp.,
_ d P. siphonophorae were the most abundant hyperparasites
Qffecting the primary parasite L. testaceipes. Hippodamia

 were the most abundant predators.

  

FTRODUCTION

v_ Better qualitative and quantitative characterization of pest
 pulations — the damage they cause, their genetic variability,
Heir relative numbers and mobility, and the many interactions
fitween these parameters and various other environmental
 tors—is necessary. Assessment of seasonal distribution for
Fests such as greenbug, a key pest of grain sorghum in the Texas
High Plains since 1968, is essential in the development of pest
lgnanagement strategies. Likewise, an assessment of important
parasites and predators is required. Research results provide
Quantitative information on relative numbers of greenbugs

iid beneficial arthropods for defining seasonal trends in abun-
lance as an aid in developing sound pest management strategies.

 Seasonal abundance data for biotype C greenbug in grain
ibrghum were recorded in 1969 (Bottrell 1971). He reported

.- greenbug reproduction begins immediately after invasion of

 ' sorghum, with the greenbug population sometimes increasing
13a rate of twentyfold per week. If not controlled, such popula-
A,“ continue to increase until mid-July to early August. There-
 , they usually decline rapidly. Parasitization is an important
i; or in population decline (Bottrell 1971). Several major
_ators of the greenbug also contribute to this decline,

ough their role has not been quantified.

   
  
  
  
  
 
   

'pectively, associate professor, The Texas Agricultural Experiment
f» (Department of Entomology) and graduate research assistants,
 Texas Agricultural Experiment Station, Lubbock.

THE TEXAS AGRICULTURAL EXPERIMENT STATIONI J. E. Miller, Director/ Texas A&M University/ College Station, Texas

BULLETIN

B-l 162
December 1975

Predators and parasites of the greenbug, both indigenous
and exotic, have been studied but often in relation to aphids

and host plants other than the greenbug and grain sorghum.
Daniels and Chedester (1972) reported on developmental studies
of the indigenous predator species Hippodamia convergens (Guer)
fed biotype C greenbug. In similar studies, Rogers et al.

(1972a, b) reported on the biology, voracity, and survival of

an exotic coccinellid, Propylea l4-punctata L.

The native parasite Lysiphlebus testaceipes (Cresson) has
long been associated with the greenbug in small grains (Webster
and Phillips 1912). Since 1968, when biotype C first appeared
in damaging numbers in grain sorghum (Anonymous 1969),
research interest in this parasite has been renewed (Hight et al.
1972, Jackson et al. 1970, Starks et al. 1972, Walker et al. 1973
Exotic parasites suitable for possible introduction as biological
control agents have been studied by several researchers (Jackson
and Eikenbary 1971, Jackson et al. 1971, Esmaili and Wilde
1972, Archer and Eikenbary 1973). Secondary parasites collecte
from biotype C greenbug mummies are Aphidencyrtus aphidivoru
(Mayr), Pachyneuron siphonophorae (Ashmead), Charips sp.,
Asaphes lucens, T etrastichus minutus (Howard), (Archer et al.
1974, Walker et al. 1973, Jackson et al. 1970). Primary parasite
besides L. testaceipes are Aphelinus nigritus (Howard), A. varipes
(Foerster), (Archer et al. 1974, Jackson et al. 1970), and
Diaeretiella rapae (M’ Intosh), (Walker et al. 1973).

METHODS AND MATERIALS

During the 1971-1973 growing seasons, abundance of the
greenbug and associated predators and parasites was determined
weekly in grain sorghum at the Texas Agricultural Experiment
Station, Lubbock County, Texas. The commercial heteroyellow
endosperm hybrid was planted in early May and fertilized, irri-
gated, etc. according to agronomic practices customarily employe
in the area. Rainfall records were taken during the growing
season of each year. Population densities of insects were deter-
mined from seedling emergence until September. On each sample
date, at least 100 whole plants were selected at random and ex-
amined thoroughly. Parasitism determination was based on

 

Mention of a trademark or a proprietary product does not constitute a
guarantee or a warranty of the product by The Texas Agricultural Experi-
ment Station and does not imply its approval to the exclusion of other
products that also may be suitable.

All programs and information of The Texas Agricultural Experiment
Station are available to everyone without regard to race, color, religion,
sex, age, or national origin.

mummy counts. Mummies were inspected t0 exclude those
from which adults had emerged. Adult parasites were identified
after emerging from samples of field-collected mummies, which
were confined in 2-ounce blood sample cups in the laboratory.

Major predators recorded weekly were: Hippodamzkz spp.,
Chrysopa spp., Scymnus spp., Syriphid spp. (larvae), spiders, and
three hemipteran species, Orius spp., Nabis spp., and Geocoris spp.

RESULTS AND DISCUSSION

Greenbugs infested grain sorghum soon after emergence of
the plants, generally during the last week in May (Figures 1, 2, 3).
Rainfall reduced population density early in the season when
plants were small. Levels of infestation differed each year, but
peak greenbug infestation occurred during the third week in
Iuly and declined rapidly thereafter. Mean weekly observed
rates of increase for greenbug were 6.6X, 3.5X, and 4.6X for
1971, 1972, and 1973, respectively, or approximately fivefold
oer week.

Although abundance of parasites cannot accurately be
determined by mummy counts because they are an “after the
fact” measure, the presence of mummies provided a means of
expressing the number of greenbugs eliminated by parasitism.
Sreenbug populations each year reached a high density before
JHIEISlICS reduced the population significantly. However,
aarasitism suppressed the greenbug populations and prevented
:ontinuing abundance increases in August. The period of

1000.0

100.0

10.0

'1 h-IQI‘!

1.0

\II\i\QI\LJ\I\IsJ

.01

 

202s 2 916233573421554 111s 25
MAY JUNE JULY AUG.

ig. 1. Seasonal abundance and parasitism of the greenbug in grain sorghum
1971.

   
   
   
 

"1oooo P
1972
1oo.o _
1o.o -

I'-

Z

<

5' RAIN

\ 3.55

8 1.0 _ -

D

ED

Z

LL]

LLl

{I

9 .1

.01 - PARASITIZED
. i. viv-

9

  
    
  
 
 
 
   
 
   
    

 

31 7 14 2s 5121926 2' 17233
MAY JUNE JULY AUG. §

Fig. 2. Seasonal abundance and parasitism of the greenbug in grain sorgh l
in 1972. -

peak greenbug abundance was short, and if the economic v
threshold was reached, chemical control was required only for 7‘
a brief period. Teetes and Johnson (1973) attempted to defm
the economic injury level of greenbugs and showed that green- g
bugs in excess of 1,300 to 1,500 per plant were required to l
cause economic yield loss. The population data presented
here indicate that the greenbug does not often attain damaging Y
levels. When it does, the damaging period lasts only for 1 to i’
2 weeks.

The braconidrwasp, Lysiphlebus testaceipes (Cresson), ,
was the major primary parasite attacking the greenbug (Table 1 i.
Two other primary parasites, Diaeretiella rapae (M’ Intosh) and ‘
Aphelinus nigritus (Howard), were collected, but they represent
a small percentage of the total parasites reared from greenbug '
mummies. Hyperparasites (parasites of parasites) collected were"
Charips sp., Pachyneuron siphonophorae (Ashmead) Asaphes
lucens (Provancher), and Aphidencyrtus aphidivorus (Mayr). v
Charips sp. and P. siphonophorae were the dominant secondary l.
parasites, with Charips sp. more abundant in early season 3'
collections and P. siphonophorae more abundant in August
collections. p.

Abundance of secondary parasites apparently was sufficie
to adversely affect primary parasitism by L. testaceipes. The l
hyperparasites destroyed a high percentage of the primary g
parasites in the mummified greenbugs collected June 28, July 2,
and during August, when only one-fourth or fewer of the adul
emerging from mummies were primary parasites. Parasitism by 
L. testaceipes apparently could be greatly enhanced if secondary.
parasites could be suppressed. A

 

1111.0

INSECTS PER PLANT

1.0

    

PARASITIZED

24
MY

18 lll2l295l2l8fl3 915
JUlE JULY PUGUST

g. 3. Seasonal abundance and parasitism of the greenbug in grain sorghum
1973.

Predators in grain sorghum feed extensively on greenbugs
1d corn leaf aphids, Rhopalosiphum maidis (Fitch). Abundance
’aphid predators peaked during the last week of July and the
st week of August and then declined as the greenbug popula-
m decreased (Figures 4, 5, 6). Early in the season, predators
ere sometimes more abundant than greenbug (Figure 4) as

vrn-leaf aphid apparently served as a food source. Hippodamia
p.pwas the most abundant predator (Table 2) and in most

ses constituted more than one-half of the total predator
rpulation.

1971

15730-0 — GREENBLGS

' PREDATORS

1113.0

*5
o

.-
o
u
‘o
-

b-l
Z

.01

Z026 2 91623307 111212811 ll 1825
MY JUNE JULY AUGUST

Fig. 4. Seasonal abundance of the greenbug and associated predators in
grain sorghum in 1971.

Greenbug was affected by natural mortality factors
throughout the growing season. Aphid predators did not
prevent the greenbug from reaching high populations, and
parasitism occurred too late to prevent greenbug damage to
sorghum.

CONCLUSIONS

These data and those reported by Bottrell (1971) show
a definite trend of increase in abundance of greenbugs and major
predators and parasites in grain sorghum on the Texas High
Plains. Knowledge of these trends further support the reliability
of the integrated control approach by Cate et al. (1974) where '
extremely low dosage rates are used to suppress greenbug and

kBLE 1. PARASITES EMERGING FROM MUMMIES COLLECTED FROM GRAIN SORGHUM, LUBBOCK, TEXAS, 1973

l'___}

 

F
Mummies collected Percent of parasites consisting of
late of Mean "umber P91’ Plant Percent L. Charips P. siph0n0- Other
Pection Greenbugs Mummies Number emerged testaceipes sp. phorae speciesl
1171'} <12 35 77 25 42 25 s
4 84 < 1 100 9 3 14 71 8 7
984 < 1 200 90 55 3 3 1 0 2
1,864 6 300 88 48 3 3 12 7
1,102 79 300 91 71 21 8 <1
2 45 142 300 83 23 41 35 1
9 1 14 300 44 1 8 90 1
16 ' ' ' ' ' ' ‘ ' ' " 300 13 2 3 95 0

 

Iyuded D. rapae, A. aphidivorus, A. lucens, and A. nigritus.

   

mummies were detected m-im m Inna 7R

 
 
  
   
   
     
    
  
      
   
     

4
_ 1972 1000.0 - 
11173-0 f- GREElBlJGS _ GREEN
 PREDATORS FREDA 
1mg . 100.0 '
g 10.0 - '5 10-0 '
é a?
E g 
g Lg . Z _l.0 '
.1 - -1 '
.01 - -01 '
l l l l l l l l l l l l I l 0 l l l l l l l l l l l l
0 3171421285121926291723306 2111 814212451218273915
PAY JUNE JULY NJGUST SEPT. MAY JUNE JULY AUGUST a
Fig. 5. Seasonal abundance of the greenbug and associated predators in Fig. 6. Seasonal abundance of the greenbug and associated predat

grain sorghum in 1972. grain Sfifighllm if! 197 3- 

TABLE 2. MAJOR PREDATORS ASSOCIATED WITH THE GREENBUG

[N GRAIN SORGHUM Cate, J. R., Jr., D. G. Bottrell, and G. L. Teetes. 1974. Manag

the greenbug on grain sorghum. III. Integration of insec 1“
Seasonal mean percentage of aphid predators bi0l0gi¢a1 COIIIIOI- Ellwmflphflgfl (In Press) :-
Daniels, N. W., and L. D. Chedester. 1972. Developmental stu‘,

the convergent lady beetle. Tex. Agric. Exp. Stn. PR-31 ‘i

Hippodamia Predaceous Chrysopa Scymnus Syriphid

Y“ SPP- bugs SPP- SPP- SPP- SPideIS Esmaili, M., and Gerald Wilde. 1972. Behavior 0f the parasite 

h" lt' t th b d tinhsts. En
1911 e6 1 13 1 0 16 ‘$563.1? r“? ‘E5222... ° gm "g a“  a °  
1972 52 7 9 1 24 Hight, Susan C., R. D. Eikenbary, Rudolph J. Miller, and Kenn i?
1973 47 20 3 2 1 27 gbsglgeggreenbug and Lyszphlebus testacezpes. Enviro 
Mean 55 10 3 4 1 22 Jackson, H. B., and R. D. Eikenbary. 1971. Bionomics of Aph

asychis (HymenopterazEulophidae) an introduced parasite 1f,
sorghum greenbug. Ann. Entomol. Soc. Amer. 64: 81-8 p

2 Jackson, H. B., Leon W. Coles, E. A. Wood, Jr., and R. D. Eike 
Larvae only. 1970. Parasites reared from the greenbug and corn leaf =1;

- - - _ Oklahoma in 1968 and 1969. J. Econ. Entomol. 63: 73‘,
spare beneficial arthropods. The data also illustrate that green Jackson’ H_ B“ O E. Rogers, and R_ D. Emenbary. 197L Colo

1 Included Orius spp., Nabius, spp., Geocoris spp.

bugs do not always reach economlcally damagmg levels’ and and release of Aphelinus asychis, an imported parasite of F"
when they do reach this level, the damaging time period is short. greenbug. J. Econ. Entomol. 64: 1435-1438. a

- Rogers, C. E., H. B. Jackson, and R. D. Eikenbary. 1972a. Vorl‘
ACKNOWLEDGMENT survival of Propylea I 4-punctata preying upon greenbugs. "

Entomol. 65: 1313-1316. .1
Rogers, C. E., H. B. Jackson, G. W. Angalet, and R. D. Eikenbary,
Biology and life history of Propylea I 4-punctata (Coleopt  a

This research was partially funded by the Texas Grain
Sorghum Producers Board.

Coccinellidae), an exotic predator of aphids. Ann. Ento 1f’
LITERATURE CITED Amer. 65: 648656 w,
Anonymous. 1969. The greenbug situation on sorghum — 1968. Plant Starks, K. J., R. Muniappan, and R. D. Eikenbary. 1972. Inter

Pest Control Div., USDA, Coop. Econ. Insect Rep. 19 (5): 63-65. between plant resistance and parasitism against the green
Archer, T. L., and R. D‘. Eikenbary. 1973. Storage of Aphelinus asychis, barley and sorghum. Ann. Entomol. Soc. Amer. 65: 65f
a parasite of greenbug. Environ. Entomol. 2: 489-490. Teetes, George L., and Jerry W. Johnson. 1973. Damage asses

Archer, T. L., R. H. Cate, R. D. Eikenbary, and K. J. Starks. 1974. greenbug on grain sorghum. J. Econ. Entomol. 66: 1181
Parasitoids collected from greenbugs and corn leaf aphids in Oklahoma Walker, A. L., D. G. Bottrell, and J . R. Cate, Jr. 1973. Hymenop-l
in 1972. Ann. Entomol. Soc. Amer. 67: 11-14. sites of biotype C greenbug in the High Plains of Texas. A = '.

Bottrell, Dale G. 1971. Concepts for insect pest management in grain Soc. Amer. 66: 173-176. j
sorghum. In Proc. Twenty-Sixth Ann. Corn and Sorghum Research Webster, F. M., and W. J. Phillips. 1912. The spring grain-aphis 
Conf. USDA Bur. Entomol. Bull. No. 110. 

The Texas Agricultural Experiment Station, J . E. Miller, Director, College Station, Texas
0.8M—12-75