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SUSCEPTIBILITY OF BERMUDAGRASS CULTIVARS TO EOREUMA
LOFTINI (LEPIDOPTERA: PYRALIDAE) IN SUBTROPICAL MEXICO
L. A. Rodriguez-del-Bosque, J. Palomo-Salas, and
A. Mendez-Rodriguez
Abstract
Susceptibility of eight bermudagrasses (Tifton 68,
Tifton 78, Tifton 85, Gigante, Brazos, Cruza 1, Callie, and NK
37) to the Mexican rice borer, Eoreuma loftini (Dyar) was evaluated
monthly during 1994 in northern Tamaulipas, northeastern Mexico.
Damage by E. loftini occurred year around, peaking in April and
December. Borer attack was reduced substantially after mowing
the pastures to 3-5 cm height. Susceptibility of the cultivars
to borer damage was influenced by stolon width, an important characteristic
for E. loftini tunneling. This relationship between stolon width
and borer damage was explained closely (R2 = 0.86) by the curvilinear
model y = (1.2 + 0.1757 x3)2, where y = borer damage and x = stolon
diameter. The widest stemmed bermudagrass, and hence the most
susceptible to E. loftini, was Tifton 68. Tunneling behavior of
E. loftini, as affected by stem width of host plants, is discussed.
Key Words: Mexican rice borer, host plant resistance,
seasonality, tunneling behavior.
Resumen
Se evalu- mensualmente durante 1994 la susceptibilidad
de ocho cultivares de zacate bermuda (Tifton 68, Tifton 78, Tifton
85, Gigante, Brazos, Cruza 1, Callie y NK 37) al ataque del barrenador
del tallo Eoreuma loftini (Dyar) en el norte de Tamaulipas, México.
Los da-os de E. loftini ocurrieron durante todo el a-o, aunque
la mayor incidencia se present- en Abril y Diciembre. El ataque
del barrenador se redujo substancialmente después de cosechar
los pastos a una altura de 3-5 cm sobre el nivel del suelo. La
susceptibilidad de los cultivares al da-o del barrenador result-
asociada con el grosor de los estolones, una característica
importante en los hábitos de da-o de E. loftini. Dicha
relaci-n entre el grosor del tallo y el da-o del barrenador fue
explicada (R2 = 0.86) por el modelo y = (1.2 + 0.175 x3)2, donde
y = da-o del barrenador y x= diámetro del estol-n. El cultivar
Tifton 68 result- tener los estolones más gruesos, y por
lo tanto fue el más susceptible al da-o de E. loftini.
Se discute el comportamiento de da-o de E. loftini en relaci-n
al grosor de los tallos de las plantas hospederas.
The Mexican rice borer, Eoreuma loftini (Dyar), is
an important pest of sugarcane, Saccharum officinarum L., field
corn, Zea mays L., grain sorghum, Sorghum bicolor (L.) Moench,
and forage grasses in Mexico and southern Texas (Browning &
Hussey 1987, Rodriguez-del-Bosque et al. 1988, Youm et al. 1988,
Meagher et al. 1994). In addition, a number of wild grasses serve
as hosts to E. loftini (Osborn & Phillips 1946, Browning &
Hussey 1987). Although earlier reports acknowledge the distribution
of E. loftini in southern California and southern Arizona (Dyar
1917, Osborn & Phillips 1946), there is no recent evidence
on the pest status of this species in those areas. Feeding by
E. loftini on leaves and stems causes varied damage, including
tunneling near the plant growing point during the early growth
stages, and a symptom called “dead heart”, which appears
as a dead or necrotic center whorl on green shoots (Browning et
al. 1989).
Management of E. loftini in sugarcane has focused
on several tactics, including biological control (Smith et al.
1987), insecticidal suppression (Meagher et al. 1994), male mating
disruption technique (Shaver & Brown 1993), and host plant
resistance (Pfannenstiel & Meagher 1991). A major concern,
particularly in Texas where E. loftini was first detected in 1980,
is the potential of this insect pest to expand its geographical
range via transportation of infested plant material such as pasture
grasses (Browning & Hussey 1987). In northern Tamaulipas,
a subtropical agricultural region south of the Texas border, the
main agronomic crops are corn and sorghum planted over approximately
one million hectares (30% irrigated; 70% dryland). However, recent
reductions in international grain prices and the increasing production
costs for corn and sorghum are forcing many producers to consider
production alternatives, such as forage grasses for feeding livestock.
Several cultivars of bermudagrass, Cynodon spp., are being evaluated
in northern Tamaulipas for their establishment characteristics,
dry matter yield of forage, nutritional quality, and cattle performance
(Palomo & Mendez 1993, 1994). The objective of this investigation
was to detect possible differences in susceptibility of eight
bermudagrass cultivars to E. loftini.
Materials and Methods
This study was conducted in the Campo Experimental
Rio Bravo (Rio Bravo Experiment Station), near Rio Bravo, Tamaulipas.
In April 1992, eight bermudagrass cultivars (Tifton 68, Tifton
78, Tifton 85, Gigante, Brazos, Cruza 1, Callie, and NK 37) were
established in 3x4 m plots arranged in a randomized complete block
design with four replications. Plots were evaluated for E. loftini
damage during the first week of each month during 1994 by counting
and removing at ground level stolons exhibiting dead heart symptoms.
Excised stolons were transported to the laboratory and examined
for evidence of E. loftini tunneling or living larvae. A proportion
(25-50%) of the collected larvae was reared on artificial diet
(Martinez et al. 1986) in the laboratory for completion of development
to corroborate the borer species by examining genitalia of emergent
moths (Bleszynski 1969). Stolons exhibiting dead heart symptoms
caused by factors other than E. loftini (<5%) were omitted
from the evaluations. The diam of 10 undamaged stolons per plot
was measured (about 5 cm above ground level) at each sampling
date. During 1994, plots were mowed to a height of 3-5 cm during
the second week of January, April, May, July, and September. After
mowing, plots were fertilized with urea (46 kg N/ha) and irrigated
(10 cm). No insecticide was applied during the study.
Dead heart data were subjected to analysis of variance
as a factorial design (A, cultivars; B, months), and means separated
by Tukey’s studentized range test (p = 0.05) (PROC ANOVA, SAS
Institute 1988). Average dead hearts (over 12-mo) of each cultivar
(y) were fit to the curvilinear model y = (a + bx3)2, where a
and b are constants and x the average (12-mo) stolon diam.
Results and Discussion
The only stalk borer attacking bermudagrass throughout
the study was E. loftini. The analysis of variance indicated damage
was significantly different (p < 0.05) among bermudagrass cultivars
(A), and months (B), with no A×B interaction. Incidence of
E. loftini occurred throughout the year, with the greatest damage
occurring in April and December (Fig. 1). Mowing the pastures
substantially reduced E. loftini attack, a result similar to the
findings by Browning & Hussey (1987). Overall, the occurrence
of dead hearts was 51% lower in those months when mowing was practiced
during the previous month (Fig. 1). The practice of periodically
harvesting the grasses removed or killed the larvae and prevented
a continued recruitment of E. loftini larvae throughout the period
of study. The maximum incidence of dead hearts (22 per plot) observed
in Tifton 68 in April represented only about 0.2% of the total
stolons in the plot, a proportion that probably did not affect
either forage yield or quality. However, these damage figures
are much lower than those observed in larger semicommercial plots
planted with Tifton 68 in Rio Bravo in previous years (L.A.R.B.,
unpublished data) and in south Texas, where an average of 38%
of the Tifton 68 stolons exhibited E. loftini damage (Browning
& Hussey 1987). One possible explanation of the higher damage
in Texas is that counts of damaged stolons included not only dead
hearts, but also other symptoms such as entry holes and discoloration
at the area of attack. Although dead hearts may represent a reasonable
and practical parameter for measuring stolon attack by borers,
this method likely underestimates the actual damage and yield
loss. In addition, in the study by Browning & Hussey (1987),
mowing was less frequent than in our study, and borers were probably
removed less frequently, allowing more borer attack and/or pest
population buildup.
The most susceptible cultivar throughout the study
was consistently Tifton 68 (Table 1). Average dead hearts (12-mo)
observed in Tifton 68 were 3.4 times greater than the average
of the remaining seven cultivars. In April, when E. loftini incidence
peaked, Tifton 68 had 6.6 times more dead hearts than the average
for the other grasses. A closer look at the data showed that borer
damage was positively associated with stolon diam (Table 1). This
relation was explained (R2 = 0.8632, df = 5, p < 0.01) by the
curvilinear model y = (1.2 + 0.1757 x3)2, where y = dead hearts
per plot, and x = stolon width (mm) (Fig. 2). This partially explained
the greater susceptibility of Tifton 68, the cultivar with the
greatest stolon diam. The possible influence of stolon diam in
bermudagrass susceptibility to E. loftini was also suggested by
Browning & Hussey (1987), although data were not conclusive
because only two cultivars were evaluated. They also suggested
that grasses must provide a certain minimum width in order to
afford sufficient space for tunneling by E. loftini.
Stalk width may have implications in the tunneling
behavior of E. loftini within the stem of susceptible grasses.
Stalk or stolon tunneling in small-stemmed host plants such as
bermudagrass, johnsongrass, Sorghum halepense (L.) Pers., rice,
Oryza sativa L., and wheat, Triticum aestivum L., is longitudinal,
usually causing dead hearts or heads, a result of larval feeding
near the growing point (Browning et al. 1989). In contrast, larval
tunneling in larger stemmed hosts like corn, sugarcane, and sorghum
can be vertical, horizontal, or diagonal within the stem (Van
Zwaluwenburg 1926, Rodriguez-del-Bosque et al. 1988, Browning
et al. 1989). In these larger-stemmed hosts, stalk width may not
be an important mechanism for differential susceptibility within
cultivars as shown for forage sorghums (Browning & Hussey
1987), probably because space for tunneling is not a limiting
factor.
In summary, E. loftini damaged bermudagrass throughout
most of the year in northern Tamaulipas, although forage harvesting
at regular intervals reduced the pest incidence. Bermudagrass
cultivars with smaller stolon width may preclude E. loftini damage
by not providing sufficient space for larval tunneling. In contrast,
Tifton 68, the cultivar with the largest stolon, sustained the
most damage of all bermudagrasses tested.
Acknowledgment
We thank Rosalío Navarro and Julian Fuentes
for their assistance with field samplings, and J. W. Smith, Jr.
(Texas A&M University) for his valuable comments to an early
version of the manuscript. Approved by the Centro de Investigaci-n
Regional del Noreste as INIFAP-CIRNE-A010.
References Cited
Bleszynski, S. 1969. The taxonomy of the Crambinae
moth borers of sugar cane, pp. 11-59 in J. R. Williams, J. R.
Metcalfe, R. W. Mungomery, and R. Mathes [eds.]. Pest of sugar
cane. Elsevier, New York.
Browning, H. W., and M. A. Hussey. 1987. Susceptibility
of ‘Tifton 68’ and ‘Coastal’ bermudagrass to the Mexican rice borer. Crop Sci.
27: 359-360.
Browning, H. W., M. O. Way, and B. M. Drees. 1989.
Managing the Mexican rice borer in Texas. Texas Agric. Ext. Serv.
Bull. 1620: 1-8.
Dyar, H. G. 1917. Seven new crambids from the United
States. Insecutor Inscitiae Menstruus 5: 84-87.
Martinez, A. J., J. Bard, and T. Holler. 1986. Mass
rearing sugarcane borer and Mexican rice borer for production
of parasites Allorhogas pyralophagus and Rhacanotus rosilensis.
USDA-APHIS, 800 series publication.
Meagher, R. L., Jr., J. W. Smith, Jr., and K. J.
R. Johnson. 1994. Insecticidal management of Eoreuma loftini (Lepidoptera:
Pyralidae) on Texas sugarcane: A critical review. J. Econ. Entomol.
87: 1332-1344.
Osborn, H. T., and G. R. Phillips. 1946. Chilo loftini
in California, Arizona, and Mexico. J. Econ. Entomol. 39: 755-759.
Palomo-Salas, J., and A. Mendez-Rodriguez. 1993.
Bermuda Tifton-68, nuevo pasto para establecer praderas de riego
en el norte de Tamaulipas. Campo Experimental Río Bravo,
CIRNE, INIFAP, SARH. Folleto Técnico 14: 1-11.
Palomo-Salas, J., and A. Mendez-Rodriguez. 1994.
Nuevos pastos Bermuda para establecer praderas bajo riego en el
norte de Tamaulipas. Tercera Reuni-n Científica y Tecnol-gica,
Forestal y Agropecuaria del Estado de Tamaulipas, CIRNE, INIFAP,
SARH. Memoria Científica 1: 57.
Pfannenstiel, R. S., and R. L. Meagher, Jr. 1991.
Sugarcane resistance to stalkborers (Lepidoptera: Pyralidae) in
south Texas. Florida Entomol. 74: 300-305.
Rodriguez-del-Bosque, L. A., J. W. Smith, Jr. and
H. W. Browning. 1988. Damage by stalkborers (Lepidoptera: Pyralidae)
to corn in northeastern Mexico. J. Econ. Entomol. 81: 1775-1780.
SAS Institute. 1988. SAS/STAT User’s guide, release
6.03 edition. SAS Institute, Cary, NC.
Shaver, T. N., and H. E. Brown. 1993. Evaluation
of pheromone to disrupt mating of Eoreuma loftini (Lepidoptera:
Pyralidae) in sugarcane. J. Econ. Entomol. 86: 377-381.
Smith, J. W., Jr., H. W. Browning, and F. D. Bennett.
1987. Allorhogas pyralophagus (Hym.: Braconidae), a gregarious
external parasite imported into Texas for biological control of
the stalkborer Eoreuma loftini (Lep.: Pyralidae) on sugarcane.
Entomophaga 32: 477-482.
Van Zwaluwenburg, R. H. 1926. Insect enemies of sugarcane
in western Mexico. J. Econ. Entomol. 19: 664-669.
Youm, O. H., H. W. Browning, and F. E. Gilstrap.
1988. Population dynamics of stalk borers attacking corn and sorghum
in the Texas Rio Grande Valley. Southwest. Entomol. 13: 199-204.
Figure 1. Seasonal damage by E. loftini to bermudagrass
(average of eight cultivars and four replications in plots of
3×4 m) in northern Tamaulipas, Mexico. Arrows indicate mowing
practices. Means (bars) with the same letter are not significantly
different (p < 0.05; Tukey’s studentized range test).
Table 1. Average numbers of dead hearts caused by
E. loftini and average stolon diam of eight bermudagrass cultivars
in northern Tamaulipas, Mexico.
Cultivar
1Means within a column followed by the same letter
are not significantly different (p<0.05; Tukey’s studentized
range test). Mean values averaged over 12 months and 4 replications
in 3×4 m plots.
Figure 2. Relation of dead hearts caused by E. loftini
to stolon diam of eight bermudagrass cultivars (average of 12
months and four replications in plots of 3×4 m) in northern
Tamaulipas, Mexico.
Campo Experimental Río Bravo, INIFAP-SAGAR
Apartado Postal 172
Río Bravo, Tamaulipas, México 88900
Dead Hearts
(Mean±SEM)1
Stolon Diam (mm)
(Mean±SEM)1
Tifton 68
7.96±1.47a
2.09±0.07a
Tifton 78
3.71±0.60b
1.26±0.05b
Brazos
3.31±0.59bc
1.29±0.03b
Cruza 1
2.38±0.47bc
1.32±0.05b
Tifton 85
2.33±0.49bc
1.42±0.04b
Gigante
2.25±0.41bc
0.89±0.03cd
NK 37
1.58±0.33bc
0.84±0.06d
Callie
0.98±0.25c
1.17±0.06bc