Temporal Occurrence of Spodoptera exigua (Lepidoptera: Noctuidae) in Cameron Highlands, Pahang
Adult of Spodoptera exigua populations were monitored in
Cameron Highlands using pheromone traps between 24 January 2003 and 27
February 2004 in the vegetables farm and between 24 March 2003 and 27
February 2004 in the carnation farm at Kampong Raja. They were captured
all the time in the studied areas, although the numbers fluctuated. The
highest number of adult catches per trap per day was 5.75 individuals
between 6 to 13 June 2003, followed by 5.14 individuals between 23 to
30 May 2003 at the vegetables farm. The lowest number of adult catches
per trap per day was 0.25 individuals between 3 to 10 October 2003. Whereas,
at the carnation farm, the highest number of adult catches per trap per
day was 1.22 individuals between 25 July to 8 August 2003. The lowest
number of adult catches per trap per day was 0.06 individuals between
31 October to 7 November 2003 and 30 January to 6 February 2004. In general,
capture increased towards the middle part of the year with four capture
peaks occurring between April and June 2003 at the vegetables farm. Whilst,
at the carnation farm, there were several capture peaks occurred between
April and October 2003. Thus, this date could be used as a benchmark to
determine when and if population levels are high enough to have the potential
to cause economic damage to crops in Cameron Highlands, Pahang.
A vast study on adults` population of the beet armyworm, Spodoptera exigua
(Hübner) has been done in the United States of America (Adamczyk et
al., 2002; Hendricks et al., 1995; Raulston et al., 1997),
since it has become a serious pest especially on cotton (Hendricks et al.,
1995; Ruberson et al., 1994a,b). However, in Malaysia, such study was
scanty (Azidah, 2006; Palasubramaniam et al., 2000; Sivapragasam and
Syed, 2001). The beet armyworm has been considered an occasional pest associated
with hot and dry conditions (Stewart et al., 1996). They have found severe
beet armyworms outbreaks occur following early seasons with multiple insecticide
applications or when it is unusually dry. Eveleen et al. (1973) suggested
that S. exigua abundance is favored by frequent insecticide use; otherwise
it is considered a secondary or induced pest in some crops. However, the adults`
population was found throughout the whole year in Sekinchan, Selangor as Malaysia
is not a seasonal country (Azidah, 2006). Thus, this study was conducted to
determine the presence of adult S. exigua, particularly the male species
and to monitor their population in the studied areas.
MATERIALS AND METHODS
Study Site: Field study was carried out in Kampong Raja, Cameron Highlands,
Pahang. Two sites were chosen i.e., a vegetables and a carnation farms. Size
of the study area is 3 acres each. Crop which has been planted in the vegetables
farm during the study was English cabbage, French beans, spinach and celery,
while in the carnation farm was pink, purple and red variety of carnation flower.
Adults Trapping: Adult population was monitored by using DELTA trap
baited with synthetic beet armyworm sex pheromone impregnated into rubber septa
that lured males to the traps. Twelve traps were allocated in the vegetables
farm from 24 January 2003 to 18 April 2003, eight traps from 18 April 2003 to
22 August 2003 and nine traps from 22 August 2003 to 27 February 2004. Whilst
in the carnation farm, three traps were allocated from 24 March 2003 to 18 April
2003 and seven traps from 18 April 2003 to 27 February 2004. The traps were
arranged randomly. They were suspended about 1 m above ground from a 1 reinforcement
stick formed in an inverted L shape anchored in the soil. Each trap was separated
by about 10 m. Traps were serviced between 6 to 8 days in the vegetables farm
and between 6 to 11 days in the carnation farm, but usually every 7 days in
both places. During the trap servicing, the adult catches were counted and recorded
on site and also the pheromone and plastic layer with sticky glue sprayed on
it was changed. Trapping was made from 24 January 2003 until 27 February 2004
in the vegetables farm and from 24 March 2003 until 27 February 2004 in the
Weather records on temperature, relative humidity and rainfall were obtained
from the Meteorological Department at Petaling Jaya. They actually gathered
the data from a meteorological station at the Cameron Highlands.
Data Analysis: Number of moths caught per trap per day was
used as the basic unit for purposes of analyses and graphic illustrations. The
data were handled this way because the number of days for trapping the adults
was quite varied. This is due to the weather condition. Correlation analyses
were performed to determine the relationship between the moth populations and
Adults of S. exigua were captured all the time in the studied areas,
although the numbers fluctuated (Fig. 1, 2).
A total number of 6105 and 1019 male moths were caught at the vegetables and
carnation farms throughout the study, respectively.
||Adult catches in vegetables farm, Kampong Raja, Cameron Highlands,
||Adult catches in carnation farm, Kampong Raja, Cameron Highlands,
The highest number of adult catches per trap per day was 5.75 individuals
between 6 to 13 June 2003, followed by 5.14 individuals between 23 to 30 May
2003 at the vegetables farm. The lowest number of adult catches per trap per
day was 0.25 individuals between 3 to 10 October 2003. Whereas, at the carnation
farm, the highest number of adult catches per trap per day was 1.22 individuals
between 25 July to 8 August 2003. The lowest number of adult catches per trap
per day was 0.06 individuals between 31 October to 7 November 2003 and 30 January
to 6 February 2004. In general, capture increased towards the middle part of
the year with four capture peaks occurring between April and June 2003 at the
vegetables farm. Whilst, at the carnation farm, there were several capture peaks
occurred between April and October 2003 (Fig. 1, 2).
Relatively, the total number of moth caught at the vegetables farm was higher
compared to the carnation farm.
The averaged temperature ranges from 16.58 to 19.14°C, relative humidity
84.00 to 97.74% and rainfall 0.00 to 21.25 mm. Generally, the climatic factors
were mostly did not influence the moth populations, although there was a moderate
correlation between the adult catches with the means of temperature (r = 0.5097)
at the vegetables farm. However, there were no correlation with the means of
relative humidity (r = 0.2725) and rainfall (r = 0.0678) at the vegetables farm.
Whereas, there were no correlation between the adult catches with the means
of temperature (r = 0.0509), relative humidity (r = 0.0921) and rainfall (r
= 0.0616) at the carnation farm.
This study has found that the S. exigua adults were present throughout
the study, i.e., from the 24 January 2003 until 27 February 2004 in Kampong
Raja, Cameron Highlands, Pahang, although the number was lower compared to Sivapragasam
and Syed (2001). Their maximum number of male caught in Cameron Highlands was
10.57 per trap per day. While result of this study also was fairly low compared
to Azidah (2006), where the highest number of male caught in Sekinchan, Selangor
was 6.63 per trap per day. Further, Palasubramaniam et al. (2000) caught
a higher number of male compared to this study. Their short period survey (i.e.,
one week in October, 1998) in Batang Kali, Selangor at the onion plantation
caught 21.43 individuals of moth per trap per day. Besides Selangor, they also
have done some survey in several places in Johor such as in Johor Bahru, Batu
Pahat, Kluang and Kota Tinggi for six months (i.e., from July until December,
1997) and in Air Hitam for one week (i.e., in February, 1998), using the pheromone
trap. However, the number of catches per trap was not as high as in Batang Kali,
i.e., 24.0, 1.0, 5.1, 2.0 and 37.0, respectively. Meanwhile, in Mississippi,
USA, Hendricks et al. (1995) reported that during the growing season,
captures ranged from 2.1 moths to 399.8 per trap per night.
Since Malaysia is not a seasonal country, the abiotic factors were generally
found not influencing the moth populations in this study, although the temperature
at the vegetables farm was moderately correlated to the number of the adults`
moth. This is somewhat similar to Jaipet`s (1998) finding. He stated that climatic
factors did not have much influence on the moth accept they showed highest negative
correlation with maximum humidity. Nevertheless, it was observed that the availability
of the host plant is the factor that attracting the moths to the study plot.
The same phenomenon was encountered by Raulston et al. (1997) in northeastern
Mexico. They reported that the increases in trap capture in the fall could have
resulted from increased of host availability associated with the onset of the
high rainfall season. Thus, the fluctuation in the number of adult catches in
this study could be due to the larval host range and their abundance within
or between the study areas, where there were other vegetables cultivated area.
Similar occurrence was also reported by Adamcyzk et al. (2002) in Mississippi.
However, during the field study very few larvae were existed or collected, although
the pheromone traps catches a considerable number of the adults moth. This
phenomenon is contradicted with the normal situation, where the number of larvae
should more or less reflect the number of adult`s moth or vice versa. The larvae
also were not found at the vicinity of the studied areas. This shows that the
adults came from other places. This occurrence is supported by and Feng et
al. (2003) who stated that the beet armyworm is capable of long distance
dispersal of hundreds of miles in relation to weather patterns. Thus, the migration
and dispersion of this moth at the Cameron Highlands need further investigation.
On contrary, Smith (1989) has often observed that beet armyworms outbreaks
are more serious in the dry years than in wet ones. There are several possible
explanations for this phenomenon. The availability of moisture and free water
can greatly enhanced the induction and spread of entomopathogen epizootics.
Beet armyworms are attacked by various fungal and viral pathogens. The beet
armyworms are fairly easily dislodged from plants and heavy rains may knock
larvae from plants and drown them (Ruberson et al., 1994b). However,
during this study the weather in Kampong Raja, Cameron Highlands was considered
moderate i.e., not really dry, in order to cause outbreak of the S. exigua.
Perhaps, a more prolonged duration of study should be made in the future, in
order to determine the relationship between the weather and their population
in much detail.
Stewart et al. (1996) found that there were relationship between the
number of early season insecticide applications and rainfall, but not temperature
to percent yield loss caused by beet armyworm. They indicate that the more early
season insecticide applications are made and the drier the weather, the greater
the risk of beet armyworm outbreaks. Further, Eveleen et al. (1973) stated
that S. exigua on cotton in California is typically a secondary pest,
likely to become abundant after insecticide applications against Lygus hesperus.
While, in this study, the farmers were observed to spray insecticides at least
once a week and were more frequent during the raining days. Perhaps, this could
be another reason of the moth existence year around in the study plot due to
the elimination of its natural enemies by the insecticides. However, their relationship
was not certain and further studies are needed to document these patterns more
This study has shown that the pheromone trap is useful for monitoring and to
determine the entry of the S. exigua into the studied areas at the Kampong
Raja since the existence of its larvae were very low in order to determine their
infestation. The used of this trap for these purposes is also complemented with
Parker et al. (1995) who stated that the pheromone is useful for monitoring
and to determine the entry of the pest into the field.
I would like to thank Dr. Lim Guan Soon for his suggestion and initiative of
this project. I am grateful to the Institute`s support staffs who have been
kindly helping me during this project. I also would like to thank the owner
of the vegetables and carnation farms for letting me using their farms and the
Meteorological Department for the weather records. This work is supported by
the Malaysian government research grant, IRPA No. 01-02-03-0695.
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