Epilachninae are economically important beetle pests. In Malaysia, Yusof and Khoo (1989) reported that Epilachna indica are found attacking Phaseolus vulgaris L., sweet potato Impomoea batatas (L.) Lam, bitter gourt Momordica charantia L., eggplant Solanum melongena L., cucumber Curcumis sativus L. and watermelon fruit Citrullus vulgaris. In Taiwan, both larvae and adults of some species of Epilachninae feed on the leaves of Solanaceae, Cucurbitaceae and Urticaceae (Richards and Filewood, 1990).
Epilachna indica can be differentiated from Epilachna vigintioctopunctata from the twelve spots found from adult beetles (Fig. 1). The E. vigintioctopunctata has twenty-eight round spot on its elytra whereas the body is red similar to Epilacha indica. The only difference in the larvae is that those of E. indica is often more yellowish in color and armed with numerous branched yellowish spines (Fig. 2).
||An adult E. indica has twelve black spot differentiating
it from E. vigintioctopunctata. The leaf area eaten are shown
||Larva of E. indica is yellowish in colour and armed
with numerous branched yellowish spines
Adult E. vigintioctomaculata and E. vigintioctopunctata attacks cucubitaceous plants when they cannot find solanaceous plant to feed (Abe and Matsuda, 2000). Abe and Matsuda (2000) reported both E. vigintioctomaculata and E. vigintioctopunctata were not stimulated to feed by solanine found in S. tuberosum and S. nigrum and tomatine contained in Lycopaersicon esculentum the solanaceous host plants. Solanum nigrum contain alkaloid, solanine. Alkaloids have never been reported to act as feeding stimulant. Both species are possibly stimulated to feed by some other substances contained in solanaceous host plants such as potato and tomato (Abe and Matsuda, 2000). In E. vigintioctomaculata methyl linolenate maximized the feeding activity of sugars at the concentration contained in the potato leaves suggesting that methyl linolenate plays an important role in the host selection of E. vigintioctomaculata (Endo et al., 2004).
Food preference is influenced by odor, taste, vision, age of plant and thickness
of leaves and proportion of crude fibre, parenchymatous tissue and water content
present (Katakura et al., 1989). The feeding preference was influenced
by chemical factors as in three Aulocophora leaf beetle species (Abe
and Matsuda, 2005). Insect plant interaction may be evaluated by quantitative
measurement of leave area consumed by herbivorous insect. Katakura et al.
(1989) accessed leaf tissue removal by scoring and approximating percentange
visually. Escoubas et al. (1993) measured leaf eaten areas using video-image
analysis software when screening Hokkaido plants for antifeedant activity against
Spodoptera litura. Imura and Ninomiya (1998) reported on the quantitative
measurement of leaf area consumption by Epilachna vigintocpuntata towards
solanaceous weed Solanum carolinense using image processing. Imura and
Ninomiya (1998) showed that leaf area removal is a better measure for herbivore
impact on the host plants than fresh or dry weight measure in terms of photosynthesis
Fauziah and Subramaniam (2008) reported that 100 ppm of metholic extract of Azadirachtin caused optimal antifeeding behavior of E. indica.
Solanum nigrum is a widely distributed tropical plant. The leaves of the plant have been used in some parts of Plateau State, Nigeria for food and medicinal purposes (Wannang et al., 2008). Unlike the egg plant S. melongena, the fruits of S. nigrum does not have economic importance, since it is not consumed by human.
Katakura et al. (1989) reported that adult beetles selected their natural hosts when given choices. This study investigated the potential use of Solanum nigrum as a trap plant in pest management of egg plant Solanum melongena by studying the feeding behavior and optimal feeding time of E. indica on the black nightshde plant Solanum nigrum.
MATERIALS AND METHODS
This study was conducted from 1st April until 3rd December 2002. The laboratory
experiments were conducted at the Institute of Post Graduate Study, University
Malaya, Kuala Lumpur, Malaysia. The field studies were conducted in the fields
of Malaysia Agricultural Research Institute Jalan Kebun, Ulu Kelang, Malaysia.
Beetles and Plants
The 12-spotted ladybird beetles Epilachna indica (Coleoptera: Coccinellidae:
Sub family Epilachninae), used in the study were collected from Solanum nigrum
L. Black nightshade plants (Fig. 3, 4) grown
in the field station of Malaysian Agricultural Research Development Institute
(MARDI) at Jalan Kebun, Ulu Kelang, Selangor, Malaysia.
||Solanum nigrum plants used in the observation
||Fruit of the blacknight shade a S. nigrum plant at
Jalan Kebun, Ulu Kelang, Selangor, Malaysia
The ladybirds were freshly collected prior to each experiment. The plants used
for the study were about 0.4 m in height. Beetle of the same size were used
for all experiments.
Experiment 1. Field Observation of Epilachna indica Behavior on Ten
S. nigrum Plants
A field observation was conducted in farm at MARDI, Jalan Kebun on Oct 2nd
2002 from 08:00 until 19:00 h on 51 beetles on 10 plants of S. nigrum
randomly chosen. The behavioral activities under conditions were observed for
12 h. The number of beetles feeding, resting, walking, mating and flying on
all ten plants was recorded every 30 min throughout the observation period.
The aim of this experiment was to determine the behavioral pattern of E.
indica on S. nigrum in the field.
Experiment 2. Twenty Four Hours Observation on Feeding Duration of E.
indica in a Control Condition in a Rearing Cage
Ten beetles were placed in a rearing cage together with a wild Solanaceous
plant, Solanum nigrum (Fig. 5). Observation was undertaken
every hour for 24 h from 06:00 on 3rd October 2002 until 06:00 h the following
day. The number of beetles feeding and duration of each feeding was recorded.
The method was modified from Fauziah et al. (2003), who observed feeding
behavior of E. indica on Solanum melongena for 12 h then repeated
the observation twice on every alternate days.
Experiment 3. Measurement of Leaf Area Consumption by S. nigrum and
Optimal Feeding Time of E. indica
Ten ladybird beetles, Epilachna indica were individually placed
in the cylindrical plastic container of diameter 4.0 cm and 5.5 cm in height
together with a leaf of S. nigrum. The feeding activity of the beetles
was recorded every half an hour for 3 days continuously from 06:00 h on Oct
3rd until 06:00 h on 6th Oct 2002. In this experiment, leaf consumption was
determined by measuring leaf removal by area eaten by the beetles. Each leaf
was traced onto a graph paper after 24 h and after 72 h. The rate of consumption
of the beetles per day in square millimeter square (mm2) was determined
by counting the areas eaten. The optimal feeding time on each of the 3 days
was also assessed.
||Population of feeding E. indica on ten S. nigrum
plants in the field
Experiment 4. Feeding Preference of E. indica between Leaf Discs
of S. melongena and S. nigrum and Between Leaf Discs of S.
nigrum and the Leaves of a Wild Solanaceous Plant
Beetles were given a choice whether to feed on leaf disc from S. melongena
or S. nigrum following the method used by Wada and Munakata (1986). Two
pieces of S. melongena leaf disc of 2.0 cm diameter and two pieces S.
nigrum leaf discs 2.0 cm diameter were placed opposite each other in a petri
dish of 9.0 cm in diameter. Five beetles were released in the center of the
petri dish and their feeding preference was recorded. Two days prior to this
experiment, beetles to be used in this experiment were not given food but only
water. The experiments began at 10:00 h and ten replicate petri dishes were
observed. The number of beetle found on each leaf disc was recorded at 10:30
h. This experiment was conducted during the peak feeding time for E. indica
on S. nigrum plants after result obtained from earlier experiments. Beetle
preferences were calculated by comparing the mean numbers recorded on each leaf
type. Three treatment was given in this experiment:
||S. nigrum compared with S. melongena
||S. nigrum compared with a wild solanaceous plant and
||S. melongena compared with a wild solanaceous plant
The Behavior of Fifty One E. indica on ten S. nigrum Plants
in the Field
The behavioral pattern of E. indica in the field can be obtained
from the results summarized in Fig. 5, 6,
7 and 8. Table 1 shows
the number of beetles showing different behaviors at each half hour observation
from 08:00 h to 18:30 h on ten S. nigrum plants in the field. Epilachna
indica fed and mated (Fig. 9) on the leaves or branches
of the S. nigrum plants. Some beetles were motionless and some were walking
on the leaves whilst other beetles were flying in between the leaves and branches
or from one S. nigrum plant to another. The mean frequency of each behavior
throughout the study was recorded. The frequency of beetles showing the behavior
of feeding, mating, walking or motionless and flying on all ten plants were
235, 58, 401 and 100 times, respectively.
||No. of motionless and walking E. indica on ten S.
nigrum plants in the field
||Population of mating pairs of E. indica on ten S.
nigrum plants in the field
This study shows E. indica beetles spent most time motionless or walking
followed by feeding, flying with the least activity mating during the period
of 08:00 to 18:30 h.
Figure 5 shows two cycles of feeding periods for E.
indica on S. nigrum plants in the field. The first cycle of feeding
was from 08:00 to 10:00 h with the first peak of feeding with a maximum number
of beetles feeding at 09:30 h (N = 28). Fewer beetles were feeding between 10:30
to 14:00 h, with a mean of 4.5±1.05.
||The population of E. indica on ten S. nigrum
plants in the field from 08:00 h until 18:30 h observed every half an hour
on 2nd October 2002
||Population of flying beetles on ten S. nigrum plants
in the field
The second cycle of feeding was from 16:00 to 18:30 h and has a lower peak.
The second peak of beetles feeding was at 17:30 h (N = 18). The mean number
of beetles feeding throughout the first cycle was 24.0±3.54 while the
mean number of feeding beetles during second cycle was lower at 20.285±3.55.
The minimum number of feeding beetles on S. nigrum plant throughout the
observation was at 15:00 h (N = 2). No beetle was feeding at 14:30 and 19:00
Walking and Motionless Behavior
Figure 6 shows the number of beetles motionless or walking
on ten S. nigrum plants in the field from 08:00 to 17:00 h. There were
always some beetles motionless or walking throughout the observations. The highest
number of beetle motionless or walking was from 11:00 to 16:30 h (N = 24 to
N = 25). The least number of beetles walking or motionless was at 09:00 h (N
= 7), 09:30 h (N = 9), 17:00 h (N = 11) and 17:30 h (N = 8). The mean number
of beetle walking or motionless throughout the observation period was 18.23±6.68.
Figure 7 shows that mating activity of E. indica
occurs in daytime on S. nigrum plants in the field at Jalan Kebun, Ulu
Kelang Selangor, Malaysia. The adult size of E. indica in this study
was between 1.3 to 1.5 cm (Fig. 1). The males and females
can be identified by looking at the size and observing the end of the ventral
side of the abdominal segments. The abdomen showed differences between the sexes
of the beetle. Mounting pairs began mating from 08:00 h (N = 5) and occurred
throughout the day until 17:00 h (Fig. 7). The highest number
of pairs mating was at 11:30 h (N = 7). The mean number of mating pairs throughout
the observation period was 3.5±1.79 which was rather low compared to
The number of E. indica flying every half an hour on ten S. nigrum
plants in the field between 08:00 to 18:30 h is shown in Fig.
8. The beetles flew sporadically throughout the day moving in between the
leaves or from leaf to branch or onto another S. nigrum plant nearby.
The mean number of flying beetles on S. nigrum plant in the field was
4.70±2.67. The maximum number of flying beetles (N = 9) was at 08:30,
10:30, 13:00 and 17:30 h.
Feeding Duration of Ten E. indica on a S. nigrum Plant in
the Rearing Cage in Control Condition
Over a 24 h period, the activity of ten beetles on a single S. nigrum
plant in a cage in control condition was recorded. Figure 10
shows that 34% of time was spent on feeding, 18% walking, only 1% flying and
most of the time, 47%, the beetles were motionless. This is due to the resting
time during the night which was included in the 24 h continuous recording period.
The total time spent by ten E. indica B1 to B10 on feeding, walking,
flying and motionless was 8.31±0.99 h, 4.20±1.23 h, 1.30±0.48
h, 11.30±1.25 h, respectively. Figure 9 shows the feeding
activity within 24 h of ten beetles on a single S. nigrum plant in the
cage. The optimal feeding time was between 09:00 to 14:00 h whereby all ten
beetles were feeding throughout.
||Feeding pattern of E. indica for 24 h on a S. nigrum
plants in a rearing cage
||Percentage time spent by E. indica on different behavior
during a 24 h study
||Feeding pattern of ten E. indica on 3 successive days
4th, 5th and 6th Oct 2002 in caged S. nigrum plant
No beetle was feeding at 19:00 to 20:00 h and 23:00 to 24:00 h. Feeding began
to stop completely from 02:00 to 08:00 in the cage (Fig. 9).
Optimal Feeding Time of E. indica on S. nigrum in Control
Condition Observed for 72 h Observation
Figure 11 shows the feeding pattern of E. indica
over 3 successive days from 3rd Oct to 6th Oct 2002 on a S. nigrum plant
in a rearing cage. On the first two days the optimal feeding time was from 10:00
to 13:00 h with all ten ladybird beetles feeding every hour for duration of
3 h. Then, the numbers of beetles feeding decrease with only one feeding at
15:30. There was further feeding activity throughout the evening between 17:00
until 01:00 when all feeding ceased until 06:00 h. However, on the third day,
feeding occurred sporadically throughout the day with no obvious peak period.
||Solanum nigrum leaf consumption by E. indica
||No. of beetles found feeding on leaf discs of S. melongena,
S. nigrum and a wild solanaceous plant in feeding preference experiment
Leaf Consumption of S. nigrum by E. indica
Table 2 shows the measurement of S. nigrum
leaf area removal after being eaten by beetles in pill bottles after 24, 48
and 72 h. The mean leaf area of S. nigrum eaten per bottle after 24,
48 and 72 h was 29.2±4.308 mm2, 61.4±5.660 mm2
and 80.0±5.812 mm2. The feeding rate was 1.217 mm2
h-1 per beetles after 24 h. 1.279 mm2 h-1 per
beetles after 48 h and 1.111 mm2 h-1 per beetle after
72 h. The mean feeding rate over 3 days was 1.202±0.085 mm2
h-1 per beetle.
Feeding Preference of E. indica on Leaf Disc Choice Test
Table 3 summaries the result of the leaf disc choice test.
The mean number of beetles found feeding on S. melongena leaf disc was
4.0±0.816 compared to 1.454±0.788 on control wild solanaceous
plant leaf disc. Similarly, the beetles exhibited preference to feeding on S.
nigrum plant with the mean number of beetle 4.0±0.816 compared to
2.4±0.699 on control the wild solanaceous plant. Beetles not found on
any leaf disc were not scored in the experiment. However, there was no significant
difference between the mean numbers of beetles found feeding on the leaf disc
of S. melongena which was 2.4±0.6999 compared to on S. nigrum
leaf disc which was 2.2±0.421. Results of this experiment shows that
E. indica have equal preference to eat S. melongena and S.
nigrum leaf over the wild plant (control).
This study is the first study that reports a continuous observation of all the behavioural activity of Epilachna indica on Solanum nigrum plants in the field. Results of this study confirms that E. indica feeds on Solanum nigrum plants in the field, cage and in the laboratory. The optimal feeding time of fifty one E. indica on ten S. nigrum plants under the sun in the field at Ulu Kelang Selangor was from 08:00 to 10:00 h whereas the optimal feeding time for ten E. indica on a S. nigrum plant in the cage was from 09:00 to 14:00 h. In natural conditions in the field physical factors such as the heat of the sun, wind speed, relative humidity, air temperature and other environmental factors will have the effect on beetle activity. In the cage the plant is sheltered from the heat of direct sunlight. There was two feeding cycle exhibited by E. indica on S.nigrum in the field. The periods of the first feeding cycle was 08:00 to 10:00 h and with the second cycle from 16:00 to 18:30 h. The period between 10:00 to 15:30 h are the hottest time in the field. At these time the beetles were mostly motionless or walking on the plant.
Similarly, the optimal feeding period of E. indica on egg plant S. melongena in the field at Somme Estate, Kedah was from 08:00 to 10:00 h (Fauziah et al., 2003). The second cycle of feeding by E. indica on S. melongena was from 17:00 to 20:00 h (Fauziah et al., 2003) whereas on the black nightshade S nigrum plant the second cycle of feeding period starts earlier from 16:00 to 18:30 h. These long feeding periods contrast with that of E. tredecimnotata which lasts for only 1 or 2 h each morning (Carroll and Hoffmann, 1980).
Bioassay using leaf disks in this study shows that E. indica prefers to eat S. melongena over control leaf disk of an unknown wild Solanacea plant. Similarly E. indica prefers S. nigrum over the control. However when given choices between leaf disks of S. melongena and S. nigrum equal number of beetles were found feeding on both S. melongena and S. nigrum confirming that E. indica like to eat both S. melongena and S. nigrum.
Food preferences in Epilachnines are influenced by odor, taste and age of the food plant (Katakura et al., 1989). The basis for discrimination is chemical with scent being detected by olfactory and gustatory sensilla on maxillary palps and antenna (Fischer and Kogan, 1986). Restriction to a particular plant family and species selection within the family is dependent on both odor and taste. However Srivasta (1957) contended that the age of food plant was not important in food selection trials with E. vigintitioctopunctata. Endo et al. (2004) suggested that methyl linoleate plays an important role in host selection of E. vigintioctomaculata. Cucurbitacins, contained specifically in cucurbitaceous plants, acted as feeding stimulants for E. admirabilis, E. boisduvali, E. vigintioctopunctata and E. vigintioctomaculata (Abe and Matsuda, 2000). Abe and Matsuda (2005) reported that chemical factors influences the feeding preferences of three Aulocophora leaf beetle species. This study shows that E. indica likes to eat both S. melongena and S. nigrum suggesting that S. nigrum contain chemical compound that stimulates E. indica to feed on it. Fauziah et al. (2003) reported 2-furancarboxaldehyde was the feeding stimulant which caused feeding behavior by Epilachna indica towards Solanum melongena. Behavioral bioassay towards chemical components extracted from the leave of S. nigrum would enlighten our understanding on host plant selection in the ladybird beetle E. indica.
This study confirms that S. nigrum can be used in pest management strategy of egg plants against E. indica. Results of this study is important and of significance providing a new strategy for Malaysian vegetable farmers. Solanum nigrum maybe grown in margins surrounding egg plants S. melongena. This would lure E. indica to stay feeding on S. nigrum protecting S. melongena from E. indica attack thus increasing the quality and quantity of egg plant production in Malaysia without the need to use pesticide ensuring safe product for Malaysian consumer and safer environment for all.
This study was supported by a research grant from University Malaya No: FP002/2002A and British Council-University Malaya link project No.361 under DFID grant. Thank you to Professor Wilf Powell from Rothamsted Research, Harpenden United Kingdom for advice concerning the project and comments on the manuscript.