Directional movement and density of migratory swarms at different locations
Migration of
C. pyranthe was started in early September (07.09.2020) and lasted up to end of September. Observations recorded on the migration of butterflies at different location’s which revealed the variation in density of swarm movement. Highest density of swarm (1131 butterflies /10m /5 minute) was recorded in Lathi area on September 19
th which equivalents to the 13,572.00 butterflies /10m/Hour and 81,432.0 butterflies /10m /day, if extrapolated. Similarly, another peak of 1360 butterflies /10m /5 minute was recorded in Keru of Jodhpur district on September 29
th which corresponds to the 16, 320.00 butterflies /10m / Hour and 97,920.00 butterflies /10m /day. Density of swarm movement was higher near to breeding areas and declined with increased distance. Therefore, the least density of 135 butterflies /10m /5 minute was recorded in Beawar of Ajmer district. Direction of movement of butterfly swarms in general was South West. However, slight variation was also recorded in some locations (Table 1).
Ramesh et al., (2012) observed the North-South migration of butterflies at Kalpakkam during October and July, respectively. They considered avoidance of rain, resource competition at emergence sites and available larval host plants as the major reasons of migration.
Williams (1927) indicated that the migratory tendency among butterflies was predominately evolved during March-July and October-November, to avoid unfavorable climatic or weather conditions, especially North-East Monsoons (NEM) and South West Monsoons (SWM). Movements of butterflies to South West direction under present study could be the reason to avoid the onset of North East Monsoon. In best of our knowledge, this is the first report on butterfly migration in western arid region while
Williams (1927) was the first who analyzed the butterfly migrations and concluded that in Kodaikanal, October flight was very definite to the South and the March and May-June flight towards the North while in Ceylon both the flights were towards the westerly quarter (
i.e. between N.W. and S.W.).
Evershed (1910) observed southward migration of
Catopsilia sp in Kodaikanal (TN) during October- November and remained unaffected from the wind direction.
Shull (1952) reported the southerly movement of
Catopsilia during September at Bombay Presidency which supports the present study.
Bharos (2000) noted north wand migration of
C. pomona during June 1999 in Madhya Pradesh.
Larsen (1978) reported Southerly migrations of
Appias albino,
A. libythea,
C. pomona,
C. pyranthe,
C. crocale crocale,
Phalanta phalanta during May in Nilgiri mountains (TN) while
Atrophaneura hector and
Pachlioptra aristolochiae in south direction during October. Studies of
Mathew and Biony (2002) are in concurrence to the present findings who reported South West Migration of five butterfly species in the Nilgiri Biosphere reserve (Kerala part) of Western Ghats.
Santhosh and Basavarajappa (2017) mentioned the
Tirumala sp and
Euploea sp migration towards South-West during September-November in Western Ghats of Karnataka. Kunte (2005) observed swarm density of
T. septentrionis (Butler) and
Euploea sp in Western Ghats @ 195 butteflies /10m/5 minute which comes to 2,340/10m/hour or 58,500/50m/day (5 hours count in a day).
Diurnal migratory pattern
Total butterflies recorded at hourly interval between 8.0 AM to 6.0 PM have been denoted the percentage of the total numbers sighted in a day. Fig (1) shows the pattern of movement during the day and density varied with different time hours. The curve of diurnal movement was more or less like bell-shaped and this trend indicated that butterflies activity was started in early hours of day (8.0 AM), attained peak around noon (12.0-1.0 PM) and then declined gradually, thus 56% activity was around 11.0 AM to 2.0 PM. Therefore, it can be inferred that butterfly activity is greatly influenced by weather parameters, particularly temperature and sunshine hours. It was also observed that cloudy weather completely ceased the movement and regained with the appearance of bright sunshine. Observations were also made on the flying height of butterfly which indicated the butterfly movement was mainly at a height of 0.5 to 4 meter. However at one place, butterflies were crossing a flyover bridge without change in direction which may be elevated upto 10 m. In case of any obstacle, butterflies slightly deflected or increased its height but didn’t change the direction.
Ramesh et al., (2012) also observed the maximum density during the mid day and then gradual decline.
Mathew and Biony (2002) observed the peak hours of flight density between 12-13 hrs when as many as 160 butterflies per minute were recorded which gets nearer to 9600/hour or 57600 /day (6 hours count in a day). Bharos (2000) viewed the
C. pomona flying at a height of 0.5-4.0 m.
Walker and Riordan (1981) stated that climatic factors including the cloud cover govern the migration. Flying bout duration generally increased with temperature and decreased with cloudiness
(Cormont et al., 2011).
Correlation between swarm density and abiotic factors
In present study it was found that weather parameters
viz., temp, RH, wind speed and sunshine significantly affected swarm movement. Pearson correlation was analyzed for swarm density and weather parameters, butterfly swarm density was found positively correlated with temperature (r=0.54) while negatively correlated with RH (r=0.60). Activity of butterflies started early morning, however the movement remained less distinct but with the progress of the day, it became more distinctive. Highest activity of butterflies (404 Butterflies /10m strip/5 minute) was recorded during 1.00 PM corresponding to the period when maximum temperature was 36.7°C, humidity 37 per cent and wind speed 6.3 kmph. Increase in temperature was seen to increase the activity of butterflies while decrease in humidity was found to increase the abundance of butterflies. The correlation study revealed that the sunshine hours had positive correlation with appearance and population density of butterflies. Wind speed had lesser influence on butterflies swarm. The correlation co-efficient values were presented in Table 2.
Findings of the
Ramesh et al., (2012) corroborate the present study who found the positive correlation of temperature and wind speed with butterfly swarm. However, relative humidity and sunshine found to be negatively correlated during October which is partly in agreement with the present study.
Larsen (1978) noted the direction of butterfly movement remain unaffected with the wind direction.
Nature of damage, extent of infestation and adult behavior
Large scale breeding of
Catopsilia sp observed on senna in and around areas of Pokhran of Jaisalmer district (Fig 2). Damage was mainly due to caterpillars. Larvae of this pest found to be serious defoliator. Larval feeding resulted in denuding of plants (Fig 4a). Larvae pupated on plants and remain attached with the silken thread. About 44-96 per cent infestation was recorded on senna. Female laid white color eggs on both surface of foliage. They deposited an average of 94.8 eggs per plant, of this 59.50 per cent laid on upper surface while 40.50 per cent on lower surface (Table 3 and Fig 3a, b, c, d). Apart from senna, pupal exuviae were also found in large numbers attached to the
ber and other desert vegetation. Butterfly adults were also found to exhibit the puddling process through which they were imbibing nutrients from the moist soil (Fig 4b).
Chaudhary and Saravanan (2013) reported 15 to 40 eggs/plant and subsequently 5 to 35 mottled butterfly larvae/senna plant during June and September, respectively in Gujarat conditions. They also reported an infestation level of 88-100 per cent in senna.
Arms et al., (1974) associated the mud puddling behavior with sodium salts requirement and linked more water and salts requirement during migration as one of the reasons.
Table 3 depicts last 10 years rainfall data of Jaisalmer which revealed that during 2020 rainfall received in monsoon months (238.0 mm) and in particular September month (45.60 mm) is the highest in last One decade. All the arid districts received very good rains during September month. This may be one of the reasons of outbreak which favored either the multiplication of pest or increased the foliage of the plants. Thus, caterpillars received the more amount of palatable food.
Richard et al., (2017) found positive association between precipitation and caterpillar abundance of
Platyprepia virginalis. Synchrony with host plant has been suggested as an important factor in the dynamics of many forest pests
(Van Asch and Visser, 2007). For instance, 69% of
Rhopobota naevana neonates die before feeding when presented with only old cranberry leaves compared to 11% on young expanding foliage. Population growth is thus five times higher if larvae hatch in synchrony with host bud burst
(Cockfield and Mahr, 1993). First-instar
Zeiraphera canadensis show dramatically lower survivorship (> 50% to < 25%) when fed on 4-5 day old white spruce foliage
(Carroll and Quiring, 1994).
Host acceptance to other plants
At present, only the senna crop has been under attack from this caterpillar but with rapid changes in agro ecology and climate of the region, this butterfly pest of
C. angustifolia, may switch over to other crops of the fabacea family. To find out the host acceptance of larvae on other crop plants, larvae of
Catopsilia sp were fed on the leaves of
kharif crops namely mungbean, groundnut, cluster bean, moth bean and pearl millet but the larvae didn’t feed on the leaves and died due to starvation.
C. pomona reported serious pest on
Cassia fistula and
C. angustifolia,
(Anonymous, 1995;
Anonymous, 2000).
Saji et al., (2020) reported
C. fistula,
C. javanica,
Senna sp,
Ormocarpum sp,
Sesbania sp, belonging to Fabaceae and
Gnidia glauca (Thymelaeaceae), as larval host plants of
C. pyranthe. Since introduction of IGNP and exploitation of groundwater in last two decades, the Agro-ecology of arid regions has been tremendously changed. With this changing agro-ecology, some pests of non significance have become pests of major importance. Insect like the cetoniid beetles
Protaetia terrosa which were very active on grasses has now been well established on cluster bean crop.
Clovia puncta Walker established on pulses
(Verma, 1979) from grasses.
Maladera insanabilis has been established as a regular pest on several crops in the IGNP area
(Verma, 1999).
