Seasonal Occurrence and Predatory Efficiency of Spalgis epius (Westwood) on Mealy Bug, Paracoccus marginatus (Williams and Granara De Willink) infesting Cotton

Spalgis epius (Westwood) is a lycaenid predator of the mealy bug Paracoccus marginatus . Seasonal occurrence of S. epius in cotton field and its predatory efficiency on P. marginatus were studied. Peak activity of this predator was observed during the months of June and July. Mean occurrence of S. epius was more in cotton compared to alternate hosts. Significantly higher number of mealy bug crawlers was predated by the 3 rd instar larvae of the predator followed by 2 nd instar and 4 th instar larvae. Percentage of predation by S. epius was directly proportional to the level of infestation of mealy bug indicating the pest-density dependent behaviour of the predator.

Several economically important crops are infested by various species of mealy bugs across the world (Browning, 1992;Franco et al., 2001). The papaya mealy bug, Paracoccus marginatus (Williams and Granara de Willink) is a polyphagous pest causing damage to a large number of crops such as papaya, tapioca, pigeon pea, cotton, okra, tomato, brinjal, silk cotton, jatropha, mulberry and plumeria; numerous weeds including Parthenium hysterophorus, Sida acuta, Acalypha indica, Eupatorium adenophorum and Cassia sericea; and some forest trees like teak, rain tree and prosopis. Dhara Jothi et al. (2008) reported P. marginatus for the first time on cotton in Coimbatore district, Tamil Nadu. The toxic substance injected into the leaves while feeding results in chlorosis, plant stunting, leaf deformation, early leaf drop and death of the plant (Galanihe et al., 2010).
The parasitoids, Anagyrus loecki Noyes, Pseudleptomastix mexicana Noyes and Schauff and Acerophagus papayae Noyes and Schauff (Hymenoptera: Encyrtidae) were imported from Puerto Rico and released into field in Palau for the control of P. marginatus and successful control was achieved with A. loecki and A. papayae (Muniappan et al., 2006).
The predatory activity of S. epius on the mealy bug, Paracoccus lilacinus infesting citrus, pomegranate, ber and guava has been reported in Southern India (Mani and Krishnamoorthy, 1998). Feeding efficacy of S. epius was observed on the mealy bugs, Paracoccus citri (Vinodkumar et al., 2008) and P. marginatus (Thangamalar et al. 2010). Larvae of S. epius have been found to feed voraciously on P. marginatus (Dharajothi et al., 2009) (Fig. 2). Vinodkumar et al. (2008) described the characteristics of S. epius. The pupa exhibits a characteristic appearance like the face of a monkey hence it is commonly called 'Ape fly'. Although many studies were carried out on the control of P. marginatus, accounts on endemic biocontrol agent for this pest infesting cotton are meagre. This study reports the seasonal occurrence of S. epius in cotton field and alternate hosts and the predatory efficiency on P. marginatus.

Seasonal occurrence of S. epius on cotton and alternate hosts
Seasonal occurrence of S. epius on cotton and other alternate hosts namely parthenium, glyricidia, crotons, hibiscus, guava, papaya, silk cotton, banana and Ixora was recorded from the experimental fields of Central Institute for Cotton Research (CICR), Regional Station, Coimbatore during 2008-11. Weekly observations were made on the predator activity on cotton and other hosts. Ten plants were tagged and twigs of 15 cm length were observed for the population of S. epius larvae and the infestation grade of mealy bug.

Natural occurrence of S. epius on cotton
Under field conditions, the predatory efficiency of S. epius was recorded on the mealy bug infested cotton plants in an area of half an acre, which was divided into nine strips each with 42 rows. The number of healthy plants, mealy bug infested plants and mealy bug infested and predated plants were recorded and the percentage of mealy bug infestation as well as predation was calculated.

Rearing of S. epius and P. marginatus
Both S. epius and P. marginatus were collected from the experimental field of the Central Institute for Cotton Research, Regional station, Coimbatore and cultured in laboratory. P. marginatus was mass cultured using potato sprouts under laboratory condition at 25 ± 1 ° C and 65 ± 2 % RH and 14:10 (L:D) photoperiod adopting the methodology of Branigan (1916). Potatoes with many eyes were kept in wet gunny bags under dark condition for four to five days to induce sprouting. The tubers were sown in plastic bucket (23×18 cm), filled with sterile moist sand. When the sprouts reached a height of 15 to 20 cm, the crawlers from the infested papaya leaves collected from the field were introduced onto the green sprouts using a camel hair brush (Series No. 68). Larval instars of S. epius collected from the cotton field were reared individually on P. marginatus grown on potato sprouts.

Predatory efficiency
Laboratory experiments were conducted to evaluate the predatory efficiency of S. epius on P. marginatus. The larval instars of the predator were released individually in Petri plates at 10/plate and prey was provided. Second, third and fourth instar larvae of the predator were provided with 500 mealy bug crawlers and observations on predation were made at 1, 24 and 48 h after releasing. In another experiment, second and third instar larvae of the predator were provided with 20 egg masses/day and observation on predation was taken at 24 h. Total number of crawlers and egg masses fed by each larval instar was recorded by counting the remaining prey stages in the Petri dishes. Each experiment was replicated ten times. Data on the predation on crawlers were subjected to ANOVA followed by Student-Newman-Keuls test (SPSS 16.0. 2007).

Seasonal occurrence of S. epius on cotton and other alternate hosts
Periodical observations during 2009-10 on cotton (summer crop) and other hosts revealed that there was no activity of the S. epius during March and April and the activity resumed during the month of May. Peak activity of this predator was observed on cotton during the month of July. Highest number of S. epius was recorded on cotton followed by parthenium, crotons, hibiscus, guava and glyricidia (Fig.3).
During 2010, mealy bug infestation grade ranged from 1 to 3 among the different hosts. parthenium and Tridax porcumbens recorded maximum level of grade III. Maximum population of S. epius was recorded in Hibiscus followed by parthenium (Fig.4). Seasonal dynamics of S. epius was recorded from June to January. S. epius occurred from June to September and no population was recorded thereafter up to January. Maximum population was recorded during the month of June on hibiscus followed by parthenium and Annona squamosa (Fig.5).

Natural occurrence of S. epius on cotton
Infestation of mealy bug was observed in all the strips with the highest infestation of 98.29 in the second strip followed by first strip with 98.01%. The percent predation gradually decreased in the subsequent strips from 1 to 9. Activity of the predator was intense in the first four strips and it gradually decreased towards 9 th strip. As the percentage mealy bug infestation gradually decreased from first to ninth strip, percentage of predation also decreased and became nil in the last strip (Table 1). This clearly depicts the density dependent behaviour of the predator in predation.

Predatory efficiency of S. epius on P. marginatus
Significantly higher number of mealy bug crawlers was predated by the 3 rd instar larvae of the predator followed by 2 nd instar larvae and the least number of crawlers by 4 th instar (Table 2). Among the 2 nd and 3 rd instar larvae of the predator, 3 rd instar predated significantly more number of egg masses per day compared to 2 nd instar (Table 3).

Discussion
In the present study, maximum population was recorded during the month of July on cotton and hibiscus and it is in agreement with the report of Thangamalar et al. (2010) who stated that S. epius was the dominant predator feeding on mealy bugs during June to October. Venkatesha et al. (2004) reported that the first instar larvae fed only on the egg masses of the mealy bugs, while the second instar consumed significantly more number of crawlers followed by 2 nd and 4 th instar larvae. The significant decrease in the prey consumption of the fourth instar larvae might be due to the time taken for the preparation for the pre-pupal stage.

Fig. 2. Mealy bug infestation and predation by S. epius
Plant Showing residue of predated mealy bugs Mealy bug infested plant larvae fed on the egg masses as well as young nymphs and the third and fourth instar larvae voraciously fed on all stages of the mealy bugs. In the present study, it was observed that among the 3 stages of the predator larvae, 3 rd instar larvae Preliminary observations made on S. epius in the field revealed that a full grown larva consumed 300 nymphs of M. hirsutus per day (Pushpaveni et al., 1973). Though the predator recorded its voracious feeding behaviour on the mealy bug, natural control of the pest by the predator did not take place in cotton because of many reasons. Cotton cropping system is pesticide dependent and the lycaenids are sensitive to the insecticides. These predators were scarce in cotton because of regular spray of pesticides (Thangamalar et al., 2010). In the present study, the occurrence of the predator was not observed during the cropping season (February-May) due to the application of pesticides for the management of sucking pests. The peak activity of the pest was observed during June to July which was the end of the cropping season and predator coincided with the peak pest activity. Density dependant behaviour of the predator was evident from the level of occurrence and the pest infestation status on different hosts.   application hence the build up of the predator is not facilitated. Males of the predator outnumbered the female which influences the number of eggs laid. Rearing of the predator under artificial conditions is not successful because of the fact that the females do not oviposit under captivity. The adoption of integrated pest management strategies with more emphasis on biocontrol methods instead of using chemical pesticides alone may facilitate the conservation of this predator in the field.