CONTROL STRATEGIES OF PAPAYA MEALYBUG, PARACOCCUS MARGINATUS WILLIAMS AND WILLINK IN THE LABORATORY CONDITION

Th e laboratory experiment was conducted at the laboratory of the Department of Entomology, Bangladesh Agricultural University to determine the effectiveness of polythene band, predatory ladybird beetles (available species found in Bangladesh viz. Coccinella transversalis (F.), Micraspis discolor (F.), Menochilus sexmaculatus (F.), Cyclonida sanguinea, Adalia bipunctata, Coccinella novemnotata and Illeis koebelei), four chemical insecticides and three botanical oils in controlling papaya mealybu g, Paracoccus marginatus Williams and Granara de Willink. Th e chemical insecticides were Sevin 85 SP, Dimethoate 40 EC, Fipronil 50 EC, Deltamethrin 2.5 EC, and the botanical oils were Neem oil, Mahogany oil and Karanja oil. In the laboratory experiment, polythene banding failed to prevent the plant from the infestation of papaya mealybug. Seven commonly available species of ladybird beetles in Bangladesh did not provide any control to papaya mealybug. Among the chemical insecticides, Sevin 85 SP and Dimethoate 40 EC showed significant mortality of papaya mealybug. Deltamethrin 2.5 EC and Neem oil (2%) provided moderate control of the pest. The remaining insecticides and botanical oils were less effective to control papaya mealybug.


Introduction
The papaya mealybug, Paracoccus marginatus Williams and Granara de Willink is a small, soft bodied insect pest belongs to the Family Pseudococcidae under the Order Hemiptera. According to Williams et al., (1992), Paracoccus marginatus was first recorded in Mexico during 1955. Walker et al., (2003 stated that Paracoccus marginatus was recorded from the 14 Caribbean countries. Invasion of papaya mealybug in Asia was first reported by Muniappan et al., (2008) from Java, Indonesia and Tamil Nadu in India. Papaya mealybug was first reported in Bangladesh in 2009 (Muniappan, 2010). Within a short period of time, the papaya mealybug is now spread all over the country. The papaya mealybug, Paracoccus marginatus feeds on the sap of plants by inserting its stylets into the epidermis of the leaf and also into fruits and stem. At the time of feeding, it injects a toxin into the plant which causes chlorosis, stunting, leaf deformation and heavy build-up of honeydew ultimately leading to the death of the plant. Honey dew produced by this bug results in the development of sooty mould that covers the leaves, fruits and stems, obstructing photosynthesis and gaseous exchange. Heavy infestations are capable of rendering fruit inedible due to the buildup of thick white wax. Heavily attacked plants were killed (Walker et al., 2003;Hue et al., 2007). The papaya mealybug, Paracoccus marginatus is a noxious insect pest attacking papaya and other agricultural plants of economic importance (Miller & Miller, 2002). It is therefore necessary to find out appropriate management strategies to control this insect in Bangladesh.

Host plant
The Sinta papaya seed variety of Lal Teer Company was used for raising seedlings in polythene bags (12 x 8 cm size with 3-4 holes at the bottom) filled with prepared soil media. The soil media was prepared with the mixture of loam soil and well decomposed cowdung in equal proportion. Two seeds were sown per bag at 1cm depth in the soil media and watered regularly to keep the media moist for higher germination. The seedlings were grown at 28±2⁰C temperature with the photoperiod 12L: 12D in the IPM lab. Thirty five (35) days old seedlings were used in this experiment to study the effectiveness of different control approaches.

Rearing of papaya mealybug
Papaya mealybugs were collected from the papaya field and reared on papaya plant in the insect rearing room of the department of Entomology, Bangladesh Agricultural

Research Article
University. New plants were added roughly every 4 weeks, and old plants were removed after the mealybug had settled on the new plants. Population of the papaya mealybug was maintained until completion of the research work. The reared mealybugs were used in this experiment to perform different treatments.

Use of polythene band
In this experiment three types of plants were used such as mealybug infested plants as source of mealybug, uninfested plants with polythene band as treatment, and uninfested plants without polythene banding as control plants. In polythene banding, the trunk of papaya plants were covered with 3 inch polythene band at the base, 1 inch apart from the soil surface. Total five plants were banded with polythene sheet. Later on, plants were arranged in three rows, where mealybug infested plants were placed in left row, the ploythene banded plants were kept in middle row, and the uninfested control plants were kept in right row.The distances between plant rows were 35 cm. All plants were carefully observed for the next 60 days to observe the movement of mealybug and their possible infestation.

Use of predatory ladybird beetles to control papaya mealybug Free choice test
In the free choice test experiment for the selected ladybird beetles, both papaya mealybug and cowpea aphids were provided together to feed on. In a 15 cm petridishes, ten papaya mealybugs were kept at one side and ten cowpea aphids were kept on another side along with their host plant parts, where one ladybird beetle was released in the middle. Continuous observation on feeding behavior of ladybird beetle was made for the next 6 hours and data were recorded.

Forced feeding experiment
In force feeding experiment, a pair of adult beetle was released in a petridesh and ten mealybugs/petridesh were supplied as food for the predator. The supplied mealybugs were tiny immature stages to adult. Predation behavior of the selected ladybird beetle was observed hourly for the first 12 hours, and after wards observation was made at every 24 hours.

Methodology for testing botanicals and chemical insecticides
Four synthetic insecticides such as Sevin 85 SP, Dimethoate 40 EC, Fipronil 50 EC, Deltamethrin 2.5 EC and three botanical oils viz. Neem oil, Mahogany oil and Karanja oil were evaluated to compare their efficacy against papaya mealybug. The doses of insecticides were according to the manufacturer recommendations and presented in table 1. In case of botanical oils, 2% solution was prepared by adding 2 ml oils in 100 ml water with detergent powder at the rate of 1 gram/L. The efficacy of insecticides and botanical oils was tested against papaya mealybug on standing papaya plant organized according to a Randomized Complete Block Design in the laboratory. Ten mealybugs per plant were released on papaya plant from the cultured populations with the help of a fine camelhair brush and special care was taken during transferring mealybugs to avoid injury. After the release of mealybugs, each plant was placed individually on a special plastic tray with an inner and outer ring. The plant was place on inner ring and the outer ring was filled with detergent water to prevent mealybugs escaping. When all mealybugs were properly settled on experimental plants within 3 days, different treatments were employed. Five plants per treatment were used and plants were sprayed 2 times at 15 days interval. The first and the second spraying were made on 26 January 2014 and 10 February 2014, respectively with the help of a hand-operated sprayer. Care was taken to avoid spray drift on adjacent plants. The spraying was done in such a way that the whole plant was thoroughly covered by spray material. The control plants were sprayed only with water. Pre-treatment data were collected one hour before application of insecticides and botanical oils. For recoding the data all plants parts along with polythene bag and soil media were observed. The number of mealybugs and its progeny were counted using magnifying glass. The data on the number of adults survived per plant under different treatments were recorded after one, seven and fifteen days of the first and second spraying. The number of offspring per plant for each treatment was recorded on the last date of data collection (after fifteen days of the second spraying).

Statistical analysis
Results were subjected to a one-way analysis of variance.
Differences between mean values were tested using Tukey's-HSD-test at p = 0.05.

Effectiveness of polythene band to prevent papaya mealybug
Infestation of papaya mealybug was first noticed in control plants on 30 days, while mealybugs were first noticed in polythene banded plants little bit later on 36 days and subsequently attacked all of the polythene banded plants.
Visual observation showed that polythene band can prevent the climbing of only mature mealybug to the papaya plant and they remained on the stem below the band and suck sap from there (Fig. 1). However the tiny immature stage can easily walk onto the polythene band and established successfully to the top of the plant (Fig. 2). Therefore, polythene band did not prevent the plant from the infestation of papaya mealybug. In India, some of the farmers attempted to stem banding by tying black polythene paper around stem above ground level to prevent the migration from infested material (Ayyasamy & Regupathy 2010). But the efficacy was limited similar to the present study. Tanwar et al., (2010) reported that application of sticky bands or alkathene sheet or a band of insecticide on arms or on main stem can prevent movement of crawlers. The findings of this study revealed that polythene band alone cannot prevent the movement of tiny crawlers. However, any sticky substances on the polythene band may prevent the infestation.

Effectiveness of ladybird beetle to control papaya mealybug
Seven ladybird beetle species such as Coccinella transversalis (F.), Micraspis discolor (F.), Menochilus sexmaculatus (F.), Cyclonida sanguinea, Adalia bipunctata, Coccinella novemnotata and Illeis koebelei were used as bio control agent to control the papaya mealybug. In the free choice test, it was found that three species of lady bird beetles prefer aphids to feed on and did not feed any papaya mealy bug. The other four species neither prefer aphids nor mealy bugs to eat (Fig. 3). In the force feeding experiment with papaya mealybug only, it was observed that adult of the selected seven ladybird beetles did not feed on papaya mealybug and all were died due to starvation. Therefore, the commonly available ladybird beetle in Bangladesh did not provide any control to papaya mealybug.   Creeping of minute nymph on the stem above the polythene band  Several natural enemies of papaya mealybug exist and are commercially available including the mealybug destroyer/Australian mealybug ladybird (Cryptolaemus montrouzieri), lacewings, hover flies, Scymnus sp. and some hymenopteran and dipteran parasitoids (Tanwar et al., 2010). Importation and conservation of new predator, particularly the mealybug destroyer Cryptolaemus montrouzieri which is widely used in foreign countries such as Australia, USA and India may be helpful to control this noxious insect in Bangladesh.

Effect on mortality
The result of the experiments after 1day, 7days and 14 days of first and second spraying of chemical insecticides and botanicals is represented in Table 2 and Table 3 respectively.
Efficacy of all chemical insecticides and botanical oils were increased with the progress of post treatment time and application frequency.  (2008), cited that azadirachtin disrupts the juvenile hormone titers and ovarian ecdysteroid production, leading to a reduction in the number of viable eggs and live progeny. Azadirachtin affects the formation of spermatozoa. Although Neem had less effect on mortality, it can be used to suppress the population increase when the number of papaya mealybug remains below economic injury level. In severe attack, Sevin 85 SP or Dimethoate 40EC can be used for immediate control of this insect pest.