Studying the effects of Paracoccus marginatus (Mealybug) attack on forming of Tagets spp. (Indian Marigold) flower

Abstract

Merigold (Asteraceae: Tagets spp.) is native plant to America and Mexico which is introduced

to Sri Lanka for ornamentation. Widely grows in home gardens throughout the country,

cultivates for cut-flowers and use as insects repellant (Vennila et al., 2011). The plant use to

medicinal remedies and cultivates as a food crops in some other countries but not in Sri Lanka.

Managing Mealybug (Hemiptera: Pseudococcidae; Paracoccus marginatus) insects presents unique challenges. Mealybugs are polyphagous and multiply on different hosts. These have been recorded on many plant species including field crops, vegetables, ornamentals, weeds, bushes and trees in Sri Lanka. Important host plants include okra, holly hock, brinjal, potato, maize, sorghum, groundnut, pigeon pea, sunflower, beetroot, mulberry, Amaranthus spp, Marigold and cucurbits (Anon, 2008). The severity of problem may be estimated from the fact that this insect produces as many as 15 generations per year. The nymphs and adults suck plant sap from tender shoots, leaves and even hard tissues including main stem and branches and cause damage (Anon, 2008) which cause direct plant injury by feeding on plant fluids or sap in the vascular tissues, primarily the phloem or mesophyll or both, with their piercing-sucking mouthparts. In addition, Mealybugs excrete a clear sticky liquid called honeydew which serves as a growing medium for black sooty mold fungi that is secreted on to the leaves which interferes with photosynthesis (Lysandrou et al., 2012). As a result of Mealybug attack, plants become stunted and in severe cases may die. They may also inject a toxin. This may cause leaf yellowing, plant stunting, and wilting. Mealybugs are also capable of transmitting diseases, including viruses. Mealybugs tend to congregate in large numbers at leaf junctures where the petiole meets the stem, on leaf undersides, on stem tips, and under the leaf sheaths. Mealybug is origin in Central America (Williams and Granara, 1992) has its spread at the Caribbean and Ecuador, Chile, Argentina, Brazil, Pakista, India, Nigeria, China, Australia and Sri Lanka (Prishanthini and Laxmi, 2009). Such a vast and fast distribution of Mealybug across the globe largely during the past few years and its economic damage to several crops make it necessary to characterize the ecological factors associated with the pest. In this study, evaluate Mealybug attack on the damage of marigold flower forming.

Materials and Methods

Seeds of Indian Merigold were purchased from the Seed and Planting Material Division, Huggala botanical garden, Sri Lanka. In this study was conducted in green house at the Department of Agriculture Biology, Faculty of Agriculture, University of Ruhuna, Mapalana, Kamburupitiya, Sri Lanka. Four pot replicates were conducted on Merigold plants that was infested with Paracoccus marginatus. Two pots were used as controls. Potting medium was taken 1:1:1 Sand, compost and topsoil and two Merigold plants were cared in each pot. At the

flowering stage, two adults of Paracoccus marginatus were taken from infected Papaya plant

(Carica papaya) and introduced to the every branch of Merigold plant. Data were collected from maturity stage of the flower (after blooming 3days). Data regarding Merigold flowers diameter reduction were subjected to analysis mean average value and compared with the control. Experiment was repeated 3 times.

Results and Discussion

Mean average flower diameter in control pots was 5.85 cm and average mean flower diameters of the infected plants were 3.5 cm. It showed significant reduction of flower formation which were attacked by mealy bug. Merigold flowers were used as insects repellant in biologically. In this study, 59.8% of flower were damaged by Mealy bugs’ activities (Figure 1;d,e,f,). Same result was also showed in many ornamental plant species (Vennila et al., 2011; Janet et al, 2009). Merigold flowers infected by Mealy bug showed reduction of number of petals, decrease the bud size and further infected changed the colour to brown and died.