Morphological differentiation and host record of Phenacoccus spp. complex in Tamil Nadu

Introduction

Mealybugs (coccids) belong to the insect order homoptera and the super family coccoidea. They cause direct damage by way of feeding and in addition they also inject toxic saliva, excrete honey dew paving way for the growth of sooty mould fungus giving an ugly look resulting in poor quality of the produce. It also causes yellowing of leaves and malformation of affected portions due to salivary infection. They also cause indirect damage by way of spreading many viral diseases by acting as vector. The presence of red ants causes the nuisance while harvesting fruits/nuts in mango, coconut, citrus, Cotton, Ornamentals, flower and medicinal crops etc. The honey dew also causes the sooty mould due to capnodium growth and it reduces the photosynthesis. However, at times mealy bug infestation may occur within the vegetative shoot apex and may be extremely difficult to detect. This ability of mealybugs to form dense colonies particularly with in the shoot apex often makes chemical control of this pest quite difficult. Among the various coccids Phenacoccus spp. cause a severe damage by reducing the photosynthesis of the plant due to honeydew secretion and sooty mould attack in Cotton, Sun flower Gingelly, Flower and Medicinal crops. Farmers mainly rely chemical control and the cost of chemical is very high. Some of the chemicals cause phytotoxicity in certain plants (Dhawan, 2007) [2] . There are reports that releases of predators like coccinellids and Chrysopa controlled coccids effectively. Hence, under the above circumstances, it is essential to develop an eco-friendly management practices for the above pests. Despite considerable economic importance there is no systematic study on flower and medicinal crops though these are few records in different parts of India (Varshney, 1985; Shafee, 1989; Suresh, 1994) [9,3,4] .

Materials and Methods

Extensive surveys were made in different flora in cultivated fields, Plant nurseries, range lands and waste lands of Tamil Nadu viz., Coimbatore, Dindigul, Erode, Madurai, Kanyakumari, The Nilgiris, Trichy and Theni (Fig. 1). The infested plant specimens alongwith predators and parasitoids were collected from all places and brought to the laboratory for further study. During sampling, whole plants of the species under observation were examined for occurrence and infestation level as described below were followed. Phenacoccus solenopsis Tinsley was recorded on more than 40 hosts for the first time in India. This pest has been recorded earlier on Hibiscus rosa sinensis (Ben-Dov, 1994) [1] . The other species studied was P. solani (Ferris) on H. rosa sinensis for the first time in Tamil Nadu.

Earlier it was recorded on Chrysanthemum morifolium (Moghaddam et al., 2004). The increased incidence of the above pests in flower crops may be due to succulent nature of the plant which is more attractive and they are also surrounded by other alternative hosts (Randhawa and Mukhopadhyay, 1998). P. madeirensis (Green) is also recorded for the first time on Acalypha bicolor, Crotons variegatum, H. rosa sinensis and Tagetes erecta. This pest can easily recognized by the presence of egg sac. Increased incidence/outbreak may be due to introduction of this pest either from Pakistan or from Sri Lanka and the absence of efficient natural enemies (Ben-Dov, 1994) [1] , with the prevailing hot climatic conditions coupled with increase in reproductive capacity and short life cycle resulted in wider dispersal. Improper use of insecticides also resulted in increased incidence of mealybugs in cotton. This view is also in accordance with the findings of Surulivelu (2006) [8] . Accidental introduction of an insect by travelers or transport into a new area (country) absence of its natural enemies allows it to breed in an unrestricted manner. Among different insecticides, profenophos 50%EC (@ 1250 ml / ha) was reported to be highly effective against the Phenacoccus spp. Though the pest has been managed by the insecticides, it can possess a threat to cotton cultivation in the future as cotton plants continue to have very low population of mealybug. Four sprays of insecticides (acephate 75% WSP @ 2000 g / ha; profenophos 50% EC @ 1250 ml / ha; monocrtophos 36% SL + DDVP 50% EC (@ 625 ml + 375 ml / ha are recommended for the management of this pest with good results (Dhawan, 2007) [2] . Saeed et al. (2007) [14] reported that recommended application rates of methomyl, profenofos and chlorpyrifos provided the best control of Phenacoccus gossypiphilous the lethal time studies proved their efficiency for better and timely control of this sporadic pest. It might be due to the good penetrative reaction of the chemical. However, main reliance on insecticidees may result in resurgence, environmental hazards and discontinuation of their use (Sparks et al., 1996; Mascarenhas et al., 1996,1998) [, 12, 13] . Vast host range of Phenacoccus species requires alternate control measures. Information regarding biological control parameters of insects and their host preference for feeding oviposition are very important to develop alternate strategies effective for its control like other important pests (Greenberg et al., 2001, 2002) [10, 11] . Diversity of hosts suggests that the Phenacoccus species may attack many more plants with passage of time. Therefore, effective manipulation of weeds and ornamental plants, adopting crop rotation and quarantine measures etc. will be of high significance while devising integrated management strategy for this pest

Acknowledgement

AcknowledgementWe gratefully acknowledge the Zonal Project Directorate (Zone-X), Hyderabad and National Bureau of Agriculturally Important Insects, Bengaluru, ICAR KVK, TANUVAS, Namakkal and Authors are acknowledged to Dr. S. Suresh. Professor, Agricultural Entomology, TNAU, Coimbatore for this study.

References

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