The cotton mealybug Phenacoccus solenopsis Tinsley (Hemiptera: Pseudococcidae) is native to the Neotropical zone, invasive in Pakistan has become the major pest since 2005 and spread very quickly on cotton and reduced the production. No any chemical control is effective to control mealybugs in the country as well as in the world due to protection of waxy cover on its body. Field and laboratory experiments on biological control of cotton mealybug were carried out at Sindh Agriculture University, Tandojam, Sindh, Pakistan and Benaki Phytopathological Institute, Kifissia-Greece from 2007-10. The preliminary field survey for prevalence of natural enemies and host plants of cotton mealybug resulted Brumus suturalis, Menochilus sexmaculatus Fabricius, Scymnus suturalis Thunberg, Scymnus coccivora Ayyar, Hyperaspis trifurcate Schaeffer, 7-spotted beetle Coccinella septumpunctata, Adalia bipunctata L. (Coleoptera: Coccinellidae), Diadiplosis sp. (Diptera: Cecidomyiidae), big-eyed bug Geocoris punctipes Say. (Heteroptera: Geocoridae), greenlace wing Chrysoperla carnea Stephens (Neuroptera: Chrysopidae) and parasitoid Aenasius bambawalei Hayat (Hymenoptera: Encyrtidae) and also 37 host plants in 17 families were first time documented. Out of 37 host plants preferred host plants were studied for population fluctuation of mealybug and its natural enemies in field. Four host plants belonging to Malvaceae family (cotton Gossypium hirsutum L., okra Abelmoschus esculentus L., China rose Hibiscus rosa- sinensis L. and velvet-leaf Abutilon theophrasti Medik) and three to Solanaceae family (brinjal Solanum melongena L., common winter cherry Withania somnifera L. and thorn apple Dhatura stramonium L.). The mealybug P. solenopsis appeared on cotton after one month of crop sowing (1 st week of June to 2 nd week of November). The mealybug population was maximum on abutilon 5881, cotton 4829, okra 4429 and China rose 3970 followed by thorn apple 603, winter cherry 455 and brinjal 145, throughout the study period. In this study mealybug had positive correlation with temperature. In laboratory, biology of predator C. monrtouzieri pre-mating period for beetles 5.60±0.08 days, pre- oviposition 9.90±0.19 days and for incubation 5.30±0.07 days were recorded. The oval cylindrical white pale yellowish eggs (capsule shaped) were laid by females singly or in groups in ovisacs of mealybug P. solenopsis. After hatching from eggs the grubs developed through four instars. Grubs hatched from egg as first instar with mean period of 5.90±0.15 days, which were smooth, pale grey and increased gradually in size. Period for 2 nd , 3 rd and 4 th instars 5.00±0.16, 700±0.18 and 8.30±0.13, respectively with total 26.20±0.61 days for grub development. The pre-pupal and pupal periods were recorded 2.90±0.07 and 8.50±0.20 days, respectively. Total development period from egg to adult 42.90±0.95 days was observed. The adult longevity for male 80.90±0.89 and female was 84.40±0.90 days. The predator copulation period ranged between 5-48 minutes. The male mounted and dismounted over the female body and mated repeatedly throughout their life. The overall oviposition period was 76.40±1.30 days. The fecundity was 486.90±1.41 xifemale -1 . C. montrouzieri was no acclimatized in cotton environment due to temperature and interaction of ants. Effect of heat treatments on C. montrouzieri survival in laboratory at Benaki Phytopathological Institute Kifissia, Greece was tested at five temperatures (35±0.5, 38±0.5, 40±0.5, 42±0.5 and 44±0.5 o C). C. montrouzieri was treated at 35±0.5 o C for 1, 2 and 3 hours survived for 23, 18 and 17 days, at 38±0.5 o C for 20 and 16 days, at 40±0.5 o C for 12, 7 and 5 days, at 42±0.5 o C for 9, 4 days and 44±0.5 o C for 4 days, respectively. However, mortality in beetles was observed in treated beetles at 42±0.5 o C for 3 hours and 44±0.5 o C for 2 hours. Studies on age specific life table of mealybug P. solenopsis indicated that lower mortality was in developing instars due to predation and high mortality in adult stage due to parasitism. Studies on biology of the parasitoid A. bambawalei showed that parasitoid female watched the mealybug adult females with the help of antennae and then inserted ovipositor through ventral side of body. Swelling and lazy movement of mealybugs was observed after 2-3 days by turning into light yellowish hard cuticle. These mummies were observed after the period of 5-7 days. Dark brown colour of mummy indicted the emergence of parasitoid between 11-15 days. Life span of adult parasitoid ranged between 10-37 days and fecundity of female 32-170. It was also observed that female of parasitoid preferred egg depositing in mature mealybugs. The study on parasitism of mealybug P. solenopsis through parasitoid A. bambawalei on cotton plants in the field indicated that majority of mealybug population aggregated on top portion (growing region) of the plant and minimum numbers scattered on the rest of plant parts. Results also revealed that ten pairs of parasitoid were effective against 1000 mealybugs on 5 plants m -2 . Parasitoid A. Bambalalei had better searching ability and parasitized the mealybug colonies as well as in the scattered form. It is concluded that cotton mealybug is a serious pest of cotton growing regions. Abutilon is preferred host of mealybug. Indigenous predators can play partial role to control mealybug. The exotic predator C. montrouzieri was not much effective due to their acclimatization in these harsh weather conditions and attack of ants. Mealybug population must be controlled on the host plants for further spread over cotton. The results showed that A. bambawalei proved effective against mealybug P. solenopsis and is suggested for field release.