The status of augmentative bio-control in selected crops is briefly presented herein:
1. Rice:
Releases of mirid bug @ 100 bugs or 50-75 eggs/m2 at 10-day intervals have been found effective for the control of brown planthopper. Inundative releases of exotic Trichogramma japonicum Ashmead at 50,000 ha-1 during egg laying period of rice stem borer reduced borer damage and increased crop yield. It has been found that 7-9 releases of T. chilonis Ishii and T. japonicum @ 1,00,000/ha, starting at 30 days after transplanting proved as effective as the standard insecticide treatment for the control of stem borer and leaf folder.
A total of 11 releases of T. japonicum and T. chilonis @ 50,000 per ha per week on a long duration variety of rice (Swarna) reduced the tiller damage caused by yellow stem borer and folded leaves by rice leaf folder, to the tune of 50.1-61.3 and 63.8-75.5 per cent, respectively. Similarly, reduction in tiller damage and folded leaves varied from 78.1 to 81.6 and 72.6 to 81.8 per cent, respectively, when the egg parasitoids were released @ 1,00,000 per ha per week during the season.
2. Sugarcane:
The relatively stable sugarcane agro ecosystem provides ideal conditions for the colonization of natural enemies. During recent years, releases of T. chilonis have been found effective for the management of various shoot and stalk borers in different parts of the country.
The parasitoid releases @ 1,25,000 ha-1 are recommended against shoot borer in Andhra Pradesh. Weekly releases at 1,25,00 parasitic wasps per ha from 4th to 11th week stage of the crop provided effective control of internode borer, Chilo sacchariphagus indicus Kapur in Tamil Nadu.
The release of 12 ml of parasitoid adults (3,00,000) per ha in six split doses effectively checked internode borer infestation in an area of about 500 ha. In Punjab, the sequential releases of T. chilonis (12 releases @ 50,000/ ha at 10-day intervals) and Cotesia flavipes (Cameron) (6 releases @ 10,000/ha at 10-day intervals) during July to October proved very effective for the control of stalk borer.
For the control of early shoot borer, Chilo infuscatellus Snellen, 6-9 releases of T. chilonis during April to June at 10-day intervals @ 50,000/ha proved effective. Similarly, stalk borer and Gurdaspur borer have been controlled in parts of sub-tropical India by large-scale releases of T. chilonis.
In addition to egg parasitoids, field releases of the larval parasitoid, Isotima javensis (Rohwer) exercised effective control of top borer in Tamil Nadu and Karnataka. Releases of Sturmiopsis inferens Townsend at 312 gravid females per ha provided effective control of C. infuscatellus in coastal areas of Tamil Nadu.
Sugarcane pyrilla has been effectively controlled by redistribution and periodic release of 8000-10,000 cocoons or 8,00,000-10,00,000 eggs per ha of parasitoid Epiricania melanoleuca (Fletcher). In 1999, there was an outbreak of pyrilla in 6 lakh ha in north India, perhaps due to indiscriminate burning of trash. However, the parasitoid overpowered the pest within 20 days and the spraying cost of about Rs 480 million crores was saved.
3. Cotton:
A number of promising natural enemies have been found attacking cotton pests in the country. However, large scale use of insecticides has reduced the population of most of these natural enemies to insignificant levels. In the fields where bio-control was practiced, 25 natural enemies were recorded as compared to only 2 in the fields sprayed with insecticides.
Releases of Trichogramma spp. at 1,50,000 parasitized eggs ha-1 at weekly intervals have proved promising for bollworm control. The green lacewing, C. carnea, can be released @ 2 larvae per plant during the peak egg hatching of cotton bollworms. Sucking pests may be checked by releasing chrysopids at 1 lakh per ha at fortnightly intervals.
Recently, a new parasitoid, Aenasius bambawalei Hayat, has been reported to cause 50-80 per cent parasitization of the nymphs of mealybug, Phenacoccus solenopsis Tinsley. The parasitoid could kill the mealybugs within a week, which turned into reddish dark brown mummies. The parasitoid population could be augmented in cotton through collection of mealybug mummies from various host plants and releasing them onto the cotton plants.
4. Horticultural Crops:
Augmentative and inoculative release of two exotic parasitoids, Encarsia perniciosi (Tower) and Aphytis spp. proclia (Walker) group @ 2000 per infested tree have given promising results for the suppression of San Jose scale on apples. The Russian strain of E. perniciosi proved effective in Himachal Pradesh while Chinese and American strains proved better in Uttar Pradesh. Aphelinus mali (Haldeman) was found effective against woolly apple aphid in Kullu Valley but subsequent releases in Shimla Hills, Chaubattia, Conoor and Shillong were not successful.
Similarly, releases of exotic parasitoid, Leptomastix dactylopii Howard have proved effective for the control of citrus mealy bug, Planococcus citri (Risso) in Karnataka. Mass rearing and release of the Australian coccinellid predator, Cryptolaemus montrouzieri Mulsant have been found effective against citrus mealybug, grape mealybug, guava scale and other scales in a number of plantations.
In case of vegetable pests, inundative releases of egg parasitoid, Trichogramma brasiliensis (Ashmead) @ 4000 adult’s ha-1 for six weeks suppressed the attack of fruit borer on tomato. Phytophagous mites on okra and brinjal can be effectively checked by augmentative releases of phytoseiid mites, Phytoseiulus persimilis Athias-Henriot and Amblyseius tetranychivorus (Gupta) @ 10 adult’s plant-1.
5. Plantation Crops:
Inundative release of native parasitoids, Goniozus nephantidis (Muesebeck) and Bracon brevicornis Wesmael at 3000 and 4500 per ha, respectively, has given encouraging results for the management of Opisina arenosella Walker on coconut. The inoculative release of coccinellid, Curinus coerulens Mulsant, against subabul psyllid, Heteropsylla cubana D.L. Crawford has proved very effective in the management of this pest.