Biological Control ~ Backfiring in India (Weed Control with Insects) ~ an insight
Prickly Pear (Tamil: Sappaathik Kalli) Opuntia dillenii, is a menacing weed on road sides and field bunds in India and Sri Lanka and it is one of the earliest success stories for use of bio-control agents.In this case, a mealy bug (Tamil: Maavup Poochi) was used. This bio-control agent is called, Dactylopius tomentosus.
Based on this success story, many countries (Australia, Cuba etc) used different bugs (Species of Dactylopius on different species of Opuntia). Nearly five decades later, in India, we still find Opuntia dillenii coming back to life and still the insect (Dactylopius tomentosus) clinging on to its dear life.
Opuntia is too strong and comes back to life, in the very same place where it perished after being sucked sapless by the bug. Science has learnt a certain lesson here..Nature does fight back !.
The second lesson that Bio-control Advisors learnt from this particular insect is that once the main host (in this case Opuntia) is not available aplenty, then the bio-control can also turn into a pest damaging crops. A very valuable lesson learnt, as mealy bug today is a serious threat on commercial farms / plantations of Papaya, Rose and also to home garden plants like Hibiscus, Custard Apple, Guava, Crotons, Plumeria, Mussaenda, Poinsettia etc.
This bug has a white wooly covering and pesticides cannot penetrate the cover the kill the insect at later stages. Dichlorvos is the only compound (with its vapourizing action) that is found effective to clean by swabbing. This guy (Mealy bug) is sedantary and cannot move by itself. Therefore, it attracts ants by secreting a syrupy concoction, liked by ant brotherhood, who for returning the favour, transport the mealy bugs from one host plant to another. Hence, as an additional precaution, ant powder is applied at the base of host plants to prevent this transport getting anywhere nearer.
This is how a successful Bio-control agent has turned into a pest !
Who said Bio-control agents are host specific..?
Ask our papaya growers and rose farmers in India !
