Before we can get into trying to understand whether biological pest control is the answer to the pest-control related environmental concerns, it would be proper to give ourselves a little background home elevators this whole pest control business; for the benefit of those who may be encountering it for the very first time.
Now, pests are organisms (typically insects) that are injurious to the interests of the people who refer to them as such. Thus to farmers, the insects that invade and eat up their crops (whether in the fields or during storage), would be termed as pests.
On the other hand, the 'domestic insects' that tend to mess up with things in domestic settings (like moths, that can mess up with cloths in storage), are seen as pests by housekeepers. Worth keeping in mind is that although most pests are insects, there are also quite are number that are non-insects: with the likes of rodents (that can mess up with crops in farms of things stored in domestic settings) being seen as pests too, the fact that they are not insects notwithstanding.
Having seen that pests are injurious, it would be natural that the people who happen to 'fall victim' to them would want to get rid of them. In the meantime, people who haven't yet fallen victim to pests would be keen to avoid such a 'fate.' Hosting pests, by the way, can be a serious fate: thousands of hectares of farmland have been known to be wasted by pests in one day, leading to losses that often run into millions of dollars. It is the steps taken to avoid pest invasion then, or to resolve pest invasion if it has already taken place, that are referred to as constituting pest control.
Now pest control takes various forms, depending on the pests one is trying to get rid of (or to prevent the invasion of). And while bigger pests like rodents may be controlled through mechanical means like trapping, for a long period of time, it is chemical control that has worked for the vast majority of pests, which are usually insects as previous mentioned.
The chemicals used in this endeavor are what are termed as pesticides. And while pesticides are usually very effective in pest-control, the downside to them tends to come up when we consider the fact that they tend to be extremely environmentally unfriendly. Worth keeping in mind, at this point, is the fact that the chemicals referred to as pesticides are usually very potent ones. So it often happens that traces of them remain where they were used, even after the pests are gone. Those traces are eventually washed down to the water bodies where they wreck great havoc to the (non pest) plants and animals resident in the water bodies.
It is concern about this environmental impact of chemical pest-control that led to questions as to whether a more environmentally friend method for controlling pests couldn't be developed. The end result was the exploration of alternatives like the biological pest control, which we are trying to see whether it is really the answer to concerns raised about (chemical- based) pest control.
In biological pest-control, it is other organisms that are known to be predators to the ones considered pest that are unleashed upon the said pests; eating them up and therefore resolving the pest problem. Thus if the troublesome pests are aphids, the other organisms that are known to feed on aphids are introduced into the field where the problem is, to feed on the aphids, rather than spraying an environmentally unfriendly chemical.
The problem with biological pest-control, though, is that it tends to be of questionable efficiency. While chemical pest control tends to be thorough, leaving no pests or even traces of them, in biological pest control, that can't quite be assured. Implementing biological pest control on a large scale basis (for instance on a thousand hectare plantation) can also prove to be a herculean task.
Ultimately, it is considerations like these that make us keep on thinking of more environmentally friendly pest control approaches. It is because biological pest control, while definitely being an approach that addresses the environmental concerns raised about chemical pest control, it doesn't seem to be efficient (or scalable) enough, in most people's view.