(7) BCAs are frequently very host specific.
(8) Unlike chemical methods, pests do not become resistant against BCAs.
4.2. Disadvantages of biocontrol
The disadvantages of biocontrol include as follows:
(1) Biocontrol is often slow. In biocontrol of pests, there is often a lag time between build‐up
of the pest population and build‐up of the biocontrol agent. If a pest population is already
at or above economically damaging levels, pesticides are the only alternative.
(2) BCAs do not completely eliminate their host [ 6 ]. If they do, they would also die. However,
biological control may be integrated with other pest control strategies to achieve complete
eradication.
(3) With biocontrol, there is the possibility that the BCA may tend to feed on the desired
plants or insect, that is, crossovers [ 7 – 9 ]. Careful selection of the BCA will minimize this
problem.
(4) BCAs are frequently ineffective in multiple weed complexes when used in biocontrol of
weeds. This may be because the weed and the crop are so closely related that the control
agent affects both the pest and the crop.
(5) The shipping, storage and application techniques of BCA can be relatively complex. Pro‐
duction of the BCA is also costly in some cases.
(6) Biocontrol sometimes may be costly compared to conventional methods. The high cost
is usually attributed to the research that has to be done prior to implementation of the
biocontrol strategy.
(7) Biocontrol if not well conceived may lead to dramatic changes in native biodiversity.
5. Types of biological control agents
Biocontrol of insects may include predators (e.g. spiders), parasites (parasitoids) or pathogens
like viruses, bacteria, fungi, protozoa and nematodes (see Figure 1 ).
5.1. Predators
Predators can be vertebrates or invertebrates, some of which are arachnids, but deployment of
insects is most common. The efficiency of predators in controlling populations of some ticks
in different habitats varies and may reach up to 100% [ 10 , 11 ]. For example, predation has
been observed to be lower in tall grass areas than in short grass areas [ 12 ]. Likewise, predation
has been observed to be two to eight times higher in open areas than in thick pasture areas
Biological Control of Parasites
http://dx.doi.org/10.5772/6801227