Desirable Attributes of Bio-agents
The classical practice of introduction exotic beneficial organisms or pest suppression is the only useful method under restricted conditions. While introducing beneficial organisms, the concern of the desirable attributes of a natural enemies and a consideration of some basic ecological principal have bearing as success or failure of biological pest-suppression programmes.
Desirable Attributes of Natural Enemies:
In order to search for efficient beneficial organisms for use in biological insect pest suppression it requires some idea beforehand that what we are seeking. Before introducing new natural enemies from exotic locations or analyzing those species which are already present for same way of augmenting their usefulness we must know their characteristics of species to display it an efficient regulatory relationship with the pest. Thus proper selection of natural enemies of insect is an important part of success of Biocontrol.
The Organisms should Possess Following Attributes:
1) Ecological Compatibility:
It is usually important to seek species whose ecological requirements are similar to those of the intended target insect. Parasitoids are frequently limited in effectiveness and have greater sensitivity to cold; desiccation, heat etc. and hence it is of great consideration for parasite species to withstand such condition suitable for the host. Disparity in ecological responses may be an important limiting factor in the effectiveness of native beneficial organisms and an environment manipulation of same sort may make them successful regulative agents e.g. high humidity by irrigation for development of pathogenic fungi against alfalfa aphids.
2) Temporal Synchronization:
The pest and its natural enemies should be in the same place at the same time and also their life cycles must be synchronized for adequate regulation to be possible. Thus the reproductive stage of a successful egg parasitoid must be active at the time of the hosts egg in every generation of the host. The efficacy of poorly synchronized organism may sometimes be improved. The practice of periodic inundative release of beneficial insects is another way of artificially synchronizing the occurrence of parasitoid and host e.g. release of Trichogramma spp.
3) Density Responsiveness:
The most desirable biological control agents should exhibit positive rapid density responsiveness. Proportion of natural enemy of pest should be maintained. Generally natural enemies have short life cycle, whereas pest has long life cycles. A strong functional response refers to within generation behavioral activity of the individual parasitoid or predator in increasing its attacks against increasingly numerous hosts or prey, on the other hand, numerical response refers largely to a multigenerational reproductive increase by the organism in response to increasing host density. A rapid and strong numerical response characteristic is the most important attributes of a successful agent of pest mortality.
4) Reproductive Potential:
One important factor in the display of density responsiveness is high reproductive capacity through either short generation time, high fecundity or both. In most cases, the parasitoid or predator is searched with an innate potential for increase greater than that of the host/prey.
5) Searching Capacity:
The ability to find host/prey at low density has significant bearing on the long term success of organism in the more stable situations. A beneficial organism which can successfully utilize low density population and reduce its number through efficient searching behavior is a desirable key regulative agent to be sought. A true ideal beneficial insect would possess both high reproductive potential and good searching capacity, but it case of successful biological control full utilization of former factor rarely comes into play because of low pest densities and efficient searching ability becomes the primary characteristic because it maintains those low densities.
6) Dispersal Capacity:
The ability of an introduced beneficial species to easily and rapidly expand its sphere of influence in space to coincide with that of the host is closely tied to its searching capacity and ecology adaptability. Most good biological control agents shop high dispersal capability, season ends the pest migrates and natural enemy should also ingrate.
7) Host Specificity and Compatibility:
A parasitoid or predator which is monophagous or silently Oligophagous indicates a high degree of biological adaptation to the host and probably a greater degree of direct degree of direct and rapid responsiveness to density changes in the population of the target host. Host specificity is closely ties with compatibility that is the degree of biological adaptation. Monophagous entomophagous have usually evolved a high degree of adaptation to the defensive mechanisms of their host/prey. Predator with polyphagous nature will do the purpose. Compatibility refers to combination of unnatural enemies. Likewise lady bird beetles should not eat Trichogramma spp.
8) Food Requirements and Habitats:
This attributes is another consideration in choosing a potentially useful beneficial organisms. For sustenance of natural enemy some sort of food should be available to natural enemy like pollen, Honey etc. and also shattering places. Nutritional requirement of natural enemies should get fulfilled. Habitat refers to sheltering places and they should be available for natural enemies.
This is a negative attribute to be avoided in selecting Biocontrol agents. To eliminate secondary parasitoids under certain situations Hyperparasitism is most important one.
This is an important attribute indicating ability of organism which can be mass reared under artificial condition for large scale release programmes. Hence the introduced species must be an enable to laboratory culture.