It is difficult to decide depending on case specific issues. Generally, most predators are generalists and can control a  range of pests which is advantageous to farmers because at every time they have more than one pest to deal with. Again predators being larger in size can consume higher numbers within  a short time, some may even kill more than they need to eat e.g. Orius spp. While the parasitoids are host specific and rather slow before you can achieve reasonable control. Moreover,  as they grow within their hosts, their hosts can still cause some damage. For both parasitoids and predators  long term effect can be achieved by having banker plants/flowering plants around the farms to maintain their populations during off-seasons, otherwise their effect is seasonal. On the other hand, the pathogens may be relatively slow (except nematodes which are also classified as predators because of their modes of action) yet they can cause a near 'epidemic' effect having big impact on the pest populations. Their specific requirements in terms  of temp, RH, effect of UV/direct sunlight may affect their performance but once these are met  some can stay in the soil for 15 years..e.g. EPF

Dear Jacinter

Thak you so much for your complete answer. Best regards

Evaluation of natural enemies used in acclimatization biological  control programs  (Classical biological control):

 During the last scentury:

4200 introductions of natural enemies with 600 species were conducted for the biological control of 416 pest species in 168 countries

384 natural enemies established

164 pest species were totally controlled

64 species of pests were partially controlled

Through:

82% of parasitoids

17% of predators

1% of pathogenic organisms

Hello Every body specially  Mr.M Latifian

I want to add some of my experience in the field of biological control over the many years. I noticed that the use of bio-control agents  and its isolates  in this aspect has been effective because it is important in many of the mechanisms that are characterized by this fungus. Especially in the field of promoting growth and in  another side of the elimination of pathogens and compete with many of the harmful plant host, this including the use of Trichoderma harzianum  and Chatomium elatum .

Warm regards

A.P.Dr.Nihad Alezerjawi

While I cannot speak to the efficacy of pathogens as biological control, I would argue that parasitoids are likely more effective than predators as biological control agents. Of course, this would need to be answered case by case, if you were asking about a particular predator. But as a whole, because predators are not specialists, they are often performing as intraguild predators, meaning that they can and will eat other predators. This would diminish their efficacy as biological control agents. Check out this research article: Steffan et al. 2015. Beneficial or not: decoding carnivore roles in plant protection. Biological Control, 91: 34-41. http://www.sciencedirect.com/science/article/pii/S1049964415300074

There is a great need to be very cautious considering biological control. However after careful screening, parasitoids might be the best for most biological control because they are often very specialized (tend to be more specific in many cases). You may not want to have predators eating other predators, pollinators, and decomposition insects.

any predator, parasite or parasitoids which suits in your environment of crop and pest got success

Predators, parasitoids and the microbial biopesticides can be use but this depends on the target pests.

The problem with predators they are density dependent and requires that the pest is present in the filed for them to come and lay their eggs near the predators for survival.

Predatory mites e.g. the Amblyseius species are effective in the control of the Red spider mites, the pirate bugs e.g. the Orius sp. are also effective.

Solitary endoparasitoids are normally good and quite effective in the control of certain pests depending on their habitats, for example Diadegma semiclausum and Cotesia vestalis are quite effective in the control of Plutella xylostella in the highlands and mid altitude areas, respectively. Trichogramma species which is a solitary, egg parasitoid is also effective in the control of certain pest. They are capable of keeping the pests below the economic threshold. It has also been observed that the development stage of the target insect can also affect the efficacy of the natural enemies.

Biopesticides e.g. Trichoderma, Bacillus thuringiiensis, Beauveria bassiana and Metarhizium anisopliae just to mention a few are gud but in most cases, the target pest, climatic or weather conditions, time of aplication and season determines their efficiacy

Dear colleagues,

Thank you for your brilliant remarks and useful information about limits and problems of BC.

Here you will find some extra opinions about predators and parasitoids from a practical point of view:

Predators (from Cloutier and Clotier 1992)

Advantages

Immediate control of the pest

Good mobility

Good Establishment capacity

Capability of exploiting other preys

Sometime, sufficient specificity for precise control operations

Security for human health

Inconvinients

High coasts of mass rearing

Transport problem because of cannibalism

Labor consuming Introduction techniques

High variability of predation levels

Possibilities of inactivity or migration

Interference with alternative preys

Parasitoïdes (from Cloutier et Cloutier 1992)

Advantages

High dispersion capability and host detection

Security for human health

High specificity, possibilities of precise control operations

Inconvenients  

High costs of mass rearing

Fragile, delicate transport operations

Labor consuming introduction techniques

Delayed action

Variability of parasitism levels

High specificity, restrained host range

Generally, parasitoids are more efficient than predators. I will provide you soon with more data to make this discussion richer.   

This is a very interesting question to which good answers were provided by all. As to which group of natural enemies is better, I believe that it all depends on the situation and conditions where the pest is located. In cases where rapid reduction of the pest population is required (eg. inundative releases), predators may be most appropriate however, where sustained, slower reduction of the pest population is required, parasitoids may be more suitable (eg inoculative releases). Sometimes a combination of both (predators and parasitoids) may be quite efficient (eg in some classical biological control programmes). Please do not overlook pathogens as they can also be highly effective biological control agents under the right conditions.

In most cases, predators my be of great use in areas of outbreak in certain pests to suppress the pest to to economical and manageable threshold. With the current changes in climate, many ares of the globe are prone to to pest infestation and therefore use of predators becomes the best option. However it is better to understand ecological requirements of the all the natural enemies such as hosts and prey so that they can be of consideration in agro ecosystem managements, especially when dealing with agro forestry and organic farming. This can improve the biodiversity especially in perennial farming such as in tea and coffee.

I prefer the use of entomopathogens, because it's easier to produce them in laboratories but it doesn't mean that the other strategies are worse. The use of the different biological control agents depends on the pest and its population.You can mix different agents such as parasitoids and entomopathogens to reduce the population , but I recommend to apply each one in different times.