In this article we will discuss about:- 1. Meaning of Pest Surveillance 2. Objectives of Pest Surveillance 3. Steps.
Meaning of Pest Surveillance:
An insect pest survey is a detailed collection of insect population information at a particular time in a given area. The regular surveys of same place or locality at consistent intervals to assess changes in pest species over a time is called ‘surveillance’. The word ‘surveillance’ and monitoring have been used in literature synonymously.
Sometimes, the monitoring involves determining number and life stages of pest present in a location only; however, surveillance in addition includes the loss assessment and economic benefits by adopting control measures. The basic components of pest surveillance include identification of pest, determining the stage and population density of pest and natural enemies, estimating loss the pest species may cause the economic and other benefits that pest control will provide.
The planned procedure to determine these characteristics over a defined period of time is known as survey. In general, it is a method of collecting quantitative information about insect population in a particular location at a particular time. The survey may be done in a small field, a pond, or it may be as extensive as a state or region of the country. These are carried out at certain critical periods in the insect life cycle.
Pest surveys can be grouped into following categories:
(1) Qualitative Survey:
It is generally aimed at pest detection and provides list of pest species present along with reference to density like common, abundant, and rare. These are usually employed with newly introduced pests to understand the extent of infestation. These surveys are mostly adopted at international borders where agricultural commodities are inspected to avoid invasion of any new species.
(2) Quantitative Survey:
This survey defines numerally the abundance of pest population in time and space. It provides information on the damaging potential of a species and data can be used to predict future population trends. These surveys provide the basis to decision making for adopting control measures for a pest by the farmers.
Survey/surveillance can also be classified as fixed plot and roving.
(3) Fixed Plot Survey:
In fixed plot survey, the pest population or damage due to insect pests is assessed from a fixed plot selected in a field. The data are recorded regularly from sowing till harvest of the crop from the same fixed plot in a particular field. The data collected in these surveys are used to develop forecasting models.
The direct counting of population on plant, light traps, sticky trap, pheromone traps, etc., are techniques which can be used to monitor population in this survey. Counting total tillers and number of tillers affected by stem borer from 10 randomly selected plants from fixed five spots of 1m2 in one ha is an example of fixed plot survey.
(4) Rapid/Roving Survey:
This survey includes assessment of pest population or damage from randomly selected spots in a short period of time over a large area. It provides information on pest level which helps in determining the timing of adopting appropriate control measures. The surveys are made to monitor the initial development of pests in endemic areas in the beginning of crop season.
Based on these surveys, the farmers are instructed to monitor the pest incidence in their respective fields by the agriculture extension specialists and take interventions to manage the pests accordingly. The counting of whitefly adults from lower surface of leaf from randomly selected cotton plants on a predetermined route after a definite period of intervals is an example of roving survey.
Objectives of Pest Surveillance:
i. To monitor, when pest population/ damage at different growth stages of crop reaches the economic threshold levels.
ii. To estimate the crop losses caused by pests.
iii. To study changing pest status from minor to major in a given crop ecosystem, this enables to determine the research priorities.
iv. To monitor the development of biotypes, resistance to insecticides, resurgence, etc.
v. To monitor the invasion of new pest species in a local ecosystem and determining the rate of spread of exotic pest that has already been established.
vi. To study the influence of weather parameters on pest by recording the changes in density of pest population throughout the year.
vii. To assess natural enemies population and their influence in a particular cropping system and in different seasons.
Steps for Pest Surveillance:
1. Identification of Pest:
The first most important step for surveillance/survey is correct identification of pest. If the identification of a pest is incorrect, the decision for taking intervention for the management of pest will not be reliable. The incorrect identification may occur when one known species is confused with other or when a previously unknown species is grouped into known species.
Therefore, the person deputed for survey must have expertise on identification of all the stages of pest and their common visible morphological characters. Otherwise, the samples may be collected and reared in laboratory for all stages and specialist/expert/taxonomist may be consulted.
With the advent of molecular techniques, the data on conserved gene sequences is being generated for all the biodiversity of the world through International Barcode of Life (iBOL) project. The data will be publicly available which can be useful for identification of pest specimen.
The simple procedure includes sequencing of conserved genes amplified from total DNA of insect species and alignment of the sequence with the gene sequence databank. It would help to establish the identity of new unknown species and other species, which are generally confused with other species.
2. Determination of Pest Population:
The second basic component of surveillance is estimation of pest population. Most of the economic threshold levels for different pests depend on number of pest population present in the field. The study on pest population is helpful in pinpointing the factors that bring about numerical changes in the natural population, and also in understanding the functioning of life-system of the pest species.
For a correct and scientific understanding of a pest population, it is of fundamental importance to develop sound methods of population estimation. This involves two considerations. First, the life stage (egg, larva, pupa or adult) at which counting can be made most advantageously; and secondly, the actual process of counting.
The ideal approach to population estimation would be to count all the individuals. However, it is not possible to count most of the pest species over an area large enough to be of use in a practical study and hence some method of sampling becomes necessary.
The amount of time and effort required to obtain absolute counts even on a limited area is so large that it is often uneconomical and unproductive. Thus, although we wish to have information on the true population, we are forced to take smaller collections (samples) and use these to make inferences about the total population.
Based on the goal of sampling population, sampling plans in IPM can be grouped into three categories. First, detection sampling is used when pest is not present in the field. These are planned to avoid the chance that the organism is erroneously missed. Second, estimation sampling when the actual population of pest is estimated with desired levels of precision.
It is mainly used in research and also to evaluate the effectiveness of any IPM module or pest control strategy developed to manage the insect pests in the farmers’ field. Third, decision sampling based on which the decisions are made when to intervene with management tactics. In this sampling, objective is not to quantify the actual abundance of pest, but to decide the correct timings when control measures should be adopted or not.
3. Estimation of Abundance of Natural Enemies:
The importance of natural enemies in regulating the populations of herbivorous insects was recognized much before the concept of IPM was developed. Unfortunately, few IPM programmes at the commercial level attempt to estimate the abundance and impact of these agents on insect pest populations.
The procedure generally employed to study the role of natural enemies, requires gathering different stages of the target organisms from the field, and subsequent emergence of parasitoids is recorded in the laboratory. Unless repeated frequently, this procedure underestimates total mortality since organisms are protected from any mortality factors while in the laboratory. Ovipositional probing and host adult parasitoid feeding is often responsible for more mortality than is caused by developing parasitoids, and is not well estimated except by detailed field observations.
For studying the impact of natural enemies on the rate of increase of pest population, it is essential to undertake field level studies so that potential for and degree of control exerted by the whole complex of parasitoids and predators can be quantified by comparing growth rates under a range of natural enemy levels.
There is an urgent need to develop efficient and cost reliable estimation procedures and forecasting models which incorporate the role of natural enemies in the decision making process; experimentation aimed at estimating functional relationships and not just significant differences. The ratios of pests to natural enemies estimated in the field could be used to predict trends in pest populations.
4. Estimation of Yield Loss:
One of the objectives of the surveys is to estimate the yield loss due to insect pest species in different areas and type of farming systems. The crop loss estimation holds significance to justify the control measures, which should be taken to manage the insect pest species. In general, surveys to assess the crop loss due to insect pests can be done directly by recording the yield or by recording infestation of pests.
Direct Loss Surveys:
When no information on relationship between different infestation levels of pest and yield is available and the pest distribution and farming systems are quite variable, these types of surveys are adopted to assess the crop loss. The actual crop cutting yields in field with different infestation levels and field with no pest attack are recorded.
The correlation between crop yield and degree of damage of infestation is worked out to estimate the loss in the yield. These survey techniques can be used to estimate the crop loss due to different pests over a large area. The experienced people can also evaluate the damage or loss through visual observations while surveying the crops.
Surveys of Infestation/Pest Damage:
Damage by pest tends to vary, both geographically and seasonally, as well as through the life of an individual plant. We depend on surveys to assess the severity of damage due to major insect pests. Different parameters are recorded to assess the damage based on the plant part the insect attacks, e.g., dead hearts due to rice stem borer damage, boll damage in case of cotton bollworm complex, leaf foliage damage due to defoliators, etc.
The per cent damage is calculated from these surveys, which is used to assess the crop yield loss. It is possible to assess the loss at different stages of the crop even when the crop is in the field. The uniform pest infestation and farming system and reliable models of yield infestation relationship are the pre-requisites to estimate the loss with more accuracy.
The basic information on effect of different levels of insect pests on crop yield is determined through research trials. Based on the data generated, models are developed to estimate the yield loss based on the different damage levels in the field. Through infestation surveys and using the particular models, the yield loss can be evaluated in larger areas.
It is possible to further refine the sample survey techniques and to translate the observed infestation level to actual crop loss by further experimentation at research stations.