At each locality, care must be taken to collect from different forms of the target weed, all parts of the plant, and from closely related species growing in the same habitat. Surveying methods are determined by the type and habitat of the target weed. Plants can be searched directly at field sites, or samples can be collected for processing at the field station.

Field-searches are beneficial for obtaining data on the distribution, seasonal abundance, behaviour, and habitat of herbivores, and for collecting large numbers of agents for laboratory studies or exportation. Any evidence of damage on the target plant, including defoliation, gall formation, flower and fruit damage or dead tissue, should be carefully investigated for the causative agents. Potential biological control candidates can be collected directly from the plants by hand or by using an aspirator. The niche and feeding habits of all herbivores should be recorded. Specimens not needed for rearing or laboratory trials can be placed into killing jars then preserved.
Collections of terrestrial weeds can be made using hand pruners or loppers attached to extension poles for taller trees. For aquatics, collections of the target weed can be made from shore by hand, while wading, or by using a rake or grappling hook attached to a rope. In deeper water a boat, surf ski, canoe or equivalent should be used. The plant material should be placed into a labelled collection bag for transportation back to the laboratory. Both plant material and live insect specimens should be protected from extremes of temperature during transit. When temperatures are high, insulated containers with ice bricks or evaporative cooling techniques should be utilised when air-conditioning in the vehicle is not available.

Field data sheets should be completed for each collection to record site descriptions (e.g. topography, vegetation) and details (e.g. name, locality, latitude/longitude), collection date, time, physical parameters (e.g. temperature, humidity, weather), weed parameters (height, flowering, sample weight) and general notes. Each collection should be assigned a number for specimen records and for entry into a database.

Collections processed in the laboratory can be searched by hand or by using insect extraction devices (e.g. berlese funnels). Extraction devices are especially useful for collecting internal feeders such as stem-borers and leaf-miners, and for processing large amounts of plant material. Specimens of the host plant including flowers and fruit should be collected from each region, labelled and stored or sent to specialist botanists for determination.

Immature and mature stages of each insect species should be collected and at least 10 adult specimens should be preserved; if there are different forms (polymorphic species), then specimens of each form should be collected. Where possible, adult specimens should be sent to specialist taxonomists as immature stages are generally difficult/impossible to determine. Label data of other specimens of the same species held in national collections should be requested from taxonomists as they may contain valuable information on hosts, niche, feeding habits and distribution. Pathogenic fungi should be collected, dried and sent for determination.

Immature phytophagous insects should be reared and the hosts of predators and parasitoids noted. Records of the feeding habits and life-histories of each insect should be recorded. Photographic records of specimens can also be useful.

If sufficient resources exist, a laboratory colony of promising biological control agents should be established. These colonies can be used for detailed studies and exportation.

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