When studying the ecology of an area, all insects connected with plants growing there should be correctly identified for successful research to be carried out. The field workers concerned must be familiar with certain basic rules for the preparation of insects for despatch to appropriate specialists, to ensure that material sent for determination arrives in good condition. Nothing is more disheartening than to receive parcels whose contents have been reduced to a jumble of tiny fragments or the containers, a series of glass vials, smashed beyond recognition. This wastes time and money as a second series then needs to be sent.
Field Collection
The object of this publication is the production of sound, viable seed and these notes are written with this in mind.
The ideal way of sampling populations of seed infesting insects is to collect the seed whilst the insects are in the developmental stage. Timing of the collection is important - unripe pods will shrivel and moulds develop thereby preventing insect emergence and with overripe pods the insects will usually have emerged before collection. Seed or pods collected in the field, possibly in polythene bags, should be transferred as soon as possible to rigid containers with wide necks. These should then be covered with muslin or other material through which air and moisture vapour can pass freely but which will retain emerging insects. Daily inspection of the containers is desirable so that as much biological data as possible is obtained.
Packing and despatch of material for identification
Beetles and parasitoids emerging from collected sample material should be removed from the containers as soon as possible. With live material it will be necessary to use an aspirator, otherwise known as a pooter or sucking tube (Fig. 6). These can be of a variety of designs but the most popular consists of a glass or, if possible, plastic vial with a close fitting cork or rubber stopper. Two glass or semi-rigid plastic tubes pass through this stopper, one of which has fine mesh gauze fixed over the end within the tube. To the other end of this is attached a length of rubber tubing. The companion tube passing through the cork is open at both ends. When the open end of the tube is placed near an insect and suction is applied by drawing air through the rubber tubing with the mouth, the insect will be drawn into the container. The insects can then be transferred to another glass specimen tube containing a small wad of absorbent paper (not cotton wool) on which a few drops of a killing agent (preferably ethyl acetate) have been placed.
Insects so treated can be sent to a specialist by packing them in small tubes, each with a wad of soft paper to prevent the contents shaking about. Specimens sent dry travel very well in this way. Care must be taken to ensure that if ethyl acetate or a similar killing agent has been used, the vapours have fully evaporated if plastic tubes are used as these chemicals attack plastic.
Fig. 6 - Diagram showing construction of an aspirator
(Container usually 25mm internal diameter x 75 – 100 mm)
The specimens despatched should be labelled with as much data as possible, i.e. date of emergence, geographical location, altitude, host, etc. Tubes should be wrapped individually and packed securely in a non-crushable container, i.e. tin or wooden box and packed in an outer box for despatch.
If it is desired, the specimens can be mounted on card points through which pins have been inserted. Whilst this may be desirable for reference collection at base, it does entail very careful packing if they are to be posted. Pinned material needs to be guarded by cross pins to prevent it shaking loose in transit. The material must also be mounted in a properly constructed postal box obtainable from an entomological equipment supply house. If these basic requirements are followed carefully, the material sent for identification will arrive in good condition.
The inclusion of a sample of host material (but packed separately) can also greatly assist the specialist in building up as complete a picture as possible of the habits and hosts of the insects. This is very important if specimens which eventually prove to be new to science are included. Material sent for identification should be clearly labelled “Dried insect specimens for scientific study of no commercial value”. These parcels will not then normally be opened by Customs.
Storage of a Reference Collection
For this project to proceed and expand to its fullest extent, it will be essential to maintain a central reference collection from which any worker concerned with the project may obtain data regarding insects associated with given tree species. It may also be necessary for this collection to be supplemented by smaller field laboratory working collections at base stations in arid zones. In each instance these collections need care and attention if they are to remain useful over a period of time. The greatest danger to dried, preserved insects is other insects. The larvae of some beetles of the family Dermestidae can be very destructive to preserved specimens as can also Psocids (Booklice). It is necessary, therefore, to keep a collection in properly designed storage boxes or, better still, an insect cabinet.
To prevent damage to insects stored in this way, they must be protected by some from of deterrent - usually crystals of paradichlorobenzene or naphthalene flake. Frequent inspection and renewal is essential especially in hot climates. It must be stressed that these measures are no more than a deterrent and may not be effective against some insects. Other chemicals have been recommended but these can be toxic to humans.
