Importations of foreign nursery stock and other plants have long been considered the most dangerous means of introducing foreign insect pests. Commercial importations of nursery stock made before our present regulations as to freedom from soil and mandatory treatment are known to have been the carriers of specific foreign pests. The Japanese beetle, for example, certainly entered on nursery stock as grubs in the root balls. Adult insects, which could not possibly survive the journey as stowaways aboard ship with any other type of cargo, may be found feeding on the leaves and bark of plants in transit to this country. Today the most prolific source of insect interceptions is the occasional shipment of nursery stock that escapes the scrutiny of certifying officials abroad and arrives at one of our inspection houses with the roots in soil and packed in woods moss and forest litter, both of which are prohibited as packing materials.

Fruits, vegetables, cut flowers, seed-contaminated samples of cotton, cotton waste and cotton meal, broomcorn, soil samples imported for biological, sentimental, or commercial purposes, the wood of shipping containers, and various packing materials (including those used for such items as dishes and bottled goods) may harbor insect pests. Lumber and barked and unbarked logs can be a source of forest-insect pests and the diseases some of them spread. For example, the Dutch elm disease and one of the European beetles that transmits it to healthy trees came into the United States in elm logs. Even the narrow staves used in baling cork from Spain and northern Africa have been found infested with wood-boring insects not known to be established in this country and potentially quite destructive. It is regrettable that we do not have legislation insuring adequate protection against the introduction of insects in logs and lumber.

Cut flowers and certain fruits and vegetables formerly could not be brought to our country from overseas because of unfavorable factors of time and temperature. Fast refrigerator ships now bring us cut flowers from South Africa in quantity, and insects, if present, are not ordinarily injured by the brief cold-storage periods. They simply become quiescent and resume normal activity when the temperature rises. Airplanes speed cut flowers from Europe and from the Tropics. A great number of insect pests, including the various fruit flies, might be introduced with fruits and vegetables were it not for Federal quarantines and inspection procedures. Here again ship refrigeration helps to get the insects to us alive but can be and is used to kill fruit fly larvae in certain types of fruits during transit. Dried broomcorn stalks from Italy and some other Mediterranean countries are often badly infested with the European corn borer and another moth borer, which almost certainly would become a major pest of corn and sorghum in the South if it should become established here.

The fruits and vegetables taken aboard ships and airplanes as food for passengers and crew also are suspect. Were it not for the vigilance of plant quarantine and customs inspectors, infested foodstuffs might be taken from the ship by crew members or perhaps be placed in trade channels. As it is, prohibited items in stores may be seized and destroyed or officially sealed and kept thus until the ship or plane has departed.

The risk of pests in garbage from ships or airplanes is about the same as that attending the introduction of the various fruits and vegetables that might be infested with injurious insects. The difficult thing is to enforce rules for proper disposal. Garbage dumped into salt water a safe distance from shore presents little risk, but the same material discharged into a river or bay may quickly wash ashore close to agricultural areas and food plants, upon which the insects present could subsist. Garbage brought ashore from ships or removed from aircraft must be kept in tightly closed containers until incinerated.

PLANTS BROUGHT into the country as passengers' baggage are apt to be from the gardens of relatives or friends and usually are uncertified by plant quarantine officials of the country of origin. Such plants are often prepared for shipment by persons quite ignorant of our quarantine requirements and so may be in soil and badly infested with insects; consequently they present great risk. Fruits that a passenger has forgotten or wishes to conceal frequently are discovered by alert inspectors in trunks, suitcases, and hand bundles. Often such contraband is infested with fruit flies and other injurious insects.

Insect pests are more likely to be found with plants in baggage shipments than in commercial ones even though the latter arrive in vastly greater quantity. The reason is that commercial shipments are usually from establishments with long experience in shipping to the United States; the plants have been grown under as sanitary field or greenhouse conditions as possible, are reasonably free of insects and diseases, and are packed with approved packing materials.

The mail could bring most of the insects that come to us in ballast, cargo, stores, and baggage. But for postal conventions that recognize the dangers of unrestricted international traffic in plants by mail and a permit system designed to bring mail shipments of plants and seeds to foreign plant quarantine inspection houses at certain ports of entry, it would be extremely difficult to control this broad avenue of ingress for pests.

Insect stowaways are less likely to occur in mail than in cargo shipments, and the average number of insects per container is smaller because of space considerations. It is extremely unlikely, moreover, that insects on the outside of mail parcels would be able to penetrate the packaging; in cargo, by contrast, this is relatively easy for the smaller species.

In former years, the mails did not lend themselves well to plant shipments, except dormant material and seeds, because of the time consumed and the difficulty in providing sufficient moisture to keep the plants alive. With the inauguration of international air parcel post, however, it has become possible to send parcels weighing up to 70 pounds by air to the United States.

Such comparatively delicate creatures as young leafhoppers, still actively feeding on the juices of the host plants, have been intercepted in the mails from tropical countries. Leafhoppers and their relatives, the aphids, have piercing-sucking mouth parts, which make them effective spreaders of plant virus diseases. It is not illogical to assume that plants afflicted with virus disease, quite undetectable by ordinary inspection methods at ports of entry, have come into the country and would today be economically significant if the appropriate insect vectors were available.

The mails are the most productive sources of what might be termed accidental introductions when a well-intentioned individual, in pursuit of a hobby, has requested living specimens of the caterpillars or pupae of a butterfly or moth. In 1869, before we had legislation to hinder such things, the gypsy moth was purposely brought into Massachusetts by an amateur entomologist engaged in research on silkworms. Through his carelessness, the insects escaped and became established as a bad pest of trees in the Northeast.

Even now, living insects occasionally are intercepted in the mails, having been dispatched to someone unacquainted with our laws concerning such shipments. Useful parasitic and predacious insects and other species for scientific experiment are allowed in the mails only if accompanied by a permit issued by the Chief of the Bureau of Entomology and Plant Quarantine. Such permits are issued cautiously.

Because in total war the introduction of new insect pests into the enemy economy might be a spectacular weapon in the hands of a belligerent, a survey for new insect pests near ports of entry of the continental United States was conducted under the supervision of the Bureau of Entomology and Plant Quarantine during the later years of the Second World War.

No evidence of the malicious introductions of foreign insect pests was discovered. Charges of the deliberate introduction of insect pests made by one country against another have appeared from time to time in the world press. Such charges appear to have been mere propaganda. It would be a short-sighted gesture in the present stage of world unification for one country to set free in another country a destructive pest, whose ravages the malefactor would in the end have to pay for in some measure.

RALPH B. SWAIN began part-time work for the division of cereal and forage insect investigations when he was a high school sophomore. He took his degrees at Iowa State College, Colorado Agricultural and Mechanical College, and the University of Colorado, between stretches of employment in the Bureau, and has since worked for the division of domestic plant quarantines on Mormon cricket and white-fringed beetle control projects. He was chief inspector at the Foreign Plant Quarantine Inspection House for the Port of New York in Hoboken, N. J., until July 1951, when he went to Nicaragua as entomologist with our Government's Point IV program.