We have been selecting crops in the absence of many of their original pests

Some of these crops have lost what resistance they may have had to these pests

Many of our crop plants are now uniformly susceptible to endemic pests of their ancestral stock (e.g., potatoes -- golden nematode)

Likewise the homeostatic control mechanisms (predators, parasites, and competitors) may not be well adapted to the introduced pest

High speed transport increases the likelihood of successful transport of short-lived pests

• NAPPO -- North American Plant Protection Organization

• EPPO -- European Plant Protection Organization

• CIPA -- Comité Interamericano de Protección Agrícola

• Many others

At the national level, the USDA/APHIS (Animal and Plant Health Inspection Service) has four lines of defense

1. Point-of-origin inspections (phytosanitary certificate)

2. Point-of-entry inspections (in cooperation with U.S. Customs)--may require holding and growing out in isolation plots

3. Field inspections in high risk zones (usually around points of entry)

4. Regional inspection programs (major crops only)

Interceptions (published annually) number about 40,000 per year

• Return goods to point-of-origin

• Postentry destruction of goods

• Postentry treatment (fumigation)

• Postentry quarantine

State and local

• California has a particularly stringent quarantine

• NY Dept. Ag and Markets -- mainly concerned with planting stock (bedding plants from Florida, nursery stock from Washington, etc.)

Consider the enormity of the job

• Sea ports -- arriving cargoes, both agricultural and nonagricultural

• Border crossings (roads, railroads)

• International airports (many in the interior)

• Mail

• Tremendous number of potential pest species

Strategy is to play the odds

• Inspect the plants and plant products most likely to harbor pests rather than try to look for pests themselves

• Target products from areas known to have infestations of threatening pest species

Quarantine is, at best, unstable

• Useful only where there are physical barriers to help reduce the immigration of pests

• Eventually the pest gets through
  • Golden nematode -- once confined to Long Island, now in at least 4 upstate counties

  • Mediterranean fruit fly -- dozens of known introductions, all successfully eradicated (?) (eradication claimed by APHIS but doubted by many entomologists)

  • Citrus canker -- introduced into Florida in 1910, successfully eradicated 21 years and $2.5 million (1931 dollars) later; new outbreak in 1984 (eradication claimed); and again in 1995, 1997, and 1998

  One must be prepared to mobilize an eradication campaign quickly

  Quarantine also buys time to develop alternative control measures

  Costs and benefits of quarantine must be weighed against costs and benefits of alternatives

  • Must include estimates of frequency of reintroduction and costs of consequent eradication efforts

  • Must evaluate costs and benefits in different sectors of the economy

  Once the pest population becomes well established in the quarantine area and eradication is out of the question, the quarantine is no longer useful

• Mediterranean fruit fly (Ceratitis capitata)

  World distribution -- Africa, Southern Europe, Middle East, Australia, Central and South America, Hawaii

  There are over 250 species of host plants, but commercially it is most important on citrus, cherries, apricots

  Introductions

  • Florida -- 1929, 1955, 1952, 1953, 1981, 1983-1991, 1997

  • Texas -- 1955

  • California -- 1975, 1980, 1987 (yearly since)

  Eradication techniques

  • Stripping fruit from trees in infested orchards

  • Malathion/protein hydrolysate bait (warm temperatures, once a week)

  • Fenthion (Baytex) spray of infested soil beneath trees

  • Sterile fly release

  • Parasitic wasp (not particularly useful for eradication)

  Cost of eradication of 1980 California introduction was more than $80 million

  Estimated losses if Med fly becomes established are about $413 million/year

• Citrus canker

  Caused by a bacterium (Xanthomonas citri)

  Endemic in Central and South America

  Infested nurseries and groves are destroyed by burning; fruit shipped from infested areas is dipped in chlorine solution

  Introduced into Texas in 1910, into Florida in 1914; declared eradicated in 1947 at the cost of $5 million

  Found in Florida again in 1984, 1995, 1997, and 1998; eradication effort continues (has cost the state and federal governments $30 million so far; cost to citrus industry is many times that)

• Sensitivity of detection methods
  • Must be able to detect low populations before they become firmly established

  • e.g., good detection of low populations of Med fly, but poor detection methods of golden nematode (must have 10⁷ cysts/acre before you have a 50% chance of detecting it)

• Ability to mobilize eradication effort quickly

• Effectiveness of eradication methods

• Thoroughness of mop-up

• Effectiveness of barriers to reintroduction (natural physical barriers and quarantine)

The boll weevil eradication program

• The boll weevil (Anthonomus grandis) was introduced into Texas in 1890's (probably from Mexico)

  Early eradication efforts failed -- effective measures simply not available

  Recent eradication interest stimulated by development of sterile insect techniques

• A pilot eradication project was begun in 1971
  • Covered 25 mi radius eradication zone in Mississippi

  • Surrounded by a 50-mi-wide buffer zone that included parts of Louisiana and Alabama

• Another 3-year eradication program begun in 1979 in the NE end of the cotton belt
  • Included parts of NC and VA

  • Could be isolated relatively easily from the rest of the cotton belt

• Tactics
  • In-season insecticides

  • Repeated late-season insecticides to kill weevils before diapause

  • Defoliation and desiccation of cotton plants before harvest

  • Destruction of crop residues after harvest

  • Sex attractants in spring

  • Sterile weevil release (100/acre)

• Problems
  • Sterilization of the "sterile" insects released was only 98-99% effective

  • Many small farms were run by illiterate tenants who did not understand the control measures

  • There were blocks of cotton left unreported and untreated because the growers were cheating on their acreage allotments

  • Some farmers objected to the side-effects of the intensive insecticide sprays and refused to participate

  • A wild cotton species scattered throughout the region is an alternate host

  • Volunteer cotton springs up in fallow fields

  • There are ornamental cotton plants grown by roadside businesses to attract tourists

  • Adults fly across the Rio Grande from Mexico

• Evaluation of pilot program
  • Acclaimed by the USDA as a successful demonstration of the feasibility of a nationwide eradication campaign

  • Given a negative report by a special review committee of the National Academy of Sciences

  • At issue were 15 weevils found in the pilot area at the end of the 3-year project (Does this constitute "eradication"?)

  • A deeper issue was the concept of eradication itself -- not so much whether it is achievable as whether it ought to be attempted

• The boll weevil eradication effort was set back somewhat by the NAS report, but it has continued

  The controversy has continued as well, and the advocates and opponents of the program have become strongly polarized.

  The stated goals of the program have shifted from "eradication" to "area-wide suppression"

• Eradication of many species is now feasible because of new technological advances (e.g., sterile insect release, pheromone traps)

• Long-term environmental risks of repeated insecticide sprays over years and years versus the short-term environmental risk of an intensive eradication effort

• Reduced total costs of pest control program (routine sprays over a period of years)

• By eradicating a species that requires high pesticide inputs, it makes possible biological control and other alternatives on the other species in the pest complex

• Eradication efforts have been successful only for small outbreaks of newly introduced pests

• Eradication requires unacceptably high environmental pollution and non-target effects of the pesticides used

• Removal of a particular species from an ecosystem might have far-reaching effects on the complex relationships among other organisms in the ecosystem

• We have been attempting eradication programs without adequate understanding of the biology of the target pest

• The landowner is legally responsible for removing any prohibited plant species

• Used for control of alternate hosts of some pathogens (e.g., eradication of black currant for white pine blister rust control)

• Used also for the control of some weed species