ENTOMOLOGY 135-1995-Final

ENTOMOLOGY 135

INTRODUCTION TO BIOLOGICAL CONTROL

1995 Final

  1. (15%) Transgenic cotton plants containing the Btk toxin have been planted to reduce herbivory by several caterpillar species. Unfortunately, one of them is a cutworm species (type IV insect) and is not susceptible to Btk. Among the following natural enemies, select the best one that could be used for suppression of the larval stage that feeds on foliage. Assume that the natural enemies are commercially available. Defend your answer. State why the others were not selected.
    Choices:

  2. (15%) Compare and contrast between a direct deleterious effect and an indirect deleterious effect of a pathogen upon a parasitoid. Give an example of each.

  3. (15%) Classical biological control is generally considered a tactic rather than a strategy. However, in the case of an exotic crop with only exotic pests associated with it, should not classical biological control be a strategy? Justify your answer, and be sure to integrate case histories as appropriate.

  4. (15%) The success of an inundative release of a parasite can be greatly reduced by problems both at the commercial insectary and in the target crop system. Briefly describe two examples of problems that occur at each location.

  5. (40%) The onmivorous web worm (OWW), a noctuid native to tropical Africa, has just been discovered in Orland, CA. This exotic foliage-feeding pest has a broad host range and is a considerable threat to local crops. Thus, state and federal authorities have announced plans for an eradication campaign. The latter will utilize Btk, to which OWW is highly susceptible. As a local farm advisor, you are invited to address a group of concerned citizens. In the space provided (space for a paragraph was provided on the original final), answer their questions in a manner that will inspire confidence in you as an objective and capable public servant.
    1. What is Btk? Is it really a biological control?
    2. The government has issued something called a FONSI for this action. What on earth does that mean?
    3. A scientist at UCD just discovered a fungal disease of OWW in its native home? Why don't we just spray that fungus instead?
    4. A theretical ecologist at UCD says that biological control agents are "density dependent" and therefore cannot eradicate their host population. If that's the case, why is the government going to use Btk?
      The eradication program is carried out as planned. Btk is aplied ten times over the course of the summer. The following spring you are invited back to address the group of concerned citizens.
    5. Many bird watchers report fewer birds this spring. I thought Btk wasn't toxic to birds?
    6. I understand that eradication oof OWW was not successful in the city's Botanical Garden. So the OWW there must have developed resistance to Btk?
    7. I have read that Btk spores will last for a long time in the soil environment. The pest pupates in the soil, so why were so many applications required?
    8. The Botanic Garden had to be treated several times with malathion. I live across the street and now my citrus trees are dripping with honeydew. Why is that?
    9. No OWW have been found this spring and government officials have declared it eradicated. The theoretical ecologist at UCD now says that there is no scientific evidence for this conclusion and that the OWW probably just failed to survive the winter. So what should we conclude from all this?
    10. The theoretical ecologist at UCD also says that most introduced species that do establish eventually go extinct in a year or two anyway. (Due to something he called "inbreeding depression"). So why bother with these expensive eradication programs?

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