Biocontrol Ideal

1. Biocontrol Ideal Biocontrol agent introduced Pest EIL Population Density Biocontrol Agent Time

2. Cropping System Characteristics Conducive to Biocontrol • Stability • Abiotic environment supports NE’s • Temperature, moisture & shelter are all available as needed by NE • Soils support soil-based NE’s • Biotic environment supports NE’s • Alternative food sources available • Food for all life stages available • Management practices compatible • Crop should have some damage tolerance

3. Biocontrol usually allows some injury and/or damage Biocontrol agent population always lags behind the pest population. This allows the pest population to build up to some extent. } EIL Population Density ET > EIL/3 ET = EIL/3 Time

4. Pest complex characteristics conducive to biocontrol • Few species in the target niche • Stable species composition • Few key pests, few direct pests • Ideally, minor pest species can act as alternate hosts/prey Note the benefits of biocontrol, pp 338 - 339

5. Costs/Disadvantages of Biocontrol • Usually requires change in management practice • Increases scouting effort • Intrinsic time delay • Increased risk • New NE’s may cause harm • Uncertainty about NE requirements/reliability • Always a potential for pest to escape control • Fundamentally incompatible with other control tactics

6. Characteristics of Effective NE’s • Can detect pest populations at low densities • Rapid population growth relative to pest population • High pest destruction rate per capita • Synchronized phenology • Persistence at low host density • Persistence over cropping seasons/rotations • Tolerant of management actions • Willingly adopted by pest managers & growers

7. Common Trade-off Quesitons • Generalists vs. specialists. • Multiple vs. single biocontrol species

8. Generalists vs. Specialist NE’s • Disadvantages of generalists: • Usually have lower numeric response • Kill fewer pests/unit time/NE • May be attracted to other species • Advantages of generalists: • Better survival when pest population is low • More likely present at pest establishment • Multiple generalist species can co-exist as a community (greater stability & reliability)

9. Phase Plane – Specialist NE A specific phase plane’s characteristics are determined by (1) the biological parameters of the NE and Pest and (2) how closely the NE and Pest population dynamics are coupled. Specialists tend to be highly coupled. Population Density Natural Enemy Population Pest Population Time

10. Elementary Implications of the phase plane Too Many NE’s for Pest Pop. – NE Crash Imminent Outcome Uncertain – Probably Bad NE Max Too Many Pests, Two Few NE’s – Pests Have Escaped Control Stable -- Good Pest Max Natural Enemy Population Pest Min NE Min Too Few Natural Enemies -- Pest Resurgence Danger Pest Population Must be < EIL

11. The “good” area often identified in decision guides as NE/pest ratios Spider Mite Examples • Predator mite/pest mite (spider mite) on apples must be at least 1:10 in Washington raspberries. • In N. Carolina apples: • 1 Predator mite/18 pest mites • 25 Coccinellid predators/5 trees • European red mite in W. Virginia orchards • If mites > ET, no spray if predator/mite > 2.5

12. Multiple vs. Single NE Introductions • Denoth et al. 2002 analyzed 167 biocontrol introduction projects • Multiple introductions increased success for weed control, decreased success for insects • In > half, a single NE species was ultimately responsible for almost all realized biocontrol. • Recommend that multiple introductions should be used with restraint when attacking insect pests

13. Types of Biological Control • Classical – Use of NE taken from native home of a foreign pest. Release once. • Inoculative – Release occasionally. Builds up, controls pest, then dies out & must be re-introduced. • Augmentative – Add to existing population as needed. • Inundative – Flood area with NE. Not persistent. Similar to pesticides. • Competitive Exclusion – Mostly applies to use of hypovirulent pathogen strains out competing virulent strain. • Conservation – Avoid harming existing NE complex. • Suppressive Soils – In some soils, pest (usually a pathogen) does not cause much damage.

14. Points on NE Conservation • Judicious pesticide use • Reduce other mortality caused by other management activity • Control secondary enemies • Manipulate host plant attributes • Provide NE’s ecological requirements • Genetic enhancement of NE

15. Points on Suppressive Soils • Factor responsible often not identified but is biological (lost on sterilization). • Have 3 main effects on plant pathogens • Pathogen may not persist • Pathogen establishes but doesn’t cause disease • Initial disease declines with continued monoculture • Ways to Achieve Suppressive Soils • Soil amendments to alter microbial communities • Green manures for fungal pathogens • Adding chitin for nematode control • Crop rotations/intercropping – Some crops encourage pest-antagonistic microflora.

16. Biocontrol Conclusion • Read to examples of biocontrols in the text • Evaluation of NE effectiveness • Necessary to use biocontrols in decisions • May be based on: • Statistical correlations from field observations • Numerous types of controlled experimentations • Requires that NE’s be monitored along with pest (cf. spider mite examples cited earlier)

17. Read Chapter 11, Pesticides, by March 22. • EXAM on Friday, March 12