Resurgence

1. Resurgence • Mostly documented with insect pests • Mostly associated with indirect, secondary/minor pests for several reasons. • Key pests are watched too closely to resurge • Direct pests are mainly late-season pests & there isn’t time to resurge • Pest must be held at least partially in check by some agent that is affected by the pesticide • Note Fig. 12-6 in book.

2. Pest Resurgence Pest (8) Natural Enemy

3. Pest Resurgence Pest Natural Enemy

4. Pest Resurgence pest pest

5. Pest Resurgence Note: 14 pests/leaf

6. Four processes contribute to resurgence • Reduced Biological Control (Secondary) – most common with insects • Reduced Competition – most common with weeds (mono vs. dicots) • Direct Stimulation of Pest – usually due to sub-acute doses • Improved Crop Growth

7. Resistance • Mostly a problem with pesticides (so far) but applies to all management tactics. Ex: • Biological Control – Rabbits & virus, Bt • Cultural Control – corn rootworms & rotation • Host Plant Resistance – many examples • Most serious, general problem in IPM • Arises because all management actions are selection pressures • Problem is rapidly getting worse

9. Read about Kentucky’s Herbicide Resistant Weeds Here

10. Resistance is best understood as a process Initially, a small proportion of population has a resistant mechanism by chance.

11. The Resistance Process These individuals survive at a higher rate than others

12. Resistance as a process Resistant individuals increase in frequency

13. Resistance as a process Eventually, the pesticide or other management tactic causes too little control to be effective.

14. The process has three general stages, each with its own Management Strategy Abandon Pesticide/Management Tactic Manage or Reverse Prevention Need to monitor resistance

15. Impact of Resistance • Overall agricultural productivity (during build phase) • Increased pesticide usage • Increased damage • Environmental impact • Increased pesticide usage • Increased use of non-renewable resources • Increased acreage • Pest management flexibility • Loss of pesticide tactic • Constraint on new pesticides

16. Causes of Resistance Independent of Pesticide • Genetic Factors • Ecological Factors • Severity of Selective Pressure

17. 1. Genetic Causes of Resistance • Genetic Factors • Relative dominance – More dominant is bad • Linkage to phenotype – Fewer genes is bad • Initial resistant pop – Prior exposure • Broad diversity & diversity-maintenance • Low diversity associated with foreign pests • Sexual reproduction • Haplo-diploidy

18. 2. Ecological Causes of Resistance • Population Isolation • More isolated develop resistance more rapidly • Less isolated allow resistance to spread more rapidly • Narrow host range – more selective pressure • Intrinsic population factors • Voltinism • Generation time • Fecundity • Behavioral factors

19. 3. Selection Pressure • Selective pressure is “high” if a “low” percentage of susceptibles survive to reproduce • Reduce pressure by: (1) reduce dosage & (2) reduce frequency • Site of action • Alternating modes of action reduces pressure • Spatial coverage – reduce pressure by reducing coverage • Timing – Using pesticides after reproduction reduces selective pressure

20. Resistance Categories • Resistance to individual pesticides • Delayed entrance of toxicant • Increased deactivation/decreased activation • Decreased sensitivity • Behavioral avoidance • Resistance to multiple pesticides • Cross-resistance & class resistance • Multiple resistance • Multiplicate resistance

21. Resistance Management • Strategy • Saturation • Moderation • Multiple Attack • Tactics • Prevention • Reversal

22. Specific Tactics • Prevention • Use pesticides only as needed • Time/target applications precisely • Combine chemical & non-chemical controls • Reversal • Cease use of pesticide causing resistance. Problems • Probably the preferred control • May be used for other pests • Area-wide enforcement usually necessary • Refugia • Use synergists • Genetically manipulate the pest population (Gene Driving)