Insect Infestations in Relation to Rice Crop Phenology

1. Insect Infestations in Relation to Rice Crop Phenology Michael Stout Department of Entomology LSU AgCenter/LSU A&M

2. OR Insect Infestations in Relation to Rice Crop Phenology When do Rice Pests Attack? AND To What Extent can We Predict Attack?

3. Attack by a pest depends on several factors… • Is the pest present, and at what levels? --population dynamics and life history of pest • Are environmental conditions conducive to attack? -- pests only attack under certain conditions • Is the plant susceptible to attack? --pests specialize on certain plant parts --suitability of plant parts change as plant develops

4. Attack by a pest depends on several factors… • Is the pest present, and at what levels? --population dynamics /life history of pest? • Are environmental conditions conducive to attack? -- pests only attack under certain conditions • Is the plant susceptible to attack? --pests specialize on certain plant parts --suitability of plant parts change as plant develops

5. Attack by a pest depends on several factors… • Is the pest present, and at what levels? --population dynamics /life history of pest? • Are environmental conditions conducive to attack? -- pests only attack under certain conditions • Is the plant susceptible to attack? --pests specialize on certain plant parts --suitability of plant parts change as plant develops

6. Attack by a pest depends on several factors… • Is the pest present, and at what levels? --population dynamics /life history of pest? • Are environmental conditions conducive to attack? -- pests only attack under certain conditions • Is the plant susceptible to attack? --pests specialize on certain plant parts --suitability of plant parts changes as plant develops

7. If we had reliable answers to each of these questions, we could predict attack with reasonable certainty Unfortunately, we don’t have reliable answers for many pests Whether or not the pest is causing economic losses is a related, but separate issue

8. Let’s apply these principles to the best-studied rice pest in Louisiana, the rice water weevil… Adult feeding Adult overwintering Larval feeding Mating and oviposition

9. Attack by a pest depends on several factors… • Is the pest present, and at what levels? --population dynamics /life history of pest? • Are environmental conditions conducive to attack? -- pests only attack under certain conditions • Is the plant susceptible to attack? --pests specialize on certain plant parts --suitability of plant parts changes as plant develops

10. Population dynamics of the rice water weevil over the growing season Emergence of the rice water weevil from overwintering does not begin until early April in most years, and may not be complete until late May… % emergence from overwintering April May June

11. Population dynamics of the rice water weevil over the growing season …but less is known about population fluctuations during the season and return to overwintering Weevil population densities % emergence from overwintering June July August April May June

12. Attack by a pest depends on several factors… • Is the pest present, and at what levels? --population dynamics /life history of pest? • Are environmental conditions conducive to attack? -- pests only attack under certain conditions • Is the plant susceptible to attack? --pests specialize on certain plant parts --suitability of plant parts changes as plant develops

13. 50 40 a 30 Eggs per plant 20 b bc 10 bc c 0 10.2 cm dry wet 1.3 5.1 soil cm cm soil Treatment/Flood depth Oviposition (egg-laying) by rice water weevil is triggered by flooding…

14. Attack by a pest depends on several factors… • Is the pest present, and at what levels? --population dynamics /life history of pest? • Are environmental conditions conducive to attack? -- pests only attack under certain conditions • Is the plant susceptible to attack? --pests specialize on certain plant parts --suitability of plant parts changes as plant develops

15. Suitability of rice for oviposition changes as rice grows and develops

18. What are the implications for rice water weevil management? • Rice planted early can escape, to some degree, rice water weevil infestation because weevil populations have not fully emerged before rice passes through susceptible stages • Rice can be attacked by rice water weevils for most of its development, but is most susceptible during tillering • Early flooding (e.g., pinpoint flooding) of rice extends the window of time in which rice is vulnerable to infestation • Delayed flooding of rice can reduce the window of vulnerability

19. We lack basic information (on population dynamics, environmental effects, plant susceptibilty) for most other rice pests… So, we are less capable of predicting attack by these pests

20. Pests of young / early season rice Intolerant of flooding Tolerant /dependent on flooding Rice water weevil Seed midges (feed on seeds, likes floods) Rice leafminer (likes floods) South American rice miner • Fall armyworm • Thrips • Aphids • Colaspis

21. Pests of mid to late season rice • Stem borers --population dynamics unknown, appears to require large stems, prefers reproductive stages • Rice stink bug --feeds on developing grains, susceptibility changes as grains mature • Skippers, grasshoppers, other defoliators

22. Author • Michael Stout • mstout@agcenter.lsu.edu