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Stout presentation on Insect Infestations in Relation to Rice Crop Phenology. Advanced rice entomology training at rice research station in Crowley, La on March 2, 2011
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Insect Infestations in Relation to Rice Crop Phenology
Michael StoutDepartment of Entomology
LSU AgCenter/LSU A&M
When do Rice Pests Attack? AND
To What Extent can We Predict Attack?
Insect Infestations in Relation to Rice Crop Phenology
OR
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
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
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
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
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
Let’s apply these principles to the best-studied rice pest in Louisiana, the rice water weevil…
Adult overwintering
Larval feeding
Mating and oviposition
Adult feeding
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
Population dynamics of the rice water weevil over the growing season
April May June% e
mer
genc
e fr
om o
verw
inte
ring 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…
Population dynamics of the rice water weevil over the growing season
April May% e
mer
genc
e fr
om o
verw
inte
ring
June July August
Wee
vil p
opul
ation
den
sitie
s
…but less is known about population
fluctuations during the season and
return to overwintering
June
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
Oviposition (egg-laying) by rice water weevil is triggered by flooding…
Treatment/Flood depth
Eg
gs
per
pla
nt
0
10
20
30
40
50
drysoil
wetsoil
1.3cm
5.1cm
10.2cm
cbc
bcb
a
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
Suitability of rice for oviposition changes as rice grows and develops
Plant Age
2 leaf early 3 leaf late 3 leaf 4 leaf
Mea
n n
um
ber
of
L.
ory
zop
hil
us
egg
s/p
lan
t
0
2
4
6
8
10
12
14
16
Plant Age
3/4 Leaf Mid/ Late Tillering Panicle InitiationPanicle Differentiation
Me
an n
um
ber
of
L.
ory
zop
hil
us
larv
ae/p
lan
t
0
10
20
30
40
50
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
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
Pests of young / early season rice
Intolerant of flooding• Fall armyworm• Thrips• Aphids• Colaspis
Tolerant /dependent on flooding
• Rice water weevil• Seed midges (feed on
seeds, likes floods)• Rice leafminer (likes
floods)• South American rice
miner
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
Author
• Michael Stout• [email protected]