Antibiosis to SCA in PI 550610and SCA-Greenbug Interactions

J.P. MichaudKansas State University

Sorghum – Sugarcane Aphid Research Exchange Meeting

New Orleans, LAJanuary 7 – 8, 2016

Introduction

• ‘Aggressive’ aphids such as SCA and greenbug (GB) subvert plant physiology

• Antibiotic traits prevent such aphids from ‘hijacking’ plant metabolic processes

• Host plants also mediate interactionsbetween aphids in mixed colonies

• Most such interactions are negative andasymmetric (one aphid hurts the other)

• However, ‘top down’ benefits of aggregationtend to be more important

Materials & Methods

• We reared SCA and GB, alone and together,on susceptible and resistant sorghums

• Either: 10 GB, 10 SCA, or 5 GB + 5 SCA- all 1st instars (< 12 h old)

• P8500 (susceptible) and KS116B (resistant)• Last aphid to molt to adult left to reproduce

on the same plant• All life history data recorded daily - survival, developmental time, reproduction• Life tables constructed (rm, lx, mx, DT etc.)

GB SCA0

20

40

60

80

100

Surv

ival

(%)

Susceptible

GB SCA0

20

40

60

80

100

Resistant

Sorghum cultivar

KS116B (with 550610 res) reduces nymphalsurvival (birth to adult) of both aphid species

ab

aa

GB SCA0

2

4

6

8

10

GB SCA0

2

4

6

8

10

Developmental time (birth – adult molt) of GB vs SCAon susceptible and resistant sorghums (23 °C)

a

b

aa

Susceptible ResistantResistance slows development of both aphid species and eliminates

the developmental rate advantage of SCA over GB

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 280

2

4

6

8

GB

SCA

Nym

phs /

fem

ale

Time (days)

Relative reproductive rates of SCA vs GB at (23 °C) on susceptible sorghum

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 280

2

4

6

8

GB

SCA

Relative reproductive rates of SCA vs GB at (23 °C)on resistant sorghum

Time (days)

Population doubling times (in days) at 23 °C (73 °F)

Greenbug Sugarcane Aphid

Susceptible

Resistant

2.17 1.54

2.77 3.30

90 °F daytime high, followed by 56 °F overnight low = 73 °F daily average

PI 550610 resistance changes commensalism into amensalism(facilitation turns into interference)

Strange things happen to aphid life tableswhen SCA and GB co-infest plants (GB+ and SCA+)

...and then there are ‘new’ aphids on sorghum...

Rusty plum aphid, Hysteroneura setariae

Other aphids co-infesting sorghum with SCA:

Sipha maydis Rhopalosiphum padi

These aphids cannot colonize sorghum by themselves

Key Learnings• Resistance from PI 550610 is effective

against both greenbug and SCA• Aggressive aphids such as SCA can either

improve or diminish plant suitability for other aphid species, depending on the cv.

• Both ‘bottom-up’ and ‘top-down’ effects can favor co-infestation by multiple aphid spp.

• Rhopalosiphum padi is able to colonize susceptible sorghums infested with SCA

• ‘New’ aphid species being found on sorghum with SCA, e.g., rusty plum aphid, hedgehog grain aphid.

Discussion