Role of vectors and their host plants in the epidemiology of maize lethal

necrosis disease

Nyasani, JElizabeth, KSubramanian, S

Complexities of MLN Epidemiology

Maize chlorotic mottle virus

(MCMV)

Sugarcane mosaic virus

(SCMV) or other cereal

potyvirus

Maize

Vectors of MCMV –Thrips,

beetles and others?

Vectors of potyviruses – Aphids and

others ?

Maize - MLN

Alternate hosts – Weeds or cultivated crops

Natural enemies of vectors

Information so far on insect vectors

• Maize chlorotic mottle virus• Corn thrips, Frankliniella williamsi• Cereal leaf beetle, Oulema melanopa• Corn flea beetle, Chaetocnema

pulicaria• Rootworms, Diabrotica spp

• Sugarcane mosaic virus• Aphids, Rhopalosiphum maidis

Source: Pest net and Fotoopa

What else??

Distribution of potential vectors: Kenyan situationKenyan situation

Distribution of thrips on maize in Kenya (Jun-Sep 1 4)

Distribution of aphids on maize in Kenya (Jun-Sep 1 4)

Distribution of beetles on maize in Kenya (Jun-Sep 14)

Distribution of stemborers on maize (Jun-Sep 14)

Distribution of leafhoppers on maize (Jun-Sep 14)

Distribution of whiteflies on maize (Jun-Sep 14)

Confirmed vectors of MCMV

Corn thrips

Onion thrips

Thrips

Common blossom thrips

Distribution of vector thrips in east Africa

Frankliniella williamsi Frankliniella schultzei

Thrips tabaci

Other vectors - Beetles

Curculionid weevil Sap beetle

Cereal leaf beetle

Vectors of SCMV

Cereal leaf aphid

Host range of MCMV and SCMV and their vectorsSCMV and their vectors

Role of host plants spread of MCMV and SCMV

A: Role of wild grasses in spread of SCMV

B: Role of finger millet in spread of MCMV

A B

Presence of MCMV and SCMV in non-maize plants

Finger millet showing mottle symptomTested positive for MCMV by ELISA and RT-PCR

A wild grass showing chlorotic and streak symptomsTested positive for SCMV by ELISA and RT-PCR

Presence of MCMV and SCMV in wild and domesticated grasses, and cereal crops

Plant species MCMV SCMV Wild grassesDigitaria abyssinica + +Cynodon dactylon + + Pennisetum cladestinum + + Digitaria velutina + + Cyperus rotundus + -Bracharia brizantha + + Bracharia brizantha + +

Domesticated grassesSaccharum officinarum + +Pennisetum purpureum + -

CerealsEleusine coracana + + Sorghum bicolor - +

Vector management: Thrips

16

18

Nu

mbe

r of t

hrip

s pe

r mai

ze p

lan

t

Control (seed treatment alone)

Ctrl +soil applic of Trichoderma+Nurelle-D spray at 2 weeks interval

Ctrl+soil applic of Trichoderma+Maetarhizium spray at 2 weeks interval

Ctrl+soil applic of Trichoderma+Metarhizium spray-Nurelle-D-Metarhizium spray

Ctrl+Nurelle-D spray at 2 weeks interval

Ctrl+Metarhizium spray at 2 weeks interval

Ctrl+soil applic of Trichoderma alone

0

2

4

6

8

10

12

14

Week 1 Week 2 Week 3 Week 4 Week 5 Week 6

Nu

mbe

r of t

hrip

s pe

r mai

ze p

lan

t

Vector management: Beetles

1.6

1.8

Nu

mb

er o

f be

etle

s p

er

ma

ize

pla

nt

Control (seed treatment alone)

Ctrl +soil applic of Trichoderma+Nurelle-D spray at 2 weeks interval

Ctrl+soil applic of Trichoderma+Maetarhizium spray at 2 weeks interval

Ctrl+soil applic of Trichoderma+Metarhizium spray-Nurelle-D-Metarhizium spray

Ctrl+Nurelle-D spray at 2 weeks interval

Ctrl+Metarhizium spray at 2 weeks interval

Ctrl+soil applic of Trichoderma alone

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

Week 1 Week 2 Week 3 Week 4 Week 5 Week 6

Nu

mb

er o

f be

etle

s p

er

ma

ize

pla

nt

Vector management: Aphids

10

Nu

mbe

r of a

phid

s pe

r mai

ze p

lan

t

Control (seed treatment alone)

Ctrl +soil applic of Trichoderma+Nurelle-D spray at 2 weeks interval

Ctrl+soil applic of Trichoderma+Maetarhizium spray at 2 weeks interval

Ctrl+soil applic of Trichoderma+Metarhizium spray-Nurelle-D-Metarhizium spray

Ctrl+Nurelle-D spray at 2 weeks interval

Ctrl+Metarhizium spray at 2 weeks interval

Ctrl+soil applic of Trichoderma alone

0

2

4

6

8

Week 1 Week 2 Week 3 Week 4 Week 5 Week 6

Nu

mbe

r of a

phid

s pe

r mai

ze p

lan

t

Concluding remarks

�Corn thrips, common blossom thrips, sap beetles, and onion thrips are vectors of MCMV

�Corn leaf aphid is a vector of SCMV

�There could be other vectors for the two viruses

�The distribution of the vectors differs with season and plant stageand plant stage

�Wild and domesticated grasses serve as alternative host of MCMV and SCMV

�The suitable areas for the grasses are mainly located in the key maize growing counties

�Biopesticides are effective in the management of vectors of viruses causing MLN

Way Forward: Capacity building for detection, monitoring and management of MLN and its vectors

Acknowledgements

Kenya Agricultural Productivity and Agribusiness Project