The South African Citrus Thrips (Scirtothrips aurantii) in Queensland is highly polyphagous, and does not show strong preferences for its only recorded host in the field. Brian Garms PhD Student Australian National University biosecurity built on science Cooperative Research Centre for National Plant Biosecurity
Background South African Citrus Thrips (SACT) is native to the African continent and has been recorded on over 80 plant species in 33 families. SACT feeds only on flushing new growth. SACT takes about 15-20 days to develop from egg to adult, and adults survive for ~20 days. Fecundity is unknown, but species of other Scirtothrips females lay 50-200 eggs in a lifetime. biosecurity built on science
A Pest in Africa This insect is a serious pest of citrus and mango in South Africa, economic damage caused by fruit scarring. Without treatment loss of export quality fruit is estimated to be 5-30% for mango and 10-50% for citrus, almost all citrus is treated annually for SACT. Other South African crops SACT is recorded damaging include macadamia, tea, grape, and avocado. biosecurity built on science
The Queensland Population First detected in 2002 in Brisbane. Only found on exotic Mother of Millions (MoM) weeds in the genus Bryophyllum (or Kalanchoe). Initial tests showed this insect did not survive on citrus, possible cryptic species? - All known weedy Bryophyllum hosts are native to Madagascar, where SACT is not recorded, so this insect would be expected to be a Bryophyllum specialist at best. biosecurity built on science
No Strong Evidence for Cryptic Species Genetic study indicated that SACT sampled from both citrus and MoM in South Africa and the QLD population did not differ significantly at one mitochondrial and one nuclear gene. Further work (Freebairn 2008) showed that the QLD population did indeed survive and reproduce on other hosts including citrus and mango. This thrips appears to significantly damage MoM and may be a useful biocontrol agent if it is limited to Bryophyllum only.
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How to explain behavior of the Queensland population? 1. This thrips is only able to survive on MoM - cryptic species. 2. This thrips can utilize alternate hosts, but never selects them if MoM is present – host race.
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1st instar
2nd instar
8 6
Number of Popu
4 0
0
adult
Starvation Co
2
4
6
8
Mother of Mil
2
Number of Popu
No Choice Test Part I 1
2
3
4
5
6
7
9
12
14
19
21
26
1
2
3
4
5
6
7
9
12
14
19
21
26
3
4
5
6
7
9
14
19
21
5
6
7
9
12
14
8 6
21
26
2
3
4
5
6
7
9
12
14
19
21
5
6
7
9
12
Day
7
9
14
19
21
26
8
Grape 6
14
1
2
3
4
5
6
7
9
12
14
21
26
21
26
19
Orange
0
2
Number of Popu
12
Day
2 4
6
Lemon
26
0 3
5
0 1
4
8 6 4 2 0
2
4
Day
Green Bean
1
3
2
Number of Popu 19
Number of Popu
4
2
Day
2 3
8
1
0 2
26
6
Number of Popu 26
Chili
Day
Number of Popu
12
4
8 6
Number of Popu
4 2 0
1
21
2 2
Day
Pea
19
0 1
Day
8
9
6
7
Number of Popu
6
Tea
4
5
26
8
4
21
6
3
19
4
2
14
4
8 6 4
Number of Popu
Blueberry
0
0
1
12
Day
2
4
6
8
Mango
2
Number of Popu
Day
1
2
3
4
5
6
7
9
12
Day
14
19
21
26
1
2
3
4
5
6
7
9
12
14
19
Day
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No Choice Part II
Bryophyllum performance Host
Number females
Average P value vs juveniles B. per delagoense female
Bryophyllum delagoense
19
5.2
--
B. daigremontianum x B. delagoense
16
3.1
0.095
Kalanchloe uniflora
9
5.6
0.75
K. blossfeldiana
9
4.1
0.49 biosecurity built on science
No Choice Part II
Citrus Performance Average P value vs juveniles B. per delagoense female
Host
Number females
Orange (Valencia)
9
0.33
0.010*
Lemon (Eureka)
4
0.25
NA
Grapefruit (Ruby)
0
0
NA
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No Choice Part II Other Plants Number females
Average juveniles per female
P value vs B. delagoense
Grape
12
7.4
0.35
Mango
19
6.1
0.35
Blueberry
9
2.44
0.069
Hop Bush
4
0
NA
Tea
3
0
NA
Host
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Host Choice Test Test Host
% of Females Choosing Test Host (# of females)
% of Females Choosing MoM (# of females)
P value exact binomial test, null hypothesis random selection
Mango
45 (9)
55 (11)
P= 0.82
Grape
32 (7)
68 (15)
P= 0.13
Lemon
33 (5)
67 (10)
P= 0.30
Grapefruit
8 (1)
92 (11)
P= 0.0063*
Orange
0 (0)
100 (15)
P< .001*
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Host Choice for Thrips Reared on Alternate Hosts Test Host
% of Females Choosing Test Host (# of females)
% of Females Choosing MoM (# of females)
P value exact binomial test, null hypothesis random selection
Mango
32 (5)
68 (11)
P= 0.21
Grape
55 (5)
45 (4)
P= 1
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Juvenile Production Comparison Plant
No Choice Test
Choice Test
Mean juveniles day-1 female -1 (n= total females)
Mean juveniles day-1 female -1 (n= total females)
P value Wilcoxon ranksum test
MoM
1.53 (n=19)
2.14 (n=77)
P= 0.13
Mango
3.21 (n=19)
3.82 (n=14)
P= 0.47
Grape
3.21 (n=12)
2.02 (n= 12)
P=0.13
Lemon
0.13 ( n=4)
0.08 (n= 6)
P= 0.88
0 (n=0)
0.50 (n= 1)
P= 1
0.19 (n=9)
0.25 (n=1)
P= 0. 83
Grapefruit Orange
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Conclusions about the QLD thrips population The thrips population in QLD appears to be S. aurantii. This population can successfully feed and reproduce on a wide range of hosts, broadly in line with other highly polyphagous Scirtothrips species. Host choice tests show preferences for MoM are not always strong. biosecurity built on science
Future directions The only way to endorse this thrips as a biocontrol agent for MoM requires detailed knowledge of it’s basic biology. To assess potential threats this thrips may pose to Australian agriculture, we need to know more about Scirtothrips biology and ecology in Australia. biosecurity built on science
Supervisors
Thank you
- Dr. Nancy Schellhorn - Dr. Laurence Mound - Dr. John Trueman
South African information - Tim Grout
SEM images
- Paul Cooper
Thrips location and collection - Desley Tree - Les Tanner
For more information, please email brian.garms@anu.edu.au biosecurity built on science