Thrips populations

Table 4.1 describes the populations used in the experiments. Three of the populations belong to the presumed ‘greenhouse pest’ genotype of WFT (WFT-G) and one was the separate cryptic non-pest strain of WFT (WFT-L). The populations differed in respect to geographic origin, feeding history, rearing history, virus status and presumably genotype.

Table 4.1 Classification and description of populations of western flower thrips used in the Y-tube olfactometer

experiment. Populations Greenhouse WFT-G I Laboratory WFT-G II Laboratory WFT-G III WFT-L Collection location Greenhouse,

North Canterbury Greenhouse, Auckland Greenhouse, Auckland Outside, Mid Canterbury

Original host plant Capsicum,

Capsicum annuum

Capsicum,

Capsicum annuum

Capsicum,

Capsicum annuum

Yellow tree lupin,

Lupinus arboreus

Colony

establishment date

NA November 2001 November 2010 NA

Rearing methods NA Perspex cages

25+1oC 16:8 h light:dark Environment cabinet 25+1oC 16:8 h light:dark NA Generations in the laboratory 0 > 222 generations 6 to 9 generations 0

Rearing host plant NA Chrysanthemum,

Dendranthema grandiflora (cv. Onyx time yellow)

French Dwarf Bean,

Phaseolus vulgaris (cv. Top Crop) NA Putative virus status of thrips populations

Unknown Viruliferous Non- viruliferous Unknown

Putative genotype of thrips populations Glasshouse pest genotype Glasshouse pest genotype Glasshouse pest genotype Lupin non-pest genotype

‘Greenhouse WFT-G I’ was collected from a commercial indoor capsicum crop, Capsicum

annuum (cv. ‘Cupra’) on the days the Y-tube bioassay were undertaken. The top part of

several flowering plants was gently tapped over a white tray and female WFT were collected with an aspirator. The thrips were placed in a clean polyethylene tube for transport and taken to the laboratory where they were identified under a stereo microscope (> x100) using the keys of Mound and Walker (1982) to verify that they morphologically classified as WFT.

‘Laboratory WFT-G II’ were from a long established colony originally collected from a commercial greenhouse and maintained on potted flowering chrysanthemums, Dendranthema

grandiflora (cv. ‘Onyx time yellow’) for over 10 years at The New Zealand Institute for Plant

& Food Research Limited, Lincoln. The chrysanthemum plants and thrips have previously tested positive for tomato spotted wilt virus (TSWV). The plants used for the colony were held in two temperature-controlled perspex boxes (six plants per box) with the temperature maintained at 25 + 1oC under a 16:8 h light:dark cycle. A fresh chrysanthemum plant was placed in each box every 3 days and the oldest plant was removed at the same time.

‘Laboratory WFT-G III’, a non-viruliferus colony, was established from eggs laid by

‘Laboratory WFT-G II’ females and reared to adults on potted French dwarf beans,

Phaseolus vulgaris (cv. ‘Top Crop’). Only first instar thrips larvae acquire and transmit the

tospovirus (van de Wetering et al. 1999a) and it is therefore assumed that a virus-free thrips colony could be established by rearing this colony from eggs despite the virus status of the female producing the egg. The eggs were obtained by allowing female Laboratory WFT-G II to deposit their eggs into an artificial parafilm membrane with sucrose water covering a rearing cage. The method was modified from that used by Murai and Ishii (1982) and Teulon (1992). The rearing cages were constructed from 30-ml polyethylene vials (Biolab Limited, New Zealand), from which both ends were removed (27 mm wide and 40 mm high) and subsequently covered by stretched parafilm (Pechiney Plastic Packaging, USA). At the top end of the cage, a second layer of stretched parafilm was added, and between the two layers, 0.05 ml of a 10% sucrose solution was deposited. The sucrose solution provided a nutrient medium for the adult thrips and an egg deposition site. Females were collected from the chrysanthemum colony using an aspirator and were placed in 10 individual rearing cages (10- 20 individuals per cage) and allowed to oviposit into the nutrient solutions between the artificial membranes. The rearing cages were incubated at 25 + 1oC (60% RH, 16:8 h light:dark cycle) for a 24-h period in a controlled environment cabinet (Contherm Scientific Limited, New Zealand). After 24 h, the females were removed from the rearing cages, and the cages were placed inside a clear plastic box with a lid (Tellfresh, Australia). The eggs

repeated every week for 5 weeks to ensure that a colony could establish. The bean plants used for the colony were grown in a controlled environment cabinet (Conviron E15, Controlled Environment Limited, Canada) (30–40 plants at various ages) with a temperature maintained at 25 + 1oC, RH 70% and a 16:8 h light:dark cycle. Fresh beans were planted weekly in the controlled environment cabinet to ensure a steady supply of healthy plants and old plants were removed when severely wilted. A tobacco plant was placed in the cabinet to detect the presence of tospoviruses in the thrips colony and extra care was given to not accidently transfer thrips from other colonies onto the beans.

‘WFT-L’ were collected from yellow tree lupins (Lupinus arboreus) growing in a vacant lot

(43o 33’S, 172o 31’E) on the days the Y-tube bioassay were undertaken. The top part of several flowering plants was gently tapped over a white tray and female WFT-L were collected with an aspirator. The thrips were placed in a clean polyethylene tube for transport and taken to the laboratory where they were identified under a stereo microscope (>x100) using the key of Mound and Walker (1982) and Mortz et al. (2004) to verify that they morphologically classify as WFT.