Susceptability of leafminers to insecticides 



JESO Volume 139, 2008 



proper quarantine protocols. Insects were reared on green beans (cv. Provider", Veseys 

 Inc.) grown in ProMix*, and held in growth chambers at 25 ± 2°C and 18:6 L:D. A 10 cm 

 filter paper covered in dilute honey was supplied for carbohydrate. Greenhouse collected 

 leafminers were added to the Ontario strain culture every 1-2 months to maintain similar 

 genetic diversity to field populations. 



Leaf Dip Bioassay 



Bioassay methods were modified from Ferguson (2004). Four to 6 bean plants at 

 the 2-4 leaf stage were exposed to leafminer colonies for 1-3 h depending on colony fitness 

 (number of adults). Plants were removed from the colony and placed in environmental 

 chambers (26 ± 5°C, 30-50% RH, and 18:6 L:D) for 2-3 days or until small mines appeared 

 on the leaves. Mines on each leaf were counted and marked with a permanent marker. 

 Leaves were removed and placed in flower picks filled with deionized water on a metal 

 drying rack on a cafeteria tray lined with paper towel. Seven to 15 mines per leaf were used 

 per replication for both strains. The number of mines per leaf was difficult to control due 

 to the varying number of adults in each colony for both strains at any given time. A higher 

 number of mines (> 20/leaf) decreased overall survivorship. 



Cyromazine (Citation* 75 WP, Syngenta Crop Protection Canada), abamectin 

 (Agri-Mek7Avid R 1.9 % EC, Syngenta Crop Protection Canada), spinosad (Success 6 480 

 SC, Dow AgroSciences) and chlorantraniliprole (Altacor™ 35% WG, DuPont Canada ) 

 were tested. Note: Altacor™ 35 WG (DuPont Canada) was the only formulation available 

 at the onset of this project. Coragen™ 20 SC (DuPont Canada) is now the formulation 

 appropriate for greenhouse use. The formulated insecticides were mixed with deionized 

 water. Super Spreader 8 (United Agri Products Canada Inc.) wetting agent (0.05 ml) was 

 added to each concentration to enhance wetting of the leaves (Ferguson 2004). Deionized 

 water mixed with 0.05 ml wetting agent was used as the control. One or 2 infested leaves 

 with a total of at least 7 mines were dipped into a beaker containing 200 ml of the insecticide 

 solution for 5 s and then placed on a rack in a fumehood to dry for 1 h. Leaves were then 

 removed from the flower picks and placed in 1 cm plastic Petri 8 dishes lined with filter 

 paper. Petri dishes were sealed with parafilm. Post-treatment containers were kept in an 

 environmental chamber at 26 ± 5°C, 30-50% RH, and 18:6 L:D for 7 days until pupation. 

 Pupae were then counted, the leaves were removed and the pupae were returned to the 

 Petri dishes in the chamber for 2-4 weeks until all adults had eclosed and died. Emerged 

 adults were then counted. Preliminary screening tests were done to determine a range of 

 concentrations ( 1 5-95% mortality) appropriate for construction of a dosage mortality curve. 

 Tests were replicated 4 times. 



Data Analysis 



Abbott's formula (Abbott 1925) was used to correct for control mortality 

 (< 15%o). Data were analyzed using SAS version 9. 1 (SAS institute, Cary, NC) with a type 

 1 error rate of a = 0.05. The probit procedure was used to determine LC S0 and LC 95 values 

 by log transforming the data to fit the probit scale. A Chi-square goodness of fit test w as 

 used to test the significance of the probit regression and determine the fiducial limits. The 

 difference between the 2 LC 50 values was deemed significant if there was no overlap of the 

 95% fiducial limits. Resistance ratios were calculated by dividing the resistant Ontario 



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