Australian Journal of Entomology (2000) 39, 86–88
Potential insecticides for control of Oligonychus ilicis (McGregor) (Acari: Tetranychidae), a new threat to Australian horticulture Grant A Herron* and Jeanette Rophail NSW Agriculture, Elizabeth Macarthur Agricultural Institute, PMB 8, Camden, NSW 2570, Australia.
Abstract
Oligonychus ilicis (McGregor) is a new pest in Australian horticulture, but no chemical-control data have been gathered in Australia. As a first step to generating control data, a strain of O. ilicis was challenged under laboratory conditions by using a range of registered pesticides that are used in Australia against the two-spotted mite, Tetranychus urticae (Koch) and also CGA 140408 (the light-activated carbodiimide derivative of diafenthiuron). At a dose that would be expected to control T. urticae, O. ilicis was killed by aldicarb, bifenthrin, chlorpyrifos, CGA 140408, dicofol, omethoate, propargite, tau-fluvalinate and tebufenpyrad. The implications of these data on the field control of O. ilicis are discussed.
Key words
chemical control, resistance, southern red mite, tolerance.
INTRODUCTION The southern red mite, Oligonychus ilicis (McGregor), which has previously been recorded in Brazil, Italy, Japan, Korea, Paraguay, The Netherlands and the USA, was recently detected infesting camellia and azalea in Australia (Knihinicki 1999; Knihinicki et al. 1999). Field studies in the USA have shown O. ilicis to be tolerant of a number of chemicals that are registered in Australia to control Tetranychus urticae (Koch) (Williams et al. 1991; Stephenson & Hesselen 1995). As a first step toward identifying effective chemicals for use against the Australian strain of O. ilicis, 14 pesticides were tested in the laboratory.
MATERIALS AND METHODS Eight azalea plants that were heavily infested with adult O. ilicis, the females of which were beginning to lay overwintering diapause eggs, were removed from a production nursery in the Sydney area and returned to the Elizabeth Macarthur Agricultural Institute. The plants were maintained in an insectary at a constant temperature of 23°C and under constant illumination to halt transition of O. ilicis into diapause. Adult mites were used in the laboratory tests. Azalea leaves that were infested with adult female mites were removed and a portion of the proximal end of the leaf was placed ventral-side up onto wetted cotton wool in a 36-mm Petri dish. Adult females of O. ilicis were counted, and other stages, if present, were ignored. Petri dishes with mites were then sprayed with 2 mL of insecticide solution using a Potter spray tower (Burkard Scientific, Uxbridge, UK), which produced a wet deposit of 1.6 mg cm–2 after a *Author to whom correspondence should be addressed (email:
[email protected]).
3-s settling time. The sprayed leaf pieces were maintained in a constant environment cabinet at 25°C and 60% relative humidity for 48 h, after which mortality was assessed. Mites were counted as dead if they could not move forward in a coordinated manner when touched with a fine bristle. The pesticides that were evaluated are given in Table 1. The product rates and the formulations that were tested are as described in Infopest PC (Queensland Department of Primary Industries 1999) to control Tetranychus urticae (Koch). Tests were conducted at 10-fold the registered label rate, at the registered label rate and at 0.1-fold the registered label rate to control T. urticae. Exceptions to the use of the registered product were that technical aldicarb was used instead of Temik® granules (Rhone-Poulenc Ag Company, Research Triangle Park, North Carolina), CGA 140408 was used instead of diafenthiuron (CGA 140408 is the lightactivated, carbodiimide derivative), and chlorpyrifos 500 g L–1 emulsifiable concentrate was used instead of chlorpyrifos 300 g L–1 ultra-low-volume formulation. The technical aldicarb was sprayed according to the method described by Herron et al. (2000). For aldicarb, CGA 140408 and chlorpyrifos, any differences in the amount of active ingredient between formulations were accounted for when making up solutions. If the application rate was given in litres of product per hectare only, then we assumed the application of 1000 L of diluent per hectare. Nine sets of leaves with mites were sprayed in each pesticide evaluation. A water spray was used as a control. Mortality was corrected using Abbott’s formula (Abbott 1925).
RESULTS Aldicarb, bifenthrin, CGA 140408, dicofol and tebufenpyrad killed all adult female O. ilicis at all rates tested (Table 1). At a dose expected to control T. urticae (i.e. a 100% kill),
Control of Oligonychus ilicis
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Table 1 Southern red mite, Oligonychus ilicis, tested against 14 pesticides each at 10-, 1.0- and 0.1-fold the recommended rates to control two-spotted mite Tetranychus urticae Pesticide product Abamectin (18 g
L–1
Product rate per 100 L EC)
Aldicarb1
Bifenthrin (100 gL–1 EC)
Chlorfenapyr (360 g L–1 SC)
Chlorpyrifos2 (300 g L–1 )
CGA 1404083
Dicofol (240 g L–1 EC)
Dimethoate (400 g L–1 EC)
Fenbutatin oxide (550 g L–1 EC)
Maldison (500 g L–1 EC)
Omethoate (800 g L–1 EC)
Propargite (300 g kg–1 WP)
Tau-fluvalinate (240 g L–1 EC)
Tebufenpyrad (200 g kg–1 WP)
No. tested
Corrected mortality
22 27 27 11 19 21 25 17 21 31 18 22 10 10 12 19 21 33 29 25 49 14 13 16 15 20 21 18 21 18 18 17 21 16 18 15 15 23 20 20 13 7
100 85 59 100 100 100 100 100 100 19 17 9 100 100 12 100 100 100 100 100 100 91 0 0 84 0 0 50 14 2 100 100 83 100 100 36 100 100 71 100 100 100
500 mL 50 mL 5 mL 1100 g ai (1100 kg ha–1 ) 110 g ai (110 kg ha–1 ) 11 g ai (11 kg ha–1 ) 600 mL 60 mL 6 mL 1100 mL (11 L ha–1 ) 110 mL (1.1 L ha–1 ) 11 mL (0.11 L ha–1 ) 2500 mL (25 L ha–1 ) 250 mL (2.5 L ha–1 ) 25 mL (0.25 L ha–1 ) 800 mL (8 L ha–1 ) 80 mL (0.8 L ha–1 ) 8 mL (0.08 L ha–1 ) 2000 mL 200 mL 20 mL 750 mL 75 mL 7.5 mL 400 mL 40 mL 4 mL 1000 mL 100 mL 10 mL 750 mL 75 mL 7.5 mL 1 kg 0.1 kg 0.01 kg 400 mL 40 mL 4 mL 1000 g 100 g 10 g
1 Granules registered but technical grade material tested. 2 Ultra-low volume product registered but 500 g L–1 emulsifiable concentrate tested.3 CGA 140408 is the light-activated carbodiimide derivative of diafenthiuron. EC, emulsifiable concentrate; SC, suspension concentrate; WP, wettable powder.
O. ilicis was also controlled by aldicarb, bifenthrin, chlorpyrifos, CGA 140408, dicofol, omethoate, propargite, taufluvalinate and tebufenpyrad. Therefore these chemicals may be useful in O. ilicis control under field conditions. Abamectin, chlorfenapyr, dimethoate, fenbutatin oxide and maldison did not kill all O. ilicis tested at the rates recommended to control T. urticae and so may not be efficacious against O. ilicis in the field. Abamectin, chlorfenapyr, chlorpyrifos, dimethoate, fenbutatin oxide, maldison, omethoate, propargite and tau-fluvalinate did not kill all the O. ilicis tested at 0.1-fold the recommended rate for T. urticae. Control mortality did not exceed 15%, except
for tests with abamectin (27%), bifenthrin (23%), CGA 140408 (17%), fenbutatin oxide (17%) and propargite (17%).
DISCUSSION We consider that the tolerance of the Australian strain of O. ilicis to dimethoate may exacerbate control problems on azalea. In Australia, azalea lace bug, Stephanitis pyriodes (Scott), is a serious pest of azalea, requiring chemical control (McMaugh 1985) and consequently a number of pesticides, including dimethoate and omethoate, are registered for this
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purpose (Queensland Department of Primary Industries 1999). Clearly, if dimethoate is used to control S. pyriodes, it is unlikely to control concurrent O. ilicis. Frequent use of dimethoate against S. pyriodes may also make it more difficult to control O. ilicis by eliminating any natural enemies, while not significantly reducing mite numbers. Under such conditions, omethoate would be a better choice for control of S. pyriodes because it is more likely to control concurrent O. ilicis. Williams et al. (1991) found O. ilicis to be controlled by bifenthrin and tau-fluvalinate, but not abamectin. In contrast, Stephenson and Hesselen (1995) found O. ilicis to be tolerant of bifenthrin, tau-fluvalinate and abamectin. It is possible that the change in pesticide tolerance that was detected by Stephenson and Hesselen (1995) may have been due to the evolution of resistance. If the American O. ilicis is becoming resistant, then it is likely that resistance will also develop in the Australian strain of O. ilicis. Currently, only aldicarb, bifenthrin, chlorpyrifos, CGA 140408, dicofol, omethoate, propargite, tau-fluvalinate and tebufenpyrad control the Australian strain at the rate recommended for T. urticae (Table 1). We consider it prudent to assume that the Australian strain of O. ilicis does carry some resistance, and therefore resistance management should be taken into account when considering field control. However, it will not be possible to prove resistance without the importation of susceptible strain(s) of O. ilicis to generate comparative base-line data.
ACKNOWLEDGEMENTS We thank Marcus McAlister, Camelia Grove Nursery, Glenorie, NSW, for supplying the O. ilicis infested azalea plants. Graham Thwaite and Stephen Goodwin provided editorial comment on an early draft of this study.
REFERENCES Abbott WS. 1925. A method of computing the effectiveness of an insecticide. Journal of Economic Entomology 18, 265–267. Herron GA, Edge VE, Rophail J & Wilson L. 2000. Development and use of a method to measure aldicarb resistance in Tetranychus urticae Koch (Acari: Tetranychidae) from cotton in Australia. Proceedings of the 10th International Congress of Acarology, Canberra, 5–10 July (in press). Knihinicki DK. 1999. A new spider mite for Australia, the southern red mite. Agnote DPI/238. NSW Agriculture, Orange. Knihinicki D, Fletcher M & Nash J. 1999. Southern red mite identified in NSW. Agnote DPI/241. NSW Agriculture, Orange. McMaugh J. 1985. What Garden Pest or Disease Is That? Lansdowne Press, Dee Why West. Queensland Department of Primary Industries. 1999. Infopest PC, PC Version 2.2 (Build 69 July 1999). Queensland Department of Primary Industries, Brisbane. Stephenson JC & Hesselen CP. 1995. Southern red mite control on azalea. Research Report Series, Alabama Agricultural Experimental Station, Auburn University 10, 25. Williams ML, Stephenson JC & Miller GL. 1991. Evaluation of labelled miticides for control of southern red mite on azaleas. Research Report Series, Alabama Agricultural Experimental Station, Auburn University 7, 33–34. Accepted for publication 31 January 2000.
