LABORATORY STUDIES ON THE CONTACT TOXICITY OF SOME INSECTICIDES TO THE EUROPEAN SKIPPER, THYMELICUS LINEOLA (LEPIDOPTERA: HESPERIIDAE)

Abstract

The European skipper, Thymelicus lineola (Ochs.), first reported in Quebec by Arthur (1966), has spread throughout much of the province (McNeil et al. 1975). Control methods considered at the experimental level include: early harvesting to reduce potential oviposition sites (Arthur 1966;Arthur and Smith 1972); silica sprays combined with feeding and(or) oviposition deterrents (Arthur and Smith 1972); and Bacillus thuringiensis Berliner (Arthur and Angus 1965;Arthur 1968). Doyle and Richard (1971) suggested carbaryl would be effective and, as the skipper has been at epidemic levels in the Lac St-Jean region for several years, some producers treated with carbaryl (85W), 3/4 Ib/ac, in 1974 and 1975. As no insecticide screening tests had been made, this study was undertaken as the first step in the development of a realistic chemical control program. Methods and MaterialsInsects used were field collected as T. lineola is difficult to culture. Collections were made from two separate locations in order to obtain both third and fifth stage larvae for testing. Third stage larvae were collected at St-FClicien, approximately 170 miles NW. of Quebec City, while fifth stage larvae were obtained at St-Ftlix de Valois, approximately 50 miles N. of Montrtal. All larvae were held at 23k 1°C, 6 0 t 5 % R.H., and 16L:8D photoperiod in plastic containers with a fresh supply of timothy grass, for 24-48 h prior to treatment.Details of the bioassay technique have been described elsewhere (Harris and Mazurek 1961). The direct contact toxicity of 11 insecticides (95-99% purity) was assessed using a Potter spray tower. Chemical designations of insecticides without accepted common names are: Niagara 33297: 3-phenoxy (+) cis-trans-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropanecarboxylate); Stauffer N2596: S-(p-chlorophenyl) 0-ethyl ethylphosphonodithioate. Carbaryl was considered the standard for purposes of comparison. The solvent for all insecticides was 19: 1 acetone : olive oil mixture. For each insecticide a control (solvent only) and concentrations of 0.001, 0.01, 0.1, and 1 .O% were tested with the exception of Nia 33297 where 1.0% was not used. Two replicates, each containing 10 fifth stage larvae, were treated at each concentration. After treatment the insects were placed in waxed-paper cups (10 larvaelcup) with ample timothy grass and held at 27+ 1°C, 65 +5% R.H., and a 24L:OD photoperiod. Mortality counts were made 24 h after treatment. No control mortality occurred.The five insecticides most effective against fifth stage larvae were then utilized to test for differences in larval susceptibility. Two replicates (10 larvaelreplicate) of third and fifth stage larvae were used with each insecticide. The insecticide concentration utilized varied with each compound, being the dose calculated to cause 0-10% mortality of fifth stage larvae (based on the results obtained in the first part of the experiment). Control groups were treated with solvent only. Posttreatment conditions were as above.Correction for natural mortality (never > 5%...

FIELD EVALUATION OF INSECTICIDES FOR THE CONTROL OF THE EUROPEAN SKIPPER, THYMELICUS LINEOLA (LEPIDOPTERA: HESPERIIDAE), IN QUEBEC

“…In 1977 (Table 111) the efficacy of the products tested fell into three distinct groups. As in previous studies (McNeil et al 1976;Thompson 1977;Thompson and Lund 1977) skipper larvae were highly susceptible to synthetic pyrethroids and .Mean larval density prior to treatment was 190 larvae/m2. bMean defoliation prior to treatment was 6.3%.…”

“…Field trials were conducted at Saint Felicien (Lac Saint Jean West County), Sainte Elizabeth (Joliette County), and Saint LCon Le Grand (Matapedia County) in 1975, 1976. Each year, a series of 5 m2 plots, sufficient to permit three replications at each concentration (3) of all products tested, were set out in a commercial timothy hay field where the skipper was present at epidemic levels.…”

“…Doyle and Richard (1971) suggested that carbaryl might provide satisfactoj control of this pest and during the recent epidemics, several farmers treated with this insecticide. Thymelicus lineola larvae have been found susceptible to a number of chemical insecticides in laboratory tests (McNeil et al 1976) and to Bacillus thuringiensis Berliner (Arthur and Angus 1965;Arthur 1968;McNeil et al 1977). Therefore in1975, 1976, and 1977 a series of field trials were undertaken to test a variety of compounds that could be most effectively employed to control this pest in Quebec.…”

SEASONAL BIOLOGY IN QUEBEC AND PREDICTION OF PHENOLOGY OF THE EUROPEAN SKIPPER,THYMELICUS LINEOLA(LEPIDOPTERA: HESPERIIDAE)

“…cornm.). Considerable effort has been invested in finding satisfactory methods of control using either chemical insecticides (McNeil et al 1976;Thompson 1977;Letendre and McNeil 1979), Bacillus thuringiensis (Arthur and Angus 1965;Arthur 1968;McNeil et al 1977;Letendre and McNeil 1979), or a naturally occurring baculovirus (Smirnoff et al 1976;Duchesne 1980). Regardless of the insecticide used, either chemical or biological, the timing of application is of major importance.…”

“…The best time to apply any insecticidal treatment is considered to be when the population consists of 50% 2nd and 50% 3rd instars for three reasons: (i) the majority of the larvae have left the protective tunnels that the young instars form by tying the leaf edges together with silk, (ii) the damage caused by the young instars is small compared with the later instars (Comeau 1976), and (iii) the quantity of insecticide required is less for earlier instars (McNeil et al 1976). Thus, it is evident that a generalized spray programme based on calendar dates would be rather ineffective and a more accurate method of predicting appropriate times of treatment is required.…”