Assessment of the effects of novel insecticides on green peach aphid (Myzus persicae) feeding and transmission of Turnip mosaic virus (TuMV)

BACKGROUND

Laboratory bioassays using treated leaf disks of peach were conducted to determine the efficacy of nine insecticides against the green peach aphid (GPA), Myzus persicae (Sulzer). The effects of these insecticides on aphid feeding behaviors and rates of transmission of Turnip mosaic virus (TuMV) to potted rutabaga plants were also determined.

RESULTS

Median lethal concentration (LC₅₀ ) values after 48 h feeding varied considerably, ranging from lows of 1.5 and 4.6 μg a.i./L for sulfoxaflor and λ-cyhalothrin, respectively, to 97.2 and 167.9 μg a.i./L for flonicamid and spirotetramat. LC₅₀ values were lowest and roughly equivalent for λ-cyhalothrin (1.2) acetamiprid (2.1), sulfoxaflor (0.23) and flupyradifurone (2.3) after 72 h feeding. Electrical penetration graph (EPG) recordings showed modest effects on feeding behaviors for certain insecticides, with sulfoxaflor, spirotetramat, and acetamiprid non-significant reduction in feeding duration and number of pathway and potential drop phases occurring during the first 5 min compared with the control. However, greenhouse experiments carried out to investigate the effect of these insecticides on rates of transmission of TuMV, which is transmitted non-persistently by GPA, resulted in only modest non-significant reductions in infection rates for acetamiprid, pymetrozine, λ-cyhalothrin, and flonicamid of 27%, 23%, 20%, and 17%, respectively.

CONCLUSION

All test materials were efficacious to GPA at differing levels, and some such as sulfoxaflor and acetamiprid non-significantly reduced the duration and number of pathways and potential drop phases of feeding within the first 5 min. None, however, resulted in significant reductions in rates of transmission of TuMV. © 2020 Her Majesty the Queen in Right of Canada. Pest Management Science © 2020 Society of Chemical Industry.

Aphid Transmission of the Ontario Isolate of Plum Pox Virus

Utilization of timed virus acquisition access probes in studies of plum pox virus (PPV) transmission by aphids demonstrated that endemic species transmitted the virus readily from plum, Prunus domestica (L.) Batsch; peach, P. persica (L.); or dwarf flowering almond, P. glandulosa Thunberg., to peach seedlings. The green peach aphid, Myzus persicae (Sulzer), was shown to be the most efficient vector. Acquisition of virus by green peach aphids from infected peach leaves resulted in 18-28% infected peach seedlings, while aphids previously fed on infected leaves of plum transferred virus to 36% of peach seedlings. Although the spirea aphid, Aphis spiraecola (Patch), was a less efficient vector than M. persicae it is perhaps more important for the spread of PPV due to its greater abundance and occurrence earlier in the season when peach trees are thought to be more susceptible to infection. Virus transmission rates varied depending on the virus source and healthy test plant species. In contrast to many previous studies, aphid inoculation of the experimental host Nicotiana benthamiana Domin occurred at a low rate, never exceeding 4%. Acquisition of PPV by M. persicae from infected peach fruit was greatly reduced compared with acquisition from leaves. The results of this research indicate that the Ontario isolate of PPV-D is readily transmissible by aphids to peach and natural spread of the virus needs to be considered in future management or eradication programs.

Mechanisms of resistance to organophosphorus insecticides in populations of the obliquebanded leafroller Choristoneura rosaceana (Harris) (Lepidoptera: Tortricidae) from southern Ontario

Populations of Choristoneura rosaceana (Harris) from orchards in Ontario were shown to be resistant to azinphos-methyl and to other types of organophosphorus insecticides. Resistance extended to methyl carbamates and to methomyl. The laboratory population used for these assays and selected with azinphosmethyl was also resistant to the pyrethroid, cypermethrin. Resistance was associated with increased esterase activity and was reduced by the addition of the synergist DEF. IEF studies of esterases also indicated increased activity in resistant populations, but did not identify any unique esterases associated with the resistance. Resistance was highly correlated (r = 0.78) with elevated esterases but not with increased glutathione-S transferase activity (r = 0.13). Other mechanisms did not appear to be related.

Characterization of resistance to clofentezine in populations of European red mite from orchards in Ontario

Resistance to clofentezine was identified in four populations of the European red mite, Panonychus ulmi (Koch), from apple orchards in Ontario after ca. 5 years use. Resistance was expressed at high levels (> 2000-fold at the LC 50) to clofentezine in a population selected in the laboratory. This population was resistant to hexythiazox and to the organotin compounds cyhexatin and fenbutatin-oxide. However, a population selected with fenbutatin-oxide did not show cross resistance to clofentezine. The clofentezine-resistant population was not resistant to pyridaben, propargite or dicofol. The synergists, piperonyl butoxide and DEF, were ineffective in overcoming the resistance. Resistance to clofentezine declined rapidly in a mixed population (most resistance was lost in fewer than three generations). There were several fitness factors (fewer eggs/female, longer egg stage, longer development time for males) associated with the resistant population which may have contributed to the loss of resistant phenotypes. However, in a second test in which selection was removed from a resistant population, resistance persisted for at least 10 generations. Observations on field populations indicated that resistance persisted for at least two seasons.