Effects of synthetic pyrethroids on fall armyworm, Spodoptera frugiperda (J. E. Smith)

Nine synthetic pyrethroids were tested in the laboratory for acute and chronic effects to the fall armyworm, Spodoptera frugiperda (J. E. Smith). In ovicidal tests LC₅₀ values ranged from 0.320 ppm (Pay-Off®) to 12.230 ppm (Pydrin®). All 9 pyrethroids were more toxic to eggs than diazinon, a standard.

All 9 pyrethroids were ovipositional repellents at the concentrations tested. At their respective ovicidal concentrations cypermethrin (FMC) was least repellent. At one-tenth their respective ovicidal concentrations Ammo® and cypermethrin (FMC) were least repellent.

In no-choice feeding deterrent tests all 9 pyrethroids were effective at 50 ppm. At 5 ppm all but Pounce® were significant deterrents.

LD₅₀ values for 3rd instar ranged from 0.0041 µg/insect [permethrin (FMC)] to 0.1558 µg/insect (Ammo®). All pyrethroids were more toxic than diazinon, a standard, to 3rd instar. LD₅₀ values for 6th instar ranged from 0.213 µg/insect [permethrin (FMC)] to 5.841 µg/insect (Ammo®). Ammo® was the only pyrethroid less toxic than diazinon to 6th instar.

The pyrethroids were not readily synergized by piperonyl butoxide (1:8, pyrethroid:PB). The cypermethrins (FMC and ICI) were the only pyrethroids to synergize ovicidal activity (SR = 3.531 and 6.328, respectively). Cypermethrin (FMC) (SR = 3.0700) and Ammo® (SR = 9.1111) were the only pyrethroids to have synergized activity to 3rd instar. Ammo® (SR = 8.641) was the only pyrethroid to have synergized activity to 6th instar.

In growth and development tests all 9 pyrethroids significantly increased the time to maximum larval weight. Pounce®, permethrin (ICI), permethrin (FMC), and cypermethrin (FMC) had significantly lower maximum larval weights than the control. All 9 pyrethroids significantly reduced the relative growth rates of FAW. Pupation and emergence of adults were normal for pyrethroid-treated insects; however, many subsequent adults were unable to inflate their wings. Number of eggs/female was reduced in all pyrethroid-treated populations except those treated with Pydrin® in which there was a 2 fold increase. Eggs laid by females of treated populations had 6x (Ammo®) to 20x [permethrin (FMC)] less survival than control eggs.

In final evaluation, pyrethroid rankings (in descending order) were; permethrin (FMC), cypermethrin (ICI), cypermethrin (FMC) , Pay—Off®, permethrin (ICI) , Pounce®, Mavrik®, Pydrin®, and Ammo®.