Comparative Toxicity of Helicoverpa armigera and Helicoverpa zea (Lepidoptera: Noctuidae) to Selected Insecticides.

Fernando R Da Silva,Woodward D Bailey,Jose Carlos Verle Rodrigues,Daniel Carrillo,Todd M Gilligan,Dario Trujillo,Oderlei Bernardi

doi:10.3390/insects11070431

Abstract

Until recently, the Old World bollworm (OWB) Helicoverpa armigera (Hübner) and the corn earworm Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae) were geographically isolated. Both species are major pests of agricultural commodities that are known to develop insecticide resistance, and they now coexist in areas where H. armigera invaded the Americas. This is the first study to compare the susceptibility of the two species to conventional insecticides. The susceptibility of third instar H. armigera and H. zea larvae to indoxacarb, methomyl, spinetoram, and spinosad was determined using a diet-overlay bioassay in a quarantine laboratory in Puerto Rico. Mortality was assessed at 48 h after exposure for up to eight concentrations per insecticide. Spinetoram exhibited the highest acute toxicity against H. armigera, with a median lethal concentration (LC50) of 0.11 µg a.i./cm2, followed by indoxacarb and spinosad (0.17 µg a.i./cm2 for both) and methomyl (0.32 µg a.i./cm2). Spinetoram was also the most toxic to H. zea (LC50 of 0.08 µg a.i./cm2), followed by spinosad (0.17 µg a.i./cm2) and methomyl (0.18 µg a.i./cm2). Indoxacarb was the least toxic to H. zea, with an LC50 of 0.21 µg a.i./cm2. These findings could serve as a comparative reference for monitoring the susceptibility of H. armigera and H. zea to indoxacarb, methomyl, spinetoram, and spinosad in Puerto Rico, and may facilitate the detection of field-selected resistance for these two species and their potential hybrids in areas recently invaded by H. armigera.

Highlights

The noctuid moths Old World bollworm (OWB), Helicoverpa armigera (Hübner, 1809) and corn earworm, Helicoverpa zea (Boddie, 1850), are major lepidopteran pests attacking crops worldwide.The latter is restricted to the New World and attacks more than 120 host species in 29 plant families [1,2,3,4].Helicoverpa armigera feeds on more than 180 hosts in 70 plant families, and it is widely distributedInsects 2020, 11, 431; doi:10.3390/insects11070431 www.mdpi.com/journal/insectsInsects 2020, 11, 431 in Europe, Africa, Asia, and Oceania [5,6,7,8,9]
The Indoxacarb-induced mortality of third instar larvae for both H. armigera and H. zea was concentration-dependent (Table 2)
The LC50 of indoxacarb on H. armigera was 0.17 μg a.i./cm2, and the LC90 was 1.70 μg a.i./cm2 ; they were slightly higher for H. zea at 0.21 and 2.64 μg a.i./cm2, respectively

Summary

Introduction

The noctuid moths Old World bollworm (OWB), Helicoverpa armigera (Hübner, 1809) and corn earworm, Helicoverpa zea (Boddie, 1850), are major lepidopteran pests attacking crops worldwide.The latter is restricted to the New World and attacks more than 120 host species in 29 plant families [1,2,3,4].Helicoverpa armigera feeds on more than 180 hosts in 70 plant families, and it is widely distributedInsects 2020, 11, 431; doi:10.3390/insects11070431 www.mdpi.com/journal/insectsInsects 2020, 11, 431 in Europe, Africa, Asia, and Oceania [5,6,7,8,9]. The noctuid moths Old World bollworm (OWB), Helicoverpa armigera (Hübner, 1809) and corn earworm, Helicoverpa zea (Boddie, 1850), are major lepidopteran pests attacking crops worldwide. The latter is restricted to the New World and attacks more than 120 host species in 29 plant families [1,2,3,4]. Insects 2020, 11, 431 in Europe, Africa, Asia, and Oceania [5,6,7,8,9] It was first reported in the New World in 2013, infesting soybean and cotton fields in Brazil [10]; a year later, it was detected in Argentina and Puerto Rico [11,12].

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