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

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.

Improving Risk Assessment of Noctuid Pests at North American Ports and Farms by Differentiating Egg Morphology

Heliothine eggs are commonly found on agricultural commodities and ornamental plants transported through domestic and international commerce. Tobacco budworm [Chloridea (Heliothis) virescens (F.)], Chloridea subflexa (Guenée), and the corn earworm [Helicoverpa zea (Boddie)] are indigenous pests of the American continent. Interceptions of the Old World bollworm [Helicoverpa armigera (Hübner)] at various ports of entry into the United States have been detected due to the invasion of this pest in South America, adding to the complexity and importance of decision making at plant inspection stations. The ability to distinguish the eggs of C. virescens from C. subflexa and Helicoverpa species is a critical component for conducting risk assessments by quarantine authorities, taxonomists, and crop consultants. We developed a simple, rapid (~60 min), inexpensive ($0.06 per sample), and accurate (100% reliability) technique to distinguish C. virescens eggs from the possibility of being H. armigera based on the presence, number, and/or size of aeropyle holes on the primary ribs of eggs, near the micropylar rosette. In this location, aeropyles were easily visible at 40× magnification in 213 fresh and ethanol-preserved C. virescens eggs once treated with Hoyer’s solution. A small number of C. subflexa had one or two aeropyles on a few of the primary ribs, whereas no aeropyles were found on 411 H. zea and 269 H. armigera eggs analyzed using optical, electron, and confocal microscopy. We conclude that in most cases multiple aeropyle holes positively identify H. virescens eggs from H. zea or H. armigera, and C. subflexa. This technique potentially will reduce the number of specimens that need to be sent for molecular identification thereby saving program time and resources.

Plant Protection and Quarantine: Recognizing Program Successes in 2015

In many ways, 2015 was extraordinary for plant health protection. We had more new pest detections and saw higher numbers of pest outbreaks than in previous years, including the first-ever detection of old world bollworm in the continental United States and a record-setting 12 fruit fly outbreaks. The year 2015 was also an impressive year for agricultural trade. The value of U.S. agricultural exports exceeded the value of imports again, making the last 7 years the strongest period for American agricultural exports in the history of our country.