Chlorpyrifos spraying of no‐tillage corn during tasselling and its effect on damage by Helicoverpa zea (Lep., Noctuidae) and on its natural enemies

Abstract

Corn plants were twice sprayed at 3‐day intervals during tasselling to evaluate the effect of chlorpyrifos on ear damage by H. zea and also on the populations of the natural enemies associated with this moth. The abundance of H. zea eggs and larvae and of predators on the whole plant, the egg parasitism by Trichogramma pretiosum Riley and the percentage of injured ears were sampled weekly. Chlorpyrifos did not show any significant effect on population levels and on ear damage by H. zea. Natural parasitism of eggs ranged from 52 to 75% and did not differ between treated and untreated plots; furthermore, the percentage of non viable eggs and adult emergence were not influenced by insecticide application. Among the predators found in the plots, Doru luteipes was not affected by spraying, whereas the abundance of Orius sp. decreased 21 days after insecticide application. The frequency of the ant Pheidole sp. was not affected by chlorpyrifos; however, foraging activity of Crematogaster sp. on treated plots was rapidly reduced and remained low during the following 2 weeks. The small number of damaged ears suggests that the insecticide did not affect the efficiency of the natural enemies of H. zea.

Field evaluation of sweet corn varieties for their potential as a trap crop forHelicoverpa zeaunder tropical conditions

“…Concerning egg laying by H. zea on brown (i.e. senescent) silks, our results are consistent with those of previous studies reporting that H. zea can lay eggs on dry silks in corn fields (Archer & Bynum 1994;Filho et al 2002). According to M ol et al (2004), pollinated silks are involved in ethylene synthesis, and, according to Kapu and Cosgrove (2010), once pollinated, the silks stop elongating, and senescence begins.…”

Efficacy of Three Insecticides for Controlling Corn Earworm, <i>Helicoverpa zea</i> (Boddie) in Maize

“…Several insecticides from endosulfan to synthetic pyrethroids and insect growth regulators have been demonstrated to give effective control of Helicoverpa (Sehgal and Ujagir, 1990). Filho et al (2002) reported that chlorpyrifos gave effective control of H. zea in maize for 21 days after insecticide application Resistance to insecticides is widespread, particularly in crops where pyrethroids are used frequently (Greenstone, 1995;Kanga et al, 1995). Pesticides manufacturers have produced more potent and toxic pesticides whenever Helicoverpa developed resistance to the prevailing insecticides.…”

Bioensayos de insecticidas biológicos y orgánicos sintéticos en larvas del gusano de la mazorca del maíz [Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae)]

“…Desafortunadamente, el uso excesivo de ciertos ingredientes activos ha causado resistencia del gusano de la mazorca a los insecticidas orgánicos sintéticos. Por ejemplo, se ha reportado resistencia de larvas de H. zea a insecticidas convencionales dentro del subgrupo de organofosforados y piretroides (Abd-Elghafar et al, 1993;Bentivenha et al, 2016;Filho et al, 2002;Pietrantonio et al, 2007;Reisig y Kurtz, 2018). Jacobson et al (2009) evaluaron la resistencia a piretroides en larvas de H. zea de tercer estadio, mediante la aplicación tópica del insecticida bifentrina en dosis desde 0.02 hasta 6.00 µg de producto disuelto en acetona, colocando 1 uL de la solución (bifentrina+acetona) en el tergum (torax) de 30 larvas de H. zea.…”