Battle in the New World: Helicoverpa armigera versus Helicoverpa zea (Lepidoptera: Noctuidae)

Abstract

The corn earworm Helicoverpa zea (Boddie) and the old world bollworm Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) are allopatric species and occur in important agricultural crops. In maize, both species tend to infest the ear. The introduction of H. armigera in Brazil has created a new scenario, where these Helicoverpa species might cohabit and interact with one another, affecting the prevalence of each species in the agroecosystem, integrated pest management, and insect resistance management. In this study, larval occurrence and proportion of these species in maize was assessed in three regions of Brazil during three crop seasons. Interaction between the species was evaluated in interspecific and intraspecific scenarios under laboratory and field conditions. Helicoverpa zea was predominant in Rio Grande do Sul and the Planaltina, DF (central Brazil). In western Bahia, H. zea was predominant in the first collection, but approximately equal in number to H armigera in the second crop season. Both species exhibit high cannibalism/predation rates, and larval size was the primary factor for larval survival in the interaction studies. Larva of H. zea had higher survival when interacting with H. armigera, indicating that H. zea has an advantage in intraguild interactions with H. armigera in maize. Overall, the results from this study indicate that maize might play a role as a source of infestation or a sink of insecticide or Bt protein unselected H. armigera populations, depending on the H. zea:H. armigera intraguild competition and adult movement in the landscape.

Intraguild interactions and behavior of Spodoptera frugiperda and Helicoverpa spp. on maize

“…Helicoverpa zea prevailed over S. frugiperda only in the fourth versus second instar scenario, where S. frugiperda was disadvantaged owing to its smaller size. When both species occur on a maize plant, there is a higher probability that S. frugiperda will be more developed than H. zea and several other lepidopteran species, suggesting the tendency of S. frugiperda to prevail over these other species. This mismatch in development is due to the timing of when each species colonizes the maize plant; for example, S. frugiperda tends to infest maize crops earlier, during the vegetative stage, and then migrates to the ear, while H. zea tends to infest maize during the reproductive stages and larvae typically begin feeding on silks and kernels at the ear tip before consuming kernels down the maize ear …”

“…In order to keep the vigor of the colony, insects were frequently collected from the field, identified and transferred to the specific colony. More details on the rearing methodology used may be found in the literature …”

“…These cited characteristics pose questions concerning behavior, dispersion, population dynamics and the prevalence of noctuid species in maize. Studies involving intraguild interaction of noctuids on maize are still scarce, as well as cannibalism, predation and other larval behaviors when interaction occurs, particularly under field conditions …”

Mines over matter: Effects of foliar particulate matter on the herbivorous insect, Helicoverpa armigera

“…Considering neonates were in groups of ten within a confined space, cannibalism and intraspecific competition could also have contributed to high mortality (Bentivenha et al., ). In a study testing inter and intraspecific competition between Heliothinae species, 20% of 2nd instar H. armigera survived when reared together on maize in confined laboratory tubs compared with 30% when on maize ears in the field with unlimited dispersal potential (Bentivenha et al., ). Contrastingly, cannibalism is thought not to be a major issue in H. armigera laboratory rearing until they reach the 3rd instar (Kakimoto, Fujisaki, & Miyatake, ) We observed and removed the dead bodies of larvae in survival experiments, suggesting that cannibalism was also not a major reason for high fecundities in our experiment.…”

BRS 430 B2RF and BRS 432 B2RF: Insect-resistant and glyphosate-tolerant high-yielding cotton cultivars

“…Genetic advances (Morello et al 2010, Morello et al 2012, Morello et al 2015, Barroso et al 2017) along with a better production system ensures high fiber yields, providing competitiveness to the Brazilian cotton in the international market. However, this tropical region is subject to high biotic stress pressure, highlighting pest damages (Bentivenha et al 2016) and weed competition (Salgado et al 2002). Unfortunately, pest management relied almost exclusively on regular insecticides sprays, which can led to selection for resistance in important pests and other undesirable environmental effects.…”