Helicoverpa armigera is one of the primary agricultural pests in the Old World, whereas H. zea is predominant in the New World. However, H. armigera was first documented in Brazil in 2013. Therefore, the geographical distribution, range of hosts, invasion source, and dispersal routes for H. armigera are poorly understood or unknown in Brazil. In this study, we used a phylogeographic analysis of natural H. armigera and H. zea populations to (1) assess the occurrence of both species on different hosts; (2) infer the demographic parameters and genetic structure; (3) determine the potential invasion and dispersal routes for H. armigera within the Brazilian territory; and (4) infer the geographical origin of H. armigera. We analyzed partial sequence data from the cytochrome c oxidase subunit I (COI) gene. We determined that H. armigera individuals were most prevalent on dicotyledonous hosts and that H. zea were most prevalent on maize crops, based on the samples collected between May 2012 and April 2013. The populations of both species showed signs of demographic expansion, and no genetic structure. The high genetic diversity and wide distribution of H. armigera in mid-2012 are consistent with an invasion period prior to the first reports of this species in the literature and/or multiple invasion events within the Brazilian territory. It was not possible to infer the invasion and dispersal routes of H. armigera with this dataset. However, joint analyses using sequences from the Old World indicated the presence of Chinese, Indian, and European lineages within the Brazilian populations of H. armigera. These results suggest that sustainable management plans for the control of H. armigera will be challenging considering the high genetic diversity, polyphagous feeding habits, and great potential mobility of this pest on numerous hosts, which favor the adaptation of this insect to diverse environments and control strategies.

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Insecticide impact on non-target species, such as insect predators and parasitoids, is an ever-growing concern in agriculture and recent studies have been shifting focus from lethal to sub-lethal effects since they may prevail in field conditions, although more difficult to assess. Synthetic insecticides are the main concern, but the recent spread of biopesticide use in agriculture draws attention, particularly the main botanical insecticide currently in use - azadirachtin. Here we assessed the lethal and behavioral sub-lethal response of predatory larvae of the lacewing species Chrysoperla externa and Ceraeochrysa cubana to two frequently used synthetic insecticides, malathion and permethrin, and to the bioinsecticide azadirachtin. The recommended field concentration of the synthetic insecticides led to low survival time of lacewing larvae from both species, in contrast with azadirachtin. However, all three compounds led to 100% mortality of the lacewing larvae from both species. Insecticide repellence (i.e., avoidance without contact) was similar for both synthetic insecticides in both species, but azadirachtin was a stronger repellent for C. externa, but not C. cubana. In addition, insecticide irritability (i.e., avoidance after contact) occurred in both lacewing species to all three insecticides tested. The notion that natural compounds are safer than synthetic compounds to non-target species is refuted in the present study, which also detected significant irritability to all of the insecticides regardless of their origin, and species-specific repellence elicited particularly by azadirachtin. Therefore, bioinsecticides should not be exempted from risk assessment, and non-target sub-lethal effects should not be neglected when considering potential insecticide use in agriculture.

Sublethal responses to insecticides are frequently neglected in studies of insecticide resistance, although stimulatory effects associated with low doses of compounds toxic at higher doses, such as insecticides, have been recognized as a general toxicological phenomenon. Evidence for this biphasic dose–response relationship, or hormesis, was recognized as one of the potential causes underlying pest resurgence and secondary pest outbreaks. Hormesis has also potentially important implications for managing insecticide‐resistant populations of insect‐pest species, but evidence of its occurrence in such context is lacking and fitness parameters are seldom considered in these studies. Here, we reported the stimulatory effect of sublethal doses of the pyrethroid insecticide deltamethrin sprayed on maize grains infested with a pyrethroid‐resistant strain of the maize weevil (Sitophilus zeamais) (Coleoptera: Curculionidae). The parameters estimated from the fertility tables of resistant insects exposed to deltamethrin indicated a peak in the net reproductive rate at 0.05 ppm consequently leading to a peak in the intrinsic rate of population growth at this dose. The phenomenon is consistent with insecticide‐induced hormesis and its potential management implications are discussed.