Knockdown of a Mosquito Odorant-binding Protein Involved in the Sensitive Detection of Oviposition Attractants

Odorant-binding proteins (OBPs) were discovered almost three decades ago, but there is still considerable debate regarding their role(s) in insect olfaction, particularly due to our inability to knockdown OBPs and demonstrate their direct phenotypic effects. By using RNA interference (RNAi), we reduced transcription of a major OBP gene, CquiOBP1, in the antennae of the Southern house mosquito, Culex quinquefasciatus. Previously, we had demonstrated that the mosquito oviposition pheromone (MOP) binds to CquiOBP1, which is expressed in MOP-sensitive sensilla. Antennae of RNAi-treated mosquitoes showed significantly lower electrophysiological responses to known mosquito oviposition attractants than the antennae of water-injected, control mosquitoes. While electroantennogram (EAG) responses to MOP, skatole, and indole were reduced in the knockdowns, there was no significant difference in the EAG responses from RNAi-treated and water-injected mosquito antennae to nonanal at all doses tested. These data suggest that CquiOBP1 is involved in the reception of some oviposition attractants, and that high levels of OBPs expression are essential for the sensitivity of the insect’s olfactory system

The genetic structure of an invasive pest, the Asian citrus psyllid Diaphorina citri (Hemiptera: Liviidae).

The Asian citrus psyllid Diaphorina citri is currently the major threat to the citrus industry as it is the vector of Candidatus Liberibacter, the causal agent of huanglongbing disease (HLB). D. citri is native to Asia and now colonizes the Americas. Although it has been known in some countries for a long time, invasion routes remain undetermined. There are no efficient control methods for the HLB despite the intensive management tools currently in use. We investigated the genetic variability and structure of populations of D. citri to aid in the decision making processes toward sustainable management of this species/disease. We employed different methods to quantify and compare the genetic diversity and structure of D. citri populations among 36 localities in Brazil, using an almost complete sequence of the cytochrome oxidase I (COI) gene. Our analyses led to the identification of two geographically and genetically structured groups. The indices of molecular diversity pointed to a recent population expansion, and we discuss the role of multiple invasion events in this scenario. We also argue that such genetic diversity and population structure may have implications for the best management strategies to be adopted for controlling this psyllid and/or the disease it vectors in Brazil

Analysis of molecular variance (AMOVA) for <i>Diaphorina citri</i> samples using <i>COI</i> sequences.

<p>Analysis of molecular variance (AMOVA) for <i>Diaphorina citri</i> samples using <i>COI</i> sequences.</p

Haplotype network of populations of <i>Diaphorina citri</i> from Brazil based on partial sequences of the COI gene (996 bp), built by using the TCS program.

<p>Each circle represents a haplotype and circles are gradually colored depending on the frequency haplotypes were observed, from one occurrence (light yellow) to more than 40 occurrences (dark red).</p

The Genetic Structure of an Invasive Pest, the Asian Citrus Psyllid <i>Diaphorina citri</i> (Hemiptera: Liviidae) - Figure 2

<p>a) Membership probability of each individual to belong to group I or II, b) Membership probability plot on a map of the state of São Paulo. Group I in grey and Group II in black. Numbers on the map refer to the different localities sampled as reported in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0115749#pone-0115749-t001" target="_blank">Table 1</a>.</p

Mismatch curves of <i>Diaphorina citri</i> from the whole sample (a), and from group I (b) and II (c) independently.

<p>Mismatch curves of <i>Diaphorina citri</i> from the whole sample (a), and from group I (b) and II (c) independently.</p

Group, localities, coordinates, host plant, number of individuals analysed (N), haplotypes, and nucleotide and haplotype diversity of <i>Diaphorina citri</i> in each sampled locality in Brazil.

<p>Group, localities, coordinates, host plant, number of individuals analysed (N), haplotypes, and nucleotide and haplotype diversity of <i>Diaphorina citri</i> in each sampled locality in Brazil.</p

Fitness costs associated with spinetoram resistance in<i>Spodoptera frugiperda</i>is driven by host plants

AbstractInsecticide resistance is usually associated with fitness costs. The magnitude of fitness costs is affected by environmental and ecological factors. Here, we explored how host plants could affect fitness costs associated with insecticide resistance. Initially, spinetoram-resistant (RR) and susceptible (SS) strains ofSpodoptera frugiperdawere selected using F2screen from a population collected in São Desidério, Bahia State, Brazil in 2018. Besides de RR and SS strains, fitness costs were also assessed for a heterozygous strain (RS). Life-history traits were evaluated to estimate population growth parameters of neonate larvae of each strain fed on corn, soybean and cotton plants. Compared to the SS strain, the relative fitness of the RR strain, based on intrinsic rate of population increase, was 1.06, 0.84 and 0.67 on plants of corn, soybean and cotton respectively. The relative fitness of the RS strain was similar to the SS strain regardless the host plant, suggesting a recessive fitness cost. No differences were found between the strains fed on corn plants. The larval development time was greater for RR strain fed on soybean and cotton plants compared to RS and SS strain. Low survival rate and fecundity of the RR strain were found when larvae fed on plants of soybean and cotton. The results of this study demonstrated that fitness costs of spinetoram resistance inS. frugiperdadepend strongly on the host plants thatS. frugiperdalarvae fed on. Such information can be used to design resistance management strategies considering the host plants of the agricultural landscape.Key messagesThe presence of fitness costs associated with resistance can be exploited in resistance management strategies.Host plant influences the fitness costs associated with spinetoram resistance inS. frugiperda.Information considering the host plants in an agricultural landscape is essential to design effective resistance management programs.</jats:sec

Investigating life history and predation defense costs associated with emamectin benzoate resistance in Spodoptera frugiperda (Lepidoptera: Noctuidae)

Evidence of field-evolved resistance to emamectin benzoate has already been reported in Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae) in Brazil. To investigate the fitness costs associated with emamectin benzoate resistance, we used an F2 screen to select resistant (Ben-R) and susceptible (Ben-S) strains of S. frugiperda from a field-collected population in Mato Grosso State, Brazil. Fitness costs were quantified by comparing biological (life history traits) and behavioral (ability to escape from predation by Podisus nigrispinus (Dallas) (Heteroptera: Pentatomidae)) parameters of Ben-R, Ben-S, and heterozygote strains reared on non-Bt maize and artificial diet. The resistance ratio of S. frugiperda resistance to emamectin benzoate was ∼ 2445-fold. Based on life table parameters, Ben-R and heterozygote strains had a higher mean generation time (T) than Ben-S strain on both food sources. The intrinsic rate of population increase (rm) of Ben-R strain was ∼ 35% lower than Ben-S and heterozygote strains. In contrast, there was no significant difference in predation rate of 3rd instar larvae of Ben-R, Ben-S and heterozygote strains by P. nigrispinus. Our findings suggest the presence of strong fitness costs associated with emamectin benzoate resistance in S. frugiperda, as evidenced by life history traits. Conversely, no fitness costs were linked to the defensive response against predation by P. nigrispinus.Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Department of Entomology and Acarology University of São Paulo (USP), Av. Pádua Dias 11, PiracicabaInstitute of Biosciences São Paulo State University (UNESP), BotucatuDepartment of Plant Protection Federal University of Santa Maria (UFSM), Rio Grande do SulInstitute of Biosciences São Paulo State University (UNESP), BotucatuFAPESP: 2019/20385-0FAPESP: 2023/09661-1CNPq: 314160/2020-0CNPq: 314160/2020-5CAPES: 88882.317558/2019–0