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

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

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

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

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

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

Geographic variation of sex pheromone and mitochondrial DNA in Diatraea saccharalis (Fab., 1794) (Lepidoptera: Crambidae)

(9Z,11E)-hexadecadienal and (Z11)-hexadecenal, the main sex pheromone components of the sugarcane borer, Diatraea saccharalis, were identified and quantified from four Brazilian and one Colombian populations using GC-EAD, GC-MS and GC analyses. Three different ratios were observed, 9:1,6:1, and 3:1. The pheromone concentration for the major component, (9Z,11E)-hexadecadienal, varied from 6.8 ng/gland to 21.9 ng/gland and from 1.7 ng/gland to 6.5 to the minor component, (Z11)-hexadecenal. The 25 D. saccharalis cytochrome oxidase II sequences that were analyzed showed low intra-specific variation and represented only 11 haplotypes, with the most frequent being the one represented by specimens from Sao Paulo, Parana, and Pernambuco states. Specimens from Colombia showed the highest genetic divergence from the others haplotypes studied. Data on the genetic variability among specimens, more than their geographic proximity, were in agreement with data obtained from analyses of the pheromone extracts. Our data demonstrate a variation in pheromone composition and a covariation in haplotypes of the D. saccharalis populations studied. (C) 2010 Elsevier Ltd. All rights reserved.INCTCAPESCNP