Mate recognition and reproductive isolation in the sibling species Spodoptera littoralis and Spodoptera litura

Abstract

Mate recognition is crucial for reproductive isolation and for maintaining species integrity. Chemosensory-mediated sexual communication with pheromones is an essential component of mate recognition in moths. Confronted with sex pheromone stimuli released from conspecific and closely related heterospecific females, which partially overlap in chemical composition, male moths are under strong selection to recognize compatible mates. Here, we investigated the role of pheromone signals in premating communication in the sibling species Spodoptera littoralis and S. litura (Lepidoptera, Noctuidae). Further, we measured the reproductive consequence of conspecific vs. heterospecific matings. Both species use Z 9,E11-14:Ac as the major pheromone compound, and the 11-component blend found in pheromone glands of S. littoralis comprises the compounds found in S. litura. Accordingly, S. littoralis and S. litura males readily responded to conspecific and heterospecific calling females in no-choice behavioral tests. In contrast, in a dual-choice test, S. littoralis males choose conspecific calling females, whereas S. litura males did not discriminate between conspecific and heterospecific females. In S. littoralis females, heterospecific matings had a negative fitness effect as compared to conspecific matings. Female longevity, egg-laying and hatching of larvae were significantly reduced by matings with heterospecific males. Reciprocal crossings, between S. litura females and S. littoralis males, were prevented by genital morphology, which is consistent with reduced heterospecific attraction of S. littoralis males in a dual-choice assay. On the other hand, matings between S. littoralis females and S. litura males, under a no-choice situation, show that interspecific matings occur in zones of geographical overlap and corroborate the idea that mate quality, in these closely related species, is a continuous and not a categorical trait.

Evolution of two receptors detecting the same pheromone compound in crop pest moths of the genus Spodoptera

“…It is a serious pest of more than 80 agricultural productions such as cotton, maize, rice, sorghum, alfalfa, soybean and vegetables, all over Africa, the Mediterranean Basin and the Middle East (Salama et al, 1971). Its sex pheromone blend, variable according to the strains and areas, is composed of up to eleven 14-carbon acetates, among which (Z,E)-9,11-14:OAc is always the major component (Muñoz et al, 2008;Saveer et al, 2014). Electrophysiology experiments on male antennae identified one OSN population specifically tuned to this component (Ljungberg et al, 1993;Quero et al, 1996) and housed in one class of long trichoid sensilla, further referred as LT1 sensilla.…”

Identification and field evaluation of the sex pheromone of a Brazilian population of Spodoptera cosmioides

“…The antennae did not show a clear response to the other acetates present in female gland extracts. The biosynthetic route of the pheromone components in moths shows that 16:OAc and Z11-16:OAc are the precursors of Z9-14:OAc, Z7-12:OAc and Z9,E12-14:OAc (Jurenka, 2004;Groot et al, 2008;Saveer et al, 2014), therefore, these compounds are not directly involved in male attraction. Batista-Pereira et al (2006) reported that Z11-16:OAc did not increase male attraction to a synthetic blend of S. frugiperda pheromone containing Z7-12:OAc and Z9-14:OAc.…”

Concurrent modulation of neuronal and behavioural olfactory responses to sex and host plant cues in a male moth

“…Pheromone glands were extracted in redistilled heptane (Labscan, 20 ml/10 glands) as previously described [18]. A subsample of extracts was used for chemical analysis.…”

“…The initial temperature of the GC was set to 808C (5 min hold) and then increased 108C min 21 to a final temperature of 2258C (10 min hold). Pheromone components were identified by co-injection of authentic synthetic samples and comparison with a NIST mass spectra library (Agilent) and our own library [18].…”

“…(e) Synthetic chemicals Synthetic compounds used for electroantennogram (EAG) and optical imaging (OI) analyses included plant-related components (benzaldehyde, benzyl methyl ether, (E)-bocimene, phenylacetaldehyde, acetophenone, benzyl alcohol, (þ)-(S)-linalool, 1,4-dimethoxy benzene, estragole, b-myrcene, Z3-hexenyl acetate, p-cymene, (þ)-(R)-limonene and nonanal), female-emitted sex pheromone components (Z9,E11-14Ac, Z9,E12-14Ac, Z9-14Ac, E11-14Ac, Z11-14Ac and 14Ac) and the synthetic mimic of the sex pheromone blend (ratio according to [18], 10(Z9,E11-14Ac) : 0.4(Z9,E12-14Ac) : 1(Z11-14Ac) : 2(E11-14Ac) : 3(Z9-14Ac) : 0.3(14Ac); see electronic supplementary material, table S5, for further details on the synthetic chemicals). For single sensillum recordings (SSRs), Z9,E11-14Ac, Z9,E12-14Ac and Z9-14Ac were tested individually.…”