Reproductive Isolation in the Cryptic Species Complex of a Key Pest: Analysis of Mating and Rejection Behaviour of Onion Thrips (Thrips tabaci Lindeman).

Thrips tabaci Lindeman is a serious pest of various cultivated plants, with three, distinct lineages within a cryptic species complex. Despite the well-known significance of this pest, many attributes of these lineages are not yet fully understood, including their reproductive behaviour. We performed no-choice-design cross-mating experiments under a controlled laboratory environment with virgin adult individuals from all three lineages. The behaviour of thrips was recorded with a camera mounted on a stereomicroscope, and the recordings were analysed in detail. We found that the so-called leek-associated lineages of this cryptic species complex are reproductively isolated from the tobacco-associated lineage; therefore, they represent different species. Divergence in the behaviour of conspecific and heterospecific pairs became evident only after contact. There were no marked differences between the lineages in their precopulatory and copulatory behaviour, except in the duration of the latter. We confirmed mating between thelytokous females and arrhenotokous males; however, we assume some form of loss of function in the sexual traits of asexual females. The post-mating behaviour of males indicated the presence and role of an anti-aphrodisiac pheromone. We also demonstrated differences between lineages regarding their activity and their propensity for exhibiting an escape response upon interaction with heterospecific thrips.

Host Plant Association and Distribution of the Onion Thrips, Thrips tabaci Cryptic Species Complex.

Onion thrips, Thrips tabaci Lindeman, 1889 (Thysanoptera: Thripidae) is a pest of economic importance traditionally treated as a polyphagous, cosmopolitan single species. Recent genetic evidence, however, suggests that it is rather a cryptic species complex of three lineages referred to by their host association and displaying different biological and ecological characteristics: leek-associated 1, leek-associated 2 and tobacco-associated. This study reviews host plant associations and distribution of the lineages of this cryptic species complex and discusses its consequences from an agronomical perspective. Overall, leek-associated 2 lineage has the broadest host range, including major crops from different plant families, and it is the only lineage with a confirmed worldwide distribution. Leek-associated 1 lineage shares some host plants with leek-associated 2. It is often found in Allium crops and its geographic distribution is limited to a few dozen countries. Finally, tobacco-associated lineage has only been collected from tobacco and their associated weeds in central and east Europe, and the Middle East. Additionally, this work presents a list of 391 plant species on which breeding and development of T. tabaci occurs, regardless of lineage. These host plant species belong to 64 different families, most importantly Asteraceae, Fabaceae, Brassicaceae, Poaceae, and Solanaceae.

Spectral sensitivity of L2 biotype in the Thrips tabaci cryptic species complex.

The onion thrips, Thrips tabaci (Lindeman, 1889), is a cosmopolitan pest of economic importance on a wide range of crops. Despite being one of the most studied thrips species, there is very limited knowledge available about its ability to perceive light. The T. tabaci cryptic species complex consists of a tobacco-associated (T) and two leek-associated (L1, L2) biotypes. We made electroretinogram recordings on the most widespread thelytokous (where unfertilized eggs produce females) T. tabaci L2 biotype and measured attraction to light sources in this biotype as a function of wavelength in behavioural experiments. The spectral sensitivity of the T. tabaci L2 biotype shows a unimodal curve peaking at λmax = 521 nm. Contrary to this spectral sensitivity curve, L2 biotype attraction in an arena is bimodal with local maxima at 368 nm (UV) and 506-520 nm (green) being practically of the same magnitude. Although being similar to the arrhenotokous (where unfertilized eggs produce males) L1 biotype in phototaxis, significant differences regarding photoreceptor cell responses emerged. This study contributes to our understanding of light perception in Thysanoptera as well as to the development of more effective monitoring tools for this economically important pest species.

A simple molecular identification method of the Thrips tabaci (Thysanoptera: Thripidae) cryptic species complex.

The onion thrips (Thrips tabaci Lindeman, 1889) is a key pest of a wide range of crops because of its ecological attributes such as polyphagy, high reproduction rate, ability to transmit tospoviruses and resistance to insecticides. Recent studies revealed that T. tabaci is a cryptic species complex and it has three lineages (leek-associated arrhenotokous L1-biotype, leek-associated thelytokous L2-biotype and tobacco-associated arrhenotokous T-biotype), however, the adults remain indistinguishable. T. tabaci individuals were collected from different locations of Hungary to create laboratory colonies from each biotypes. Mitochondrial COI (mtCOI) region was sequenced from morphologically identified individuals. After sequence analysis SNPs were identified and used for CAPS marker development, which were suitable for distinguishing the three T. tabaci lineages. Genetic analysis of the T. tabaci species complex based on mtCOI gene confirmed the three well-known biotypes (L1, L2, T) and a new biotype because the new molecular evidence presented in this study suggests T-biotype of T. tabaci forming two distinct (sub)clades (T1 and T2). This genetic finding indicates that the genetic variability of T. tabaci populations is still not fully mapped. We validated our developed marker on thrips individuals from our thrips colonies. The results demonstrated that the new marker effectively identifies the different T. tabaci biotypes. We believe that our reliable genotyping method will be useful in further studies focusing on T. tabaci biotypes and in pest management by scanning the composition of sympatric T. tabaci populations.