A morphometric analysis of Thrips tabaci Lindeman species complex (Thysanoptera: Thripidae).

The onion thrips, Thrips tabaci Lindeman, is a cryptic species complex of three distinct lineages: L1, L2, and T, which exhibit considerable variation in their biological and ecological traits. The most accurate method for their identification is based on molecular techniques. This study aimed to investigate the morphometric variation of T. tabaci cryptic species complex and to distinguish characters that may be useful in discriminating the lineages. For this purpose, morphometric measurements were performed on the eggs, newly hatched first instar larvae, and newly emerged adults. Our results revealed significant differences in egg size between the three lineages. Moreover, the PCA analysis conducted on morphometric measurements of the first instar larvae and adults showed that females of the T lineage are very well separated from the females of the L lineages in the adult stage but not in the first instar larval stage. The distinction between the females is partially congruent with the results of genetic studies. Moreover, our results indicate that adult sexual dimorphism with regard to size in L1 and T lineages is not mediated by the size of eggs and first instar larvae, and this may be due to the different growth rates of males and females.

There Is No Influence of Egg Size on Sex Allocation in Arrhenotokous Lineages of Thrips tabaci Lindeman.

In two haplodiploid species, sex allocation in young arrhenotokous females is mediated by egg size. We tested if sex allocation is mediated by egg size in two arrhenotokous lineages of the haplodiploid species complex of T. tabaci: L1 and T. We measured the size of eggs produced by very young mothers, 3-5-day-old mothers (just like in the case of Tetranychus urticae) and 7-10-day-old mothers (as in Pezothrips kellyanus). Moreover, we measured the size of eggs oviposited by mothers in their entire lifespan. We found that in T. tabaci, sex allocation is not mediated by egg size. Egg size and gender were independent of maternal age in the L1 lineage, whilst in the T lineage, the observed egg size difference between males and females was only present in the progeny of young females (7-10-day-old mothers). Furthermore, we found that male eggs produced by mated mothers were larger than those produced by virgin mothers in the L1 lineage, but in the T lineage, there were no differences in the size of male eggs produced by mated and virgin mothers. Our results indicate that these two subspecies have different resource allocation strategies in response to maternal mating status.