Comparison Between Egg Batch and Egg Characteristics of the Two Pine Processionary Moth Species, Thaumetopoea wilkinsoni and T. pityocampa in Turkey

Abstract

Pine processionary moths (Thaumetopoea wilkinsoni and T. pityocampa [Lepidoptera: Notodontidae]) are among the most important forest pests in the Mediterranean basin. Being close relatives yet having significant genetic differences, the two species has been shown to hybridize under laboratory conditions and in nature in Turkey. Ongoing research has focused on the comparison of the larval and adult morphological traits between the two species without any apparent interest in egg characteristics. In this study, we aimed to reveal differences in egg batch and egg characteristics between the two species. We also compared these characteristics among altitudes. For this purpose, we collected 61 and 11 egg batches from T. wilkinsoni and T. pityocampa ranges from different altitudes (30-260 m) in Turkey, respectively. Two months after sampling, when parasitoid emergence nearly completed, we removed scales on the egg batches and measured the following traits: egg arrangement, egg batch length, egg batch circumference, clutch size, egg diameter, and larval emergence, unhatched egg and parasitism ratios. We used t-test and Mann-Whitney U test for statistical comparisons between species and between altitudes. We found significant differences between the two species in terms of egg arrangement, egg diameter, larval emergence and unhatched egg ratios. We also found significant differences among altitudes in terms of egg batch circumference, clutch size and egg diameter. We conclude that egg characteristics, particularly those related to fecundity and survival, have much more to reveal about the differences between the two species and among different altitudes. Our results also show that pine processionary moth species complex could be a good biological system for studying insect reproductive ecology and evolution, such as trade-offs between egg and clutch sizes. A larger sampling will greatly favor testing hypothesis relevant to the dynamics of pine processionary moth reproduction.