Effects of heat waves on larval emergence of Thaumetopoea pityocampa Schiff. (Lepidoptera, Thaumetopoeidae) in Aleppo pine forests in Central West Tunisia
Résumé
Background: In recent years, organisms have largely been impacted by extreme climate events, essentially heat waves. In Tunisia, the pine processionary moth (PPM), Thaumetopoea pityocampa, is a highly damaging pine defoliator, which usually lays eggs in summer. Understanding the effect of extreme temperatures on the fecundity of this insect as well as the impact on its natural enemies is crucial to explore the overall effects of climate change on this species. The aim of this present work was to assess the effects of extremely high temperatures on the PPM fecundity, and on the emergence of larvae and parasitoids from eggs that were collected in 2017 at the extreme southern limit of PPM distribution range, following a very hot summer.
Materials/Methods: A total of 124 egg masses were collected in four stations in the center-west of Tunisia: Thèlepte (22/08/2017), Jebel Motlag (10/10/2017) and Jebel Rihana (in Rgueb) (10/10/2017) and El Faj (11/10/2017). In laboratory, emergence of larvae and parasitoids were observed each day to draw the emergence curves. As soon as egg hatching was completely achieved, the protective scales have been removed to study egg mortality. Statistical analysis was performed using SPSS software. Daily maximal temperatures were retrieved from AccuWeather website.
Results and discussion: The difference in female fecundity was not significant between the sites (P=0.74). It varied from 45 to 216 with an average of 139 eggs/clutch. No larva has emerged from Thélepte station. Nonetheless 17.9-66.2% of eggs hatched in the other sites. Parasitism rate was significantly different between the sites (P<0.001), the highest rate was recorded in J.Rihane: 11.1% and no parasitoid has emerged in Thélepte. The percentage of flattened and dried eggs was the highest in Thélepte (8.5 % and 15% respectively). The difference between the sites may occur due to the extreme temperatures observed in Thèlepte. Daily maximal temperature was between 40°C and 44°C during 10 consecutive days from 01st to 10th August 2017, while the maximum temperature did not exceed 34°C on the other sites from 18th September to 10th October.
Conclusion: A larger percentage of unhatched eggs and lower parasitism rate in an area with extremely high temperatures highlight possible detrimental effects of climate warming at the southern edge of the PPM distribution.