Efficacy of Beauveria bassiana and Beauveria pseudobassiana isolates against the pine processionary moth, Thaumetopoea wilkinsoni Tams, 1926 (Lepidoptera/Notodontidae)

Background The pine processionary moth, Thaumetopoea wilkinsoni Tams, 1926 (Lepidoptera/Notodontidae) is one of the most harmful insects that destroys pine ecosystems by feeding on pine leaves at its larval stage. Because of its urticating setae, the insect also causes severe skin reactions to animals and humans. Instead of chemical control, eco-friendly biological control methods are preferred to combat this species. Results The purpose of this study was to evaluate the efficacy of five different Beauveria bassiana Vuill, 1912 (Hypocreales/Cordycipitaceae) isolates (TR-SM-10, TR-SM-11, TR-SM-2, TR-SK-1 and TR-D-1) and one B. pseudobassiana Rehner & Humber (Hypocreales/Cordycipitaceae) isolate (TR-SM-1) against the fourth instar larvae of T. wilkinsoni under laboratory conditions. T. wilkinsoni larvae were collected from the Ondokuz Mayıs University Kurupelit Campus in Samsun, Turkey, in 2021, and the fourth instar larvae were used in the experiment. Two ml of spray of the six fungal isolates were applied to every ten larvae at each concentration (1 × 107 and 1 × 108 conidia ml−1). The experiment was carried out in five replicates per group, and the larvae were observed for 10 days. As a result, all isolates of B. bassiana caused 100% mortality at 1 × 108 conidia ml−1 concentration. B. pseudobassiana isolate also caused 100% mortality at both concentrations. At 1 × 107 conidia ml−1 concentration, the larvae treated with the B. pseudobassiana isolate (TR-SM-1) had the lowest LT50 (2.89 days) and LT90 values (4.79 days), while the larvae treated with TR-SM-10 isolate had the highest LT50 (5.65 days) and LT90 values (9.39 days). At 1 × 108 conidia ml−1 concentration, the larvae treated with TR-SK-1 isolate had the lowest LT50 (2.89 days) and LT90 values (4.79 days), while those treated with TR-SM-10 isolate had the highest LT50 (3.95 days) and LT90 values (8.15 days). Conclusion It has been recommended that the five different isolates of B. bassiana and B. pseudobassiana isolates were virulent to T. wilkinsoni larvae and can be used for biological control of T. wilkinsoni.

IMPACT OF NATURAL ENEMIES ON LARVAE OF THAUMETOPOEA BONJEANI (LEPIDOPTERA NOTODONTIDAE) IN ASSOCIATION WITH THAUMETOPOEA PITYOCAMPA IN NORTHERN ALGERIA

The cedar processionary moth, Thaumetopoea bonjeani (Lepidoptera: Notodontidae), is a serious pest of the Atlas cedar Cedrus atlantica in north-western Africa and it is involved in the decline of this endangered tree species. Natural enemies of the cedar processionary moth are poorly known, especially for parasitoids, predators and pathogens of the larval-pupal life stages. Mature larvae were collected and examined in 2014 and 2015 in natural stands of Atlas cedar in the Djurdjura (northern Algeria), in occurrence with pine processionary moth Thaumetopoea pityocampa. The overall mortality rate of larvae of Thaumetopoea bonjeani ranged from 26.4% to 31.1%, with generalist predators and parasitoids being more effective than pathogens. Four primary parasitoid species were recorded, of which four tachinid flies and one braconid wasp, as well as four predatory beetles and one fungus. The most important species were the carabid Calosoma sycophanta and the tachinid Compsilura concinnata. The cooccurrence of T. bonjeani and T. pityocampa may offer to generalist natural enemies an extended period of availa- bility of similar preys, as the two processionary moths have different life cycles. The sharing of natural enemies between the two species of Thaumetopoea can mitigate the outbreaks of both species.

Effects of climate warming on the pine processionary moth at the southern edge of its range: a retrospective analysis on egg survival in Tunisia

In recent years, ectotherm species have largely been impacted by extreme climate events, essentially heatwaves. In Tunisia, the pine processionary moth (PPM), Thaumetopoea pityocampa, is a highly damaging pine defoliator, which typically lays eggs in summer. Its geographical range is expanding northwards in Europe while retracting from South Tunisia where summer temperatures can reach extremely high values. In this study, we aimed at exploring the effects of climate change on this species at its southern range edge. We investigated variations of fecundity and causes of egg mortality over time using historical and contemporary collections of egg masses from different Tunisian sites to seek relationships with regional climate change over three decades (1990-2019). Our results suggest negative effects of summer heat on egg survival, reflected in a decrease of hatching rate down to 0% in one site during a heatwave. Such a high hatching failure was found to result from both high egg sterility (our results did not allow distinguishing impeded mating success from failed egg maturation or early death of the embryo) and increased abortion of more developed embryos, but little effects of parasitism rate, thereby suggesting vulnerability to heat during embryonic development. We also observed decreasing female fecundity (i.e., number of eggs laid per female) in regions where data were available both in the 1990s and the 2010s, which was associated with a decrease in parasitism rate, while the climatic variability increased. This study investigated direct hatching failure in nature that may be related to the magnitude of warming in summer. Previous studies have confirmed the thermal sensitivity of early instars of the PPM to temperatures observed in the present work, including one population from South Tunisia. However, further work is required to evaluate the relative importance of warming summers among populations because the risk of heat stress depends on the phenology of sensitive instars, and populations from the warmest areas may not necessarily be the most vulnerable to climate change if they already evolved phenological heat avoidance. In addition to heat-induced mortality, the ultimate fitness of individuals that survive challenging heat stresses during early developmental stages should also be explored to determine potential carry-over effects on subsequent life stages.

Factors affecting Thaumetopoea pityocampa emergence in laboratory conditions

To investigate the factors affecting the emergence of the pine processionary moth (Thaumetopoea pityocampa) in laboratory conditions, a number of 1487 larvae, prepupae and pupae were collected in the period February-May 2019 from five pest habitats: Fotinovo and Kandilka villages (inhabited by a summer phenological form), Sandanski and Klisura towns (winter phonological form occurs) and Sarnak village (both forms occur). At the date of collection, the rate of parasitism was very low (0-0.1%). Throughout the study, significant differences in the characteristics of pupal stage and mortality between both phenological forms were established. The rate of emerged adults varied from 21.4% to 77.6% in the observed habitats. The sex ratio between female and male specimens was almost equal. Only 0.6% of samples emerged in the second year, after diapause. In four localities (Fotinovo, Kandilka, Sandanski and Sarnak), the rate of infection by entomopathogens was between 6.0% and 20.8%, and the parasitism caused by tachinids – between 0.9% and 3.4%. The flight period of the summer and winter phenological forms of T. pityocampa were clearly differentiated with about a month. In summer form, the flight began in late May and ended in the last decade of June, and in winter form – from early July to the end of August. The duration of the flight period in both forms lasted 30 to 50 days with an equal number of emerged male and female specimens.

A Viral Pathogen from Pine Processionary Moth, Thaumetopoea pityocampa (Denis & Schiffermuller, 1775) (Lepidoptera: Notodontidae)

Pine processionary moth, Thaumetopoea pityocampa (Den. & Schiff.) is a serious defoliator in pine forests. Its larvae cause defoliation by eating leaves mainly on coniferous species, Pinus brutia, P. nigra, P. pinaster, and P. pinea in Turkey. Cypovirus is the most common entomopathogen in T. pityocampa populations. In this study, the ultrastructure of the cypovirus of T. pityocampa was observed in the intestine lumen of the predatory beetle, Calasoma sycophanta L. (Coleoptera: Carabidae), which supports the hypothesis of possible transmission of the virus to T. pityocampa populations by the predatory beetle. Polyhedral occlusion bodies (OBs) and virions were examined by electron microscopy. OBs of the virus were of irregular shape and 2.1 µm (1.2-3) in diameter, and each of them included up to 50 virions in a cross-section. Virions were icosahedral and 78.3 (65-90) nm in size and each virion had surface spikes. Smaller OBs, larger virions and a high number of virions per cross-section were the main features of the cypovirus in T. pityocampa. Our observations make us conclude that the predator beetle, C. sycophanta, may disseminate OBs of cypovirus when preying upon infected T. pityocampa larvae.