Seasonal parasitism of hemlock looper (Lepidoptera: Geometridae) eggs in eastern Canada

Abstract

A 2-year field study was conducted using sentinel traps to determine the seasonal distribution of the egg parasitoid (Hymenoptera) complex attacking hemlock looper, Lambdina fiscellaria (Guenée), throughout eastern Quebec and western Newfoundland. Hemlock looper populations remained low in all areas over the course of the study. Parasitism of eggs in sentinel traps was generally lower in fall than in spring. Trichogramma Westwood (Trichogrammatidae) as well as Telenomus flavotibiae Pelletier and an unidentified species of Telenomus Haliday (Scelionidae) only parasitized eggs in the fall. Telenomus droozi Muesebeck only parasitized eggs in the spring, whereas T. coloradensis Crawford attacked eggs during both fall and spring. Telenomus coloradensis was the most abundant parasitoid species collected and was far more abundant in spring than in fall collections.Résumé-Une étude de terrain d'une durée de deux ans a été entreprise pour déterminer la répartition saisonnière de l'attaque des oeufs de l'arpenteuse de la pruche, Lambdina fiscellaria (Guenée), par son complexe de parasitoïdes (Hyménoptère). Des pièges sentinelles ont été placés à l'automne et au printemps dans des sapinières situées dans l'est du Québec et sur la cô te ouest de Terre-Neuve. Les densités de populations de l'arpenteuse ont été faibles pendant toute la durée de cette étude dans tous les sites échantillonnés. Le parasitisme des oeufs des pièges sentinelles a été généralement plus faible en automne qu'au printemps. Trichogramma Westwood (Trichogrammatidae), Telenomus flavotibiae Pelletier et une espèce non-identifiée de Telenomus Haliday (Scelionidae) ont parasité les oeufs de l'arpenteuse seulement à l'automne. Telenomus droozi Muesebeck n'a parasité les oeufs qu'au printemps, alors que T. coloradensis Crawford les a attaqué au cours des deux saisons. Telenomus coloradensis a été l'espèce de parasitoïde la plus abondante dans nos échantillons tant en automne qu'au printemps et ce dans les deux provinces.

Effects of seasonal variation in host quality and availability on parasitism by the egg parasitoid Telenomus coloradensis

“…However, T. coloradensis still have a considerable egg retention capability during periods of host deprivation. Both field and laboratory studies have shown that egg retention before adult overwintering is one of the most important conditions for effective parasitism early in the season (Hébert et al., ; Carleton et al., , ; Legault et al., ).…”

“…Telenomus coloradensis Crawford (Hymenoptera: Platygastridae; formerly Scelionidae according to Sharkey, ), a common natural enemy of hemlock looper eggs in northeastern Canada (Pelletier & Piché, ), plays a significant role as biological control agent (Hébert et al., ). Telenomus coloradensis can attack hemlock looper eggs either in their pre‐diapause and early diapause phase in fall or during the post‐diapause phase in spring (Carleton et al., , ; Legault et al., ). Parasitism reaches high levels only during spring, but underlying mechanisms remain to be explored (Hébert et al., ; Carleton et al., , ; Legault et al., ).…”

“…Telenomus coloradensis can attack hemlock looper eggs either in their pre‐diapause and early diapause phase in fall or during the post‐diapause phase in spring (Carleton et al., , ; Legault et al., ). Parasitism reaches high levels only during spring, but underlying mechanisms remain to be explored (Hébert et al., ; Carleton et al., , ; Legault et al., ). For example, parasitism levels exceeding 50% were reported for Telenomus spp.…”

“…Laboratory experiments further showed that fertilized, field‐collected T. coloradensis females in the spring have the capacity to attack hemlock looper eggs at temperatures as low as 4 °C (Legault et al., ), when development of the host embryo is slow. Telenomus coloradensis can enter diapause as immatures within the host egg (Carleton et al., , ), but probably in greater proportion as fertilized females (Legault et al., ). In a previous study using a degree‐day model, we predicted that T. coloradensis spring progeny from populations located along the Lower St. Lawrence region would emerge in midsummer (Legault et al., ).…”

Density‐dependent and density‐independent responses of three species of Telenomus parasitoids of hemlock looper eggs

“…Telenomus flavotibiae Pelletier parasitized hemlock looper eggs in the autumn, Telenomus droozi Muesebeck parasitized eggs during the spring, and Telenomus coloradensis Crawford parasitized hemlock looper eggs in both autumn and spring, with the vast majority of parasitism by T . coloradensis occurring during the spring (Carleton et al., 2009). It remains unclear, however, whether all or only a subset of these parasitoid species can contribute to suppressing hemlock looper populations.…”