Egg mass structure of the processionary caterpillar Ochrogaster lunifer (Lepidoptera: Notodontidae): is the outer egg layer sacrificed for attack by the egg parasitoid Anastatus fuligispina (Hymenoptera: Chalcidoidea: Eupelmidae)?

Abstract

Each life stage of an insect faces the challenge of various mortality factors. Through experimental and observational studies, we use those mortality agents to our advantage to control outbreaks of pest insects. The processionary caterpillar Ochrogaster lunifer Herrich‐Schäffer, 1855, is a widespread native moth in Australia that defoliates host trees and causes medical problems in humans and animals. Anastatus fuligispina (Girault 1939) is an egg parasitoid described from eggs of O. lunifer in eastern Australia nearly 80 years ago for which few life history traits are known. This is the first study to investigate the life history of A. fuligispina, factors associated with parasitism levels in O. lunifer egg masses and its impacts on egg mortality. We found that parasitism level was related to the total number of eggs in an O. lunifer egg mass, with higher parasitism occurring in masses with fewer eggs. The inaccessible physical structure of the O. lunifer egg mass by layering and encasing eggs with other eggs and the searching efficiency of the parasitoid are possible key factors. Other variables such as exposure time in the field, host tree species and number of undeveloped eggs in the egg mass did not affect the level of parasitism. Further investigations on the life history of A. fuligispina may open possibilities for its application in controlling O. lunifer populations.

A trunk‐nesting form of the processionary caterpillar Ochrogaster lunifer (Lepidoptera: Notodontidae) restricted to a single host species Corymbia tessellaris (Myrtaceae), with some comparisons to the ground‐nesting form

“…The difference in colour of the egg masses between tree‐hugger and ground‐nester moths is due to one of the two types of scale from the female's anal tuft used to cover the cluster of eggs. The size of eggs is the same as reported by Floater (1996) for ground‐nesters, and the average number of eggs per egg mass is similar; 294 for tree‐huggers at Gatton compared with an average of 268, 333, 297 and 301 reported by Floater (1996), Floater & Zalucki (2000), and Uemura et al (2019) for ground‐nesters at different sites and in different years. The orientation of tree‐hugger egg masses was uniform whereas the orientation of ground‐nester eggs was not.…”

“…Of the 24 tree-hugger egg masses monitored in the field for the entire 2016/17 season, 11 cohorts of larvae built a nest and completed development (46%). The wasp Anastatus fuligispina (Hymenoptera: Chalcidoidea) commonly found parasitising ground-nest eggs (Uemura et al 2019) was not observed in tree-hugger eggs.…”

“…The O. lunifer life cycle is univoltine. Female moths lay their eggs in a single mass (Floater 1996; Uemura et al 2019) during spring and cover the eggs with urticating scales from the anal tuft. The larvae are gregarious and co‐habit in a silk nest feeding on their host tree and growing over summer.…”

Host Specificity in Canopy Nesting Forms of Ochrogaster lunifer: The Larger Children Do Not Care

“…Differences between the canopy nesting forms on acacias and eucalypts can be seen at different levels and, as such, compared with what is known for other nesting forms. Canopy nesting forms have a lower realised fecundity than the ground nesting form on acacias from the same geographic area where Floater [ 6 ] recorded egg mass size of 150–550 eggs (mean ca 268, SD 95, n = 24) and Uemura et al [ 23 ] recorded 67–479 eggs (mean ca 301, SD 97, n = 65). Perhaps the difference reflects the greater distance this form must travel to garner its first meal, as the egg masses are laid at the base of the tree.…”

Response of the egg parasitoids of the pine processionary moth to host density and forest cover at the southern edge of the range

“…First, mean realized fecundity of the host is also lower at the southern edge of the range than at higher latitudes, likely because lower plant quality for larvae associated with hot and dry conditions (Pimentel et al ., 2010); this results in a reduced availability of eggs per egg batch, which may limit the access of the parasitoids to the resources (Mills & Getz, 1996). Second, egg batches from the southern populations of the pine processionary moth are characterized by a different type of scales covering the eggs (Petrucco‐Toffolo et al ., 2018), which may negatively affect the activity of the egg parasitoids that are known to respond to the quality of the eggs (Zovi et al ., 2008; Uemura et al ., 2019). Third, the climate at the southern edge of the range can make it difficult for parasitoids to exploit the resources, because of a bad synchronization between parasitoid emergence and moth oviposition (Auger‐Rozenberg et al ., 2015) or because of a higher probability to be exposed to excessively high temperatures.…”