The influence of host tree species on timing of pupation of Thaumetopoea pityocampa Schiff. (Lep., Thaumetopoeidae) and its exposure to parasitism by Phryxe caudata Rond. (Dipt., Larvaevoridae)¹

Abstract

Differences in the timing of pupation of pine irocessionary caterpillars on a native pine and on an exotic species caused marked differences in t e exposure of the caterpillars to parasitism by the tachinid Ph'hryxe caudatu. This result may help to explain the occurrence of outbreaks of the caterpillar in plantations, especially of exotic line?.The possibility t at, in addition to direct defences, plants may have evolved indirect defences based on manipulation of the plant herbivore relationship, to allow suppression of the herbivore population by its parasites or predators, is discussed. , ,However BILIoTrr (1956) reported that this expectation is not fulfilled, especially in areas prone to severe outbreaks of the caterpillars. In autumn the young caterpillars are all susceptible throughout the time when the flies from the summer generation lay their eggs, but in spring a large proportion of caterpillars pupate, and become unavailable, before the winter generation of P. caudatu emerge as adults.Pinus rudiuta has been introduced to the Mediterranean area from California. Apart from fortuitous effects (JANZEN 1980), we may expect this species to lack the specific defences against Th. pityocumpa which we would expect to have evolved in indigenous /~l~t r , t r i , , r ) p o c . , i -S ! . m p ,~\ i i i n i . TVcii\t.i~lt ,I. Rhs~.. nT.ir Fl.iiiiio\ TI' 5.-7.jul\ 1989. U.S. Copyright Clearance Cenrer Code Statement: 093 1 -2048/90/0903-0302 $ 02.50/0 Influence of host tree species on timing of pupation of Th. pityocumpa 303 species of pine ( RHOADES and CATES 1976). In a mixed plantation of P. radiata and the native Pinus pinaster, the American species was preferred for oviposition, and on it the caterpillars grew larger and pupated earlier than on the indigenous trees (own unpublished data). The earlier pupation meant that the proportion of caterpillars available for parasitism by Phryxe caudata was much lower on P. radiata than on P. pinaster. This is consistent with the hypothesis that P. radiata lacks specific defences and poses the question of whether the defence strategy of P. pinaster has been selected to effect synchrony of the caterpillars with its parasitoid. Fig. 4. The proportions of eclosed Phryxe cuudutu puparia in each nest dissolved (frequency of nestsfor any proportion and day), the aggregate proportion for all nests taken on one day (-) and for comparison, the cumulative percentage of P. cuudutu taken from the net traps (2)

Temperature as a predictor of survival of the pine processionary moth in the Italian Alps

“…It is possible that during this period, larvae need to feed longer to complete their development, and thus become more exposed to natural enemies (e.g. the tachinid Phryxe caudata Rondani; Buxton, 1990). Our ability to understand and predict responses of organisms to global warming is of increasing importance, particularly for species that have already been undergoing changes in their distributions, such as T. pityocampa .…”

Host utilisation by moth and larval survival of pine processionary caterpillar Thaumetopoea pityocampa in relation to food quality in three Pinus species

“…obs. ), and T. pityocampa grow in cluster pine (Avtzis, 1986; Breuer et al ., 1989; Buxton, 1990; Devkota & Schmidt, 1990; Masutti & Battisti, 1990; Schmidt, 1990; Pérez‐Contreras & Tierno de Figueroa, 1997), although infestation rates are much lower than in the Scots and black pine. Furthermore, the apparent growth rate of older larvae feeding on the three species did not differ significantly (Table 3), and cluster pine needles may even be a preferred food, as shown by the cafeteria experiments, although this is an artificial situation; in nature, larvae never have needles of three different hosts available at the same time.…”

“…; Mesón & Montoya, 1993), thus discouraging T. pityocampa from reaching outbreak proportions. A forest structure with suitable hosts in a density low enough and scattered among unsuitable hosts would dilute the effect of the population explosion, because unsuitable hosts, such as cluster pine, would receive egg batches that would not develop into adult T. pityocampa (Buxton, 1990). Where pine species with different suitabilities for T. pityocampa development grow intermingled, unsuitable hosts would act as sinks for moths coming from suitable hosts, those acting as sources; however, the massive pine plantations during the last century (Junta de Andalucía, 1990; see also Masutti & Battisti, 1990), characterised by monospecific, even‐aged stands, high density, regular spacing, and low variability among individuals, created a habitat in which T. pityocampa moths easily find suitable hosts at high density.…”

Range-Expansion in Processionary Moths and Biological Control

“…Several studies showed that Phryxe caudata is the most prevalent parasitoid of PPM and it can be found consistently across years and sites, but parasitism rates are often less than 5% [59][60][61]. The host range of this tachinid fly is probably narrow and it produces two generations per year, the first one in PPM caterpillars and the second one in the pupae [62]. Carcelia iliaca is a specialist tachinid parasitoid of OPM caterpillars (Figure 2), known from many countries, including Turkey, Romania, France, the Netherlands and the United Kingdom [37,[63][64][65].…”