Effect of Variable Photoperiod on Development and Survival of Cirrospilus sp. nr. Lyncus (Hymenoptera: Eulophidae), an Ectoparasitoid of Phyllocnistis citrella (Lepidoptera: Gracillariidae)

The eulophids Cirrospilus sp. near lyncus and Pnigalio pectinicornis L. are the most abundant parasitoids of the citrus leafminer, Phyllocnistis citrella Stainton, in Spain (Urbaneja et al. 2000). These were opportunistically recruited onto this pest after its introduction in 1993. C. sp. near lyncus is a late larval solitary idiobiont ectoparasitoid which can also behave as a hyperparasitoid. Its impact on P. citrella relies on both parasitism and host feeding (Urbaneja et al. 1998a). C. sp. near lyncus populations in citrus orchards increase from mid-July until the end of October, but remain almost undetectable during the rest of the year (Urbaneja et al. 1999). A previous study demonstrated that C. sp. near lyncus was very well adapted to temperatures prevailing on the western part of the Mediterranean Basin. That is the range between 7.1 ° C, mean of minimum temperatures of the coldest month (January), and 29.0 ° C, mean of maximum temperatures of the hottest one (August) (Urbaneja et al. 1999). To further study the influence of environmental conditions on the biology of this wasp, the effects of photoperiod on development and survival were investigated. Environmental chambers were used to check the effects of three different photoperiods: 16:8, 12:12 and 8:16 (L:D). Temperature fluctuated from 10 ° C to 30 ° C in eight 3h-steps of 5 ° C (mean temperature 20 ° C). Highest temperature always coincided with the mid-point of the photophase. This sequence mimics the regime of field temperatures both in spring and autumn. Therefore results obtained under both 16:8 and 8:16 (L:D) photoperiods are presumed to reflect field conditions at those seasons. Insects were reared at the Institut Valencià d’Investigacions Agràries as described by Urbaneja et al. (1998b). Eggs of C. sp. near lyncus were obtained by offering detached citrus leaves containing P. citrella third instar larvae (LIII) to isolated mated females (12 LIII per female). Exposure took place in Petri dishes (140 mm diameter) where leaves were placed on a layer of agar (2% weight) under a temperature of 25 ± 1 ° C during 4 hours. After exposure, leaves were checked under a stereoscopic binocular microscope and those containing parasitized hosts (recognized by the presence of C. sp. near lyncus eggs on them) were randomly transferred to the corresponding experimental photoperiod on a layer of