Comparing and Contrasting Life History and Development Strategies in the Pupal Hyperparasitoids Lysibia Nana and Gelis Agilis (Hymenoptera: Ichneumonidae)
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Appl. Entomol. Zool. 40 (2): 309–316 (2005) http://odokon.ac.affrc.go.jp/ Comparing and contrasting life history and development strategies in the pupal hyperparasitoids Lysibia nana and Gelis agilis (Hymenoptera: Ichneumonidae) Jeffrey A. HARVEY* and Leontien M. A. WITJES Netherlands Institute of Ecology (NIOO-KNAW), Department of Multitrophic Interactions, Centre for Terrestrial Ecology; Boterhoeksestraat 48, 6666 ZG Heteren, The Netherlands (Received 12 November 2004; Accepted 3 February 2005) Abstract Since the concept of the ‘niche’ was proposed by Hutchinson almost 50 years ago, many researchers have investigated factors that enable species within ‘guilds’ (i.e., species that exploit a common resource and are likely to compete with one another) to co-exist and to persist. Here, development, host utilization, and life-history characteristics are com- pared in two species of solitary secondary hyperparasitoids, Lysibia nana and Gelis agilis, attacking pre-pupae of their primary parasitoid host, Cotesia glomerata. More than 80% of the host cocoons presented to L. nana successfully pro- duced adult hyperparasitoids compared with only about 20% for G. agilis. Adult hyperparasitoid body mass increased with host mass, but there was little difference in the mean overall body mass of either species. However, egg-to-adult development time for L. nana was significantly less than that for G. agilis. When provided with unlimited food (honey solution), G. agilis had a lifespan that was almost twice that of L. nana. However, dissections of the ovaries of adult wasps at death revealed that L. nana usually had accumulated more than 20 mature eggs, whereas G. agilis was effec- tively sterile. We suggest that several eco-physiological factors, as well as differing degrees of specialization amongst the guild of secondary hyperparasitoids attacking C. glomerata cocoons, enable them to successfully co-exist in nature. Key words: Competition; Cotesia glomerata; guild; hyperparasitoid; niche experienced by hosts that feed in exposed or con- INTRODUCTION cealed locations, resulting in trade-offs between fit- Life-history strategies in parasitoids are often ness functions such as development time and adult based on a long period of co-evolution between the size (Harvey and Strand, 2002). Furthermore, vari- parasitoid and its host(s). Compared with most ations in the abundance and mortality risks of dif- arthropod predators, which attack many different ferent host stages are reflected in the form and kinds of prey, interactions between parasitoids and structure of adult female parasitoid morphology their hosts are usually highly intimate (van Alphen and reproductive biology in ways that optimize and Visser, 1990; Godfray, 1994). For this reason, fecundity and survival (Price, 1972). parasitoids exhibit a suite of developmental, physi- However, there are bound to be exceptions to ological, and morphological traits that are often these examples because such ‘laws’ in nature, even strongly correlated with the eco-physiological between species exploiting a common resource, are characteristics of their hosts (Price, 1972; Vinson rarely absolute. Amongst parasitoid complexes and Iwantsch, 1980; Jervis and Kidd, 1986; God- within defined ‘guilds’ [i.e., groups of species that fray, 1994; Strand and Pech, 1995; Quicke, 1997; exploit the same host stage and are thus liable to Harvey and Strand, 2002). For example, develop- compete with one another (Root, 1967)], there may mental strategies of many koinobiont parasitoids be considerable variation in the expression of cer- (i.e., parasitoids that attack hosts that continue tain traits. For instance, Price (1970, 1972) found feeding and growing after parasitism) appear to be that six species of idiobiont parasitoids (i.e., para- adaptive responses to differential mortality risks sitoids that attack non-growing or paralyzed hosts) *E-mail: [email protected] DOI: 10.1303/aez.2005.309 309 310 J. A. HARVEY and L. M. A. WITJES successfully co-exist on cocoons of the Jack Pine (Hymenoptera: Ichneumonidae) is an asexually Sawfly (Neodiprion swaineii) in the boreal forests reproducing facultative hyperparasitoid that is also of eastern Canada. He attributed the ability of these potentially a primary parasitoid of many other parasitoids to co-exist on several possible factors, hosts in nature. In addition to parasitoid cocoons, including inter-specific differences in the oviposi- Gelis species are known to parasitize such evolu- tor length of female parasitoids and on subtle tionarily divergent hosts as moth pupae and even forms of niche partitioning based on differing spider egg sacs (Bezant, 1956; Schwarz and Bori- responses (and preferences) of the parasitoids to a ani, 1994; van Baarlen et al., 1996). range of microclimatic conditions occupied by the The main aims of this study are (a) to determine host. if the specialist hyperparasitoid exploits host Another important factor that enables parasitoids resources differently and more effectively (in terms within guilds to persist over time, but which is of fitness correlates) than the generalist hyperpara- often overlooked or under-emphasized, is the de- sitoid, and (b) to compare life-history and morpho- gree of host specialization they exhibit. Many para- logical characteristics of the two species to see if sitoids, and in particular idiobionts, possess broad they differ in ways that enable them to co-exist host ranges, and will readily attack other suitable under natural conditions by further reducing com- hosts that are available (Godfray, 1994; Mayhew petition. Lastly, we discuss the role of other envi- and Blackburn, 1999). The studies by Price (1970, ronmental and biological factors that may influence 1972) also reported that all but one of the six the local distribution of secondary hyperparasitoids cocoon parasitoids of N. swaineii are facultative of C. glomerata in the field. hyperparasitoids; this suggests that all were also generalists. The ability to attack other hosts within MATERIALS AND METHODS a habitat acts to diffuse competition by enabling the parasitoids to reduce niche overlap (Hutchin- Insects. Hosts and parasitoids were reared at son, 1959). On the other hand, parasitoids that are 25Ϯ2°C under a 16L : 8D regime. Cultures of C. specialized (i.e., attack one or only a few host glomerata and P. brassicae were obtained from in- species in nature) probably exhibit phenotypic sects maintained for many years at Wageningen traits that more closely reflect strong co-evolution University (WUR), The Netherlands, and which with the preferred host than is the case for general- were originally collected from agricultural fields in ists that might attack many other unrelated hosts in the vicinity of WUR. All P. brassicae larvae used nature. Thus, we might expect more specialized in these experiments had been maintained on Bras- parasitoids to be (a) better competitors for their sica oleracea var. Cyrus (i.e., brussel sprouts) at preferred hosts than generalists, and (b) to exploit a WUR. given amount of host resources more effectively in In these experiments, P. brassicae larvae were terms of survival, adult size, and development maintained on Sinapis arvensis plants that origi- time. nated from the seeds of plants growing along a This study compares and contrasts development road near the Institute of Ecology at Driel, The and life-history characteristics in two species of Netherlands. It was decided to use S. arvensis as all solitary, secondary idiobiont hyperparasitoids that of the species in this study are known to be directly attack fully cocooned pre-pupae of the same pri- or indirectly associated with it under natural condi- mary parasitoid host. Cotesia glomerata L. (Hy- tions (Harvey, personal observations). Moreover, menoptera: Braconidae) is a gregarious koinobiont S. arvensis is a wild crucifer that has not been arti- primary parasitoid that attacks young larvae of ficially selected via domestication and, like its white butterflies, including the large cabbage but- close relatives including Brassica nigra, it contains terfly Pieris brassicae L. (Lepidoptera: Pieridae). higher levels of secondary plant compounds (glu- Lysibia nana Gravenorst (Hymenoptera: Ichneu- cosinolates) than cultivated species such as B. oler- monidae) is an sexually reproducing obligate hy- acea (Harvey et al., 2004; Harvey et al., unpub- perparasitoid that only attacks closely related pri- lished). mary hosts in the braconid subfamily Microgastri- Cotesia glomerata were reared according to the nae, including C. glomerata. Gelis agilis Fabricius protocol described by Harvey (2000). Adult female Comparing Hyperparasitoid Development 311 wasps oviposit 10–40 eggs into the first (L1) to larvae to parasitoids at the end of a brush in plastic third (L3) instars of P. brassicae. During their de- vials. Parasitism was verified by allowing wasps to velopment, parasitoid larvae feed primarily on host sting hosts for at least 5 s, which represents the ap- hemolymph and egress from the host caterpillar late proximate threshold between host acceptance and during its final instar. After egression, wasp larvae rejection in this species (Harvey, 2000). Parasitized immediately spin cocoons on the host plant adja- caterpillars were immediately placed in large rear- cent to the host, which perishes within a few days. ing cages (1 mϫ60 cmϫ60 cm) containing four S. Lysibia nana was originally obtained from co- arvensis plants. These were refreshed every 3 d, or coons of C. glomerata recovered from