DOI: 10.1111/j.1570-7458.2007.00595.x

Blackwell Publishing Ltd Maternal size and age affect offspring sex ratio in the solitary egg parasitoid nitens Serena Santolamazza-Carbone1*, Montserrat Pestaña Nieto1 & Adolfo Cordero Rivera2 1Centro de Investigación e Información Ambiental de Lourizán, Sección de Fitopatología, Apartado de Correos 127, Lourizán, Pontevedra, Spain, 2Grupo de Ecoloxía Evolutiva e da Conservación, Departamento de Ecoloxía e Bioloxía , Universidade de Vigo, EUET Forestal, Campus Universitario, Pontevedra, Spain Accepted: 3 May 2007 Key words: biological control, nutritional status, fecundity, clutch size, , , Mymaridae,

Abstract In this study, the effects of maternal age, diet, and size on offspring sex ratio were investigated for the solitary egg parasitoid, Girault (Hymenoptera: Mymaridae), both outdoors, during the winter, and inside a climatic chamber under favourable constant conditions. During the winter of 2005–2006, each of seven groups containing 40 1-day-old females was mated and randomly distributed among two treatments: (treatment 1) a droplet of undiluted honey ad libitum + one fresh egg capsule of the snout beetle Gonipterus scutellatus Gyllenhal (Coleoptera: Curculionidae) as host; (treatment 2) drops of water + one fresh egg capsule of G. scutellatus. We recorded the lifetime fecun- dity, the daily sex allocation, and the lifetime offspring sex ratio to study the existence of a relationship with maternal characteristics. Moreover, we assessed the effect of location (outdoors vs. indoors) and group (groups are representative of early, mid, and late winter) on sex ratio. The most important factor that biased the sex ratio was maternal body size: larger females of both treatments produced more female offspring. As females of A. nitens could gain more advantage than males from body size, larger mothers have a higher fitness return if they produce more daughters. The effect of the treatment was significant: starved females produced more females. Location and group were not significant. Fecundity and sex ratio were age dependent. Old mothers that received honey (treatment 1) had fewer offspring and a more male-biased offspring sex ratio, probably due to reproductive senescence and sperm depletion. Starved females (treatment 2) experienced reproductive decline earlier, perhaps because they invested more energy in maintenance rather than in reproduction.

daughters she has produced, then the benefit of producing Introduction males and females is not equal, but depends on offspring In parasitic Hymenoptera, mated females store sperm in mating opportunities (Godfray, 1994). Female-biased sex the spermatheca and can manipulate the sex ratio (males/ ratios are common among hymenopterous parasitoids total offspring) of their progeny by controlling fertilization that live in subdivided populations, with a few foundresses during oviposition. The haplodiploid sex-determination inside the patch and some degree of sib-mating (Hamilton, system (arrhenotokous parthenogenesis) provides the 1967; Antolin, 1993; Hardy, 1994). mothers with a mechanism to control progeny sex ratio, In the context of the study of sex allocation, attention because males develop from unfertilized eggs (haploid) and has been focused especially on resources (host and food) females from fertilized eggs (diploid) (Gould & Bolton, quality and abundance, to which the females are expected 1996). If we measure maternal fitness by adding the to respond in an adaptive way. The consequences of host number of mates of her sons to the lifetime number of abundance (Bai & Smith, 1993; King et al., 1995), host size (Charnov et al., 1981; King & Lee, 1994; Heinz, 1996; Napoleon & King, 1999), host age (King, 2000), host *Correspondence: Serena Santolamazza-Carbone, Centro de Investigación e Información Ambiental de Lourizán, Sección de species (King, 1987; Uçkan & Gülel, 2002), and host quality Fitopatología, Apartado de Correos 127, Lourizán, 36080 Pontevedra, (healthy vs. parasitized) (King, 1996a; van Baaren et al., Spain. E-mail: [email protected] 1999) on sex ratio have been intensively studied during

© 2007 The Authors Entomologia Experimentalis et Applicata 125: 23–32, 2007 Journal compilation © 2007 The Netherlands Entomological Society 23

24 Santolamazza-Carbone et al. the last two decades, generating important theories and Moreover, if the reproductive success varies seasonally, guidelines for practical applications in biological control mothers may use variation in abiotic factors as seasonal programmes. Evolutionary models, such as the local mate cues to predict future mating opportunities for their off- competition model (Hamilton, 1967; Werren, 1983; Cook spring (Godfray, 1994). et al., 1994; Hardy, 1994), which study the consequences of Anaphes nitens Girault (Hymenoptera: Mymaridae) is a female wasp density inside the patch, and other models solitary, idiobiont egg parasitoid of the Eucalyptus snout related to the response to adult sex ratio inside the popula- beetle Gonipterus scutellatus Gyllenhal (Coleoptera, Cur- tion, such as the perturbation model (Werren & Charnov, culionidae) (Tooke, 1955). This wasp was introduced to 1978), the constrained females model (Godfray, 1990), or northwestern Spain in 1992 as a biocontrol agent of the the crowding model (Waage, 1982), explain the existence weevil, quickly obtaining excellent results (Cordero Rivera of adaptive mechanisms that mothers adopt to increase et al., 1999). Gonipterus scutellatus females lay clumped their fitness through sex ratio manipulation (King, 1996b). eggs on young Eucalyptus spp. leaves and cover the eggs with On the other hand, maternal characteristics, such as age, a dark secretion mainly composed of faeces, which becomes egg load, diet, size, experience, time until mating, or number hard after some hours (so-called egg capsule). The egg of matings (King, 1987), are also important factors that capsules contain a mean of 8–10 eggs (Tooke, 1955). This shape sex allocation; however, in comparison with host situation makes A. nitens a parasitoid whose offspring variables, these have received less attention. The relation- develops in a quasigregarious fashion, because even if the ship between maternal age and offspring sex ratio could be larvae develop alone, the adults emerge together. Females more complicated than expected, because, depending on are weakly synovigenic, because they are born with a the ovigeny index and mating opportunities, old females mean egg load of 46 eggs, which can be increased by may experience an increase, a decrease, or no change of the about 20% during adulthood (Santolamazza Carbone & offspring sex ratio (King, 1987). In general, reduction of Cordero Rivera, 2002); under natural conditions, egg the female ratio among offspring when the mother is aged resorption can take place especially among starved is due to sperm depletion or reduced sperm viability, females (S Santolamazza-Carbone, M Pestaña Nieto & A but if the mother chooses to mate again, sex ratio may Cordero Rivera, unpubl.). Previous investigations have decrease. shown that this parasitoid adopts a female-biased sex ratio Maternal size could affect offspring sex ratio, as in the both in the field (male proportion = 0.24 ± 0.01) and in aphid parasitoid Aphytis melinus, where the positive rela- the laboratory (0.28 ± 0.04), that superparasitism usually tionship between maternal age and sex ratio is true only for increases male progeny (0.40 ± 0.07), and that the classical large females because they live longer and exhaust their local mate competition theory does not completely explain sperm supply (King, 1987). Large size may also improve the sex ratio estimated in the field under different conditions the female’s ability to obtain larger hosts, which are generally of population density (Santolamazza Carbone & Cordero used to produce daughters (Seidl & King, 1993; Heinz, 1996). Rivera, 2003). On the other hand, paternal characteristics such as age, Until now, no data are available on the effect of maternal time elapsed between matings, or the number of matings characteristics on offspring sex ratio in A. nitens. Hence, could also influence quality and size of ejaculates, produc- the main aim of this work was to test the effect of biotic ing biased sex ratios (King, 1987). Sperm replenishment factors such as maternal age, size, and nutritional status on requires a variable amount of time, thus the male ability to offspring sex ratio. Moreover, by conducting the experi- fertilize after a first mating could be weak if males mate in ments outdoors and inside a climatic chamber, we tested rapid succession (Damiens & Boivin, 2005). the effect of temperature (constant indoors and naturally As female access to food could enhance longevity, it fluctuating outdoors) on sex-ratio bias. If sperm supply should also contribute to variation in sex-ratio decisions. constitutes a limiting factor for our study species, then we In Bracon hebetor, for example, well-fed mothers live longer expected that old females should produce more sons. and produce more females (Rotary & Gerling, 1973). Also, Furthermore, if body mass is maternally inherited and environmental factors such as photoperiod, temperature, large females tend to produce larger offspring, as in and humidity may bias offspring sex ratio because they A. nitens (S Santolamazza-Carbone, M Pestaña Nieto, R may cause differential mortality of male and female pro- Pérez Otero, PJ Mansilla Vázquez, A Cordero Rivera & FJ geny, reduce food provision for the mother, or decrease the Fernández de Ana-Magán, unpubl.) and in other rate of movement of the insects, making mating less likely (Iyengar & Eisner, 1999), we predicted that large mothers (King, 1987). An example of this is A. melinus, which after should invest more in female offspring as has been shown a long-term exposure to winter temperatures produced a in other parasitoids (van den Assem et al., 1989; Rivero more male-biased sex ratio (Hoffmann & Kennet, 1985). Lynch & West, 2002).

Sex ratio in Anaphes nitens 25

itdesc.html). To test the effect of temperature on maternal Materials and methods sex allocation decisions, besides the adults reared out- Host and parasitoid rearing doors, we introduced into a climatic chamber (L9:D14 The parasitized egg capsules from which we obtained photoperiod, 70–80% r.h., and 20 ± 2 °C) three groups of the experimental adults were provided by the Biological 50 parasitized egg capsules each. Eclosed adults received Control Laboratory of the Estación Fitopatolóxica do the same treatments as described above. We reared a second Areeiro (Lourizán, Pontevedra, Spain). The snout beetle generation of parasitoids (three groups both outdoors and colony that provided the fresh egg capsules was originally indoors), which received the same treatments as above, to collected in the field, reared in the laboratory inside test the strength of the results obtained on the first genera- plastic boxes, and fed with fresh Eucalyptus globulus Labill. tion. At the experimental site, temperature and humidity (Myrtaceae) leaves. To obtain parasitized hosts, several were recorded by an official climate station of the local groups of 30 egg capsules were introduced in a Petri dish government (Xunta de Galicia). of 11 cm and exposed inside a climate chamber (24 °C, L14:D10 photoperiod, and 65% r.h.) during 24–48 h to 20 Data analysis 1-day-old females and 15 males of A. nitens. Sex-ratio variation was analyzed with a generalized linear mixed model (GLMM) with binomial errors, with genera- Outdoor and indoor treatments tion, location, treatment, and body size as fixed effects From 1 November 2005 to 9 February 2006, seven groups and group as a random effect. All interactions between of 50 parasitized egg capsules of G. scutellatus were exposed fixed effects were fitted, and the dispersion parameter was to outdoor conditions (one group every 2 weeks) at the estimated from the data. The number of males was the Centro de Investigación e Información Ambiental of Lourizán response variable and the total number of parasitoids was (Pontevedra, Spain). Each group was parasitized 24–48 h the binomial total. Group 3 reared outdoors was not before the exposure. considered in the analysis because only four adults eclosed. The egg capsules were introduced individually into To study the existence of a relationship between maternal marked plastic tubes (6 × 1 cm) perforated with small age and offspring sex ratio, we used a GLMM with bino- holes to allow air circulation and were maintained under mial errors, with generation, location, age, and body size as natural photoperiod, temperature, and humidity. The egg fixed effects and female and group as random effects. All capsules were checked daily. Adult parasitoids at birth were interactions between fixed effects were fitted and the dis- sexed by checking the shape and length of the antennae persion parameter was estimated from the data. (Tooke, 1955). For every replicate group, we randomly Statistical analyses were performed using GenStat 9.0 chose 40 1-day-old females, which were mated once and (VSN International Ltd, Hemel Hempstead, UK). randomly distributed between two treatments (n = 20 for every treatment): (treatment 1) a droplet of undiluted Results honey ad libitum + one fresh egg capsule of G. scutellatus and (treatment 2) drops of water + one fresh egg capsule of Table 1 summarizes lifetime sex ratio and fecundity indoors G. scutellatus. Adults were individually introduced into the and outdoors of both generations of the experimental marked plastic tubes provided with holes for air circulation females. We excluded data from females that did not and checked daily to record the date of death. The females produce any offspring or that produced only males. received a fresh egg capsule every day. The parasitized egg Results from the GLMM indicated that both generations capsules were removed, introduced individually in a new behaved in a similar way (Wald statistic = 0.29, d.f. = 1, P = marked plastic tube and checked daily. All adults of the 0.589), the effect of location was not significant (Wald = 3.19, experiment were studied until they died naturally. All d.f. = 1, P = 0.074), but both treatment (Wald = 7.62, parasitized egg capsules were dissected under a stereo- d.f. = 1, P = 0.006) and body size (Wald = 8.70, d.f. = 1, P = microscope to record the presence of uneclosed parasitoids. 0.003) were highly significant, that is, starved and larger We recorded the lifetime fecundity (dead offspring + females produced more daughters. The only significant eclosed offspring), the daily sex allocation, and the lifetime interaction term was generation*location (Wald = 10.93, sex ratio (males/total offspring) to study the relationship d.f. = 1, P<0.001), because the overall sex ratio (treatment with maternal age, size, and treatment. 1 + 2) was more similar between locations in the first Adult body size was estimated based on right forewing generation (indoors 0.34; outdoors 0.36) than in the length. The wing was mounted on a glass slide and its image second generation (indoors 0.30; outdoors 0.38). was digitized and measured using Image Tool 3.0 software Combining all the females reared outdoors, which received (San Antonio, TX, USA) (http://ddsdx.uthscsa.edu/dig/ honey (treatment 1) or water (treatment 2), respectively,

26 Santolamazza-Carbone et al. Lifetime fecundity ratio Sex oup indicates the replicate/groups. Means ± SE are Means oup indicates the replicate/groups. Gr eatment 1 2 Treatment Tr Lifetime fecundity ratio Sex entage rc of mean humidity Pe ature ature ean C ) ° (min/max) M temper ( and environmental conditions during the experiment. Date refers to the time during which females received hosts. hosts. the time to during refers which during Date conditions females received the experiment. and environmental il/20 May 8.8/19.7 80.6 24.1 ± 2.5 0.38 ± 0.034 7.2 ± 1.2 0.24 ± 0.041 naphes nitens r A Ap January/9 April January/9 April March/10 5.7/15.4 9.8/17.1 85.4 82.3 25.6 ± 3.0 27.6 ± 3.2 0.32 ± 0.046 0.46 ± 0.039 7.3 ± 1.5 13.1 ± 1.9 0.46 ± 0.098 0.30 ± 0.043 January/6 FebruaryApril March/3 20 9.9/17.6 75–80 82.5 20.2 ± 2.1 0.36 ± 0.031 31.2 ± 3.2 11.8 ± 1.5 0.40 ± 0.058 0.35 ± 0.050 11.8 ± 1.4 0.29 ± 0.037 February/18 March 20 75–80 22.8 ± 2.7 0.36 ± 0.026 15.1 ± 1.3 0.31 ± 0.030 19 December/14 February 3.4/15.0April 19 March/22 April 26 March/29 80.6 9.7/18.2 9.7/20.4 29.7 ± 2.2 81.2 75.9 0.31 ± 0.023 9.4 ± 0.9 21.7 ± 3.2 22.4 ± 2.2 0.28 ± 0.036 0.40 ± 0.043 0.35 ± 0.039 8.9 ± 1.6 12.2 ± 1.6 0.35 ± 0.073 0.34 ± 0.052 17 January/13 February 20 75–80 29.5 ± 8.7 0.37 ± 0.035 17.9 ± 2.7 0.20 ± 0.029 24 January/26 February 20 75–80 35.1 ± 3.8 0.36 ± 0.039 14.0 ± 2.1 0.32 ± 0.030 2 41 56 6 7 22 3 27 35 2 37 doors 1 14 December/31 January 20 75–80 30.7 ± 3.1 0.40 ± 0.045 12.7 ± 1.3 0.31 ± 0.006 doors 1 1 January/6 February 20 75–80 23.3 ± 2.0 0.28 ± 0.020 9.9 ± 2.8 0.34 ± 0.075 In In Offspring sex ratio and lifetime fecundity of n; sample size = 20 n; eatment 1 = honey + hosts, treatment 2 = water + hosts. Group 3 outdoors was not included because only four females eclosed. was not included because 3 outdoors only four females eclosed. Group + hosts. treatmenteatment 2 = water 1 = honey + hosts, ve Tr Table 1 First Outdoors 1 14 December/7 February 3.7/14.8 80.9 21.8 ± 2.2 0.38 ± 0.052 12.7 ± 1.7 0.36 ± 0.043 gi Generation Location Date Group Second Outdoors 1April March/25 3 9.0/16.0 80.5 27.9 ± 3.0 0.53 ± 0.066 8.3 ± 1.2 0.32 ± 0.054

Sex ratio in Anaphes nitens 27

Figure 1 The relationship between Anaphes nitens female size and sex ratio, for fed (treatment 1) and unfed (treatment 2) females (A) outdoors and (B) inside the climatic chamber. The two generations were combined. Treatment 1 = dotted line; treatment 2 = solid line. we found that larger females produced more daughters of female behaviour between generations (Wald = 0.28, (Figure 1A). The same trend was found indoors, but it d.f. = 1, P = 0.594), the absence of an effect of the location was less evident because adults that were born inside the (Wald = 1.37, d.f. = 1, P = 0.243), a significant effect of climatic chamber were smaller (Figure 1B). body size (Wald = 6.82, d.f. = 1, P = 0.009), and further To study the effect of age on sex-ratio adjustment (only indicate that sex ratio increased with maternal age for fed females), we estimated sex ratio for young (1–5 days (Wald = 25.87, d.f. = 2, P<0.001; Table 2). Again, the only old), mature (6–15 days), and old (more than 15 days) significant interaction term was between generation and females. Results from the GLMM confirmed the repeatability location (Wald = 10.27, d.f. = 1, P = 0.001).

28 Santolamazza-Carbone et al.

Table 2 Longevity and sex ratio (male/total offspring) of Anaphes nitens young mothers (1–5 days old), mature mothers (6–15 days), and old mothers (>15 days), which received honey (treatment 1) or water (treatment 2). Group 3 was not included because only four females eclosed. The sample size for the sex ratio refers to mothers that produced offspring in each age class. Those that produced zero offspring or only male offspring were eliminated. Mean ± SE with sample sizes in parentheses are given

Sex ratio of Sex ratio of Sex ratio of Generation Location Treatment Longevity (days) young mothers mature mothers old mothers First Outdoors 1 27.14 ± 1.1 (125) 0.38 ± 0.03 (108) 0.44 ± 0.03 (91) 0.42 ± 0.06 (49) 2 3.8 ± 0.1 (123) 0.31 ± 0.02 (49) – – Indoors 1 21.7 ± 1.0 (48) 0.32 ± 0.02 (37) 0.42 ± 0.04 (46) 0.55 ± 0.09 (44) 2 3.8 ± 0.2 (60) 0.31 ± 0.03 (35) – – Second Outdoors 1 23.76 ± 0.76 (59) 0.41 ± 0.04 (51) 0.46 ± 0.04 (50) 0.47 ± 0.09 (22) 2 3.07 ± 0.11 (59) 0.28 ± 0.02 (47) – – Indoors 1 23.13 ± 0.77 (61) 0.32 ± 0.02 (47) 0.31 ± 0.03 (50) 0.41 ± 0.07 (20) 2 3.79 ± 0.19 (61) 0.32 ± 0.01 (54) – –

Figures 2 and 3 show that daily fecundity and sex males from large size, because it means a larger egg supply, allocation were also age dependent. Irrespective of the a longer lifespan, and a greater capability to attack larger, location, we found that 13-day-old, honey-fed mothers higher-quality hosts (van den Assem et al., 1989). Anaphes (treatment 1) experienced a substantial increase of the sex nitens females show a positive relationship between body ratio that reached almost at a 1:1 investment (Figures 2A size and egg load (Santolamazza Carbone & Cordero Rivera, and 3A). On the other hand, starved females (treatment 2) 2002), fecundity, and longevity, while large size did not experienced a rapid decline of the fecundity and an increase male mating success (S Santolamazza-Carbone & increase of the sex ratio, when they were just 4 days old M Pestaña Nieto, unpubl.). Consequently, a biased invest- (Figures 2B and 3B). ment of large mothers on female progeny was expected. Our data indicate that both indoors and outdoors, honey-fed mothers (treatment 1 of the two generations) Discussion had a higher sex ratio than starved mothers (treatment 2). In agreement with our prediction, we found that maternal Actually, as fed mothers lived longer, longevity translated size and age biased the offspring sex ratio. The absence of into a higher realized fecundity, and in comparison with significant difference in mortality rate between sexes in our starved females, into a higher lifetime sex ratio. This was study species (S Santolamazza-Carbone, M Pestaña Nieto, confirmed by studying the relationship between maternal age R Pérez Otero, PJ Mansilla Vázquez, A Cordero Rivera & FJ and sex ratio (Table 2), where we show that mothers of the Fernández de Ana-Magán, unpubl.) implies that there were same age of both treatments produced a very similar sex ratio. no sex-biased mortality factors during larval development. Fecundity and sex allocation in insects are also age Larger females, irrespective of their group or treatment, dependent, because egg supply and sperm reserves are produced more female progeny. This effect is stronger out- depleted and the mother’s investment in terms of clutch doors, because adults born indoors are in general smaller. size, egg size, and nutrient contents decrease with time Few studies have attempted to assess the effect of body size (Giron & Casas, 2003). Among parasitoids, the existence of beyond fecundity and longevity (Petersen & Hardy, 1996; a positive relationship between maternal age and male Otten et al., 2001), and we are unaware of the existence of production has been documented (Uçkan & Gülel, 2002; a similar result with a wasp parasitoid. In a study conducted Akman Gündüz & Gülel, 2005). Given that a single mating with the encyrtid wasp Anagyrus kamali, larger females seems to be the rule in parasitoid wasps (van den Assem, had a lower sex ratio because adult size influenced the 1986), large and well-fed females that live longer should quality of the host attacked and smaller females were prone have higher sex ratios because they have exhausted their to attack smaller, low-quality hosts, which were more sperm supply (Godfray, 1994). Females in our experiment appropriate to allocate male progeny (Sagarra et al., 2001). mated only once, so that the sex ratio we observed for The sex allocation theory predicts that a female should mature and old females could be produced either by sperm invest preferentially in the sex that will be most efficient to depletion or reduced sperm viability. Nevertheless, also convert her investment into inclusive fitness for a given unfed females (treatment 2) that lived only a few days and environment (Frank, 1983). Females benefit more than had no time to be sperm depleted showed a similar trend.

Sex ratio in Anaphes nitens 29

Figure 2 Relationship between the mean daily fecundity (separate for each sex) and maternal age (both generations) of Anaphes nitens treated outdoors with (A) honey (n = 184) and (B) with water (n = 184). Bars represent SE.

Anaphes nitens is a semigregarious parasitoid whose weakly synovigenic), (ii) the depletion of the sperm supply, females lay small clutches similar to other Mymarids and (iii) the production of smaller clutches. (Mayhew, 1998). Given that it is probable that some form Figures 2A and 3A show that, irrespective of the loca- of local mate competition (Hamilton, 1967) takes place in tion, daily fecundity and the mean proportion of males its natural habitat, females produced at least one male in and females of honey-fed mothers reached a plateau of a every clutch. Therefore, three main factors could have con- 1:1 sex ratio when they were 13 days old. On the other strained the observed male-biased sex ratio when mothers hand, starved females experienced this when they were just aged: (i) the reduction of the egg supply (females are 4 days old (Figures 2B and 3B), probably because under a

30 Santolamazza-Carbone et al.

Figure 3 Relationship between the mean daily fecundity (separate for each sex) and maternal age (both generations) of Anaphes nitens treated indoors with (A) honey (n = 109) and (B) water (n = 121). Bars represent SE.

condition of nutritional stress, they invest more energy in oudoors produced more males than those of the first genera- maintenance than in reproduction, as was shown with tion. Moreover, temperature caused a dramatic failure of another hymenopterous parasitoid (Bezemer et al., 2005), parasitoid development and eclosion in group 3 reared and increase egg-resorption (S Santolamazza-Carbone, M outdoors (data not shown). As the minimum threshold Pestaña Nieto & A Cordero Rivera, unpubl.). Temperature temperature for A. nitens is 5.09 °C (Santolamazza Carbone did not influence sex-ratio decisions, even if it produced et al., 2006), it is possible that the fall of the temperature a significant effect in the interaction with generation, below 0 °C on some nights during the first weeks of because honey-fed females of the second generation reared development could have had a lethal effect.

Sex ratio in Anaphes nitens 31

In conclusion, understanding the proximal factors that Cook JM, Rivero Lynch AP & Godfray HCJ (1994) Sex ratio and affect A. nitens sex allocation may help to discover con- foundress number in the parasitoid wasp Bracon hebetor. straints on adaptive sex-ratio biases and offer the oppor- Animal Behaviour 47: 687–696. tunity to improve the protocol for the mass rearing of this Cordero Rivera A, Santolamazza Carbone S & Andrés JA (1999) parasitoid, which is the only tool available to control the Life cycle and biological control of the Eucalyptus snout beetle (Coleoptera, Curculionidae) by Anaphes nitens (Hymeno- spread of the Eucalyptus snout beetle (DeBach & Rosen, ptera, Mymaridae) in north-west Spain. Agricultural and Forest 1991). Laboratory populations often yield parasitoids with Entomology 1: 103–109. small size and low productivity and experience an undesir- Damiens D & Boivin G (2005) Why do sperm-depleted parasitoid able shift toward male-biased sex ratios due, for example, males continue to mate? Behavioural Ecology 17: 138–143. to superparasitism (Godfray, 1994). In A. nitens, super- DeBach P & Rosen D (1991) Biological Control by Natural Enemies. parasitism determines an increase of the sex ratio and the Cambridge University Press, Cambridge, UK. reduction of adult size, with females being more affected Frank SA (1983) A hierarchical view of sex-ratio patterns. Florida than males (Santolamazza Carbone & Cordero Rivera, 2003). Entomologist 66: 42–75. We further stress the importance of finding an appropriate Giron D & Casas J (2003) Mothers reduce egg provisioning with parasitoid/host ratio and preventing overcrowding inside age. Ecology Letters 6: 273–277. laboratory cultures, in order to maximize the production of Godfray HCJ (1990) The causes and the consequences of con- strained sex allocation in haplodiploid . Journal of large females, which are prone to produce more daughters, Evolutionary Biology 3: 3–17. as we have shown in the present work. Godfray HCJ (1994) Parasitoids Behavioral and Evolutionary Ecology. Princeton University Press, Princeton, NJ, USA. Acknowledgements Gould I & Bolton B (1996) The Hymenoptera. Oxford University Press, Oxford, UK. We thank the Biological Control Laboratory of the Hamilton WD (1967) Extraordinary sex ratios. Science 156: 477– Estación Fitopatolóxica do Areeiro for providing both the 488. healthy and parasitized egg capsules of G. scutellatus, and Hardy ICW (1994) Sex ratio and mating structure in the parasitoid Dr. Christopher D. Beatty for checking the English. Hymenoptera. Oikos 69: 3–20. Heinz KM (1996) Host size selection and sex allocation behavi- our among parasitoid trophic levels. Ecological Entomology References 21: 218–226. Akman Gündüz E & Gülel A (2005) Investigation on fecundity Hoffmann RW & Kennet CE (1985) Effects of winter tempera- and sex ratio in the parasitoid Bracon hebetor Say (Hymeno- tures on the sex ratios of Aphytis melinus (Hym. Aphelinidae) ptera: Braconidae) in relation to parasitoid age. Turkish Zoology in the San Joaquin Valley in California. BioControl 30: 125– 29: 291–294. 131. Antolin MF (1993) Genetic of biased sex ratios in subdivided Iyengar VK & Eisner T (1999) Heritability of body mass, a sexually populations: models, assumptions, and evidence. Oxford selected trait, in an arctiid moth (Utetheisa ornatrix). Proceed- Survey of Evolutionary Biology 9: 239–281. ings of the National Academy of Sciences of the USA 96: 9169– van den Assem J (1986) Mating behaviour in parasitic wasps. 9171. Parasitoids (ed. by JK Waage & DJ Greathead), pp. 137– King BH (1987) Offspring sex ratios in parasitoid wasps. The 163. Academic Press, London, UK. Quarterly Review of Biology 62: 367–395. van den Assem J, van Iersel JJA & Los-den Hartogh RL (1989) Is King BH (1996a) Fitness effects of sex ratio response to host quality being large more important for female than for male parasitic and size in the parasitoid wasp Spalangia cameroni. Behavioral wasps? Behaviour 108: 160–195. Ecology 7: 35–42. van Baaren J, Landry BL & Boivin G (1999) Sex allocation and larval King BH (1996b) Sex ratio responses to other parasitoid competition in a superparasitizing solitary egg parasitoid: com- wasps: multiple adaptive explanations. Behavioral Ecology peting strategies for an optimal sex ratio. Functional Ecology and Sociobiology 39: 367–374. 13: 66–71. King BH (2000) Sex ratio and oviposition responses to host age and Bai B & Smith SM (1993) Effect of host availability on reproduction fitness consequences to mother and offspring in the parasitoid and survival of the parasitoid wasp Trichogramma minutum. wasp Spalangia endius. Behavioral Ecology and Sociobiology Ecological Entomology 18: 279–286. 48: 316–320b. Bezemer MT, Harvey JA & Mills NJ (2005) Influence of adult King BH & Lee HE (1994) Test of the adaptiveness of sex ratio nutrition on the relationship between body size and reproduc- manipulation in a parasitoid wasp. Behavioral Ecology and tive parameters in a parasitoid. Ecological Entomology 30: Sociobiology 35: 437–443. 271–280. King BH, Crowe ML & Skinner SW (1995) Effect of host density Charnov EL, Los-den Hartogh RL, Jones WT & van den Assem J on offspring sex ratios and behavioural interactions between (1981) Sex ratio evolution in a variable environment. Nature females in the parasitoid wasp Nasonia vitripennis (Hymeno- 289: 27–33. ptera: Pteromalidae). Journal of Insect Behavior 8: 89–102.

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Mayhew PJ (1998) The life-histories of parasitoid wasps developing Santolamazza Carbone S & Cordero Rivera A (2003) Superpara- in small gregarious broods. Netherlands Journal of Zoology sitism and sex ratio adjustment in a parasitoid wasp: results at 48: 225–240. variance with local mate competition? Oecologia 136: 365–373. Napoleon ME & King BH (1999) Offspring sex ratio response to Santolamazza Carbone S, Rodríguez-Illamola A & Cordero host size in the parasitoid wasp Spalangia endius. Behavioral Rivera A (2006) Thermal requirements and phenology of the Ecology and Sociobiology 46: 325–332. Eucalyptus snout-beetle Gonipterus scutellatus Gyllenhal. Otten H, Wäckers FL, Battini M & Dorn S (2001) Efficiency of Journal of Applied Entomology 130: 368–376. vibrational sounding in the parasitoid Pimpla turionellae is Seidl S & King BH (1993) Sex-ratio manipulation by the parasitoid affected by female size. Animal Behaviour 61: 671–677. wasp Muscidifurax raptor in response to host size. Evolution Petersen G & Hardy ICW (1996) The importance of being larger: 47: 1876–1882. parasitoid intruder-owner contests and their implications for Tooke FGC (1955) The Eucalyptus snout-beetle, Gonipterus clutch size. Animal Behaviour 51: 1363–1373. scutellatus Gyll. A study of its ecology and control by biological Rivero Lynch AP & West SA (2002) The physiological costs of means. Entomology Memoirs Department of Agriculture being small in a parasitic wasp. Evolutionary Ecology Research Union of South Africa 3: 1–282. 4: 407–420. Uçkan F & Gülel A (2002) Age-related fecundity and sex ratio Rotary N & Gerling D (1973) The influence of some external variation in Apanteles galleriae (Hym., Braconidae) and host factors upon the sex ratio of Bracon hebetor Say (Hymenoptera: effect on fecundity and sex ratio of its hyperparasitoid Braconidae). Environmental Entomology 2: 134–138. Dibrachys boarmiae (Hym., Pteromalidae). Journal of Applied Sagarra LA, Vincent C & Stewart RK (2001) Body size as an indi- Entomology 126: 534–537. cator of parasitoid quality in male and female Anagyrus kamali Waage JK (1982) Sex ratio and population dynamics of natural (Hymenoptera: Encirtidae). Bulletin of Entomological Research enemies – some possible interactions. Annals of Applied Biology 91: 363–367. 101: 159–164. Santolamazza Carbone S & Cordero Rivera A (2002) Egg load and Werren JH (1983) Sex ratio evolution under local mate competi- adaptive superparasitism in Anaphes nitens, an egg parasitoid tion in a parasitic wasp. Evolution 37: 116–124. of the Eucalyptus snout-beetle Gonipterus scutellatus. Entomo- Werren JH & Charnov EL (1978) Facultative sex ratios and logia Experimentalis et Applicata 106: 127–134. population dynamics. Nature 272: 349–350.