Introduction
Interactions between parasitoid wasps and their hosts typically reflect a high level of coevolution and are therefore good model systems for studying coevolutionary relationships (e.g., Dupas et al., Reference Dupas, Carton and Poirie2003; McLean and Parker, Reference McLean and Parker2020). Although parasitoids are lethal to their hosts and usually prevent their reproduction (Pennacchio et al., Reference Pennacchio, Diglio and Tremblay1995; Digilio et al., Reference Digilio, Isidoro, Tremblay and Pennacchio2000), reproduction post-parasitism may occur in hosts of koinobiont parasitoids that survive for some period during parasitoid development (Mackauer and Kambampati, Reference Mackauer and Kambhampati1984; Sequeira and Mackauer, Reference Sequeira and Mackauer1988; English-Loeb et al., Reference English-Loeb, Karban and Brody1990). It is clearly beneficial for parasitized aphids to attempt to maximize their reproductive success prior to their inevitable demise, but such reproduction is also of potential benefit for the parasitoid, as it may help prolong the persistence of a host patch, and thus improve reproductive opportunities for the next parasitoid generation. Thus, we would expect post-parasitism reproduction to be favored by selection in aphids without being subject to much counter selection in the parasitoid population, provided it had negligible effects on immature parasitoid survival.
Most aphidiine species will suppress host reproduction entirely when they parasitize early instar aphids, and negatively impact reproduction when they parasitize later instars or adults (Sequeira and Mackauer, Reference Sequeira and Mackauer1988). The destruction and extraoral digestion of host embryos is the first and most dramatic physiological change within the host aphid following parasitism, and it is largely a function of the teratocytes released upon egg eclosion and the biochemical processes they mediate (Pennacchio et al., Reference Pennacchio, Diglio and Tremblay1995; Digilio et al., Reference Digilio, Isidoro, Tremblay and Pennacchio2000). Whereas hosts are expected to experience strong selection pressure to block parasitoid development and evolve varying levels of resistance to parasitism, parasitoids are expected to evolve counteradaptations (e.g., Li et al., Reference Li, Falabella, Giannantonio, Fanti, Battaglia, Digilio, Volkl, Sloggett, Weisser and Pennacchio2002; Casanovas et al., Reference Casanovas, Goldson and Tylianakis2018; Vorburger and Perlman, Reference Vorburger and Perlman2018).
Few studies as yet have examined the fitness of offspring that survive maternal parasitism, the consequences for their life history, or how their suitability as subsequent hosts for the parasitoid might be altered. Maternal effects on fitness, largely associated with variation in maternal body size, have been demonstrated in the Aphidiinae (Ameri et al., Reference Ameri, Rasekh and Michaud2014; Najafpour et al., Reference Najafpour, Rasekh and Esfandiari2018). Because of the complex physiological changes induced in aphid embryos by parasitoid venom (Digilio et al., Reference Digilio, Isidoro, Tremblay and Pennacchio2000) and phagocytic teratocytes (Falabella et al., Reference Falabella, Tremblay and Pennacchio2000), it seems likely that these would translate into negative maternal effects for nymphs that escape death by virtue of being sufficiently well developed. However, some authors have suggested that aphids, when lacking effective immunity, may use ‘fecundity compensation’ (increased reproductive effort) to salvage some fitness when parasitized or infected with a pathogen (Barribeau et al., Reference Barribeau, Sik and Gerardo2010), or in response to associated cues such as aphid alarm pheromone (Leventhal et al., Reference Leventhal, Dunner and Barribeau2014).
Lysiphlebus fabarum Marshall (Hymenoptera: Braconidae) is a common aphidiine parasitoid in central Europe where it attacks more than 70 species of aphids in agricultural and horticultural crops (Stary, Reference Stary1986; Volkl, Reference Volkl1992), although the black bean aphid, Aphis fabae Scopoli, serves as a primary host species (Rakhshani et al., Reference Rakhshani, Stary and Tomanovic2013). Although both sexual (arrhenotokous) and asexual (thelytokous) strains of this species exist in Iran (Rakhshani et al., Reference Rakhshani, Talebi, Kavallieratos, Rezwani, Manzari and Tomanovic2005; Rasekh et al., Reference Rasekh, Michaud, Allahyari and Sabahi2010a), the former appear to be more widely distributed, and the asexual strain has only been reported from one geographical region (Rasekh et al., Reference Rasekh, Kharazi, Michaud, Allahyari and Rakhshani2011). In the present study, we examined the development and life history consequences of maternal parasitism for A. fabae that survived as offspring of parasitized mothers. We also tested their acceptability and suitability as hosts for L. fabarum. We hypothesized (1) that maternal parasitism would impose fitness costs on developing aphids via maternal effects, and that these costs would increase with superparasitism, (2) that maternal parasitism impacts on surviving progeny would be greater when larval parasitoids were female rather than male, and (3) that maternal parasitism would render surviving progeny less suitable as hosts for parasitoid development, and these effects would have transgenerational consequences.
Materials and methods
Insect rearing
Stock colonies of all insects were held in growth chambers at 21 ± 1°C, 65–75% RH, and a 16:8 (L:D) photoperiod and all experiments were performed under these physical conditions. A stock colony of black bean aphids was established on potted broad bean, Vicia faba L., grown in pots (20 cm diam × 20 cm ht) filled with sawdust and fertilized weekly (N:P:K = 20:20:20, 2% solution). The aphid colony was held in wood frame cages (100 × 65 × 65 cm) covered in organdy mesh. Each cage held nine bean plants which were replaced as required, about one plant every 3 days.
Mummies of the sexual strain of L. fabarum were obtained from parasitized black bean aphids, A. fabae Scopoli (Hemiptera: Aphididae), collected in bean fields in Khuzestan province (31°19′N, 48°41′E), in winter 2018. Sexual (arrhenotokous) reproduction was confirmed by observing the sex of progeny produced by virgin mothers (all males). The parasitoid colony was maintained in cages (as above), containing a series of excised bean shoots immersed in small vials of fertilized water (N:P:K = 20:20:20) to maintain turgor, and sealed with parafilm, each infested with ca. 50 A. fabae. Aphid-infested shoots were introduced into the cages twice weekly to maintain a continuous culture of parasitoids; mummies were harvested from bean shoots as needed for experiments.
Production of synchronous insect cohorts
Excised stems of bean plants were immersed in small vials of fertilized water (as above), and then placed in a plastic cylinder (8.0 cm × 15.0 cm). Synchronous cohorts of black bean aphid (±6 h old) were established on these stems by allowing 100 adult A. fabae to deposit nymphs on each for a period of 12 h, at which time the adult aphids were removed and the nymphs left to develop in situ until the third instar, the stage used for parasitism in all experiments. Preliminary observations revealed that A. fabae require a median of 3 days from birth to molt to the third instar. Third instars were selected for parasitism because aphids parasitized at this stage are still able to give birth to several nymphs before mummification.
To produce synchronous wasp cohorts, 2-day-old L. fabarum females, without prior exposure to aphids, were provided aphids in a 1:5 ratio (one wasp for each five aphids) in plastic cylinders (as above). The wasps were removed after 6 h and the parasitized aphids were reared on potted bean seedlings until mummies formed. Mummies were then transferred into ventilated Petri dishes (3.5 cm diam, ca. 50 per dish) until the emergence of wasps, whereupon these were transferred to ventilated plastic cylinders (8.0 cm diam × 15.0 cm ht, ca. 20 wasps per cylinder) and provisioned with droplets of diluted honey (50% in distilled water) on a strip of wax paper and water on a ball of cotton. The water was refreshed daily, and the diluted honey, every second day. All females had access to males for their first 24 h of life and were 2 days old when used in experiments.
Aphid life history following maternal parasitism or superparasitism
Excised bean shoots (n = 20), each bearing 40 third instar A. fabae nymphs, were isolated in plastic cylinders (8.0 cm × 15.0 cm). Two-day-old mated females were then introduced into these cylinders at one of two densities; either one or five wasps per cylinder. A preliminary experiment in which aphids were dissected ca. 60 h post exposure revealed that, under these conditions, the five wasp treatment resulted in superparasitized aphids with (mean ± SE) 2.25 ± 0.25 eggs per aphid, whereas the single wasp treatment never resulted in more than one egg per aphid. After 24 h, female wasps were removed and aphids were reared out until they each laid a few nymphs prior to mummification. These nymphs were then reared out on excised bean shoots (as described above) and, once they molted to adult, each was transferred to a broad bean leaf placed abaxial side up on a layer of agar (1.5%) in a glass Petri dish (9.0 cm diam). All nymphs produced in each replicate were tallied and removed daily, and data collection continued for the first 7 days of adult life, the time required for the first daughter to complete development (Bayoumy et al., Reference Bayoumy, Ramaswamy and Michaud2015). In the control treatment, nymphs (n = 20) born of healthy mothers (n = 10) were similarly reared to adult and their life history parameters recorded.
In order to determine any effect of parasitoid larval gender on the maternal effects of parasitism for the aphids, the above experiment was repeated with one wasp per replicate and the development and reproduction of nymphs born to parasitized mothers was determined as above, and the parasitized mother was also reared until wasp emergence to determine the sex of the parasitoid. The hind tibia length (HTL) was recorded for neonate nymphs, and developmental time and HTL for resulting adults. Aphid tibia were photographed under a stereomicroscope equipped with a digital camera (Nikon Coolpix S10; Nikon Corporation, Tokyo, Japan) attached to a binocular microscope at 100× magnification and HTL was measured to a precision of 3 μm.
Development of L. fabarum in aphids that survived maternal parasitism
Synchronous cohorts of aphids, born to either healthy or parasitized mothers, were reared to the third instar as follows. Leaves of broad bean, each infested with ten treatment or control aphids (n = 20 control, 40 treatment), were placed abaxial side up on a layer of agar (1.5%) in a glass Petri dishes (9.0 cm diam). A single mated, 2-day-old L. fabarum female was then released into each dish and observed continuously under a stereomicroscope until she attacked (probed with the ovipositor) five aphids, until a total of 100 aphids were attacked in each treatment. Each attacked aphid was removed and placed on an excised bean shoot in a mini-cage sitting on a small container of water and reared to the emergence of wasps. We recorded wasp developmental times, the proportion of aphids parasitized, the proportion of mummies producing wasps, and the sex ratio. A subset of newly emerged wasps were killed by exposure to alcohol vapor, whereupon their hind tibias were photographed at 100× magnification, in the same manner as the aphids. Subsequently, the right ovary of female wasps was dissected on a glass slide in saline solution (7.5 g NaCl liter–1), whereupon the mass of eggs was photographed at 100× magnification. Egg images were digitally enhanced (in Adobe photoshop cs5) so that eggs could be accurately counted. For each wasp, a randomly selected group of 15–20 mature eggs was photographed at 240× magnification and the two-dimensional area of each egg was determined to an accuracy of 1 μm2 using ImageJ software. The average egg size of each female was estimated as the mean area of 15 images.
In order to assess wasp fitness, the remaining wasps derived from each treatment were paired (n = 15 in both cases) on their second day of life and each female was then provided with 15 s instar aphids on a bean leaf in a Petri dish for 8 h. The aphids from each replicate were then reared (as above) to the emergence of wasps and their developmental times, percentage of aphids mummified, percentage mummies emerging, female HTLs, egg loads, and egg 2D areas were all determined.
Calculation of life table parameters
Because aphid generation time is so short, mothers can continue to reproduce long after their daughters become reproductive, albeit at low to insignificant rates. Thus, estimates of fecundity used in life table calculations for a particular treatment are best tallied for a period equal to the developmental time in that treatment, plus one day to allow for adult maturation (Bayoumy et al., Reference Bayoumy, Ramaswamy and Michaud2015), so that lifetime fecundities will not lead to underestimates of r m. Therefore, estimates of age-specific survival (lx) and fecundity (mx) were calculated for individual aphids using data from the first 7 days of adult life. Net reproductive rate, R 0, was defined as the product of age-specific survival and age-specific fecundity (R 0 = Σlxmx), where lx is the proportion of females alive on a given day, and mx is the mean number of female births on that day (Southwood and Henderson, Reference Southwood and Henderson2000). The mean generation time [GT = (Σlxmxx)/(Σlxmx)], intrinsic rate of natural increase (r m = Ln R 0/T), and finite rate of increase (λ = er m) were all estimated according to Carey (Reference Carey1993) using the program MicroSoft Excel . The population doubling time (DT = Ln 2/r m) was calculated according to Mackauer (Reference Mackauer1983).
Statistical analysis
Percent aphids mummified, percent mummies emerging, and sex ratio data were analyzed by G-test using GLM with a binomial error distribution (Crawley, Reference Crawley1993). One-way ANOVA followed by Tukey's test was used to analyze biological features and morphological characteristics (SPSS, 1998).
Results
Aphid life history following maternal parasitism or superparasitism
Analysis of population growth parameters revealed significant fitness costs for A. fabae that survived maternal parasitism, including lower intrinsic rate of increase (r m), net reproductive rate (R 0), and finite rate of increase (λ), along with a longer generation time (GT) and population doubling time (DT) and these differences were amplified when mothers were superparasitized (table 1). The presence of a female parasitoid larva in the aphid mother had a greater negative impact on all A. fabae population growth parameters than did the presence of a male larva (table 2). Maternal parasitism by a male larvae decreased progeny body size, as estimated by HTL, of both neonate nymphs and the resulting adults compared to aphids born of healthy mothers, and maternal parasitism by female larvae decreased it even more, although developmental time was unaffected by these treatments (table 3).
Mean (±SE) population growth parameters for Aphis fabae born of mothers parasitized or superparasitized by Lysiphlebus fabarum in the third instar compared with unparasitized (Control) aphids
Values bearing different letters were significantly different between treatments (one-way ANOVA followed by Tukey's test, α = 0.05).
Mean (±SE) population growth parameters for Aphis fabae born to mothers parasitized in the third instar and containing either male or female larvae of Lysiphlebus fabarum
Values bearing different letters were significantly different between treatments (ANOVA, α = 0.05).
Mean (±SE) hind tibia length (HTL) and developmental times for Aphis fabae born of either healthy mothers (Control) or those parasitized in the third instar (Parasitized) and containing either male or female larvae
Values bearing different letters were significantly different between treatments (ANOVA, α = 0.05).
Development of L. fabarum in aphids that survived maternal parasitism
Aphids born of healthy mothers yielded a higher percentage of mummies when attacked individually by L. fabarum than did aphids born of parasitized mothers, and a higher percentage of these mummies yielded adult wasps (table 4). These metrics were also more reduced when the mother had been parasitized by a female larva than by a male. The sex ratio (% female) of wasps emerging from aphids of male-parasitized mothers was higher than in the control treatment, with the female-parasitized treatment yielded a sex ratio intermediate to the other two treatments.
Mean (±SE) percentage of aphids mummified, percentage of mummies emerged, and progeny sex ratio when mated Lysiphlebus fabarum females attacked (probed with the ovipositor) individual third instar Aphis fabae
Maternal aphids were either healthy (Control) or parasitized in the third instar (Parasitized) and containing either male or female larvae. Values bearing different letters were significantly different between treatments (GLM followed by LSD, α = 0.05).
Developmental times were shorter, and HTLs longer, when either male or female L. fabarum developed in control aphids as opposed to those born to parasitized mothers, and both egg load and 2D egg size were reduced (table 5). For HTL, female developmental time, and egg 2D area, the presence of a female larva in the maternal aphid had a more deleterious effect than did the presence of a male larva.
Mean (±SE) developmental times (DT, in days) and morphological characteristics of Lysiphlebus fabarum that developed in third instar Aphis fabae that were born of either healthy mothers (Control) or those parasitized in the third instar (Parasitized) and containing either male or female larva
Values bearing different letters were significantly different between treatments (ANOVA followed by Tukey's test, α = 0.05).
When wasps obtained in the preceding experiment were paired within treatments and the females provided with second instar A. fabae, treatment wasps parasitized fewer aphids than did control wasps (table 6). Furthermore, females from hosts maternally parasitized by female conspecifics parasitized fewer than those from hosts maternally parasitized by male conspecifics and the percentage of mummies yielding adult wasps was also reduced in the former treatment. Sex ratio did not vary as a function of parental host treatment. However, the developmental times of L. fabarum females were longer, and HTLs, egg loads, and 2D egg areas reduced relative to healthy controls, only when their parents emerged from hosts whose mothers were parasitized by female conspecific larvae (table 7).
Mean (±SE) percentage of second instar Aphis fabae (n = 15 per replicate) mummified, percentage of mummies emerged, and progeny sex ratio produced by Lysiphlebus fabarum females that had developed in either healthy aphids (Control) or those that survived maternal parasitism (Parasitized) by either a male or female larva
Values bearing different letters were significantly different between treatments (GLM followed by LSD, α = 0.05).
Mean (±SE) developmental times (DT, in days), hind tibia length (HTL), egg loads, and egg 2D areas for Lysiphlebus fabarum wasps whose parents had developed in Aphis fabae whose mothers were either healthy (Control) or had survived maternal parasitism (Parasitized) in the presence of either male or female larvae
Values bearing different letters were significantly different among treatments (ANOVA followed by Tukey's test, α = 0.05).
Discussion
Our results revealed that maternal effects due to embryonic development in the presence of an L. fabarum larva had negative developmental and life history impacts on A. fabae, and that the magnitude of these effects increased in superparasitized compared to singly-parasitized aphids. These reductions in aphid fitness resulted in reduced values of r m and ʎ, and increased values of GT and DT, indicating that such aphids would contribute less than healthy aphids to subsequent growth of the aphid population. These effects are likely due to the toxic effects of parasitoid venom (Digilio et al., Reference Digilio, Isidoro, Tremblay and Pennacchio2000) combined with the actions of teratocytes originating from the extraembryonic membrane as the egg hatches (Sabri et al., Reference Sabri, Hance, Leroy, Frere, Haubruge, Destain, Compere and Thonart2011). Teratocytes initially increase the activity of aphid nutritional endosymbionts that are mostly contained in bacteriocyctes, and then digest them along with aphid embryos and surrounding tissues in order to free up these nutrients for the developing parasitoid (Dahlman and Vinson, Reference Dahlman, Vinson, Beckage, Thompson and Federici1993; Falabella et al., Reference Falabella, Tremblay and Pennacchio2000; Pennacchio and Mancini, Reference Pennacchio, Mancini, Beckage and Drezen2012). Multiple ovipositions would increase the amount of venom and number of eggs (and thus teratocytes) in each host, thus accounting for the apparent dosage-dependent effects observed in superparasitized aphids.
In a similar study, Kaiser and Heimpel (Reference Kaiser and Heimpel2016) followed the offspring of Aphis glycines Matsumura born to mothers parasitized by Lysiphlebus orientalis Starý and Rakhshani and found that these aphids had higher fecundity than did the offspring of unparasitized aphids. They attributed this to the fact that the most developmentally advanced embryos (next in birth order) were larger in parasitized mothers than in unparasitized mothers, ostensibly because they benefitted from reduced nutritional competition with the smaller, more susceptible, aphid embryos killed by the teratocytes. A neonate parasitoid and its teratocytes are clearly unable to fully suppress the development of all aphid embryos in a relatively large, well-developed host, and this apparently has the potential to confer some advantages on the survivors, including attainment of a larger body size at birth. However, our results reveal that this is not invariably the case, and that the transgenerational benefits observed by Kaiser and Heimpel (Reference Kaiser and Heimpel2016) may be particular to that parasitoid–host association. A sublethal exposure to a low dose of a pesticide can sometimes stimulate rather than suppress certain biological functions, an effect referred to as hormesis (Cutler, Reference Cutler2013; Guedes and Cutler, Reference Guedes and Cutler2013). Similarly, the sublethal effects of maternal parasitism could potentially have both positive, or in the present case negative, effects on the subsequent development of large embryos able to survive the physiological stress.
The more deleterious effects of maternal parasitism by a female larvae compared with a male larvae were evident in the smaller HTLs of surviving aphids both at birth and at maturity, and greater negative impacts on their population growth parameters. The greater energetic demands of egg production relative to sperm production means that the fitness benefits of larger body size are usually greater for female insects than for males, absent any effects of sexual competition acting on males (Fairbairn, Reference Fairbairn1997; Chown and Gaston, Reference Chown and Gaston2010). When females are larger than males, as is generally true in the Aphidiinae, their development will place a larger resource demand on the host during development, resulting in greater competition for resources with the surviving host embryos. Thus, many solitary arrhenotokous parasitoids will selectively allocate female offspring to larger or better quality hosts (Charnov, Reference Charnov1982). Although this selective sex allocation is more common in idiobionts for which host size is fixed at the time of parasitism (Godfray, Reference Godfray1994), the size of aphidiine parasitoids has also been shown to correlate with the size of their host at the time of parasitism (Mackauer, Reference Mackauer1986). We infer that the greater nutritional demands of developing female parasitoids are likely responsible for these gender-specific effects on surviving aphid embryos, and suggest that nutritional limitation is at least one cause of the transgenerational impacts observed on aphids surviving maternal parasitism; female larvae compete more for nutrients with surviving embryos than do male larvae. The potential contributions of venom compounds cannot be ruled out, but these would not be expected to have a gender bias.
Although maternal parasitism did not affect the susceptibility of surviving host offspring to parasitism, or their suitability for L. fabarum development, it resulted in smaller progeny (as measured by HTL), longer developmental time, and diminished egg load and egg size (as estimated by 2D area) in female parasitoid progeny. This result indicates that the physiological impacts of surviving maternal parasitism extend to impaired host quality for the subsequent parasitoid generation, again squarely contradicting the report of a beneficial transgenerational effect by Kaiser and Heimpel (Reference Kaiser and Heimpel2016). In this case, the transgenerational effects of maternal parasitism benefit neither the aphid nor the parasitoid, and do not support the fecundity compensation hypothesis with respect to the host. The reduction in parasitism success (mummy formation) when L. fabarum attacked the progeny of maternally parasitized aphids is more difficult to interpret, as one might have expected negative transgenerational effects on aphid immunity or resistance to parasitism. This was not the case, although females may have assessed such aphids as being of lower quality and accepted them for oviposition less often following ovipositor insertion. However, the lower emergence of mummies from these hosts indicates reduced host suitability as well, so physiological impacts on developing parasitoids are also implicated, and once again the impact of a female parasitoid in the mother was greater than that of a male. The increased sex ratio resulting from hosts that developed in mothers parasitized by male larvae may reflect either differential sex allocation during oviposition, or greater juvenile mortality of male larvae in those hosts. Alternatively, the sex ratio result could easily represent a statistical anomaly without biological relevance, as both these explanations are difficult to reconcile with the assumption of greater resource-sensitivity in developing female parasitoids.
Our results indicate that the offspring of parasitized mothers can pose a hazard for foraging parasitoids that could potentially reduce their fitness and that of their offspring, especially since females do not appear to avoid them, and that the negative impacts for the parasitoid are transgenerational. Given that parasitoids and hosts exert strong and reciprocal selection pressures on each other during their coevolution, L. fabarum should experience selection to either avoid parasitizing late-stage hosts that are likely to achieve reproduction post-parasitism, or to recognize and avoid their progeny for oviposition. The intensity of such selection will depend strongly on the relative frequency of such hosts within aphid colonies, and will be higher for specialist species exploiting hosts that are relatively rare. Host-specialized aphidiines can have long patch residence times and may show considerable fidelity to their nascent host patch (Weisser and Volkl, Reference Weisser and Volkl1997). This is the case for species such as L. fabarum that are chemically camouflaged from ants and highly adapted to forage in ant-tended aphid colonies (Rasekh et al., Reference Rasekh, Michaud, Kharazi-Pakdel and Allahyari2010b) that tend to persist longer in time (Volkl and Stechmann, Reference Volkl and Stechmann1998). Although these factors should collectively serve to increase the probability that foraging L. fabarum encounter inferior quality hosts born of parasitized mothers, the species does not appear to have evolved any counteradaptations to mitigate the risk.
Aphid populations are characterized by ‘boom and bust’ cycles of abundance, with biotic sources of mortality typically intensifying during decline phases (Michaud, Reference Michaud, Hodek, van Emden and Honěk2012). As aphid populations inevitably crash, their natural enemies have typically completed one or more generations, amplifying their numbers at the same time their hosts are becoming increasingly scarce. It is precisely at this time that female parasitoids will be most likely to encounter hosts that have survived development in mothers parasitized by the previous generation, suggesting that the negative transgenerational effects of developing in such hosts will have their greatest demographic impacts precisely when the parasitoid population is itself declining and experiencing intensified intraspecific competition for hosts.
In conclusion, parasitism of A. fabae in later stages by L. fabarum results in reduced fitness of the offspring born to parasitized mothers and does not fully support the fecundity compensation hypothesis as proposed by Barribeau et al. (Reference Barribeau, Sik and Gerardo2010). Furthermore, when these offspring are parasitized, they yield parasitoids of reduced fitness, so any benefits of host reproduction post-parasitism accruing to either parasitoid or host are likely to be negligible beyond the production of some low-quality progeny.
Acknowledgements
The authors are grateful to Shahid Chamran University of Ahvaz for providing financial support for this research (Grant no. SCU.AP99.437).
Author contributions
AR and JPM conceived and designed the study, MRS conducted the experiments, AR analyzed the data, and AR and JPM wrote the MS.
