Reproductive biology of Palmistichus elaeisis ( Hymenoptera : Eulophidae ) with alternative and natural hosts

Mass rearing of parasitoids depends on choosing appropriate alternative hosts. The objective of this study was to select alternative hosts to rear the parasitoid Palmistichus elaeisis Delvare & LaSalle, 1993 (Hymenoptera: Eulophidae). Pupae of the lepidopterans Anticarsia gemmatalis Hübner, 1818 (Lepidoptera: Noctuidae), Bombyx mori Linnaeus, 1758 (Lepidoptera: Bombycidae) and Thyrinteina arnobia (Stoll, 1782) (Lepidoptera: Geometridae) were exposed to parasitism by females of P. elaeisis. The duration of the life cycle of P. elaeisis was 21.60 ± 0.16 and 24.15 ± 0.65 days on pupae of A. gemmatalis and B. mori, respectively, with 100.0% parasitism of the pupae and 71.4 and 100.0% emergence of parasitoids from the first and second hosts, respectively. The offspring number of P. elaeisis was 511.00 ± 49.70 and 110.20 ± 19.37 individuals per pupa of B. mori and A. gemmatalis, respectively. The reproduction of P. elaeisis from pupae of T. arnobia after six generations was similar to the other hosts.

Parasitoids are important for biological control of insect pests in agro-ecosystems due to their diversity and to the high levels of population regulation of insects in different orders (PENNACCHIO & STRAND 2006).Most of these natural enemies belong to several families of Hymenoptera, including Eulophidae, which are comprised of 297 genera and 4,472 species, thus far described in tropical and temperate areas exhibiting a wide range of biological traits.For example, some species are endo or ectoparasitoids, idiobionts or koinobionts.They may be solitary or gregarious, primary or hyperparasitoids, specialists or generalists and many of these species have been studied and used with success in biological control programs (GAUTHIER et al. 2000).
The success of biological control with parasitoids species depends on basic studies of hosts and other environmental features which could affect their development (PRATISSOLI et al. 2005, PASTORI et al. 2007, PEREIRA et al. 2009, 2010).Moreover, these natural enemies, reared on alternative hosts with lower production costs and without reduction on their efficiency when compared with their natural hosts, may have economic benefits (PRATISSOLI et al. 2005, ZANUNCIO et al. 2008).
The silkworm, Bombyx mori Linnaeus, 1758 (Lepidoptera: Bombycidae) can be reared with low cost and the pupae contain high levels of protein (GREISS et al. 2003, WANG-DUU et al. 2004).Anticarsia gemmatalis Hübner, 1818 (Lepidoptera: Noctuidae) has a short life cycle and can also be maintained on artificial diet in the laboratory (GREENE et al. 1976).The parasitoid P. elaeisis also has been reared on pupae of B. mori in the laboratory (BITTENCOURT & BERTI FILHO 1999, 2004).Therefore, B. mori and A. gemmatalis are potential alternative hosts for P. elaeisis and, for this reason the objective of this study was to select the most appropriate host for rearing the parasitoid and to evaluate its reproductive success from these alternative hosts, as opposed to the natural host T. arnobia.

MATERIAL AND METHODS
Considering rearing the lepidopteran hosts of the parasitoid P. elaeisis: 1) Dirphia moderata Bouvier, 1929 (Lepidoptera: Saturniidae) was reared using a methodology adapted from PEREIRA et al. (2008a).The parasitoid P. elaeisis was reared for one generation with the host D. moderata to avoid its conditioning before rearing it on B. mori and A. gemmatalis pupae.2) Bombyx mori caterpillars were reared in plastic trays (39.3 x 59.5 x 7.0 cm) with Morus alba Linnaeus, 1753 (Rosales: Moraceae) leaves supplied daily.The cocoons were transferred to plastic trays (28.3 x 36.0 x 7.0 cm) at 25 ± 2 ºC, 70 ± 10% relative humidity and photophase of 14 h.3) Eggs of A. gemmatalis were maintained on moistened paper filter inside Petri dishes (10.0 x 2.5 cm).Newly-emerged caterpillars were transferred to plastic containers where they were provided with artificial diet (GREENE et al. 1976) at 25 ± 1ºC, 70 ± 10% relative humidity and photophase of 14 h until pupation.4) Thyrinteina arnobia caterpillars were placed in glass tubes (8.5 x 2.4 cm), covered with cotton and provided with artificial diet (WILCKEN & BERTI FILHO 2006).
Adults of the parasitoid P. elaeisis were reared in glass tubes (14.0 x 2.2 cm) closed with a cotton wad and with honey droplets as food.Forty-eight to 72 h old pupae of B. mori were removed from the cocoons and exposed to parasitism by P. elaeisis females over the course of 24 h at 25 ± 2ºC, 70 ± 10% relative humidity and a photophase of 14 h.Forty-eight hour old pupae of D. moderata were exposed to P. elaeisis during 24 h.After emergence, adults of this parasitoid were divided into two groups and reared for three generations on alternative hosts A. gemmatalis or B. mori to remove preimaginal conditioning of parasitoids.Fifteen A. gemmatalis pupae (0.24 ± 0.004 g) and 15 24 h old B. mori pupae (1.2 ± 0.05 g) were placed individually in glass tubes (14.0 x 2.2 cm) and exposed to parasitism by six and 45 P. elaeisis females (PEREIRA et al. 2010), respectively, during 24 h at 25 ± 1ºC, 70 ± 10% relative humidity and photophase of 14 h.The ideal number of P. elaeisis for the different hosts was previously estimated based on the minimum number needed to overcome the host immunity (see PEREIRA et al. 2010).All P. elaeisis were removed from the tubes at the end of this period.
The reproductive performance of P. elaeisis on natural host T. arnobia was determined with adults reared for six generations on A. gemmatalis or B. mori pupae.Twenty-eight 48 h old pupae of T. arnobia were sexed, weighed (7 female = 0.60 ± 0.04 g and 7 male = 0.13 ± 0.01 g; 7 female = 0.69 ± 0.07 g and 7 male = 0.24 ± 0.02 g), and separately placed in glass tubes where they were exposed over 72 h to parasitism by P. elaeisis females reared for six generations on A. gemmatalis or B. mori pupae.Based on preliminary tests, we used six females of P. elaeisis per male pupa of T. arnobia, and 15 females per female pupa.
The duration of the life cycle (egg-adult); percent parasitism -discounting natural mortality of the host (ABBOTT 1925) -; percent emerging; number of parasitoid individuals emerged per pupa of each host; longevity of descendants and sex ratio were evaluated.
The experimental design was completely randomized using two treatments where P. elaeisis was reared with each alternative host (A.gemmatalis or B. mori) with 15 replications each with one host pupa.The same design was used, but each treatment had 14 replications represented by the biological aspects of P. elaeisis obtained from pupae of T. arnobia but on which they had been previously reared on A. gemmatalis or B. mori.The treatments were submitted to analysis of variance (ANOVA) followed by the F test using the software SAEG 8.0.Percent parasitism and emergence of P. elaeisis were analyzed with general linear models (GLM) of binomial distributions (p р 0.05) using the R Statistical System (IHAKA & GENTLEMAN 1996).
The length of the body (head to the abdominal extremity) (F = 15.445,p = 0.0005) and the width of the head capsule (F = 35.196,p = 0.0001) of P. elaeisis females emerging from B. mori pupae increased when compared to those of A. gemmatalis.However, the length of the body (F = 2.135, p = 0.155) and the width of the head capsule (F = 3.903, p = 0.06) of males were similar on both hosts (Tab.I).
The longevity of P. elaeisis females and males emerging from B. mori and A. gemmatalis was similar (F = 2.147, p = 0.147) for females (F = 0.89, p = 0.0001) for males (Tab.I).The sex ratio was similar for offspring originating from A. gemmatalis and B. mori (Tab.I).

DISCUSSION
The offspring of P. elaeisis showed a shorter development time on A. gemmatalis pupae, which may be due to differences of nutritional resources between hosts.Thus, A. gemmatalis may have a reduced availability of nutritional resources which stimulates the parasitoids to develop faster, but with a smaller size.On the other hand, parasitoids can adjust the number of its population according to the size of the natural host, thus avoiding sibling competition for a limited resource (ZAVIEZO & MILLS 2000).Furthermore, the parasitoids had increased emergence from B. mori than from A. gemmatalis, indicating that host quality can vary with the host (VINSON & IWANTSCH 1980, JERVIS et al. 2008).These results demonstrate that the host species affect the development period of this parasitoid (BITTENCOURT & BERTI FILHO 2004).
The size of P. elaeisis adults from B. mori and A. gemmatalis pupae were adequate for quality control in their production and use due to similarities in the biological parameters of P. elaesisis from T. arnobia.This is important, because the body size in many parasitoids is positively correlated with important functional traits including mating, fecundity, reproductive longevity, emergence of progeny and sex ratio (SAGARRA et al. 2001, MOREIRA et al. 2009).
The similar longevity of P. elaeisis females and males when reared on B. mori and A. gemmatalis pupae shows that this parasitoid was not affected by these hosts.This has also been reported for Hyssopus pallidus (Askew, 1964) (Hymenoptera: Eulophidae) on Cydia molesta (Busck, 1916) and Cydia pomonella (Linnaeus, 1758) (Lepidoptera: Tortricidae) pupae (HÄCKERMANN et al. 2007).However, it differs from results for M. acasta when developing on C. erythrocephala pupae of different ages (IMANDEH

Table I .
Reproductive characteristics (mean ± standard error) of P. elaeisis when reared on pupae of B. mori or A. gemmatalis.Values which differ between hosts (F-test at 5% probability) are shown in bold.TableII.Reproductive characteristics (mean ± standard error) of P. elaeisis when reared on pupae of T. arnobia after six generations on pupae of B. mori or A. gemmatalis.