Parasitoid Production Research Articles

Towards development of a parasitoid cottage industry of the parasitoid wasp Habrobracon hebetor (say): optimum rearing and releases conditions for successful biological control of the millet head miner Heliocheilus albipunctella (De Joannis) in the Sahel

Augmentative biological control by the parasitoid Habrobracon hebetor (Say) (Hymenoptera: Braconidae) is the most promising strategy to control millet head miner, Heliocheilus albipunctella (De Joannis) a major insect pest of pearl millet in the Sahel. As H. hebetor survival is somehow challenging during the nine month long off-season when the host, H. albipunctella is in diapause, there needs to be a sufficient supply of parasitoids for fresh release each year. Therefore, the aim of this study was to establish a small-scale parasitoid rearing process adjusted to the Sahel conditions that can be scaled-up as necessary. We conducted experiments to fine-tune and standardize the rearing technique of H. hebetor for cottage industrial use. The results showed that parasitoids fed with 30% honey solution and supplied daily with one late-larval-stage Corcyra cephalonica Stainton (Lepidotera, Pyralidae) produced highest number of progeny. The optimal times for mating and egg fertilization, was achieved when a male and female pair was confined for 24 h in a 30-cc vial. Our findings indicated that, compared with the conventional rearing method -2 females supplied once with 25 C. cephalonica larvae-, this new method resulted in 14-times greater parasitoid production. Furthermore parasitoid female can be stored for up to three weeks at fluctuating 23–32°C temperature and 25%–80% relative humidity for numbers accumulations prior to on-farm augmentative releases without altering its fitness.

Occurrence, Seasonal Abundance, and Superparasitism of Ooencyrtus kuvanae (Hymenoptera: Encyrtidae) as an Egg Parasitoid of the Spotted Lanternfly (Lycorma delicatula) in North America

The occurrence of egg parasitoid Ooencyrtus kuvanae (Howard) (Hymenoptera: Encyrtidae) on its new host, the spotted lanternfly (Lycorma delicatula (White) (Hemiptera: Fulgoridae)), was surveyed at 4 study plots in 2016 and 10 additional plots in 2017 in Pennsylvania through field collection and laboratory incubation. O. kuvanae adults were found on L. delicatula egg mass surfaces at two plots (ODSouth and Lutz) in 2016, but at none in 2017. The results of laboratory incubation showed that O. kuvanae adults were only recovered from host eggs collected at plot ODSouth in 2016, with adults emerging between 22 April and 2 May 2016 at 22 ± 1 °C, 40% ± 5% relative humidity (RH), and a 16:8 h photoperiod (light/dark). The overall parasitism at this study plot was 6.0% by egg mass and 1.2% by egg. Two oviposition sites contained parasitized L. delicatula eggs, with 12.3% (9.5–15.0%) host egg masses and 3.1% (1.3–5.0%) host eggs utilized by the parasitoid. O. kuvanae parasitism by egg was significantly higher on oviposition site ODSouth #7 than on ODSouth #8. No O. kuvanae adults were reared out of field-collected host eggs from the 10 plots in 2017. Seasonal abundance and superparasitism of O. kuvanae was examined at plot ODSouth in 2017. O. kuvanae-parasitized L. delicatula eggs were found on all four oviposition sites based on field monitoring of parasitoid adult emergence, resulting in a parasitism of 35.4% (18.8–55.6%) by egg mass and 2.2% (0.5–3.9%) by egg. No significant difference in parasitism by egg was observed among oviposition sites. O. kuvanae adults emerged in the field between 2 May and 1 June 2017. Superparasitism was confirmed for O. kuvanae on L. delicatula eggs based on parasitoid production (1.0–3.3 adults/parasitized egg) and adult exit holes (1–3 exit holes/parasitized egg). As the first parasitoid recorded from L. delicatula in North America, O. kuvanae has the potential to become an important biological control agent for L. delicatula in North America, with its well-synchronized life history in the spring, century-long field establishment, superparasitism, and female-biased progeny population. L. delicatula complements the gypsy moth well as an alternative host for O. kuvanae in the field.

Effects of host age and radiation dose in Diachasmimorpha longicaudata (Hymenoptera: Braconidae) mass-reared on medfly larvae of the tsl Vienna 8 genetic sexing strain

Augmentative release of parasitoids against Ceratitis capitata (Weidemann) is currently at an early stage in Argentina. The success of this environment-friendly strategy depends on suitable mass-rearing procedures. The integration of radiation in the rearing process improves both mass production and handling of fruit fly parasitoids. Diachasmimorpha longicaudata (Ashmead) is reared on larvae of tsl Vienna-8 C. capitata strain at the BioPlanta San Juan, Argentina. The aim of the current study was to identify the best combination of larval host age, exposure time, and host gamma-radiation dose to achieve the greatest parasitoid mass yield with the highest female-biased offspring ratio. The effect of host radiation doses on parasitoid fitness-related parameters from the first filial generation was also assessed. Firstly, host larvae aged 5–7 d-old were exposed to parasitoids for 30, 60, 90, 120, 150 and 180 min at a constant 4:1 host/parasitoid ratio. The most productive exposure procedure was 5–6 d-old larvae for 1.30 h. Secondly, batches of 180,000 naked host larvae aged 5–6 d-old were irradiated at 0, 60, 65, 70, 75, 80, 85, 90, 95, and 100 Gy. Suitable radiation doses for wholly suppressing host emergence were at 85–100 Gy. Thirdly, 5–6 d-old host larvae irradiated at 85, 90, 95, and 100 Gy were exposed to parasitoids. 6 d-old larva irradiated at 90 Gy was the most suitable combination to achieve the highest parasitoid emergence and female offspring values. Increasing radiation doses beyond 90 Gy did not significantly enhance parasitoid yield and did not improve female-biased offspring ratio. Fourthly, survival, fecundity, sex ratio, development time and parasitoid offspring size were not adversely affected by radiation. Gross fecundity and net reproductive rates, and sex ratio remarkably improved in comparison to that recorded on parasitoids reared on non-irradiated larvae. These findings greatly encourage the use of augmentative biological control against medfly in Argentina.

Response of two parasitoid species (Hymenoptera: Braconidae, Figitidae) to tephritid host and host food substrate cues

AbstractThe Neotropical‐native figitid Aganaspis pelleranoi (Brèthes) and the Asian braconid Diachasmimorpha longicaudata (Ashmead) are two parasitoids of Tephritidae fruit flies with long and recent, respectively, evolutionary histories in the Neotropics. Both species experienced a recent range of overlap. In Argentina, A. pelleranoi is a potential species in biological control programs against the pestiferous tephritid species, Anastrepha fraterculus (Wiedemann) and Ceratitis capitata (Wiedemann), whereas D. longicaudata is already used in open‐field releases against Medfly in central‐western Argentina. To characterize the host‐foraging strategies of A. pelleranoi and D. longicaudata, olfactometer experiments were conducted comparing responses to C. capitata and A. fraterculus larvae, in two kinds of food substrate: fruit and artificial larval medium. To control the possible influence of host larvae used for parasitoid rearing on olfactory response, two strains of both parasitoid species, reared on both tephrtid species, were studied. Volatiles directly emanating either from A. fraterculus or C. capitata larvae may be detected by both A. pelleranoi and D. longicaudata, although chemical stimuli originating from the combination of host larvae and the habitat of the host were preferred. However, olfactory cues associated with host larvae probably play a relevant role in host searching behaviour of A. pelleranoi, whereas for D. longicaudata, the host‐habitat olfactory stimuli would be highly essential in short‐range host location. The strain of the parasitoids did not affect host search ability on the two tephritid species evaluated. These evidences are relevant for mass production of both parasitoids and their impact following open‐field augmentative releases.

Parasitism, sexual dimorphism and effect of host size on Apocephalus attophilus offspring, a parasitoid of the leaf-cutting ant Atta bisphaerica.

Atta bisphaerica (Forel) is a leaf-cutting ant that specializes on grass and causes productivity losses in sugar cane fields and pastures. Three phorid species, Apocephalus attophilus (Borgmeier), Myrmosicarius grandicornis (Borgmeier) and Eibesfeldtphora bragancai (Brown), have been found parasitizing A. bisphaerica workers. These parasitoids can reduce plant material transported into the nests and ant traffic on the trails. Therefore, phorid flies have been considered potential biological control agents for leaf-cutting ants. Here, we evaluated which parasitoid species attack the leaf-cutting ant A. bisphaerica in pasture areas of a Brazilian Savannah-Atlantic Forest ecotone, parasitism rate, effect of host size, sexual dimorphism and sex ratio of the emerged parasitoids. Four nests of A. bisphaerica were selected in pasture areas from August 2016 to August 2017, with 400 workers collected from each colony monthly. A total of 23,714 A. bisphaerica workers were collected during the study, of which 236 (0.99%) were parasitized by phorid parasitoids. Apocephalus attophilus, E. bragancai and M. grandicornis parasitized 217, 17 and 2 ants, respectively. The higher parasitism rate was found in the hottest/rainy season of the year. Non-parasitized ants survived longer than those parasitized by A. attophilus. The larval and pupal periods of this parasitoid were 2.2 ± 0.8 and 16 ± 1.4 days, respectively, and the number of pupae per parasitized ant ranged from 1 to 7. The number of A. attophilus pupae per host increased with the host head size. Likewise, the size of the adult parasitoids also increased according to the host ant. Apocephalus attophilus females were larger than males and the sex ratio (male: female) did not differ from 1: 1. Our results showed that A. attophilus would be a potential biocontrol agent of leaf-cutting ants because it produces multiple larvae per host, allowing a great production of parasitoids with short developmental time and kills the host ant faster than other phorids.

Low‐temperature storage of Exorista larvarum puparia as a tool for assisting parasitoid production

AbstractTachinid parasitoids deserve to be better exploited as natural enemies of insect pests. The development of efficient mass‐rearing techniques for these entomophagous insects may encourage their use in biological control programs. Exorista larvarum (L.) (Diptera: Tachinidae) is a Palearctic species, which has been introduced in northern America for the control of the gypsy moth, Lymantria dispar (L.). The potential use of this polyphagous parasitoid of Lepidoptera against other forest and agricultural pests encourages research aimed at the improvement of techniques for its rearing, including protocols for storage at low temperature. This technology allows a certain degree of control over the speed of development of the stored insects and assists mass‐rearing facilities that have to match production with demand, especially during field outbreaks of pests. With the aim of developing storage protocols for E. larvarum, we investigated the effects of storage for 1–4 weeks of 1‐day‐old puparia at 15 °C. Lower temperatures (5 and 10 °C) and longer storage periods were excluded following the outcome of preliminary experiments. Parasitoid emergence and quality control parameters of the female flies obtained from the stored puparia were evaluated. In addition, female lipid body reserves were measured. The temperature of 15 °C proved to be suitable for all the durations tested, although some detrimental effects were observed following storage (e.g., lower longevity and fecundity). Our findings may prove useful to increase the flexibility of E. larvarum colony management.

Density of Diachasmimorpha longicaudata (Ashmead) and host Ceratitis capitata (Wied) larvae for the increase of parasitoid female production

ABSTRACT: The objective of the present study was to evaluate the ratio of Ceratitis capitata larvae/female of Diachasmimorpha longicaudata that results in the increase of parasitism and the production of females in the progeny. We used 8-day-old copulated D. longicaudata females with oviposition parasite experience and third instar larvae of C. capitata from rearing stock maintained at the Laboratory of Biological Control of Universidade Estadual de Montes Claros (Unimontes). Five densities of C. capitata larvae (10, 20, 30, 40, and 50) were offered to parasitoid females that were at five different densities (1, 2, 5, 10, and 15). The larvae were exposed to the parasitoid females by means of “parasitism units” in adapted cages for 1 hour. Sex ratio, percentage of parasitism, and pupal mortality were evaluated. Both host larval density and female parasite density influenced parasitism, female progeny production, and pupal mortality. Higher female production was observed in the progeny in ratios of 1:1 and 2:1 (larvae/females). Ratios above 1:2 reduced the sex ratio, and ratios below 1:1 caused high pupal mortality rates. The females had higher parasitism activity when they were in groups dividing the same space. Equal ratios of Ceratitis capitata larvae and parasitoid females resulted in improved efficiency in progeny females.

Oviposition Strategies of Tachinid Parasitoids: Two Exorista Species as Case Studies.

Oviposition strategies and mechanisms of host selection in parasitoids may be crucial for the success of parasitization and parasitoid production. These aspects are far less known in tachinid parasitoids than in hymenopteran parasitoids. Depending on the species, parasitoid flies may adopt direct or indirect oviposition strategies. The ‘direct type’ females lay eggs on or, in relatively a few species, inside the host body. This review describes cues involved in host selection by tachinid parasitoids and their oviposition strategies and presents 2 case studies in more detail, focusing on Exorista larvarum and Exorista japonica. These 2 polyphagous parasitoids of Lepidoptera lay macrotype eggs directly on the host cuticle. Both species have been used as biological control agents in inoculative release against the gypsy moth Lymantria dispar in the Northern United States. Improved knowledge of the mechanisms involved in host selection and oviposition strategies may increase the possibility of eliciting oviposition by these tachinids on target lepidopterous hosts (and even artificial substrates), thus facilitating their rearing and ultimately making their exploitation as regulators of target insect pests more feasible and efficient.

Impact of differences in nutritional quality of wingless and winged aphids on parasitoid fitness.

Winged aphids are described as hosts of lesser quality for parasitoids because a part of their resources is used to produce wings and associated muscles during their development. Host lipid content is particularly important for parasitoid larvae as they lack lipogenesis and therefore rely entirely on the host for this resource. The goal of this study was to determine to what extent winged and wingless aphids differ from a nutritional point of view and whether these differences impact parasitoid fitness, notably the lipid content. We analysed the energetic budget (proteins, lipids and carbohydrates) of aphids of different ages (third instars, fourth instars and adults) according to the morph (winged or wingless). We also compared fitness indicators for parasitoids emerging from winged and wingless aphids (third and fourth instars). We found that in third instars, parasitoids are able to inhibit wing development whereas this is not the case in fourth instars. Both winged instars allow the production of heavier and fattier parasitoids. The presence of wings in aphids seems to have little effect on the fitness of emerging parasitoids and did not modify female choice for oviposition. Finally, we demonstrate that Aphidius colemani, used as a biological control agent, is able to parasitize wingless as well as winged Myzus persicae, at least in the juvenile stages. If the parasitism occurs in third instars, the parasitoid will prevent the aphid from flying, which could in turn reduce virus transmission.

Effect of exposure time on mass‐rearing production of the olive fruit fly parasitoid, Psyttalia lounsburyi (Hymenoptera: Braconidae)

AbstractClassical biological control programmes rely on mass production of high‐quality beneficial insects for subsequent releases into the field. Psyttalia lounsburyi (Silvestri) (Hymenoptera: Braconidae) is a koinobiont larval–pupal endoparasitoid of tephritid flies that is being reared to support a classical biological control programme for olive fruit fly in California. The mass‐rearing system for a P. lounsburyi colony, initiated with insects originally collected in Kenya, was evaluated with the goal of increasing production, while at the same time reducing time requirements for rearing in a quarantine facility. We tested the effect of exposure time of a factitious host Ceratitis capitata (Wiedemann) (Diptera: Tephritidae), on parasitization, adult production, superparasitism, and sex ratio of P. lounsburyi and survival of the host. Parasitization rates were highest (31%) at 3‐ and 4‐hr exposure times, while adult production (i.e., emergence of wasp progeny) was highest (16%) at the 2‐hr exposure time. Superparasitism over the course of the study was 1.5% and did not appear to be a factor affecting parasitoid production. The sex ratio of wasp progeny was male‐biased and did not vary significantly over different exposure times. The rate of stings on host larvae increased with exposure time and was consistent with decreases in pupal eclosion from larvae and emergence rate of adult flies. When compared to current rearing procedures, the 2‐hr exposure time resulted in an overall 2.8‐fold increase in P. lounsburyi production when standardized for time.

Preimaginal Phases and Development of Spalangia gemina and Pachycrepoideus vindemiae (Hymenoptera: Pteromalidae) on House Fly (Diptera: Muscidae)

The development and morphology of immature phases of Spalangia gemina Boucek and Pachycrepoideus vindemiae Rondani are described from a laboratory reared culture maintained on the house fly Musca domestica L. (Diptera: Muscidae). Body width and length of pupal parasitoid were recorded. These 2 characteristics were determined for each larval instar and classified using cluster analysis in the SAS program. Developmental time from egg to adult of S. gemina and P. vindimiae was approximately 18 - 24 days and 15 - 18 days respectively at 25±3 °C and 45 - 65 % relative humidity. Eggs of S. gemina and P. vindemiae are hymenopteriform. Their incubation times are 24 - 48 h. The results show that the different numbers of larval instars in these parasitoids are well classified. The larvae of S. gemina has 3 instars with protuberances present on the last instar, whereas, P. vindemiae has 4 larval instars and the final instar lacks proturberances. The instars of P. vindemiae are morphologically similar except size and color of internal organs. Prepupae of both species are exarate and noticeably excrete meconium from the body. This information on preimaginal stages can be useful in the production and identification of parasitoids of the house fly.

Mass production of Diglyphus isaea (Hymenoptera: Eulophidae), a biological control agent of a Korean population of potato leaf miner Liriomyza huidobrensis (Blanchard) (Diptera: Agromyzidae)

AbstractThe potato leaf miner, Liriomyza huidobrensis (Blanchard), is an important pest of potato throughout the world, including Korea. A method was developed for mass rearing the parasitoid Diglyphus isaea (Walker) using faba bean, Vicia faba L. (Fabaceae), as the host‐plant and L. huidobrensis as the insect host. Faba bean plants were planted in pots and maintained in a greenhouse for about 15 d. Pots were then exposed to adult leaf miners in oviposition cages for 4 h. Plants containing late second to early third instar larvae were exposed to adult D. isaea in parasitoid cages for 24 h. The leaf area per pot after 15 d was 597.9 cm2, which produced 103.33 larvae per pot. The number of adult parasitoids emerging per pot was 72.5; about 41% of these were female. The daily cost of parasitoid production was USD20.95 per 1000 individual parasitoids. The methodology developed for D. isaea could be used to rear other ectoparasitoids such as Hemiptarsenus spp. and Pnigalio sp. with different insect hosts like L. trifolii. This is why this mass‐rearing information is important for securing test insect materials for ecological and biological study of Liriomyza species, and also for developing a biological control for Liriomyza species other than L. huidobrensis by mass production of associated natural enemies. We are facing rapid agro‐ecosystem changes including pest systems. Continuous monitoring of Liriomyza in solanaceous crops is needed.

The influence of feeding and host deprivation on egg load and reproduction of an aphid parasitoid, Aphidius gifuensis (Hymenoptera: Braconidae)

With a view to improving the establishment of Aphidius gifuensis Ashmead, a potential natural enemy for suppression of aphids on vegetables, the effects of host deprivation and honey feeding before release on the parasitoid’s egg load and reproduction were studied under laboratory conditions. Host deprivation significantly affected mummy production and survival rate of female parasitoids. A. gifuensis produced more mummies when exposed to a short period (1 and 2 days) of host deprivation, but when host deprivation lasted for 3 days, their mummy production sharply decreased. Offspring produced by parasitoids that had been deprived of hosts for 2 days were much heavier than those produced by parasitoids deprived of hosts for 1 and 3 days. However, host deprivation did not affect emergence rate or offspring sex ratio; the emergence rate was always above 80%, and the offspring sex ratio was always female biased irrespective of whether the host-deprivation period was 1, 2, or 3 days. Honey feeding greatly increased egg load, longevity and decelerated oosorption of A. gifuensis when hosts were absent, and significantly increased parasitoid mummy production in late age. We discuss the results in the context of augmentative biological control, with the view to understanding how to increase parasitoid performance after they are released.

Effects of Size and Age of the Host Musca domestica (Diptera: Muscidae) on Production of the Parasitoid Wasp Spalangia endius (Hymenoptera: Pteromalidae).

One method of control of house flies, Musca domestica L. (Diptera: Muscidae), and other filth flies is by repeated release of large numbers of pupal parasitoids such as Spalangia endius Walker. Rearing these parasitoids may be facilitated by understanding how host factors affect their production. Previous studies have examined the effects of host size and host age on parasitoid production, but have not examined the interaction between host size and host age or the effects with older females, which may be less capable of drilling tough hosts. Females were given hosts of a single size-age category (small young, small old, large young, or large old) for 2 wk. The effect of host size and of host age on parasitoid production depended on female age. On their first day of oviposition, females produced more offspring from large than from small hosts, but host age had no significant effect. The cumulative number of parasitoids produced in the first week was not significantly affected by host size or host age. However, the cumulative number of parasitoids produced over 2 wk was affected by both host size and host age, with the greatest number of parasitoids produced from small young hosts. Thus, not only are smaller hosts cheaper to produce, but these results suggest that their use may have no effect or a positive effect on the number of parasitoids that can be produced when females are ovipositing for a week or two.

Optimizing production of Tamarixia radiata (Hymenoptera: Eulophidae), a parasitoid of the citrus greening disease vector Diaphorina citri (Hemiptera: Psylloidea)

Tamarixia radiata (Waterston) (Hymenoptera: Eulophidae) established and spread throughout Florida following first release in 1999 for control of the Asian citrus psyllid (ACP) Diaphorina citri (Kuwayama) (Hemiptera: Psylloidea). Nevertheless, persistence of the pest and continued losses from citrus greening disease have created the need for more effective biological control, including mass rearing and augmentative release of T. radiata. However, information is lacking on efficiency of current rearing methods including ways to increase the proportion of hosts parasitized as a function of host density. This “functional response” has been studied under lab conditions, but not yet related to mass rearing efficiency. Three release rates of D. citri per flush shoot, four host: T. radiata ratios and five photophases were evaluated. Results indicated that 20 psyllid adults per flush provided optimal host density without excessive stickiness from honeydew. Sixty T. radiata females per cage of approximately 4800 nymphs provided most economical use of wasps and hosts. Progeny sex ratio was not influenced by parental sex ratio. A photophase of 12h maintained high fecundity. A type II functional response was observed with estimates of handling time and searching efficiency falling within previously estimated ranges. Modifications in rearing parameters suggested by this study improved parasitoid production three-fold compared to previous procedures.

Effects of temperature and nonionizing ultraviolet radiation treatments of eggs of five host insects on production of Trichogramma chilonis Ishii (Hymenoptera: Trichogrammatidae) for biological control applications

Trichogramma species are used worldwide as biological control agents. A particularly important application is mass-rearing and release for management of field-crop and warehouse insect pests. Eggs of commonly available hosts, Spodoptera litura, Corcyra cephalonica, Plutella xylostella and Helicoverpa armigera, were exposed to different temperature and nonionizing ultraviolet (UV) radiation treatments to consider whether particular combinations of treatments positively affected T. chilonis development. The treatments had different effects on three measures of parasitoid production: the rate of parasitization, adult emergence, and adult viability. At constant temperature (24, 28, 32°C), the mean percentage of egg parasitization was greatest on treatments of S. litura eggs. However, the mean percentage of adult emergence was significantly greater from C. cephalonica eggs at 28°C than from eggs in other treatments. The mean percentage of adult viability was found to be 83.9% from C. cephalonica eggs at 28°C. Ultraviolet radiation treatments (3, 6, or 9min at 254nm) significantly increased the mean percentage parasitization over that of the non-UV treatments. Also, the mean percentage of adult parasitoid emergence and viability were greater from C. cephalonica eggs exposed to non-ionizing UV radiation than from eggs of other hosts in all other treatments. This information can be used by managers of mass-rearing programs to increase the effectiveness of T. chilonis production for biological control of pest insects.

Effects of biotic and abiotic factors on phenotypic partitioning of wing morphology and development in Sclerodermus pupariae (Hymenoptera: Bethylidae).

Wing phenotype polymorphism is commonly observed in insects, yet little is known about the influence of environmental cues on the development or expression of the alternative phenotypes. Here, we report how both biotic and abiotic factors affect the wing morph differentiation of a bethylid parasitoid Sclerodermus pupariae. The percentage of winged female parasitoid progeny increased exponentially with temperature between 20 °C to 30 °C. Low intensity light and short-day photoperiod conditions also significantly induced the development of winged morphs. Interestingly, wingless maternal parasitoids produced more winged progeny. Furthermore, the degree of wing dimorphism was significantly influenced by the interactions between light intensity and maternal wing morphs. The percentage of winged female progeny was not significantly influenced by foundress densities, but increased significantly with parasitoid brood sizes. However, the percentage of male progeny increased significantly with the densities of maternal parasitoids. Our findings highlight the phenotypic partitioning of wing morphology and development in the parasitoid S. pupariae under varied environmental cues, and reveal the most favourable conditions for the production of winged females in this bethylid wasp. It is thus possible to increase winged female parasitoid production for the purposes of biological control by manipulation of biotic and abiotic conditions.

Host Egg Age and Supplementary Diet Influence the Parasitism Activity of Trichogramma zahiri (Hymenoptera: Trichogrammatidae).

Mass production of egg parasitoids mostly depends on the age of the host. Generally old eggs are less preferred by egg parasitoids, which can discriminate between eggs of different ages by using chemical cues. This study was designed to determine the preference, development, and arrestment of Trichogramma zahiri Polaszek (Hymenoptera: Trichogrammatidae) parasitizing eggs of its native host, the rice hispa, Dicladispa armigera (Olivier) (Coleoptera: Chrysomelidae). Eggs of different ages, in addition, with or without supplementary foods were evaluated. T. zahiri preferred to parasitize 1-d-old eggs rather than 2-, or 3-d-old eggs by no-choice assays. However, although the percentage emergence of parasitoids is significantly lower from 2- and 3-d-old eggs, the sex ratio is unaffected. Parasitoids lived longer when 25% honey solution was provided with the host food. Significantly higher fecundity (38.5 eggs per female) and parasitoid emergence (94.6%) occurred when 25% honey solution was provided in the diet with host food, followed by 25% sugar solution, as compared to the control (only water as food). An average of 7.9 eggs were parasitized when one parasitoid was released per 10 rice hispa eggs. Ability of T. zahiri to parasitize egg increased with an increase in the number of eggs offered. We also found that inclusion of a fresh host egg with the supplementary diet improves the mass rearing of T. zahiri for commercial purposes.

English

Factitious hosts are largely used in parasitoid production. However, changes in parasitism capacity may happen when hosts are switched. Therefore, the ability of a parasitoid species to be reared on factitious host and still keep high level of parasitism on the natural target pest after successive rearing can determine parasitoid quality and must be investigated. Thus, we evaluated Telenomus remus parasitism on Corcyra cephalonica eggs compared with its natural host, Spodoptera frugiperda eggs, for different generations. After being reared on C. cephalonica, T. remus parasitism on S. frugiperda was evaluated to measure different T. remus biological parameters and parasitism capacity (parasitoid quality). Gradual increase in C. cephalonica eggs parasitized was observed over the generations, stabilizing on generation F7. The number of parasitized C. cephalonica eggs was similar among generations (from generation F7 to F19). Taking the lifetime parasitism into consideration, parasitism capacity is similar from T. remus reared on S. frugiperda eggs from those reared on C. cephalonica eggs (generation F19). When laboratory-produced T. remus on C. cephalonica eggs was exposed to the natural host, parasitism was higher on F5 generation and stable from generations F5 to F19. Therefore, parasitoids did not lose their ability to parasitize eggs of natural host assuring good quality of the laboratory-produced parasitoid using C. cephalonica eggs as factitious host.   Key words: Spodoptera frugiperda, Corcyra cephalonica, pre-imaginal condition, egg parasitoid, biological control.

Impacts of Nosema sp. (Microsporidia: Nosematidae) on the sugarcane borer, Diatraea saccharalis (Lepidoptera: Crambidae)

In Brazil, the sugarcane borer, Diatraea saccharalis (Fabricius, 1794) (Lepidoptera: Crambidae), is controlled with massive releases of the hymenopteran parasitoid Cotesia flavipes Cam. (Hymenoptera: Braconidae); over 3 million hectares of sugarcane are treated annually with 18 billion parasitoids. In order to meet this demand, parasitoids are produced in D. saccharalis under laboratory conditions where a Nosema sp. is reported to be an important problem in mass rearing of the host. The goals for this work were to study the pathogenicity of the Nosema sp. and the progression of the disease in the host under laboratory conditions. The average median lethal time (LT50) of Nosema sp. in first instar D. saccharalis varied from 9±0.3 to 42±2.3days at concentration of 5×105–0.5 spores/mm3 artificial diet (107–10 spores/μl). For third instar, the average of LT50 ranged from 32±0.7 to 37±0.7days at concentration of 5×105–5×102 spores/mm3 artificial diet (107–104 spores/μl in saline). The concentration necessary to cause 50% mortality (LC50) of first instar larvae was 5.6 (0.9–17.6) spores/μl and the estimated LC50 for third instar larvae was 1,200 (200–4700) spores/μl. The impacts of Nosema sp. on D. saccharalis were analyzed for first instar larvae fed 0.5 spores/mm3 artificial diet. Duration and viability of the larval and pupal stages, adult longevity, pupal weight and fertility life table were measured for offspring of mating pairs composed of infected females and uninfected males or infected males and uninfected females and compared to offspring of uninfected pairs. Nosema sp. infection resulted in adverse effects on all biological parameters measured except for the duration of the larval and pupal stages and the weight of the male pupae, which did not differ statistically between infected and uninfected groups. The intrinsic rates of growth (rm) were greater for uninfected pairs compared to pairs with either male or female infected. The growth rate of individual larvae produced by uninfected adults was 48.2% faster than of larval offspring of infected females and it was negative (−0.003) when males were infected. Our study confirms the negative impact of the Nosema sp. in mass rearing of D. saccharalis for parasitoid production but shows potential for use as a microbial control agent of the sugarcane borer.