Influences of host size and host species on theinfectivity and development of Heterorhabditismegidis (strain NLH-E87.3)

The infectivity, time to first emergence of infective juveniles (IJs), total number of IJs per insect and IJs body length of the entomopathogenic nematode Heterorhabditis megidis (strain NLH-E87.3) after development in larvae of two insect hosts, Galleria mellonella (greater wax moth) and Otiorhynchus sulcatus (vine weevil) was studied. At a dose of 30 IJs, larvae of G. mellonella show to be significantly more susceptible than O. sulcatus larvae. At a dose of one IJ, vine weevil larvae were more susceptible. The number of invading infective juveniles (IJs) increased with host size while the host mortality at a dose of one IJ decreased with the increase of host size. Time to first emergence was longer at a dose of one IJ per larva and increased with the increase of host size in both insect species. Reproduction of IJs differed between host species, host sizes and doses of nematodes. Generally, the IJs body size increased with an increasing host size. The longest infective juveniles were produced at the lowest IJ doses. Results are discussed in relation to the influence of different host species and their different sizes on the performance of H. megidis (strain NLH-E87.3) as a biological control agent.     

Factors governing host discrimination byOpius dimidiatus (Ashmead) (Hymenoptera: Braconidae)

The detection of, and response to, parasitized hosts by female parasitoids can involve a number of complex phenomena, including the ability of females to discriminate between unparasitized and parasitized hosts, the physiological state of females, and the nature and longevity of the cues they are detecting. The discriminatory ability of Opius dimidiatus,a solitary endoparasitoid of Liriomyza trifoliiwas examined. Experiments showed, first, that when presented with a choice of unparasitized hosts and hosts which they had previously parasitized, O. dimidiatusfemales could discriminate between them, both upon encounter (before probing) and after probing with the ovipositor. It was further demonstrated that the detection of parasitized hosts was time dependent: females could discriminate on the basis of antennal examination for up to 2.5 h after the first egg was laid. Postprobing discrimination lasted for up to 3.5 h. Some of the causal and evolutionary factors resulting in superparasitism are discussed.     

Survival of Steinernema masoodi and S. carpocapsae (Rhabditida: Steinernematidae) on pigeonpea and chickpea after foliar application

Abstract

The survival of Steinernema masoodi and S. carpocapsae (Rhabditida: Steinernematidae) was investigated after foliar application on pigeonpea and chickpea twigs, respectively, at flowering and fruiting stage. The concentration used was 2500 infective juveniles (IJs)/ml water for both the species. On pigeonpea, the mean number of IJs of S. masoodi found alive were 303.4, 158.4 and 51.6 after 0, 30 and 60 minutes of spray in evening hours whereas 236.1, 44.4 and 6.8 IJs were found alive when sprayed in morning hours, respectively. S. masoodi survival at 30 minutes post-spray in the morning was on par with 60 minutes post-spray in the evening hours. On chickpea, the mean numbers of IJs of S. carpocapsae were 165.4, 65.8, 4 and 0 at 0, 1, 2 and 3 h post-spray in the morning hours whereas in the evening spray, 159.4, 111.8, 83.8 and 11.4 IJs found alive at 0, 1, 2 and 3 h post-spray, respectively. Overall, nematode survival in the evening hours was higher compared to morning spray at a given time. Addition of glycerine and UV retardant improved the survival of nematode. Results indicated that survival rate of IJs decreased fast and viability remained up to 3 h and in evening hours very few nematodes remained alive. Serious attempts are needed to improve the survival of nematodes after foliar spray by adding efficient adjuvant, humectant, antidesiccant and/or UV retardant for the management of aerial insect pests.     

Analysis of multiparasitism by Eupelmus vuilleti (Craw) (Eupelmidae) and Dinarmus basalis (Rond) (Pteromalidae) in the presence of one of their common hosts,Bruchidius atrolineatus (Pic) (Coleoptera Bruchidae)

Bruchidius atrolineatus (Pic) is a tropical beetle (Coleoptera Bruchidae) that develops during the larval and pupal stages in the seeds of a legume Vigna unguiculata (Walp). Two species of Hymenoptera, Dinarmus basalis (Rond) and Eupelmus vuilleti (Craw), solitary ectoparasitoids of the larvae and pupae of B. atrolineatus, were introduced successively in the presence of their hosts, varying the interval between the two introductions. When D. basalis females were introduced 24 h, 3 days or 7 days after E. vuilleti, multiparasitism was low. The females had low fecundity, and their eggs were not distributed randomly over the different available hosts. When E. vuilleti females were introduced second, they oviposited on the different hosts availabe and did not avoid multiparasitism. The presence of hosts already parasitised by D. basalis increased the reproduction of E. vuilleti, and the fecundity of the females was higher than in control batches with E. vuilleti alone. E. vuilleti seems capable of detecting the ovipositor shafts drilled by the D. basalis females, and by introducing its own ovipositors killing the D. basalis eggs or larvae. When interspecific competition was occurring the number of E. vuilleti adults emerging from the seeds was no different from that observed in control batches with E. vuilleti alone, and there were always fewer D. basalis adults than in control batches (D. basalis alone). This interspecific competition reduces the influence of the two parasitoids in the biological control of bruchid populations.     

Using hosts of mixed sizes to reduce male-biased sex ratio in the parasitoid wasp, Diglyphus isaea

Overproduction of males in mass rearing of parasitic Hymenoptera contributes to higher costs for biological control because only females directly kill pests. We present a technique, based on manipulating host composition, to generate less male‐biased sex ratios in parasitoid species that adjust their sex allocation in response to relative host size. Our system consisted of chrysanthemum, Dendranthema grandiflora Tzvelev var. ‘Miramar’; a leafminer, Liriomyza langei Frick (Diptera: Agromyzidae); and a commercially available parasitoid, Diglyphus isaea (Walker) (Hymenoptera: Eulophidae). We compared the offspring sex ratios of D. isaea females presented with different compositions of L. langei larvae on chrysanthemum. Presenting individual females with only large hosts increased mean sex ratio from 32 to 67% male over 2 days. However, presenting individual females with progressively larger hosts over 1 or 2 days reduced mean sex ratio from 90 to 100% male to less than 30% male. Groups of females produced sex ratios around 58% male if presented with both plants infested by only small hosts and plants infested by only large hosts. In comparison, groups of females produced sex ratios around 48% male if presented with plants infested by both small hosts and large hosts. We compared the use of both small hosts and large hosts to only large hosts for simulated mass rearing of wasps over 8 weeks. Using both small hosts and large hosts produced similar numbers of wasps as using only large hosts, but reduced mean sex ratio of weekly cohorts from 66% male to 56% male. The two techniques produced females of similar size, but using both large hosts and small hosts produced slightly smaller males than using only large hosts. The use of both small hosts and large hosts for mass rearing of D. isaea could reduce actual costs of females by 23%.     

Pathogenicity of five species of entomopathogenic nematodes (Steinernematidae and Heterorhabditidae) to the ixodid tick Dermacentor silvarum Olenev (Acari: Ixodidae)

We determined the mortality of adult tick Dermacentor silvarum Olenev after it was exposed to five entomopathogenic nematode species: Steinernema carpocapsae BJ (Sc BJ), S. glaseri NC32 (Sg NC32), S. ceratophorum D43 (Sc D43), S. feltiae Otio (Sf Otio) and Heterorhabditis bacteriophora E-6-7 (Hb E-6-7). All five species had lethal effects on adult ticks, and caused significant decreases in the amount of eggs laid by engorged female ticks (P < 0.05). Among them, Hb E-6-7 and Sc BJ were the most pathogenic to female adult ticks, with mortalities ranging from 70 to 90% (P < 0.05). Engorged females were more susceptible than unfed and partially fed females. The cumulative mortalities of engorged females exposed to Hb E-6-7 and Sc BJ for 14 days were 90%, with LT₅₀ at 6.3 and 7.0 days, respectively. Dose-dependent effect was observed in the oviposition of the ticks after they were exposed to nematodes at concentrations of 1000–5000 IJs/dish. When the concentration was higher than 5000 IJs/dish, dose dependent effects disappeared (P > 0.05). All five nematode species were lethal to unfed male ticks, and there was significant difference in mortality when compared to the control group (P < 0.05); however, the pathogenicity varied among them.     

Host influences on the pathogenicity of Heterorhabditis megidis

The infectivity of infective juveniles(IJs) of Heterorhabditis megidis (strain NLH-E87.3) produced on small, medium and large larvae ofGalleria mellonella, and on medium and largelarvae of Otiorhynchus sulcatus was tested underlaboratory conditions against G. mellonella andO. sulcatus larvae. Infective juvenilesoriginating from small G. mellonella exposed toan initial dose of one IJ were more infectious thanthose from small cadavers exposed to a dose of 30 IJs.Independent of the initial inoculum size, IJs fromsmall cadavers of G. mellonella were moreinfectious than those from medium and large cadavers.At a dose of one IJ per larva, IJs originating frommedium size O. sulcatus cadavers were moreinfective against G. mellonella than againstO. sulcatus larvae. Large G. mellonellalarvae were less susceptible to all IJ batches thanmedium and small sized larvae.     

In vitro production of the biological control agent Heterorhabditis indica SL0708 in different agar media

ABSTRACT

Heterorhabditis indica SL0708 is an entomopathogenic nematode isolated from Valle del Cauca-Colombia, whose bacterial symbiont, Photorhabdus luminescens subsp. akhurstii SL0708, has potential to control pests of economic importance in Colombia. Since in vivo production does not supply its demand, this investigation evaluated H. indica SL0708 production on different agar media. Five culture media (I, II, III, IV and V) were evaluated for productivity and pathogenicity of infective juveniles (IJs). IJs emerged between 11 and 16 days after inoculation in all media, with a total of 2.7?×?10⁴ and 4.7?×?10⁶ IJs produced during 15 days after IJs emergence, with maximum productivity at day five and high variability. Pathogenicity to Galleria mellonella larvae was not significantly different between in vitro and in vivo produced IJs on all media tested. Media IV and V were selected for their higher productivity. Subsequently, nematode inoculum size was evaluated in selected media at 2000, 4000 and 6000?IJs ml^?1, but significant differences were not observed in productivity and pathogenicity. Lastly, lipid source influence was evaluated in medium IV comparing canola, olive and soy oils. None of the plant-based oils had a significant effect on IJs production and pathogenicity. A medium was selected for H. indica SL0708 IJs production which was suitable in terms of productivity, culture time and pathogenicity of IJs produced. The medium and parameters selected in this study could be applied as an alternative for mass production of this entomopathogenic nematodes.     

Infectivity of Steinernema mushtaqi (Rhabditida: Steinernematidae) against insect pests and their mass production

The infectivity of entomopathogenic nematode (EPN), Steinernema mushtaqi was tested against legume pod borer, Maruca vitrata, tobacco caterpillar, Spodoptera litura, blue butterfly, Lampides boeticus, red hairy caterpillar, Amsacta moorei, brown bug, Clavigralla gibbosa, mealy bug, Centrococcus somatics, fruit borer, Earias vittella and green bug, Nezara viridula larvae and in vivo mass production of the above-tested species of EPN have been carried out during 2008. S. mushtaqi was found to be more pathogenic to A. moorei, as it brought about 100% mortality within 48 h, than to S. litura, L. boeticus, N. viriduala and E. vittella, as mortality occurred within 72 h; whereas this level of mortality was recorded in C. somatis, C. gibbosa and M. vitrata within 144 h. No mortality was observed in the control treatment. Multiplication of S. mushtaqi and the yield of infective juveniles (IJs) on these insects was the highest (0.94 × 10⁵ IJs/cadaver) from N. viriduala, followed by S. litura (0.76 × 10⁵ IJs/cadaver), L. boeticus as also C. gibbosa (0.31 × 10⁵ IJs/cadaver) and M. vitrata (0.20 × 10⁵ IJs/cadaver). Very poor populations of IJs were found from A. moorei (0.15 × 10⁵ IJs/cadaver) and C. somatics (0.01 × 10⁵ IJs/cadaver). No multiplication of IJs was found from the cadaver of E. vittella. This opens a new hope of utilising S. mushtaqi in the insect pests management programme.     

Effect of the pupal age of Calliphora erythrocephala (Diptera: Calliphoridae) on the reproductive biology of Melittobia acasta (Walker) (Hymenoptera: Chalcidoidea: Eulophidae)

A laboratory experiment was conducted to determine the effect of the pupal age of Calliphora erythrocephala (Meigen) on the reproductive biology (in terms of number, size, developmental time and longevity of progeny) of the parasitoid Melittobia acasta Walker. Melittobia acasta females of uniform size were given five C. erythrocephala pupae from one of four experimental age groups: 17–24 h, 24–48 h, 48–72 h and 72–96 h, for parasitization. The mean number of progeny produced from the experimental age groups for a 24 h period were 2, 7.6, 15.6 and 13.6, respectively. The parasitoids preferred hosts that were 48–72 h old. There were no significant differences in the mean development time (18.2 days) and size of progeny (mean head width = 0.38 ± 0.01 mm) produced from the experimental host age groups. The longevity of progeny from the four host age groups varied (range: 4–39 days), with those from the 48–72 h group living longest (mean = 25 days). The F₁ females from the 48–72 h group were reproductively more successful than those from the other groups, producing a mean F₂ progeny of 912 individuals when compared with 867, 801 and 757 individuals from the 24–48 h, 72–96 h and 17–24 h age groups, respectively. These findings make significant contributions to our knowledge of the breeding and utilization of this parasitoid for the biological control of dipteran flies in pigsties and poultry houses.     

Predation of entomopathogenic nematodes by <Emphasis Type="Italic">Sancassania</Emphasis> sp. (Acari: Acaridae)

Predation of the entomopathogenic nematode, Steinernema feltiae (Rhabditida: Steinernematidae), by Sancassania sp. (Acari: Acaridae) isolated from field-collected scarab larvae was examined under laboratory conditions. Adult female mites consumed more than 80% of the infective juvenile (IJ) stage of S. feltiae within 24 h. When S. feltiae IJs were exposed to the mites for 24 h and then exposed to Galleria mellonella (Lepidoptera: Pyralidae) larvae, the number of nematodes penetrating into the larvae was significantly lower compared to S. feltiae IJs that were not exposed to mites (control). Soil type significantly affected the predation rate of IJs by the mites. Mites preyed more on nematodes in sandy soil than in loamy soil. We also observed that the mites consumed more S. feltiae IJs than Heterorhabditis bacteriophora (Rhabditida: Heterorhabditidae). No phoretic relationship was observed between mites and nematodes and the nematodes did not infect the mites.     

Interspecific competition between entomopathogenic nematodes (Steinernema) is modified by their bacterial symbionts (Xenorhabdus)

Background  

Symbioses between invertebrates and prokaryotes are biological systems of particular interest in order to study the evolution of mutualism. The symbioses between the entomopathogenic nematodes Steinernema and their bacterial symbiont Xenorhabdus are very tractable model systems. Previous studies demonstrated (i) a highly specialized relationship between each strain of nematodes and its naturally associated bacterial strain and (ii) that mutualism plays a role in several important life history traits of each partner such as access to insect host resources, dispersal and protection against various biotic and abiotic factors. The goal of the present study was to address the question of the impact of Xenorhabdus symbionts on the progression and outcome of interspecific competition between individuals belonging to different Steinernema species. For this, we monitored experimental interspecific competition between (i) two nematode species: S. carpocapsae and S. scapterisci and (ii) their respective symbionts: X. nematophila and X. innexi within an experimental insect-host (Galleria mellonella). Three conditions of competition between nematodes were tested: (i) infection of insects with aposymbiotic IJs (i.e. without symbiont) of both species (ii) infection of insects with aposymbiotic IJs of both species in presence of variable proportion of their two Xenorhabdus symbionts and (iii) infection of insects with symbiotic IJs (i.e. naturally associated with their symbionts) of both species.     

Effect of delayed mating and prolonged engorgement on the reproductive fitness of female Amblyomma limbatum (Acari: Ixodidae) in marginal population areas

Reptile ticks mate while females are attached to their host. Following mating, females engorge, detach and then lay their eggs. This study examines whether the time that females of the reptile tick Amblyomma limbatum spend on hosts prior to mating and the time they take to engorge on hosts after mating influence their reproductive fitness, as measured by the number of viable eggs they produce. When compared with females that experienced no temperature-induced delay in mating, females attached for an initial period to hosts with body temperatures too low to induce mating had no decline in their reproductive fitness, once provided with suitable temperatures for mating. However, on hosts with suitable body temperatures for mating, female ticks that took longer to mate, took longer to engorge and had reduced reproductive fitness. In addition, females that spent more than 20 days feeding on hosts after mating had reduced reproductive fitness, irrespective of the time they spent on hosts prior to mating compared with females with shorter feeding periods. Thus, the time that A. limbatum females spent on hosts prior to mating and/or after mating has a significant bearing on the number viable progeny produced. The ecological implications of these results are discussed in relation to females colonizing marginal population areas at the edge of their distributional range.     

Host selection by the autoparasitoid Encarsia pergandiella on primary (Bemisia tabaci) and secondary (Eretmocerus mundus) hosts

In autoparasitoids, females are generally primary endoparasitoids of Hemiptera, while males are hyperparasitoids developing in or on conspecific females or other primary parasitoids. Female‐host acceptance can be influenced by extrinsic and/or intrinsic factors. In this paper, we are concerned with intrinsic factors such as nutritional status, mating status, etc. We observed the behavior of Encarsia pergandiella Howard (Hymenoptera: Aphelinidae) females when parasitizing primary (3rd instar larvae of Bemisia tabaci Gennadius [Homoptera: Aleyrodidae]) and secondary hosts (3rd instar larvae and pupae of Eretmocerus mundus Mercet [Hymenoptera: Aphelinidae]) for a period of 1 h. Females had different reproductive (virgin or mated younger) and physiological (fed elder or mated elder) status. Virgin females killed a large number of secondary hosts while investing a long time per host. However, they did not feed upon them. Mated females killed a lower number of secondary hosts and host feeding was observed in both consuming primary and secondary hosts. It was common to observe host examining females of all physiological statues tested repeatedly stinging the same hosts when parasitizing, killing or rejecting them. Fed elder females parasitized more B. tabaci larvae than E. mundus larvae or pupae, while investing less time on the primary host than on the secondary host. They also parasitized more B. tabaci larvae than mated elder females, while investing less time per host. The access of females to honey allowed them to lay more eggs.     

Offspring production and development in the parasitoid wasp Melittobia clavicornis (Cameron) (Hymenoptera: Eulophidae) from Japan

The development time, sex ratio and offspring production of Melittobia clavicornis reared with wild, facultative and factitious hosts are presented. Known hosts and different biological aspects presented in previously published reports are summarized and clarified. Immature development time was equivalent or slightly longer than that of other Melittobia species, and the sex ratio was approximately 97% female. Total offspring numbers were considerably lower than that of other Melittobia species using the same hosts. We report female dimorphism in this species for the first time. The number and relative proportion of brachypterous morph females produced was higher than that in other species of the genus.     

Orientation of Heterorhabditis megidis to insect hosts and plant roots in a Y-tube sand olfactometer

The host-searching behaviour of Heterorhabditis megidis strain NLH-E 87.3 in the presence of insect hosts and plant roots, offered individually and in combination, was studied using a newly developed Y-tube olfactometer filled with sand. Within a period of 24 hours infective juveniles (IJs) were significantly attracted to living G. mellonella larvae and caused 100% larval mortality. Otiorhynchus sulcatus larvae, however, did not elicit host-oriented movement of IJs and no larval mortality was observed. Roots of strawberry plants induced a negative response in IJs. The combination of strawberry roots and O. sulcatus larvae, however, strongly attracted IJs leading to 37% host mortality. It was shown that this type of Y-tube choice arena is a useful tool in studying the searching behaviour of entomopathogenic nematodes in a semi-natural habitat.     

Mutual interference in the mass-reared fruit fly parasitoid,Diachasmimorpha longicaudata (Hymenoptera: Braconidae)

Diachasmimorpha longicaudata is a solitary endoparasitoid produced in Mexico for the biological control of Anastrepha fruit flies (Diptera: Tephritidae). We studied the effect of mutual interference among conspecific foraging females to better understand the parasitoid-host dynamics established in the mass-rearing system of this species. We used a constant host availability of 60 third instar larvae of Anastrepha ludens (per oviposition unit type Petri dish) that were individually exposed for 3 h to 1, 2, 4, 8, 10, 14, and 20 D. longicaudata females, seven days old without oviposition experience. The following parameters were evaluated: total number of attacked hosts (i.e., larvae with at least one oviposition scar), number of attacked hosts per female, adult emergence percentage, and female proportion. We also performed a second assay at mass-rearing level, contrasting the current proportion used in mass-rearing (~?two host larvae per female) with the alternative treatments (5 and 7.5 host larvae per female). Results showed that the density of females foraging on a patch exhibits an inverse relationship to the number of hosts attacked by one female. The highest values for adult emergence (73.4%), patch exploitation (94.6%), and female proportion (0.86) were obtained in the treatments with 7.5, 6, and 3 host larvae per female, respectively. Under mass-rearing conditions, we found that a lower density of females per cage (~?five larvae per female) reduced superparasitism levels without affecting adult emergence and the proportion of females. This suggests that the mass-rearing efficiency of D. longicaudata could be improved by reducing the density of foraging females.

     

Isolation and identification of indigenous entomopathogenic nematode (EPN) isolate from Egyptian fauna

Soil samples from different Egyptian Governorates as Giza, Behera, Alexandria, Sohag, Qulupeia, El-Sadat City, Sharkia, Bani-Swif, North Sinai (El-Arish) and South Sinai (Ras-Seder), Tanta, Fayoum and Suez have been surveyed for isolation of new entomopathogenic nematode isolates. One isolate coded as IB was isolated from Sharkia (Belbies). Based on morphometric characters, the isolate was found to belong to Heterorhabditidae and identified as Heterorhabditis indica. The isolate individuals were reproduced by in vivo method using sixth larval instars of Galleria mellonella. The survival of native isolate H. indica was better at low temperature (15 °C) compared to room temperature (27 °C).The bioassay results showed reduction in stored IJs activity against G. mellonella compared with fresh IJs where the median lethal concentration LC₅₀ which recorded to be 46.87 for fresh IJs/ml then increased to 571.38 and to 1181.87 IJs/ml after storage for 2 and 4 weeks, respectively.     

Effect of host deprivation on egg quality,egg load,and oviposition in a solitary parasitoid,Chetogena edwardsii (Diptera: Tachinidae)

Solitary parasitoids are limited to laying one egg per host because larvae compete within hosts. If host encounter rate is low, females should not increase the number of eggs/host in response. The tachinid fly, Chetogena edwardsii,was used to evaluate the effect of host deprivation on egg accumulation, oviposition behavior, and egg quality in a solitary parasitoid. Females deprived of hosts for 2– 7 days accumulate about 1 day's supply of eggs. Egg output of deprived females once hosts are restored does not differ from that of control females. Deprived females retain one egg in the uterus where it undergoes embryogenesis. Maggots emerging from retained eggs are more likely to survive in hosts molting in 40 h or less after receipt of an egg than are maggots emerging from eggs fertilized shortly before oviposition. Egg retention is a consequence of host deprivation that permits females to broaden the range of hosts they can exploit to include soon-to-molt hosts and possibly multiply parasitized hosts.     

Egg allocation of the autoparasitoid encarsia tricolor at different relative densities of the primary host (Trialeurodes vaporariorum) and two secondary hosts (Encarsia formosa and E. tricolor)

Parasitism, offspring sex ratio and superparasitism of the facultative autoparasitoid Encarsia tricolor Foërster (Hymenoptera: Aphelinidae) when given access to arenae with different proportions of the primary host (Trialeurodes vaporariorum (Westwood)) and two species of secondary hosts (E. tricolor and Encarsia formosa Gahan) were studied.Parasitism and offspring sex ratio were not affected by female age in the range 3–10 days old. When the secondary hosts were young E. tricolor pupae, eggs were mostly laid on primary hosts, so the offspring sex ratio was more female-biased than expected, and secondary hosts were not superparasitized at all. When the secondary hosts were fully grown E. formosa larvae, superparasitism was small and offspring sex ratio was more male-biased than expected. E. tricolor females were able to discriminate between hosts previously parasitized by themselves and non-parasitized hosts.