Field collection of egg parasitoids of Pentatomidae and Scutelleridae in Northwest Italy and their efficacy in parasitizing Halyomorpha halys under laboratory conditions

The invasion of Halyomorpha halys (Stål) (Hemiptera: Pentatomidae) has caused severe economic damage in crops in North America and Europe, motivating research to identify its natural enemies, both in native and invaded areas. In its Asian native range, the main natural enemies are egg parasitoids, among which the most effective are Trissolcus japonicus (Ashmead) and Trissolcus mitsukurii (Ashmead) (Hymenoptera: Scelionidae) in China and Japan, respectively. In Europe, biology, host range, and impact of most native scelionid species are not well‐known. The present study aimed to investigate (1) presence and abundance of scelionid species that parasitize native Pentatomidae and Scutelleridae eggs in Northwest Italy, and (2) their ability to develop on H. halys eggs. During 4‐year field surveys, egg masses were collected and reared until bug nymph or adult parasitoid emergence. Then, the obtained scelionid females were tested for their ability to parasitize H. halys eggs in laboratory no‐choice experiments. Egg masses of all collected bug species were parasitized, and Telenomus spp. (Hymenoptera: Scelionidae), Trissolcus belenus (Walker), and Anastatus bifasciatus (Geoffroy) (Hymenoptera: Eupelmidae) were the most common parasitoids. In the laboratory, Trissolcus kozlovi Rjachovskij was the only species to significantly produce offspring from fresh H. halys eggs, whereas all tested Trissolcus species significantly induced host egg abortion (non‐reproductive effects). This study provides knowledge of the parasitoid species associated with native bugs, and represents a starting point to investigate the intricate interactions between native and exotic parasitoids recently found in northern Italy. These egg parasitoids could potentially be effective biocontrol agents of H. halys.     

Surveying native egg parasitoids and predators of the invasive Halyomorpha halys in Northern Italy

The invasive Halyomorpha halys (Heteroptera: Pentatomidae) is a key pest of fruits in the Emilia‐Romagna region of Italy. For the development of a sustainable management programme, knowledge of its native natural enemy community and its efficacy is essential. A three‐year field survey was conducted exposing H. halys egg masses in different types of habitats to investigate the efficacy of native natural enemies in reducing the H. halys populations in the Emilia‐Romagna region, where the stinkbug was first detected in 2012. Over the first year of the study, sentinel eggs from laboratory cultures were stapled to the underside of leaves in various host trees, whereas in following years H. halys adults were directly caged on branches in sleeve cages to allow natural oviposition. Over the examined years, low rates of parasitism (1%–3%) and predation (2%–5%) were observed. Parasitism was caused exclusively by the generalist parasitoid Anastatus bifasciatus.     

Intrinsic competition between two European egg parasitoids of the brown marmorated stink bug

Following the accidental introduction and spread of the invasive polyphagous agricultural pest Halyomorpha halys (Stål) (Hemiptera: Pentatomidae), the two European egg parasitoids Anastatus bifasciatus (Geoffroy) (Hymenoptera: Eupelmidae) and Ooencyrtus telenomicida (Vassiliev) (Hymenoptera: Encyrtidae) have been investigated for inundative biological control. Since the competititve outcome between the two generalist parasitoids is difficult to predict, intrinsic competition was investigated with a time-course development study. Both species readily oviposited in H. halys eggs containing eggs and early instar larvae of the competitor, but oviposition decreased when eggs contained late instar larvae and pupae. Ooencyrtus telenomicida offspring emergence from multiparasitized eggs was significantly lower than that from rearing controls, independent of the order of parasitization. Anastatus bifasciatus offspring emergence was not influenced by the presence of O. telenomicida when it parasitized as the first species, but emergence was decreased after oviposition in eggs containing O. telenomicida larvae and pupae. There was no indication that O. telenomicida can act as a facultative hyperparasitoid of A. bifasciatus. These results suggest that A. bifasciatus is the superior intrinsic competitor and no or minor negative implications for A. bifasciatus are expected if released in combination with O. telenomicida.     

A modified DNA barcode approach to define trophic interactions between native and exotic pentatomids and their parasitoids

The establishment of invasive Halyomorpha halys (Stål) outside of its native range may impact native species assemblages, including other pentatomids and their scelionid parasitoids. This has generated interest in defining species diversity and host‐parasitoid associations in this system to better understand the impact of invasive alien species on trophic interactions in invaded regions. Information on scelionid–pentatomid associations in natural habitats is lacking, and species‐level identification of these associations can be tenuous using rearing and dissection techniques. Naturally occurring pentatomid eggs were collected in areas where H. halys has established in Canada and were analysed using a modified DNA barcoding approach to define species‐level trophic interactions. Identification was possible for >90% of egg masses. Eleven pentatomid and five scelionid species were identified, and trophic links were established. Approximately 70% of egg masses were parasitized; parasitism and parasitoid species composition were described for each species. Telenomus podisi Ashmead was the dominant parasitoid and was detected in all host species. Trissolcus euschisti Ashmead was detected in several host species, but was significantly more prevalent in Chinavia hilaris (Say) and Brochymena quadripustulata (Fabricius). Trissolcus brochymenae Ashmead and Tr. thyantae Ashmead were recorded sporadically. Parasitism of H. halys was 55%, and this species was significantly less likely to be parasitized than native pentatomids. The scelionid species composition of H. halys consisted of Te. podisi, Tr. euschisti and Tr. thyantae. Although these species cannot develop in fresh H. halys eggs, we demonstrate that parasitoids attempt to exploit this host under field conditions.     

Comparative study of development parameters of four Ooencyrtus spp. (Hymenoptera: Encyrtidae) on natural and factitious hosts

Biological control approaches such as seeding and augmentation releases of populations of natural enemies mostly rely on the indoor production of predator or parasitoid species, often with the use of alternative prey/host species. In this study, we investigated several development parameters of four egg parasitoid species: Ooencyrtus fecundus, O. near fecundus, O. pityocampae and O. telenomicida, and compared their performance on their natural host, the variegated caper bug (CB) Stenozygum coloratum, and on an alternative, factitious host, the silk moth (SM) Bombyx mori. Survival was higher and development duration shorter in CB eggs, making the CB a better host for these congeners. However, adult longevity was generally longer for individuals that developed in SM eggs. Moreover, O. fecundus and O. pityocampae females that had developed in SM eggs displayed higher fecundity than all other female/host combinations. Survival also varied according to the age of the SM eggs: parasitoid survival rates were significantly higher in 9‐ to 12‐month‐old (post‐diapausing) eggs than in young (about 1 month old) ones. These results were probably influenced by differences among the egg sizes of the studied hosts. The number of non‐laying females and self‐superparasitism rates were exceptionally high in O. near fecundus. These findings suggest that SM eggs, and especially those which are being utilized after a long storage, could serve for mass rearing of the studied Ooencyrtus spp.     

Diving Into The Water: Cues Related to the Decision‐Making by an Egg Parasitoid Attacking Underwater Hosts

Although adult parasitoids spend a majority of their lives above ground, females of several species must search for their host in the water or on the soil. Adult parasitoids above ground can use a variety of sensory cues to detect their hosts from a distance. However, their sensory cues can be impaired from volatile chemicals, and their visual stimuli can be decreased while submerging or burrowing in the water of soil during their search for their hosts. Searching underwater or underground would incur high foraging costs, that is, time and energy consumption and increase risk of drowning. Therefore, to reduce such costs and increase searching efficiency, the decision on where to start submerging or burrowing for attacking hosts is important for parasitoids. Furthermore, there are no studies that have examined the cues of submerging or burrowing parasitoids on their exploit for the decision to attack their hosts. We have examined the cues used by the egg parasitoid Tiphodytes gerriphagus attacking underwater hosts. We compared the searching behaviors of T. gerriphagus among four oviposition site conditions. The four sites investigated were oviposition site with both host adult chemical residues and presence of eggs, with only the presence of eggs, with only the host adult chemical residues, and without any cue. Our results indicated that T. gerriphagus more frequently contacted and submerged at oviposition sites with the adult residues rather than at oviposition sites without them. Nonetheless, the presence of underwater host eggs did not affect the host‐searching behavior. This suggests that T. gerriphagus decided to submerge at the oviposition site in response to the adult residues. Furthermore, our observation also suggested that T. gerriphagus has already detected that the adult residues might be volatile before contacting the oviposition site. Finally, we will discuss the exploitation patterns of host‐searching cue by parasitoids that need to submerge from the context of its reliability and detectability problems.     

Egg load dynamics and the risk of egg and time limitation experienced by an aphid parasitoid in the field

Insect parasitoids and herbivores must balance the risk of egg limitation and time limitation in order to maximize reproductive success. Egg and time limitation are mediated by oviposition and egg maturation rates as well as by starvation risk and other determinants of adult lifespan. Here, we assessed egg load and nutritional state in the soybean aphid parasitoid Binodoxys communis under field conditions to estimate its risk of becoming either egg‐ or time‐limited. The majority of female B. communis showed no signs of egg limitation. Experimental field manipulations of B. communis females suggested that an average of 4–8 eggs were matured per hour over the course of a day. Regardless, egg loads remained constant over the course of the day at approximately 80 eggs, suggesting that egg maturation compensates for oviposition. This is the first case of such “egg load buffering” documented for a parasitoid in the field. Despite this buffering, egg loads dropped slightly with increasing host (aphid) density. This suggests that egg limitation could occur at very high host densities as experienced in outbreak years in some locations in the Midwestern USA. Biochemical analyses of sugar profiles showed that parasitoids fed upon sugar in the field at a remarkably high rate. Time limitation through starvation thus seems to be very low and aphid honeydew is most likely a source of dietary sugar for these parasitoids. This latter supposition is supported by the fact that body sugar levels increase with host (aphid) density. Together, these results suggest that fecundity of B. communis benefits from both dynamic egg maturation strategies and sugar‐feeding.     

Effects of Rag1 aphid‐resistant soybean on mortality,development, and preference of brown marmorated stink bug

The brown marmorated stink bug, Halyomorpha halys (Stål) (Hemiptera: Pentatomidae), poses a new threat to soybean, Glycine max (L.) Merrill (Fabaceae), production in the north central USA. As H. halys continues to spread and increase in abundance in the region, the interaction between H. halys and management tactics deployed for other pests must be determined. Currently, the soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), is the most abundant and damaging insect pest of soybean in the region. Aphid‐resistant soybean, mainly with the Rag1 gene, is commercially available for management of A. glycines. Here, experiments were performed to evaluate the effects of Rag1 aphid‐resistant soybean on the mortality, development, and preference of H. halys. In a no‐choice test, mortality of H. halys reared on Rag1 aphid‐resistant soybean pods was significantly lower than when reared on aphid‐susceptible soybean pods (28 vs. 53%). Development time, adult weight, and proportion females of surviving adults did not differ when reared on Rag1 aphid‐resistant or aphid‐susceptible soybean pods. In choice tests, H. halys exhibited a preference for Rag1 aphid‐resistant over aphid‐susceptible soybean pods after 4 h, but not after 24 h. Halyomorpha halys exhibited no preference when tested with vegetative‐stage or reproductive‐stage soybean plants. The preference by H. halys for Rag1 aphid‐resistant soybean pods and the decreased mortality when reared on these pods suggests that the use of Rag1 aphid‐resistant soybean may favor this emerging pest in the north central USA.     

Oviposition site preference and developmental performance of a gall‐inducing leafhopper on galled and non‐galled host plants

Oviposition preferences of herbivorous insects affect offspring performance. Both positive and negative links between oviposition preference and offspring performance have been reported for many species. A gall‐inducing leafhopper, Cicadulina bipunctata Melichar (Hemiptera: Cicadellidae), feeds on various Poaceae plants and induces galls of enhanced nutritional value for their offspring. Although gall induction by C. bipunctata improves nymphal performance, the oviposition preference of females between galled and non‐galled host plants is still unclear. In this paper, the nymphal performance and oviposition and feeding‐site preference of C. bipunctata were investigated using galled wheat, Triticum aestivum L., and non‐galled barley, Hordeum vulgare L., as host plants. The survival rate of C. bipunctata on wheat was significantly higher than on barley. In the choice test, significantly more eggs were laid into barley, whereas the number of eggs deposited on both hosts was not significantly different in the no‐choice test. The number of settling individuals per leaf area was not significantly different between wheat and barley, suggesting no clear preference for oviposition between these plants. Experience as a nymph with a growing host did not affect oviposition preference as adult female. The inconsistent correspondence between offspring performance and oviposition preference of C. bipunctata may reflect the high mobility of nymphs and/or differences in leaf area between host plants. The results indicate that the previous finding that oviposition preference and offspring performance are not always positively correlated in herbivorous insects is applicable to gall‐inducing insects.     

Trichobaris weevils distinguish amongst toxic host plants by sensing volatiles that do not affect larval performance

Herbivorous insects use plant metabolites to inform their host plant selection for oviposition. These host‐selection behaviours are often consistent with the preference–performance hypothesis; females oviposit on hosts that maximize the performance of their offspring. However, the metabolites used for these oviposition choices and those responsible for differences in offspring performance remain unknown for ecologically relevant interactions. Here, we examined the host‐selection behaviours of two sympatric weevils, the Datura (Trichobaris compacta) and tobacco (T. mucorea) weevils in field and glasshouse experiments with transgenic host plants specifically altered in different components of their secondary metabolism. Adult females of both species strongly preferred to feed on D. wrightii rather than on N. attenuata leaves, but T. mucorea preferred to oviposit on N. attenuata, while T. compacta oviposited only on D. wrightii. These oviposition behaviours increased offspring performance: T. compacta larvae only survived in D. wrightii stems and T. mucorea larvae survived better in N. attenuata than in D. wrightii stems. Choice assays with nicotine‐free, JA‐impaired, and sesquiterpene‐over‐produced isogenic N. attenuata plants revealed that although half of the T. compacta larvae survived in nicotine‐free N. attenuata lines, nicotine did not influence the oviposition behaviours of both the nicotine‐adapted and nicotine‐sensitive species. JA‐induced sesquiterpene volatiles are key compounds influencing T. mucorea females’ oviposition choices, but these sesquiterpenes had no effect on larval performance. We conclude that adult females are able to choose the best host plant for their offspring and use chemicals different from those that influence larval performance to inform their oviposition decisions.     

The reproductive capability of Ooencyrtus kuvanae reared on eggs of the factitious host Antheraea pernyi

Ooencyrtus kuvanae is a key egg parasitoid of Lymantria dispar (L.), an important defoliating pest in China and North America. We have developed mass rearing techniques for O. kuvanae and in this study compared the reproductive capacity of O. kuvanae when it was previously reared on the natural host, L. dispar or the factitious host, Antheraea pernyi Guerin‐Meneville. There was no significant difference in the oviposition period or total number of eggs laid between L. dispar‐reared and A. pernyi‐reared females. However, the mean number of offspring successfully emerging from those eggs was significantly larger from the A. pernyi‐reared females compared with L. dispar‐reared females. From this, we can conclude that, with respect to reproductive capability, eggs of A. pernyi are suitable factitious hosts for mass rearing of O. kuvanae.     

Specificity of systemically released rice stem volatiles on egg parasitoid,Trichogramma japonicum Ashmead behaviour

The yellow stem borer, Scirpophaga incertulas Walker (YSB), infested rice plants emit chemicals through the surface of their infested stems. These induce attractant activity and cause arrestment responses and ovipositional stimulation in its egg parasitoid, Trichogramma japonicum Ashmead. Laboratory experiments on short‐range host searching and oviposition were performed to assess the how these crude stem extracts and their fractions influence the biological control efficiency of Trichogramma. The activity of these chemicals as long‐range attractants was confirmed through wind tunnel bioassays. Stem borer‐infested plant extracts had enhanced the parasitization rate of T. japonicum, whereas host eggs treated with the extract from undamaged stems or solvent‐treated control failed to evoke changes in the parasitoid’s behaviour. A preliminary GC‐MASS analysis indicated the presence of several hydrocarbon compounds. The analysis also revealed qualitative and quantitative differences between the chemical profiles of the infested and non‐infested plants. We hypothesized that herbivore‐induced plant chemicals are released through the stem surfaces and attract T. japonicum, even over long distances. These cues elicit parasitoid arrestment on pest‐damaged plants and subsequently lead to the successful parasitization of the stem borer.     

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

The 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.     

Optimal biological parameters for rearing Ooencyrtus pityocampae on the new laboratory host Philosamia ricini

Biological control programmes involving Ooencyrtus pityocampae Mercet (Hymenoptera: Encyrtidae) have proved effective at reducing the damage caused by the pine processionary Thaumetopoea pityocampa Denis & Schiffermüller (Lepidoptera: Thaumatopoeidae). In this study, the biological variables that influence the parasitism of O. pityocampae on the new laboratory host Philosamia ricini Danovan (Lepidoptera: Saturniidae) have been investigated. Laboratory experiments were conducted under the conditions of 25 ± 1°C, 65 ± 5% R.H (relative humidity) and a photoperiod of 16 : 8 h (L : D = light : dark). The host egg age and parasitoid age are often regarded as being key factors influencing the emergence rate of O. pityocampae. The optimal age of host eggs for parasitization was 1–2 days, and the emergence rate was highest with 5‐day‐old female parasitoids. Thus, our results define the optimal conditions for the effective and economic rearing of parasitoids as follows: one 5‐day‐old female parasitoid per 50 (1–2)‐day‐old host eggs. The development time of O. pityocampae ranged between 19.5 and 22.6 days. Parasitoids that were exposed to bio‐honey survived 10.5 times longer than those that did not receive supplemental food. O. pityocampae was reared for more than nine generations on the eggs of P. ricini. Consequently, P. ricini has been found as a suitable new laboratory host for the mass rearing of O. pityocampae for the use of biological control programmes against T. pityocampa in future.     

Herbivore egg deposition induces tea leaves to arrest the egg‐larval parasitoid Ascogaster reticulata

Plants are able to activate direct and indirect defences against egg deposition by herbivorous insects. A known indirect defence is the production of synomones to help egg‐ and egg‐larval parasitoids to locate their hosts. The wasp Ascogaster reticulata Watanabe (Hymenoptera: Braconidae) is a solitary egg‐larval parasitoid of the moth Adoxophyes honmai Yasuda (Lepidoptera: Tortricidae), which lays eggs and feeds as caterpillars on the leaves of the tea plant Camellia sinensis (L.) Kuntze (Theaceae). Here, we studied whether or not oviposition by A. honmai induces tea plants to produce synomones that help the parasitoid to locate its host. An olfactometer bioassay suggested that synomones produced by the infested plants did not attract the parasitoid over a short range. However, a contact bioassay showed that tea leaves were induced to arrest the parasitoid 24 h after egg deposition and remained induced until the host‐egg masses were no more attractive to the parasitoids. Wing scales and deposits of adult moths and the contents of the egg masses did not induce the tea leaves to arrest the parasitoid, but the contents of the female moth's reproductive system did. Synomone induction was systemic: uninfested leaves in the vicinity of egg‐laden leaves also arrested the parasitoid.     

Increasing host age does not have the expected negative effects on the fitness parameters of an egg parasitoid

Host age is an important determinant of host acceptance and suitability for egg parasitoids. As host embryonic development advances, the quality of resources available to the parasitoid offspring typically declines, usually resulting in reduced acceptance levels by foraging females and lower offspring fitness. We examined the ability of the parasitoid Telenomus podisi Ashmead (Hymenoptera: Scelionidae) to parasitize and develop in Podisus maculiventris (Say) (Hemiptera: Pentatomidae) eggs of different ages. In laboratory experiments, we measured the effect of host age (6, 24, 48, 72, 96, or 120 h old) on parasitism rate and offspring fitness parameters such as survival, development time, sex ratio, and size. Contrary to our expectations, parasitism rate did not differ between host age treatments, nor did sex ratio allocation, offspring size, or the fecundity of newly emerged female offspring. However, parasitoid offspring had a longer development time with increasing host age. This trend was stronger for males than for females, which we suggest could reduce the degree of protandry among offspring emerging from older host eggs, thus increasing the rate of virginity upon leaving the emergence patch and resulting in more frequent off‐patch mating by female offspring in nature. Overall, our results suggest that all stages of P. maculiventris embryonic development are suitable for acceptance and development of T. podisi. Unlike most species of egg parasitoids, T. podisi has evolved mechanisms to utilize host resources, regardless of host developmental stage, with relatively minor fitness consequences.     

Oviposition and reproductive performance of a generalist parasitoid (Trichogramma pretiosum) exposed to host species that differ in their physical characteristics

The response of generalist egg parasitoids to alternative natural hosts that are present simultaneously is not well known. We investigated the behavior of Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae) in relation to two field hosts Helicoverpa armigera Hübner and Spodoptera litura Fabricius, in choice and no choice tests. We quantified the effects of natal host species and post-emergence adult age on the oviposition preference of the parasitoids. H. armigera eggs were consistently preferred over S. litura eggs, regardless of the natal host and adult age. When only S. litura eggs were available as hosts, they were parasitized at statistically similar rates to H. armigera eggs (average of 17 ± 2.7 vs. 13 ± 3.0, H. armigera to S. litura). The adult lifespan and lifetime fecundity of T. pretiosum were variable but were affected by natal host species and/or host species to which they were exposed. Mean lifespan and fecundity of parasitoids that had developed in H. armigera eggs and were exposed to H. armigera eggs for oviposition were 13.9 ± 1.8 days and 98.7 ± 11.0 adult offspring. By contrast, those that developed in S. litura eggs and were exposed to S. litura eggs for oviposition lived for 7 ± 0.9 days and produced 53.8 ± 8.0 adult offspring. The ovigeny index (OI) was significantly lower in the parasitoids exposed to H. armigera eggs than in those exposed to S. litura eggs, regardless of the natal host, indicating that H. armigera eggs sustain the adult parasitoids better than S. litura eggs. These results are used to predict parasitoid behavior in the field when both hosts are available.     

The roles of foraging environment,host species,and host diet for a generalist pupal parasitoid

Even for parasitoids with a wide host range, not all host species are equally suitable, and host quality often depends on the plant the host feeds on. We compared oviposition choice and offspring performance of a generalist pupal parasitoid, Pteromalus apum (Retzius) (Hymenoptera: Pteromalidae), on two congeneric hosts reared on two plant species under field and laboratory conditions. The plants contain defensive iridoid glycosides that are sequestered by the hosts. Sequestration at the pupal stage differed little between host species and, although the concentrations of iridoid glycosides in the two plant species differ, there was no effect of diet on the sequestration by host pupae. The rate of successful parasitism differed between host species, depending on the conditions they were presented in. In the field, where plant‐associated cues are present, the parasitoid used Melitaea cinxia (L.) over Melitaea athalia (Rottemburg) (Lepidoptera: Nymphalidae), whereas more M. athalia were parasitised in simplified laboratory conditions. In the field, brood size, which is partially determined by rate of superparasitism, depended on both host and plant species. There was little variation in other aspects of offspring performance related to host or plant species, indicating that the two host plants are of equal quality for the hosts, and the hosts are of equal quality for the parasitoids. Corresponding to this, we found no evidence for associative learning by the parasitoid based on their natal host, so with respect to these host species they are truly generalist in their foraging behaviour.     

Fitness‐related offspring sex allocation of Anastatus disparis,a gypsy moth egg parasitoid,on different‐sized host species

Anastatus disparis (Ruschka) (Hymenoptera: Eupelmidae) is an egg parasitoid and considered a potential biological control agent of the gypsy moth, Lymantria dispar (L.) (Lepidoptera: Lymantriidae). Only male offspring of A. disparis emerge from single eggs of L. dispar in the laboratory, and A. disparis exhibits low parasitism on L. dispar in the field. We therefore selected several lepidopteran species with various body sizes to evaluate the optimal egg size for hosting A. disparis. In addition, we explored whether the nutritional content of a single L. dispar egg influences the sex of A. disparis offspring and why female offspring can be reared from L. dispar eggs in the field. The results indicated that host egg size decisively influenced the body size and sex ratio of the parasitoid offspring. Therefore, larger hosts, especially the largest eggs of Antheraea pernyi Guérin‐Méneville (Saturniidae), might increase the fitness of A. disparis females. Lymantria dispar eggs concealed in the larger egg shell of A. pernyi produced female A. disparis, suggesting that adult A. disparis should prefer hosts with larger bodies and that the nutritional content of L. dispar eggs did not play a decisive role in the sex allocation of A. disparis. The results also indicated that the egg mass and the fur cover of L. dispar egg masses might be the key factors inducing female A. disparis to lay female offspring in L. dispar eggs.     

Species‐Specific PCR‐Based Assay for Identification and Detection of Phomopsis (Diaporthe) azadirachtae Causing Die‐Back Disease in Azadirachta indica

Die‐back disease caused by Phomopsis (Diaporthe) azadirachtae is the devastating disease of Azadirachta indica. Accurate identification of P. azadirachtae is always problematic due to morphological plasticity and delayed appearance of conidia. A species‐specific PCR‐based assay was developed for rapid and reliable identification of P. azadirachtae by designing a species‐specific primer‐targeting ITS region of P. azadirachtae isolates. The assay was validated with DNA isolated from different Phomopsis species and other fungal isolates. The PCR assay amplified 313‐bp product from all the isolates of P. azadirachtae and not from any other Phomopsis species or any genera indicating its specificity. The assay successfully detected the pathogen DNA in naturally and artificially infected neem seeds and twigs indicating its applicability in seed quarantine and seed health testing. The sensitivity of the assay was 100 fg when genomic DNA of all isolates was analysed. The PCR‐based assay was 92% effective in comparison with seed plating technique in detecting the pathogen. This is the first report on the development of species‐specific PCR assay for identification and detection of P. azadirachtae. Thus, PCR‐based assay developed is very specific, rapid, confirmatory and sensitive tool for detection of pathogen P. azadirachtae at early stages.