The responses of Ibalia species (Hymenoptera: Ibaliidae) to the fungal symbionts of siricid woodwasp hosts

The oviposition response of Ibalia drewseni and Ibalia leucospoides is described and compared. Oviposition behaviour is elicited by odours produced by the symbiotic fungus of several species of siricid woodwasps. The responses of the two Ibalia species to fungus cultures of different ages and host sources is discussed in relation to their emergence periods and the ecology of their hosts.     

The oviposition biology of siricid woodwasps in Europe

Abstract. 1. The oviposition biology of the siricid woodwasps, Sirex noctilio, S.juvencus, S.cyaneus, Urocerus gigas, U.augur, U.fantoma, U.sah and Xeris spectrum was investigated. The fecundity of each siricid species was related to adult size although S.noctilio laid relatively fewer eggs than other species.
2. Oviposition drill architecture in host trees is characteristic for the different siricid genera and was found to be related to the length of the ovipositor. The shape of the egg is also characteristic for each genus.
3. Species of the symbiotic fungus, Amylostereum , were found to be associated with all species except X. spectrum. The emplacement of fungus in relation to oviposition drills was investigated.
4. S.noctilio females have relatively larger mucus glands and reservoirs than other siricid species.
5. The response of X.spectrum females to previously infested timber was studied experimentally. A positive response to previously infested timber and Amylostereum inoculated sawdust was demonstrated.
6. The longevity of adults, oviposition rates and incubation period of eggs was investigated.
7. The results are discussed in relation to the ecology of siricids in Europe and Australia.     

Effect of Two Bark Beetle-Vectored Fungi on the On-Host Search and Oviposition Behavior of the Introduced Woodwasp Sirex noctilio (Hymenoptera: Siricidae) on Pinus sylvestris Trees and Logs

Sirex noctilio’s fungal symbiont, Amylostereum areolatum, is required for its offspring’s development. The symbiont is a weak competitor with bark beetle-vectored fungi so it would be beneficial to the woodwasp if it avoided ovipositing in substrate colonized by these competitors. The response of S. noctilio to the presence of two beetle-vectored fungi, Leptographium wingfieldii and Ophiostoma minus, inoculated into living trees, and to L. wingfieldii and A. areolatum inoculated into cut logs was investigated. The wasp avoided areas with L. wingfieldii; there were fewer signs of oviposition activity and drilling in these zones. There was no significant response to O. minus or A. areolatum. Female woodwasps can detect the presence of some fungi and make choices about oviposition sites that benefit their offspring.     

Predation on the woodwasp Tremex longicollis Konow (Hymenoptera: Siricidae) and its parasitoid Megarhyssa jezoensis (Matsumura) (Hymenoptera: Ichneumonidae) adults during oviposition

Adults of the woodwasp Tremex longicollis Konow (Hymenoptera: Siricidae) oviposit in the wood of dying Celtis sinensis trees using their ovipositors, and adults of the parasitoid Megarhyssa jezoensis (Matsumura) (Hymenoptera: Ichneumonidae) deposit eggs into the woodwasp larvae that live in the wood, also using their long ovipositors. Many T. longicollis ovipositors, both with and without abdominal segments, and a M. jezoensis ovipositor were found stuck in C. sinensis wood at two parks in Osaka Prefecture, central Japan. Field observations showed that ovipositing woodwasps and parasitoids were attacked by predators during the daytime, and their ovipositors were left behind in the wood. Woodwasps and their parasitoids, which have long ovipositors, may be vulnerable to predation during oviposition.     

Experimental studies on the responses of European siricid woodwasps to host trees

A study was made of the oviposition responses of the siricid woodwasps, Sirex noctilio, S. juvencus, S. cyaneus and Urocerus gigas to experimentally debilitated spruce and pine trees. Treatments included felled, fire-burned, logged and girdled trees which were treated at intervals before bioassay with cages siricid females. In comparable treatments, S. noctilio showed a distinct preference for pines although it was quite successful on spruce while the other siricid species displayed a preference for spruce. The Sirex species successfully attacked more recently treated material although U. gigas showed a preference for timber in a more advanced state of debility. All species showed preferences for girdled trees although other treatments were also favoured by the different siricid species. Overall, the siricids preferred the area above the girdle irrespective of tree species and there was a higher rate of eggs above the girdle in treated spruce trees. A wide range of moisture content in the timber appeared to have no effect on drilling activity or the successful development of eggs. The response of a wild population of S. juvencus to the treated spruce is also described. The results are discussed in relation to the ecology of Siricidae in Europe and the establishment of S. noctilio in Australia. It is suggested that of the species studied, only S. noctilio poses a serious threat to the living pine stands of Australia.     

First record of the invasive woodwasp,Urocerus albicornis (Hymenoptera: Siricidae), from a local forest in Japan

The woodwasp Urocerus albicornis (Fabricius, 1781) (Hymenoptera: Siricidae) is a forest pest native to North America and occasionally introduced into European countries. One of these invasive woodwasps was collected in a local forest in Nagano Prefecture, Central Japan. The collected individual was an adult female ovipositing on a log from a Japanese larch (Larix kaempferi (Lamb.) Carrière). Although several of these woodwasps have been found on imported logs in Japan, this is the first record of the alien woodwasp in a local forest within Japan and Asia. This finding indicates that a population of this invasive woodwasp may be established in Japanese forests.     

Oviposition Sites of the Cypress Seed Bug <Emphasis Type="Italic">Orsillus maculatus</Emphasis> and Response of the Egg Parasitoid <Emphasis Type="Italic">Telenomus</Emphasis> gr. <Emphasis Type="Italic">Floridanus</Emphasis>

Phytophagous insects have many strategies to escape parasitoids, for example by hiding eggs into plant tissues, but oviposition in holes made by another insect is rather scarce. The cypress seed bug Orsillus maculatus Fieber (Heteroptera: Lygaeidae) is strictly dependent on the availability of cones of Cupressus sempervirens L. to oviposit. Females lay eggs either in exit holes cut through the cone scale by emerging adults of the cypress seed chalcid, Megastigmus wachtli Seitner (Hymenoptera: Torymidae), or on the inner side of scales of partly open cones. A recently discovered egg parasitoid belonging to the genus Telenomus has been shown to attack bug eggs in both oviposition sites. In this paper we investigated the parasitoid performance according to oviposition sites. Field samplings were conducted in two evergreen cypress orchards located in the south of France. The distribution and condition of the egg patches were compared between the two locations and oviposition sites. Seed bugs preferred to oviposit in emergence holes of M. wachtli, and parasitoid performance was higher in eggs laid on cone scales. The chalcid emergence holes seemed to ensure bug eggs with enemy-free space. Oviposition site selection could be an adaptive strategy to escape parasitoid attack.     

The Evolution of Insect-Fungus Associations: From Contact to Stable Symbiosis

Insect-fungus interactions range from agonistic to mutualistic,and include several spectacular examples of complex symbioses.A potential benefit of mycophagy (the ingestion of fungal tissue)is the augmentation of digestive capacity by the ingestion offungal enzymes that remain active in the gut following ingestion.Cellulose digestion is mediated by ingested fungal enzymes inthe wood-boring larvae of cerambycid beetles and siricid woodwasps,in detritus-feeding stonefly nymphs, and in the workers of fungus-growingtermites. In this paper I discuss a plausible scenario for theevolution of stable symbiotic insect-fungus associations, inwhich the augmentation of digestive capacity through the ingestionof fungal enzymes is an important factor leading to the establishmentof interdependence between the interacting partners in a mutualism.Ingested fungal enzymes play a different role in the mutualisticassociation of the attine ants and their symbiotic fungi. Analyses of the associations of the siricid woodwasps, fungus-growingtermites, and fungus-growing ants with their symbiotic fungipermit the testing of Law's (1985) predictions concerning theconsequences of evolution in a mutualistic environment. As predicted,the rate of speciation has been slower in the protected partnerthan in the host partner, selection has favored asexual reproductionin the protected partner, and, at least in the attine ant-fungussymbiosis, the protected partner exhibits a low degree of specificitytoward different host species. Insect-fungus interactions provide rich material for the studyof both mechanistic and theoretical aspects of mutualism.     

Daldinia decipiens and Entonaema cinnabarina as fungal symbionts of Xiphydria wood wasps

The identity of symbiotic fungi associated with the Xiphydria spp. wood wasps was investigated using DNA analysis. The fungi were isolated from the mycangia of adult females of X. camelus, X. prolongata and X. longicollis reared from colonized logs of Alnus glutinosa, Salix alba and Quercus robur, respectively. Sequences of rDNA and β-tubulin were obtained. Phylogenetic analysis based on the NJ method showed that the isolates from X. camelus clustered with Daldinia decipiens, whereas those of X. prolongata belonged to Entonaema cinnabarina. In X. longicollis, both symbiotic fungi (D. decipiens and E. cinnabarina) have been found. Morphological characteristics of the anamorphs are presented. In cultures of D. decipiens, sympodial holoblastic, as well as annelidic, conidiation was observed. So far, fruit bodies of D. decipiens have only been recorded from Betula spp. whereas the host spectrum of its wasp vectors covers predominantly oaks and alders. Fruiting bodies of E. cinnabarina do not occur in Central Europe. This is the first report of Entonaema as a symbiotic fungus of siricid wood wasps.     

A comparative study of the phytotoxic effects of siricid woodwasps on conifers

The effects of siricid mucus and the symbiotic fungus injected artificially, or by oviposition of caged females on young conifer trees were investigated in a comparative study of the phytotoxicity caused by seven species of siricid woodwasps. Dilute solutions of mucus were bioassayed using detached shoots. Rapid physiological changes in the radial growth of the stem, quantity of starch in the leaves, leaf pressure and colour of the foliage of living trees were induced by only one species, Sirex noctilio. Solutions of S. noctilio and S. cyaneus mucus caused premature senescence of needles on detached shoots. The other species, Sirex juvencus, Urocerus gigas, U. augur, U. sah and Xeris spectrum , produced no phytotoxic symptoms in living trees and less rapid senescence of needles on detached shoots. These differences are discussed in relation to the ecology of siricids in the northern hemisphere and the successful establishment of S. noctilio in pine plantations of Australasia.     

Influence of the community of associates on Sirex noctilio brood production is contextual

1. Competition and predation are important components of biotic resistance, which helps define the invasibility of an ecosystem. 2. To search for evidence of biotic resistance to the European woodwasp, Sirex noctilio Fabricius, in North America, cages were used to experimentally exclude the community of associates (natural enemies and competitors) from infested logs. Specifically, the study assessed S. noctilio brood production in pine forests in Ontario and New York, where there was a rich existing community of associates (other wood borers, bark beetles and associated fungi, and parasitoids), and in South Africa, where siricid wasps and pines are not native and a similar associate community is not present. In addition, in Ontario, associates were excluded by size, and for different periods of time to identify important associates and their temporal dynamics. 3. Evidence was found that biotic factors limit S. noctilio in North America, whereby exclusion of natural enemies and competitors had a positive influence on the abundance or presence of S. noctilio brood in Ontario and New York. This influence was absent in South Africa. 4. It is unclear which member(s) of the associated insect community in North America were most important in limiting S. noctilio brood production, although they probably acted quickly (< 2 weeks) following S. noctilio oviposition. 5. Further study is needed to determine whether associates have limited S. noctilio populations in pine forests throughout northeastern North America, and which specific natural enemies and/or competitors are important.     

Asymmetric effects of adult nutrition on reproductive success of male and female Diaeretiella rapae (Hymenoptera: Aphidiidae)

The role of diet supplements (honey, water or no supplements) on egg maturation, oviposition strategy and longevity of the parasitic wasp Diaeretiella rapae McIntosh (Hymenoptera: Aphidiidae) is investigated. Parasitoids feed as larvae on hosts to acquire nutrition for growth and development, and further gain additional resources during their adult stage by feeding on either host or nonhost resources. The additional resources acquired by adults can help them to increase their reproductive activity or life expectancy, or both. Diaeretiella rapae females emerge with some developed eggs and no additional resources are required for egg maturation or successful oviposition. Females are able to oviposit and produce viable offspring immediately after emergence, and the number of eggs left in the ovaries of females decreases with subsequent oviposition, suggesting that ovigeny index of D. rapae is inclined towards pro‐ovigenic status. When unmated males and females are offered honey solution, females are attracted to it, whereas males display courtship and make mating attempts but then feed on honey after mating. The oviposition efficiency of female D. rapae increases by 30% when they feed on honey compared with when starved. Honey‐fed D. rapae adults live significantly longer (almost twice as long) than starved adults. Honey‐fed females deprived of hosts live longer than those offered hosts regularly. The positive effects of honey‐feeding on longevity are greater in females than in males. Taken together, the results of the present study suggest that the provision of additional resources to adult D. rapae parasitoids could enhance their life expectancy and parasitism efficiency in biological control programmes.     

Relations of intraspecific variations in fecundity, clutch size, and oviposition frequency to the body size in three species of stoneflies, Sweltsa sp., Isoperla aizuana, and Stavsolus japonicus

Most stoneflies oviposit several times during their adult stage. In this study, the relations among oviposition frequency, the number of eggs per egg mass, and body size were examined in the chloroperlid stonefly Sweltsa sp. and two perlodid stoneflies, Isoperla aizuana and Stavsolus japonicus. It was found that larger individuals tended to oviposit more frequently than smaller ones, but the relation was significant only in Isoperla aizuana. In Sweltsa sp. and Isoperla aizuana, the number of eggs per egg mass was higher for the less-frequently ovipositing individuals than for those ovipositing more frequently, and the number of eggs per egg mass decreased with successive oviposition events. Stavsolus japonicus showed the same tendency but it was not statistically significant.     

Effect of arbuscular mycorrhizal fungi (Glomus intraradices) on the oviposition of rice water weevil (Lissorhoptrus oryzophilus)

Root-feeding insects are important drivers in ecosystems, and links between aboveground oviposition preference and belowground larval performance have been suggested. The root-colonizing arbuscular mycorrhizal fungi (AMF) play a central role in plant nutrition and are known to change host quality for root-feeding insects. However, it is not known if and how AMF affect the aboveground oviposition of insects whose offspring feed on roots. According to the preference–performance hypothesis, insect herbivores oviposit on plants that will maximize offspring performance. In a greenhouse experiment with rice (Oryza sativa), we investigated the effects of AMF (Glomus intraradices) on aboveground oviposition of rice water weevil (Lissorhoptrus oryzophilus), the larvae of which feed belowground on the roots. Oviposition (i.e., the numbers of eggs laid by weevil females in leaf sheaths) was enhanced when the plants were colonized by AMF. However, the leaf area consumed by adult weevils was not affected. Although AMF reduced plant biomass, it increased nitrogen (N) and phosphorus concentrations in leaves and N in roots. The results suggest that rice water weevil females are able to discriminate plants for oviposition depending on their mycorrhizal status. The discrimination is probably related to AMF-mediated changes in plant quality, i.e., the females choose to oviposit more on plants with higher nutrient concentrations to potentially optimize offspring performance. AMF-mediated change in plant host choice for chewing insect oviposition is a novel aspect of below- and aboveground interactions.     

The evolutionary ecology of cheating: does superficial oviposition facilitate the evolution of a cheater yucca moth?

Abstract 1. A major question in the study of mutualism is to understand how mutualists may revert to antagonists that exploit the mutualism (i.e. switch to cheating). In the classic pollination mutualism between yuccas and yucca moths, the cheater moth Tegeticula intermedia is sister to the pollinator moth T. cassandra. These moth species have similar ovipositor morphology, but T. intermedia emerges later, oviposits into fruit rather than flowers, and does not pollinate. 2. We tested if the pollinator, T. cassandra, was pre‐adapted to evolve a cheater lineage by comparing its emergence and oviposition behaviour on yucca fruit to a distantly related pollinator, T. yuccasella, that differs in ovipositor morphology and oviposition behaviour. We predicted that if T. cassandra was pre‐adapted to cheat, then these pollinators would emerge later and be able to oviposit into fruit in contrast to T. yuccasella. 3. Contrary to expectations, a common garden‐rearing experiment demonstrated that emergence of T. cassandra was not significantly delayed relative to T. yuccasella. Moth emergence patterns overlapped broadly. 4. No choice oviposition experiments with female moths demonstrated that both pollinator species attempted to oviposit into fruit, but only T. cassandra was successful. Four out of 84 T. cassandra successfully oviposited into older fruit, whereas zero out of 79 T. yuccasella oviposited into older fruit. The rarity of the cheating behaviour in pollinators, however, meant that no significant difference in oviposition ability was detected. 5. The results suggest that a shift in emergence phenology is likely not a pre‐adaptation to the evolution of cheating, but that the ability to successfully lay eggs into fruit may be. The results also demonstrate that cheating attempts are rare in these pollinator species and, hence, the evolutionary transition rate from pollinator to cheater is likely to be low.     

Host-marking by female pepper weevils, Anthonomus eugenii

Pepper weevils, Anthonomus eugenii Cano (Coleoptera: Curculionidae), feed and oviposit in flower buds and small fruits of plants in the genus Capsicum, as well as several species of Solanum (Solanaceae). Females chew a small hole into the fruit, deposit a single egg within the cavity, and seal the hole with a clear anal secretion that hardens into an ‘oviposition plug’. Female oviposition behavior was studied in a series of small‐arena bioassays to determine whether previous oviposition in Jalapeño pepper fruit deterred subsequent oviposition and to determine what specific cues from an infested fruit influence female behavior. In choice and no‐choice tests, females preferred clean fruit to fruit that had received four eggs 24 h previously (i.e., infested fruit), whether the fruit was infested with conspecific eggs or their own eggs. Further bioassays demonstrated that the presence of female frass, or oviposition plugs alone, in the absence of eggs or any fruit damage, was sufficient to deter oviposition. In addition, females given the choice between an infested fruit with the oviposition plug removed or an unaltered infested fruit preferred the fruit with no plugs, even when eggs, frass, and feeding damage were still present. To determine whether females would avoid infested peppers under more natural conditions, we quantified oviposition on infested and uninfested sentinel pepper fruit within individually caged plants and on clean and infested plants caged together. Females consistently laid more eggs on clean fruit than on infested fruits and moved within and among pepper plants to search for more acceptable oviposition sites. We conclude that oviposition plugs, along with contaminated female, but not male, frass contain a deterrent that, in the absence of any other cue, is enough to alert a female that a patch is occupied.     

Effect of cocoa pod age on egg distribution and egg parasitism of the cocoa pod borer in Malaysia

The effects of pod age on oviposition, and on egg and larval survival of the cocoa pod borer (CPB), Conopomorpha cramerella (Snellen), were investigated. CPB were allowed to oviposit on a batch of 50 pods for a period of 7 days over several exposure dates. Numbers of CPB eggs/pod and survival to larval emergence from the pods were recorded. Pods were harvested when ripe and analyzed for larval survival within the pod. The oviposition pattern varied with pod age. Older pods less than 7 weeks before ripening (WBR) were preferred, suggesting greater nutritional value or chemical attraction of the older pods. The proportion of eggs parasitized by Trichogrammtoidea bactrae fumata Nagaraja (TBF), the number of eggs lost and the proportion surviving to larval emergence from the pod were independent of pod age. Egg parasitism was low, implying that TBF was not an effective natural enemy. Mass-releases of TBF should be intensified during cropping periods with higher proportions of susceptible pods (<10 WBR). Survival of larvae in the presclerotic layer (preSCL) was high and independent of pod age. Larval mortality at the SCL (sclerotic layer) was dependent on pod age and was high in older pods. Larval density influenced the survival of larvae inside the pod and was dependent on pod age. Larval mortality associated with SCL hardness and thickness is one of the criteria for the selection of CPB resistant cocoa clones.     

The fecundity, development and host relationships of Ceratobaeus spp. (Hymenoptera: Scelionidae), parasites of spider eggs

Abstract. 1. Ceratobaeus spp. enter the nest of their host spider and oviposit into eggs through the thin silk eggsac.
2. Temperatures below 15° C limit oviposition by slowing parasites down.
3. Males emerge prior to females and mate with their sibs. Sex ratios of 6.6–6.0:1 in favour of females were observed in the field and laboratory for two species.
4. Even though females can oviposit almost immediately after emergence their full complement of eggs (= 65) is not reached until several days later.
5. Superparasitism is low and appears to occur from subsequent accidental ovipositions. No marking of the external surface of hosts was observed.
6. Parasites overwinter as adults under bark. They do not feed as adults nor do they reabsorb their eggs, but rather oviposit as soon as host eggs become available in spring.
7. Successful oviposition occurs in later stages of host eggs reared at 15° C and 20° C than it does at 25°C. Different rates of development between host and parasite is proposed as an explanation for this phenomenon.
8. The species studied show varying degrees of specificity but each has a dominant host. Location of hosts involves cues from the habitat (bark), silk nests of spiders, and some factor associated with host eggs.     

Response of host plants to periodical cicada oviposition damage

Insect oviposition on plants is widespread across many systems, but studies on the response of host plants to oviposition damage are lacking. Although patterns of oviposition vary spatially and temporally, ovipositing insects that exhibit outbreak characteristics may have strong effects on host plants during peak abundance. Periodical cicadas (Magicicada spp.), in particular, may reduce the performance of host plants when they synchronously emerge in massive numbers to mate and oviposit on host plants. Here we provide the first experimental manipulation of host plant use by periodical cicadas to evaluate the impact of cicada oviposition on plant performance across a diversity of host species within an ecologically relevant setting. Using a randomized block design, we established a plantation of three native and three exotic host plant species common to the successional forests in which cicadas occur. During the emergence of Brood X in 2004, we employed a highly effective cicada exclusion treatment by netting half of the host plants within each block. We assessed multiple measures of host plant performance, including overall plant growth and the growth and reproduction of individual branches, across three growing seasons. Despite our thorough assessment of potential host plant responses to oviposition damage, cicada oviposition did not generally inhibit host plant performance. Oviposition densities on unnetted host plants were comparable to levels documented in other studies, reinforcing the ecological relevance of our results, which indicate that cicada oviposition damage did not generally reduce the performance of native or exotic host plants.     

Sublethal effects of chronic exposure to chlorpyrifos or imidacloprid insecticides or their binary mixtures on Culex pipiens mosquitoes

Mosquitoes represent one of the most significant threats to human and veterinary health throughout the world. Consequently, improving strategies for the control of mosquitoes is essential. In the present study, juvenile Culex pipiens (Diptera: Culicidae), the common house mosquito, are chronically exposed to sublethal concentrations of chlorpyrifos (20% of LC₅₀) and imidacloprid (5% of LC₅₀), both separately and as a mixture. Developmental time, the emergence rate of adults and the expression of five selected genes involved in detoxification and resistance to pesticides are assessed. To assess the effects on oviposition choice, gravid females are forced to oviposit into cups containing water with added chlorpyrifos, imidacloprid or a mixture of both. The time required for the development of second‐ and third‐instar larvae is observed to differ significantly between treatments. Adults of C. pipiens fail to emerge from larvae hatched in both imidacloprid and the binary mixture. The expression of the four quantified detoxification genes differs significantly in third‐larval instars exposed to chlorpyrifos and/or imidacloprid compared with controls. Gravid females also fail to lay eggs on water to which either of the insecticides or the binary mixture is added, although they do lay eggs in cups containing water only. Chronic exposure to sublethal concentrations of chlorpyrifos or imidacloprid has significant adverse effects on development and thus the reproductive fitness of C. pipiens and, accordingly, could be used in the population control of these mosquitoes.