Quarantining behaviour of ants towards infected aphids as an antifungal mechanism in ant–aphid interactions

The ecological success of social insects, including ants, is tightly connected with their ability to protect themselves and their food resources. In exchange for energy‐rich honeydew, ants protect myrmecophilous aphids from various natural enemies. Fungal infection can have disastrous consequences for both mutualist partners, wherein aphids can be disease vectors. Behavioural responses towards fungus‐infected aphids of ant species in nature have scarcely been studied. Here, we studied the behaviour of honeydew foragers of four ant species – Formica polyctena Foerster, Formica rufa L., Formica pratensis Retzius (Hymenoptera: Formicidae, Formicini), and Lasius niger (L.) (Formicidae, Lasiini) – towards Symydobius oblongus (von Heyden) aphids contaminated with the generalist fungal pathogen Beauveria bassiana (Balsamo‐Crivelli) Vuillemin in the field. Aphid milkers from Formica spp. quickly detected and removed infected aphids from the host plant (Betula pendula Roth., Betulaceae). Neither ant species, the degree of aphid‐milker specialization (medium or high), nor the number of honeydew foragers had significant effects on the behaviour of Formica milkers towards infected aphids. Unlike Formica ants, L. niger usually displayed non‐aggressive behaviour (tolerance, antennation, honeydew collection, grooming). By the immediate removal of infected insects, Formica ants seem to minimize the probability of infection of symbionts as well as themselves. Quarantining behaviour may play an important role in ant–aphid interactions as a preventive antifungal mechanism formed under parasite pressure and thus contributing to the ecological success of ants.     

A field study with geometrid moths to test the coevolution hypothesis of red autumn colours in deciduous trees

Red autumn colouration of trees is the result of newly synthesized anthocyanin pigments in senescing autumn leaves. As anthocyanin accumulation is costly and the trait is not present in all species, anthocyanins must have an adaptive significance in autumn leaves. According to the coevolution hypothesis of autumn colours, red autumn leaves warn herbivorous insects – especially aphids that migrate to reproduce in trees in the autumn – that the tree will not be a suitable host for their offspring in spring due to a high level of chemical defence or lack of nutrients. The signalling allows trees to avoid herbivores and herbivores to choose better host trees. In this study the coevolution hypothesis was tested with four deciduous tree species that have red autumn leaf colouration – European aspen (Populus tremula L.) (Salicaceae), rowan (Sorbus aucuparia L.) (Rosaceae), mountain birch [Betula pubescens ssp. czerepanovii (NI Orlova) Hämet‐Ahti], and dwarf birch (Betula nana L.) (Betulaceae), and with two generalist herbivores, the autumnal moth [Epirrita autumnata (Borkhausen)] and the winter moth [Operophtera brumata (L.)] (both Lepidoptera: Geometridae). Anthocyanin concentrations of autumn leaves were determined from leaf samples and the growth performance parameters of the moth larvae on the study trees were measured in the spring. Trees with higher anthocyanin concentration in the autumn were predicted to be low‐quality food for the herbivores. Our results clearly showed that anthocyanin concentration was not correlated with the growth performance of the moths in any of the studied tree species. Thus, our study does not support the coevolution hypothesis of autumn colours.     

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.     

Secondary hosts of the Asian citrus psyllid,Diaphorina citri Kuwayama: Survivorship and preference

The Asian citrus psyllid, Diaphorina citri Kuwayama, is the most economically important and difficult to manage citrus pest in Florida due to its role as vector of huanglongbing or citrus greening disease. Spread of the disease is a function of dispersal patterns and thus influenced by availability of suitable hosts. Young leaves of citrus or related plants are required for reproduction, but in their absence, secondary hosts may provide needed resources to enhance survival. Therefore, survivorship on and preference for three abundant weed species was investigated. The suitability of potential secondary host plants Bidens alba (L.), DC, Ludwigia octovalvis (Jacqu.) P. H. Raven, and Eupatorium capillifolium (Lam.) Small was compared to a reproductive host, Murraya paniculata (L.) Jack, in no‐choice tests by assessing survivorship of D. citri adults confined to these plants in cages. Preference was evaluated by choice tests where D. citri adults were released into cages containing all three secondary hosts alone or with M. paniculata. Both B. alba and E. capillifolium increased D. citri survivorship by twofold compared to starvation conditions with only water available. Choice trials revealed no difference in initial selection between true and secondary hosts; however, the true host was favoured over time. This result suggested that hosts were selected initially by sight, and only later by taste and/or smell. While secondary hosts are unable to support reproduction or long‐term survival, these findings establish the ability of D. citri to use secondary hosts that are ubiquitous in Florida citrus groves as temporary reservoirs for food and moisture when ideal host conditions are scarce or absent.     

Improving methods to measure critical thermal limits in phloem‐feeding pest insects

The ability to accurately assess thermal tolerance in the laboratory without compromising ecological relevance is essential to predict the impacts of global climate change on phytophagous pest insects such as the phloem‐feeding aphids. One method to study thermal tolerance employs a temperature‐controlled column to measure critical thermal limits. However, assessments are commonly made with little relation to the natural environment of the study species. This study measured critical thermal minima (CT_min) for three cereal aphids – Sitobion avenae (Fabricius), Metopolophium dirhodum (Walker), and Rhopalosiphum padi (L.) (all Hemiptera: Aphididae) – in the absence and presence of host plant material to determine the best experimental design. Results revealed that CT_min measured in the presence of the host plant was significantly lower, suggesting that performing the measurement in the absence of the host plant could result in an underestimation of insect thermal tolerance. In addition, the study highlights the importance of understanding how an insect interacts with its environment, as this can reveal behavioural variation integral to differential survival at unfavourable temperatures.     

Oviposition,larval preference,and larval performance in two polyphagous species: does the larva know best?

It is expected that females preferentially oviposit on plant hosts that allow for optimal larval performance. However, this expectation contradicts empirical evidence where adults do not always choose the best host for their descendants. Recent evidence suggests that females’ host selection depends on the number of potential hosts. Females from oligophagous species seem to be able to choose an appropriate host in terms of larval performance, whereas in polyphagous species, adult oviposition preference is not related with larval performance. This suggests that larvae in polyphagous species could be taking a more active role in host selection than their mothers. Here, we evaluated the oviposition preference and the larval preference and performance of two polyphagous species of economic importance, Copitarsia decolora (Guenée) (Lepidoptera: Noctuidae: Cuculliinae) and Peridroma saucia (Hübner) (Lepidoptera: Noctuidae: Noctuinae), on eight species of cultivated plants. In laboratory and greenhouse choice assays, we tested adult preference for oviposition and larval preference at 1 and 24 h. Larval performance was measured in terms of survival to adulthood, length of larval period, and pupal weight. We found that both adult females and larvae actively choose their hosts and that the larval preference toward the hosts is related to the females’ preference in both herbivore species. However, the females and larvae did not preferentially select the host with the best larval performance, indicating that larval performance is not related to female or larval preference and that other selective pressures are influencing the choice of the host plant in these two species.     

Effect of plant nutrition on aphid size,prey consumption,and life history characteristics of green lacewing

Plant quality can directly and indirectly affect the third trophic level. The predation by all the instars of green lacewing, Chrysoperla carnea （S.） （Neuroptera： Chrysopidae） on the cereal aphids, Rhopalosiphum padi （L.）, and Sitobion avenae （F.） at varying nitrogen fertilizer levels was calculated under laboratory conditions. Wheat plants were grown on four nitrogen fertilizer levels and aphids were fed on these plants and subsequently offered as food to the C. carnea. Aphid densities of 10, 30, and 90 were offered to first, second, and third instar larvae of green lacewing. Increased nitrogen application improved nitrogen contents of the plants and also the body weight of cereal aphids feeding on them. Aphid consumption by green lacewings was reduced with the increase in nitrogen content in the host plants of aphids. Predation of both aphid species by first, second, and third instars larvae of C. carnea was highest on aphids reared on plants with the lowest rate of fertilization, suggesting a compensatory consumption to overcome reduced biomass （lower aphid size）. Total biomass devoured by C. carnea on all nitrogen fertilizer treatments was not statistically different. Additionally, the heavier host prey influenced by the plant nutrition had an effect on the life history characteristics of green lacewings. The larval duration, pupal weight, pupal duration, fecundity, and male and female longevity were significantly affected by the level of nitrogen fertilization to the aphid＇s host plants, except for pupal duration when fed on S. avenae. This study showed that quantity of prey supplied to the larvae affects the prey consumption and thereafter the life history characteristics of green lacewings.     

Population structure of a vector‐borne plant parasite

Parasites are among the most diverse groups of life on Earth, yet complex natural histories often preclude studies of their speciation processes. The biology of parasitic plants facilitates in situ collection of data on both genetic structure and the mechanisms responsible for that structure. Here, we studied the role of mating, dispersal and establishment in host race formation of a parasitic plant. We investigated the population genetics of a vector‐borne desert mistletoe (Phoradendron californicum) across two legume host tree species (Senegalia greggii and Prosopis velutina) in the Sonoran desert using microsatellites. Consistent with host race formation, we found strong host‐associated genetic structure in sympatry, little genetic variation due to geographic site and weak isolation by distance. We hypothesize that genetic differentiation results from differences in the timing of mistletoe flowering by host species, as we found initial flowering date of individual mistletoes correlated with genetic ancestry. Hybrids with intermediate ancestry were detected genetically. Individuals likely resulting from recent, successful establishment events following dispersal between the host species were detected at frequencies similar to hybrids between host races. Therefore, barriers to gene flow between the host races may have been stronger at mating than at dispersal. We also found higher inbreeding and within‐host individual relatedness values for mistletoes on the more rare and isolated host species (S. greggii). Our study spanned spatial scales to address how interactions with both vectors and hosts influence parasitic plant structure with implications for parasite virulence evolution and speciation.     

The origin and genetic differentiation of the socially parasitic aphid Tamalia inquilinus

Social and brood parasitisms are nonconsumptive forms of parasitism involving the exploitation of the colonies or nests of a host. Such parasites are often related to their hosts and may evolve in various ecological contexts, causing evolutionary constraints and opportunities for both parasites and their hosts. In extreme cases, patterns of diversification between social parasites and their hosts can be coupled, such that diversity of one is correlated with or even shapes the diversity of the other. Aphids in the genus Tamalia induce galls on North American manzanita (Arctostaphylos) and related shrubs (Arbutoideae) and are parasitized by nongalling social parasites or inquilines in the same genus. We used RNA sequencing to identify and generate new gene sequences for Tamalia and performed maximum‐likelihood, Bayesian and phylogeographic analyses to reconstruct the origins and patterns of diversity and host‐associated differentiation in the genus. Our results indicate that the Tamalia inquilines are monophyletic and closely related to their gall‐forming hosts on Arctostaphylos, supporting a previously proposed scenario for origins of these parasitic aphids. Unexpectedly, population structure and host‐plant‐associated differentiation were greater in the non‐gall‐inducing parasites than in their gall‐inducing hosts. RNA‐seq indicated contrasting patterns of gene expression between host aphids and parasites, and perhaps functional differences in host‐plant relationships. Our results suggest a mode of speciation in which host plants drive within‐guild diversification in insect hosts and their parasites. Shared host plants may be sufficient to promote the ecological diversification of a network of phytophagous insects and their parasites, as exemplified by Tamalia aphids.     

Dietary specialization and the effects of plant species on potential multitrophic interactions of three species of nymphaline caterpillars

The diet breadth of insect herbivores influences their response to variation in plant quality, and these bitrophic interactions have implications for the higher‐level trophic interactions between herbivores and their natural enemies. In this comparative study, we examined the role of host plant species and plant secondary chemistry on the potential interactions between three species of nymphaline caterpillars and their natural enemies. The caterpillar species (all Lepidoptera: Nymphalidae) varied in their degree of specialization: the buckeye, Junonia coenia Hübner, is a specialist on plants that contain iridoid glycosides (IGs); the white peacock, Anartia jatrophae L., feeds on plants in five families, some of which contain IGs and some of which do not; and the painted lady, Vanessa cardui L., is a generalist, feeding on plants in at least 15 families. Each species was reared on leaves of an introduced host plant, Plantago lanceolata L. (Plantaginaceae), which produces two IGs, aucubin and catalpol, and on another plant species that is a common host plant. These alternate host plants were Plantago major L. (Plantaginaceae) for J. coenia, Bacopa monnieri (L.) Pennell (Plantaginaceae) for A. jatrophae, and Malva parviflora L. (Malvaceae) for V. cardui. We examined growth, sequestration, and immune response of these caterpillars on the different host plant species. Junonia coenia developed more rapidly and sequestered higher IG concentrations when reared on P. lanceolata, whereas both other species grew more slowly on P. lanceolata. Host plant did not influence immune response of J. coenia or A. jatrophae, whereas V. cardui immune response was weaker when reared on P. lanceolata. Junonia coenia was most efficient at IG sequestration and A. jatrophae was least efficient, when all three species were reared on P. lanceolata. These results indicate that diet breadth may play an important role in structuring tritrophic interactions, and this role should be further explored.     

The interaction between host and host plant influences the oviposition and performance of a generalist ectoparasitoid

The successful development of parasitoids of herbivores depends on the quality of their host, which is often affected by the host plant. Therefore, a parasitoid’s oviposition decisions will directly depend on the host, but also on plant quality. Here, we investigated the direct effects of host species and the indirect effects of the host’s food plant on the oviposition decisions and performance of the gregarious ectoparasitoid Euplectrus platyhypenae Howard (Hymenoptera: Eulophidae). With a series of no‐choice experiments, we determined the oviposition and performance of the parasitoid on: (1) two caterpillar species, fall armyworm, Spodoptera frugiperda JE Smith (Lepidoptera: Noctuidae), and velvet armyworm, Spodoptera latifascia Walker, reared on maize (Zea mays L., Poaceae), (2) the same caterpillars reared on maize, bean (Phaseolus vulgaris L., Fabaceae), or squash (Cucurbita pepo L., Cucurbitaceae) leaves, and (3) S. latifascia caterpillars reared on leaves of wild and cultivated lima bean, Phaseolus lunatus L. All these insects and plants originate from Mesoamerica where they have coexisted for thousands of years in the traditional agricultural system known as Milpa in which maize, beans, and squash are planted together. We found that the preferred and best combination of host and host plant for parasitoid performance was S. frugiperda on maize. Parasitoids laid larger clutches, had higher survival, and more females and larger adults emerged from S. frugiperda reared on maize. However, when both caterpillar species were reared on squash, S. latifascia was the better host. Contrary to the literature, S. frugiperda was not able to develop on bean plants. Results from the lima bean experiment showed that parasitoid performance was best when S. latifascia was reared on leaves of cultivated compared to wild lima bean. These findings are discussed in the context of mixed cropping in which the ability of generalist parasitoids to switch among hosts and host plant species could be advantageous for pest management.     

Natal origin affects host preference and larval performance relationships in a tritrophic system

Many insects face the challenge to select oviposition sites in heterogeneous environments where biotic and abiotic factors can change over time. One way to deal with this complexity is to use sensory experiences made during developmental stages to locate similar habitats or hosts in which larval development can be maximized. While various studies have investigated oviposition preference and larval performance relationships in insects, they have largely overlooked that sensory experiences made during the larval stage can affect such relationships. We addressed this issue by determining the role of natal experience on oviposition preference and larval performance relationships in a tritrophic system consisting of Galerucella sagittariae, feeding on the two host plants Potentilla palustris and Lysimachia thyrsiflora, and its larval parasitoid Asecodes lucens. We firstly determined whether differences in host‐derived olfactory information could lead to divergent host selection, and secondly, whether host preference could result in higher larval performance based on the natal origin of the insects. Our results showed that the natal origin and the quality of the current host are both important aspects in oviposition preference and larval performance relationships. While we found a positive relationship between preference and performance for natal Lysimachia beetles, natal Potentilla larvae showed no such relationship and developed better on L. thyrsiflora. Additionally, the host selection by the parasitoid was mainly affected by the natal origin, while its performance was higher on Lysimachia larvae. With this study, we showed that the relationship between oviposition preference and larval performance depends on the interplay between the natal origin of the female and the quality of the current host. However, without incorporating the full tritrophic context of these interactions, their implication in insect fitness and potential adaptation cannot be fully understood.     

Aphid specialization on different summer hosts is associated with strong genetic differentiation and unequal symbiont communities despite a common mating habitat

Specialization on different host plants can promote evolutionary diversification of herbivorous insects. Work on pea aphids (Acyrthosiphon pisum) has contributed significantly to the understanding of this process, demonstrating that populations associated with different host plants exhibit performance trade‐offs across hosts, show adaptive host choice and genetic differentiation and possess different communities of bacterial endosymbionts. Populations specialized on different secondary host plants during the parthenogenetic summer generations are also described for the black bean aphid (Aphis fabae complex) and are usually treated as different (morphologically cryptic) subspecies. In contrast to pea aphids, however, host choice and mate choice are decoupled in black bean aphids, because populations from different summer hosts return to the same primary host plant to mate and lay overwintering eggs. This could counteract evolutionary divergence, and it is currently unknown to what extent black bean aphids using different summer hosts are indeed differentiated. We addressed this question by microsatellite genotyping and endosymbiont screening of black bean aphids collected in summer from the goosefoot Chenopodium album (subspecies A. f. fabae) and from thistles of the genus Cirsium (subspecies A. f. cirsiiacanthoides) across numerous sites in Switzerland and France. Our results show clearly that aphids from Cirsium and Chenopodium exhibit strong and geographically consistent genetic differentiation and that they differ in their frequencies of infection with particular endosymbionts. The dependence on a joint winter host has thus not prevented the evolutionary divergence into summer host‐adapted populations that appear to have evolved mechanisms of reproductive isolation within a common mating habitat.     

Effects of quantitative and qualitative differences in volatiles from host‐ and non‐host‐infested maize on the attraction of the larval parasitoid Cotesia kariyai

Cotesia kariyai Watanabe (Hymenoptera: Braconidae) is a specialist larval parasitoid of Mythimna separata Walker (Lepidoptera: Noctuidae). Cotesia kariyai wasps use herbivore‐induced plant volatiles (HIPVs) to locate hosts. However, complex natural habitats are full of volatiles released by both herbivorous host‐ and non‐host‐infested plants at various levels of intensity. Therefore, the presence of non‐hosts may affect parasitoid decisions while foraging. Here, the host‐finding efficiency of naive C. kariyai from HIPVs influenced by host‐ and non‐host‐infested maize [Zea mays L. (Poaceae)] plants was investigated with a four‐arm olfactometer. Ostrinia furnacalis Guenée (Lepidoptera: Crambidae) was selected as a non‐host species. One unit (1 U) of host‐ or non‐host‐infested plant was prepared by infesting a potted plant with five host or seven non‐host larvae. In two‐choice bioassays, host‐infested plants fed upon by different numbers of larvae, and various units of host‐ and non‐host‐infested plants (infestation units; 1 U, 2 U, and 3 U) were arranged to examine the effects of differences in volatile quantity and quality on the olfactory responses of C. kariyai with the assumption that volatile quantity and quality changes with differences in numbers of insects and plants. Cotesia kariyai was found to perceive quantitative differences in volatiles from host‐infested plants, preferring larger quantities of volatiles from larger numbers of larvae or plants. Also, the parasitoids discriminated between healthy plants, host‐infested plants, and non‐host‐infested plants by recognising volatiles released from those plants. Cotesia kariyai showed a reduced preference for host‐induced volatiles, when larger numbers of non‐host‐infested plants were present. Therefore, quantitative and qualitative differences in volatiles from host‐ and non‐host‐infested plants appear to affect the decision of C. kariyai during host‐habitat searching in multiple tritrophic systems.     

Mechanisms of species‐sorting: effect of habitat occupancy on aphids' host plant selection

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Host specificity of two pollinating seed‐consuming fly species is not related to soil moisture of host plant in the high Himalayas

Studying the drivers of host specificity can contribute to our understanding of the origin and evolution of obligate pollination mutualisms. The preference–performance hypothesis predicts that host plant choice of female insects is related mainly to the performance of their offspring. Soil moisture is thought to be particularly important for the survival of larvae and pupae that inhabit soil. In the high Himalayas, Rheum nobile and R. alexandrae differ in their distribution in terms of soil moisture; that is, R. nobile typically occurs in scree with well‐drained soils, R. alexandrae in wetlands. The two plant species are pollinated by their respective mutualistic seed‐consuming flies, Bradysia sp1. and Bradysia sp2. We investigated whether soil moisture is important for regulating host specificity by comparing pupation and adult emergence of the two fly species using field and laboratory experiments. Laboratory experiments revealed soil moisture did have significant effects on larval and pupal performances in both fly species, but the two fly species had similar optimal soil moisture requirements for pupation and adult emergence. Moreover, a field reciprocal transfer experiment showed that there was no significant difference in adult emergence for both fly species between their native and non‐native habitats. Nevertheless, Bradysia sp1., associated with R. nobile, was more tolerant to drought stress, while Bradysia sp2., associated with R. alexandrae, was more tolerant to flooding stress. These results indicate that soil moisture is unlikely to play a determining role in regulating host specificity of the two fly species. However, their pupation and adult emergence in response to extremely wet or dry soils are habitat‐specific.     

Quantifying aphid behavioral responses to environmental change

Aphids are the most common vector of plant viruses, and their feeding behavior is an important determinant of virus transmission. Positive effects of global change on aphid performance have been documented, but effects on aphid behavior are not known. We assessed the plant‐mediated behavioral responses of a generalist aphid, Myzus persicae (Sulzer) (Hemiptera: Aphididae), to increased CO₂ and nitrogen when feeding on each of three host species: Amaranthus viridis L. (Amaranthaceae), Polygonum persicaria L. (= Persicaria maculosa Gray) (Polygonaceae), and Solanum dulcamara L. (Solanaceae). Via a family of constrained Markov models, we tested the degree to which aphid movements demonstrate preference among host species or plants grown under varying environmental conditions. Entropy rates of the estimated Markov chains were used to further quantify aphid behavior. Our statistical methods provide a general tool for assessing choice and quantitatively comparing animal behavior under different conditions. Aphids displayed strong preferences for the same host species under all growth conditions, indicating that CO₂‐ and N‐induced changes in plant chemistry have minimal effects on host preference. However, entropy rates increased in the presence of non‐preferred hosts, even when preferred hosts were available. We conclude that the presence of a non‐preferred host species affected aphid‐feeding behavior more than changes in plant leaf chemistry when plants were grown under elevated CO₂ and increased N availability.     

The nutritional landscape of host plants for a specialist insect herbivore

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Use of herbivore‐induced plant volatiles as search cues by Tiphia vernalis and Tiphia popilliavora to locate their below‐ground scarabaeid hosts

Japanese beetle, Popillia japonica Newman, and oriental beetle, Anomala orientalis (Waterhouse) (both Coleoptera: Scarabaeidae) are considered invasive species and have been reported as key pests of urban landscapes in the Northeastern USA. Tiphia vernalis Rohwer and Tiphia popilliavora Rohwer (Hymenoptera: Tiphiidae) were introduced as biocontrol agents against these beetles. These parasitic wasps burrow into the soil and search for grubs. When a host is found, the wasp attaches an egg in a location that is specific for the wasp species. It is unknown if these wasps can detect patches of concealed hosts from a distance above ground and what role, if any, herbivore‐induced plant volatiles play in their host location. This study evaluated the responses of female T. vernalis and T. popilliavora to grub‐infested and healthy plants in Y‐tube olfactometer bioassays. Also the effect of root herbivory on the composition of turfgrass (Poaceae) volatile profiles was investigated by collecting volatiles from healthy and grub‐infested grasses. Tiphia wasps were highly attracted to volatiles emitted by grub‐infested tall fescue (Festuca arundinacea Schreb.) and Kentucky bluegrass (Poa pratensis L.) over healthy grasses. In contrast, wasps did not exhibit a significant preference for grub‐infested perennial ryegrass (Lolium perenne L.) as compared with the control plants. The terpene levels emitted by grub‐infested Kentucky bluegrass and tall fescue were greater than that of control plants. Low levels of terpenes were observed for both test and control perennial ryegrass. The elevated levels of terpenes emitted by grub‐infested Kentucky bluegrass and tall fescue coincided with the attractiveness to the tiphiid wasps. Here, we provide evidence that plant exposure to root‐feeding insects P. japonica and A. orientalis resulted in an increase in terpenoid levels in turfgrasses, which strongly attracts their above‐ground parasitoids.     

Host preference and suitability of grasses for Oebalus pugnax

The rice stink bug, Oebalus pugnax (Fabricius) (Hemiptera: Pentatomidae: Carpocorini), though graminaceous, discriminates among its numerous host grass species. This could represent a feeding preference, it could be related to host suitability for growth and development. To clarify the role of host grass discrimination, two laboratory studies were conducted: (1) free‐choice tests to evaluate preferences of O. pugnax among 11 wild host grass species found in three rice‐producing counties of the central Mississippi Delta (MS, USA), and (2) no‐choice tests to evaluate the impact of rice (Oryza sativa L.), junglerice [Echinochloa colona (L.) Link], and dallisgrass (Paspalum dilatatum Poir.) (all Poaceae), on the development of O. pugnax from second instar to adult. In the free‐choice test, four experiments were conducted, each with four sets of host grass species and observed 1, 2, 4, 8, and 16 h after release in cages. Approximately 4 h was necessary for O. pugnax to settle on preferred host grasses. Oebalus pugnax showed a feeding preference for junglerice over all 10 other grass species. Bahiagrass, Paspalum notatum Flueggé, was the least preferred. The no‐choice tests showed significant effect of host grass species on O. pugnax mean development time of nymphal survival to adults. Survival of nymphs was lower and mean development time was longer on dallisgrass compared to rice and junglerice. Knowledge of O. pugnax rate of growth and development on host grasses could be useful in the future development of rice integrated pest management strategies.