Following a scented beetle: larval faeces as a key olfactory cue in host location of Stegobium paniceum (Coleoptera: Anobiidae) by Lariophagus distinguendus (Hymenoptera: Pteromalidae)

Architecture, construction, retention, and repair of faecal shields in three tribes of tortoise beetles (Coleoptera, Chrysomelidae, Cassidinae: Cassidini, Mesomphaliini, Spilophorini)

Animal constructions are the outcomes of complex evolutionary, behavioural, and ecological forces. A brief review of diverse animal builders, the materials used, and the functions they provide their builders is provided to develop approaches to studying faecal-based constructions and faecal-carrying in leaf beetles (Coleoptera: Chrysomelidae). Field studies, rearing, dissections, photography, and films document shields constructed by larvae in two species in two tribes of the subfamily Cassidinae, Calyptocephalaattenuata (Spaeth, 1919) (Spilophorini), and Cassidasphaerula Boheman, 1853 (Cassidini). Natural history notes on an undetermined Cassidini species and Stolascucullata (Boheman, 1862) (Tribe Mesomphaliini) outline the life cycle of tortoise beetles and explain terms. Commonly, the cassidine shield comprises exuviae onto which faeces are daubed, producing a pyramidal-shaped shield that can cover most of the body (up to the pronotum). In Cal.attenuata the larval shield comprises only exuviae, while in Cass.sphaerula, instar 1 initiates the shield by extending its telescopic anus to apply its own faeces onto its paired caudal processes; at each moult the exuvia is pushed to the caudal process base but remains attached, then more faeces are applied over it. The larva's telescopic anus is the only tool used to build and repair the shield, not mouthparts or legs, and it also applies chemicals to the shield. Pupae in Cal.attenuata retain part of the exuviae-only shield of instar VI, while pupae in Cass.sphaerula retain either the entire 5th instar larval shield (faeces + all exuviae) or only the 5th larval exuvia. The caudal processes are crucial to shield construction, shield retention on the body, and as materials of the central scaffold of the structure. They also move the shield, though the muscular mechanism is not known. Altogether the faecal + exuviae shields may represent a unique morpho-behavioural synapomorphy for the crown-clade Cassidinae (10 tribes, ~ 2669 species) and may have been a key innovation in subsequent radiation. Defensive shields and domiciles may help explain the uneven radiation of chrysomelid subfamilial and tribal clades.

The fecal shield is a double-edged sword for larvae of a leaf beetle

Larvae of some leaf beetles carry masses of feces covering parts or all of the body, which is called a “fecal shield”. In general, the shield is thought to be a defense structure against natural enemies. However, some studies have suggested that defense effectiveness varies depending on the natural enemy. In the present study, we used a fecal retention leaf beetle Ophrida xanthospilota (Coleoptera: Chrysomelidae), and two local generalist predators (an ant, Camponotus japonicus (Hymenoptera: Formicidae) and a stinkbug, Arma custos (Hemiptera: Pentatomidae)) as a system to test the hypothesis that the fecal shield of O. xanthospilota plays different roles in predation behavior of different predators and can provide multiple chemical communication signals in predator-prey interactions. Prey bioassays showed that the fecal shield of O. xanthospilota larvae repelled the ant C. japonicus while attracting the stinkbug A. custos. The results also strongly demonstrated that hexane extracts of the fecal shield significantly repelled C. japonicus, while dichloromethane extracts did not inhibit ant predation. Interestingly, dichloromethane extracts attracted A. custos, but hexane extracts did not. Therefore, we suggest that the fecal shield is a double-edged sword for the larvae of O. xanthospilota. Our results also indicated that the risk-benefit tradeoff of an insect should be estimated at a community level involving multiple enemies (predators and parasites) and herbivores, rather than in a single prey-predator pair.

Volatile Infochemicals from Rhyzopertha dominica Larvae and Larval Feces Involved in Theocolax elegans Host Habitat Location

Simple Summary

Food protection is a key issue to guarantee food security. One of the major criticisms is related to insect pests, which can severely damage stored products. Control of stored product pests widely relies on synthetic pesticides, which are potentially harmful to human health and the environment. In this context, the application of chemicals during post-harvest should be limited, and natural enemies, like parasitoid wasps, might be useful for biologically based pest management programs. The effectiveness of this approach under field conditions is still uncertain, and more information about parasitoid biology and behavior can be valuable to improve mass rearing and control strategies. This study investigates the host habitat location behavior of Theocolax elegans, a generalist parasitoid attacking several stored product pests, including Rhyzopertha dominica, a key pest species of stored grains. Bioassays demonstrated that the parasitoid females were not attracted by intact kernels; indeed, the parasitoid females were strongly attracted by infested wheat and by the host feces, locating the suitable hosts through the characteristic volatile infochemicals emitted by these substrates. Results from the present research are encouraging and suggest that biological control agents might be used to reduce the amount of synthetic insecticides.

Abstract

The development of biologically based approaches for stored product pest control is needed to reduce chemical inputs. Bioassays were performed to investigate host habitat location in the trophic interaction durum wheat/Rhyzopertha dominica/Theocolax elegans. GC-MS analyses were carried out to identify some chemical compounds produced by the host-related substrates. Choice and no-choice experiments demonstrated that female parasitoids were poorly attracted to intact kernels with respect to the infested substrates. Furthermore, T. elegans females performed longer residence time on infested wheat, and they generally displayed a short-term like fidelity for this cue, remaining on it during the whole observation. Infested wheat emitted one chemical (fenchone), which is possibly linked to host larvae presence, while the feces produced by host larvae emitted some other characteristic compounds. Results demonstrated that the presence of host larvae is a key factor for T. elegans host habitat location, considering that the attractiveness of the undamaged wheat is irrelevant. Furthermore, parasitoid females tended to stay on attractive cues, limiting the risk of contamination of other commodities. Biological control tools may be useful to improve the efficiency of pest management programs, but their application should be carefully evaluated.

Innate positive chemotaxis to paeonal from highly attractive Chinese medicinal herbs in the cigarette beetle, Lasioderma serricorne

Lasioderma serricorne, also known as cigarette beetle, can exploit a wide variety of stored materials as foods, but it is particularly common on tobacco and herbs. This beetle is a dominant pest species of stored Chinese medicinal materials (CMMs) causing high economic damages, making effective control strategies urgently needed. Behavioural manipulation is an important component of Integrated Pest Management. To the best of our knowledge, plant-borne volatile organic compounds (VOCs) have never been explored to develop lures for managing L. serricorne. In this study, the behavioural responses of L. serricorne to VOCs from four selected CMMs (Euphorbia kansui, Aconitum carmichaelii, Eucommia ulmoides and Pinellia ternata) were studied and their components analysed. Then, the olfactory responses of L. serricorne to the most abundant VOC identified in the preferred CMM, i.e., paeonal, was tested. L. serricorne showed significant differences in its preferences for the VOCs from the four CMMs, i.e, E. kansui > A. carmichaelii > E. ulmoides > P. ternata. From the VOCs of E. kansui, A. carmichaelii, E. ulmoides, and P. ternata, 77, 74, 56, and 81 molecules, were identified, respectively. Paeonal (23.5%), junipene (17.2%), hexanal (17.1%), and benzeneacetonitrile (14.0%) were the most abundant, respectively. Since paeonal dominated the VOC spectrum of the most preferred CMM, this compound was selected for further studies. L. serricorne showed significant positive responses to paeonal tested at various doses, with the most attractive ones being 100 μg and 500 μg. Our findings shed light on the olfactory cues routing the food searching behaviour in the cigarette beetle, providing important information on how L. serricorne targets particular CMMs. The high attractiveness of paeonal at low doses tested here may be exploited further to develop novel monitoring and control tools (e.g., lure-and-kill strategies) against this important stored product pest.

Lariophagus distinguendus (Hymenoptera: Pteromalidae) (Förster)-Past, Present, and Future: The History of a Biological Control Method Using L. distinguendus against Different Storage Pests

Legal requirements and consumer demands for residue-free products pose a big challenge for pest control in grain stores. One possible alternative to chemical insecticides is biological pest control with the pteromalid wasp Lariophagus distinguendus against the weevils Sitophilus granarius, S. oryzae (Coleoptera: Dryophtoridae), and many other storage pest beetles. The use of this wasp as a biocontrol agent was already suggested in 1919 by Prof. Dr. Hase [1]. Despite many studies on host-finding and behavioral biology, the applied aspect was neglected until 1994. Nowadays the wasps are commercially available and can now even be reared on-site, facilitating their use tremendously. This review highlights the milestones in L. distinguendus research, gives insights in current studies, and ventures a glimpse into the future.

Innate positive chemotaxis to pollen from crops and banker plants in predaceous biological control agents: towards new field lures?

Predator-prey interactions form the core of biological control of arthropod pests. Which tools can be used to monitor and collect carnivorous arthropods in natural habitats and targeted crops? Eco-friendly and effective field lures are urgently needed. In this research, we carried out olfactometer experiments assess innate positive chemotaxis to pollen of seven crop and banker plant by two important predatory biological control agents: the coccinellid Propylea japonica (Thunberg) and the anthocorid Orius sauteri (Poppius). We compared the attractiveness of pollens from crops and banker plants to that of common prey homogenates (aphids and thrips, respectively). Attractiveness of the tested odor sources was checked via field trapping experiments conducted in organic apple orchards and by release-recapture assays in organic greenhouse tomato crops. Maize and canola pollen were attractive to both P. japonica and O. sauteri, in laboratory and field assays. P. japonica was highly attracted by balm mint pollen, whereas O. sauteri was attracted by alfalfa pollen. Our results encourage the use of pollen from crops and banker plants as low-cost and eco-friendly attractors to enhance the monitoring and attraction of arthropod predators in biological control programs.

Associative learning for host-induced fruit volatiles in Psyttalia concolor (Hymenoptera: Braconidae), a koinobiont parasitoid of tephritid flies

Parasitic wasps are fascinating organisms that rely on a wide range of communication channels to locate their hosts. Associative learning for foraging kairomones has been demonstrated for various parasitic wasps, but little is known for parasitoids of Tephritidae flies. Psyttalia concolor (Hymenoptera: Braconidae) is a koinobiont parasitoid able to attack at least 14 tephritid pests. Females are innately attracted by some host-induced plant volatiles (HIPVs), whereas others of the same bouquet are unattractive. We hypothesize that females may detect unattractive HIPVs in association with key resources, such as food and hosts, learning to respond favourably to these cues in consecutive experiences. We evaluated associative learning for HIPVs in P. concolor females, testing if they are able to associate a food reward with the presence of different dosages of three HIPVs, thus developing a preference for an odour innately unattractive. Results demonstrated that P. concolor responded favourably to the learned cue in consecutive experiences. For all tested HIPVs (nonanoic acid, decanoic acid and geranyl acetone), regardless of dosage, trained females preferred the reward-associated odour, whereas naïve did not. Both HIPV-trained and naïve females did not show consistent differences in latencies when choosing HIPVs over blank. HIPV-trained and naïve wasps did not spend more time on HIPVs over blank. Odour learning is of adaptive importance for this generalist parasitoid, since it enhances host location efficiency by reducing the time wasted on the decision of where to search for hosts. From an applied perspective, these HIPVs could be used to train mass-reared P. concolor in pre-release, to potentially improve its efficacy in the field.

Bee species-specific nesting material attracts a generalist parasitoid: implications for co-occurring bees in nest box enhancements

Artificial nests (e.g., nest boxes) for bees are increasingly being used to contribute to nesting habitat enhancement for bees that use preexisting cavities to provision brood. They usually incorporate additional nesting materials that vary by species. Cavity-nesting bees are susceptible to brood parasitoids that recognize their host(s) using visual and chemical cues. Understanding the range of cues that attract parasitoids to bee nests, including human-made analogues, is important if we wish to control parasitism and increase the potential value of artificial nests as habitat-enhancement strategies. In this study, we investigated the cues associated with the orientation of the generalist brood parasitoid Monodontomerus obscurus Westwood (Hymenoptera: Torymidae) to the nests of a common cavity-nesting resin bee Megachile campanulae (Robertson) (Megachilidae). The parasitoids were reared from previously infested M. campanulae brood cells and placed into choice trials where they were presented with pairs of different nest material cues. Among different materials tested, we found that Mo. obscurus was most attracted to fresh resin collected directly from Pinus strobus trees followed by previously used resin collected from the bee nest. The parasitoid also attacked other bee species in the same nest boxes, including those that do not use resin for nesting. Our findings suggest that M. campanulae could act as a magnet, drawing parasites away from other bee hosts co-occurring in nest boxes, or, as an attractant of Mo. obscurus to nest boxes, increasing attacks on co-occurring host bee species, potentially undermining bee diversity enhancement initiatives.

Host specificity in the host-seeking larva of the dipteran parasitoid Mallophora ruficauda and the influence of age on parasitism decisions

Larvae of the robber fly Mallophora ruficauda are ectoparasitoids of white grubs and adults are an important apiculture pest in Argentina. Females oviposit on tall grasses and the second instar larva actively searches and locates hosts. There are nine potential hosts in the distribution area of this parasitoid and Cyclocephala signaticollis (Coleoptera: Scarabaeidae) is the most parasitized in the field. However, M. ruficauda has a certain degree of behavioural flexibility towards different host species, and not being a strict specialist. The conditions under which the parasitoid orientates and accepts different hosts' species are unknown. We studied the host specificity of M. ruficauda towards three species of Cyclocephala genus and we determined whether this specificity depends on larval age. We also evaluated whether larva orientation towards Cyclocephala species changes with chemical cue concentration. We assessed host specificity measuring the orientation and acceptance behaviours towards kairomones extracts and live individuals of Cyclocephala species using M. ruficauda larvae of low and high life expectancy (i.e., young and aged second instar larvae). We observed that young larvae orientated only towards C. signaticollis chemical stimulus, whereas aged larvae orientated also towards C. modesta, and the same was observed with increasing stimuli's concentration. Both young and aged M. ruficauda larvae orientate towards live C. signaticollis and C. putrida species and rejected C. modesta. Also, we found that larvae accepted all Cyclocephala hosts. In conclusion, our results indicate that specificity in the laboratory, observed through host orientation and host acceptance behaviours, depends not only on the availability of host species, but also on the nature of the host's stimuli combined with parasitoid age.