Carnivorous Insects Research Articles

Ultrastructural observation of digestive tract and the adaptative characteristics of dietary habits for ground-dwelling and omnivorous insects.

The digestive tract of insects from mouth to anus is the crop, proventriculus, gastric caecum, midgut, ileum, colon and rectum, and the Malpighian tubules attached to the ileum belong to the excretory organs. As the main organs for digesting food and absorbing nutrients, the structure of the insect digestive tract is inevitably adapted to feeding habits. Among the Orthoptera, the digestive tracts of phytophagous locusts and carnivorous katydids have been studied for their adaptations to their food habits, while the adaptations of the digestive tracts of omnivorous insects have been less studied. In order to systematically study the adaptations of the digestive tracts of ground-nesting omnivorous insects to their feeding habits, this study was carried out with Loxoblemmus taicoun Saussure, 1877, Teleogryllus emma (Ohmachi & Matsuura, 1951), and Velarifictorus micado (Saussure, 1877). Through the use of a scanning electron microscope (SEM) and a VHX digital microscope, the digestive tract structures of these three most widespread and common omnivorous crickets in China were examined in order to better understand how omnivorous insects digestive tract structures differ from those of specialists. When we compared the morphological features of these crickets digestive tracts to those of phytophagous and carnivorous insects, we discovered six adaptive traits of omnivorous insects, including: (1) they have a shorter foregut and longer midgut and hindgut; (2) they have a well-developed muscular intestinal wall; (3) the spines in the inner wall of their crop are uniformly arranged and less chitinized; (4) the proventriculus is sclerotized and spherical, and the inner wall is accompanied by ossified large teeth; (5) they have well-developed cilia at the base of the crop and at the base of the ossified denticles; (6) they have only two lobulated gastric caeca. The study summarizes six characteristics of the digestive tract of omnivorous crickets that are compatible with their food habits, providing evidence and clues for further research on the relationship between the digestive tract and food habits in Orthoptera.

Variasi perilaku mencari makan pada semut rangrang Oecophylla smaragdina (Fabricius) pada habitat yang berbeda

Weaver ants (Oecophylla smaragdina (Fabricus)) are carnivorous insects and play a role as biocontrol agents in urban habitats. This study aims to analyze the foraging behavior of O. smaragdina in two different habitats, namely urban and non-urban. The two locations are characterized by differences in the intensity of human interaction and the distance between the trees and the tree canopy. The behavioral observation method uses all sampling events with five behavioral categories: lurking (M1), approaching (M2), carrying (M3), communicating between ants in a colony (K1), and competition with other ants (K2). We tested three different types of feed: chick scraps, Tenebrio molitor Linnaeus larvae, and sugar. The results showed that there were three sequences of foraging behavior in urban areas, namely: (1) M1, M2, K1, M3, (2) M1, M2, K1, M3, K2, and (3) M1, M2, K2, M3. Meanwhile, there is only one pattern in non-urban areas, namely M1, M2, M3. Approaching food (M2) and lurking food (M1) were the dominant responses of O. smaragdina in urban and non-urban areas. In urban areas, broiler chickens were the type of feed most approached by ants, followed by sugar and beetle larvae. O. smaragdina in non-urban areas also preferred chicken pieces as feed compared to the others, but only one individual O. smaragdina approached (M2) chicken pieces and none approached the others. Foraging ants are more active at high temperature and low humidity, compared to low temperature and high humidity. Therefore, the foraging behavior of O. smaragdina is influenced by habitat factors.

The chromosome-level genome of Chinese praying mantis Tenodera sinensis (Mantodea: Mantidae) reveals its biology as a predator.

The Chinese praying mantis, Tenodera sinensis (Saussure), is a carnivorous insect that preys on a variety of arthropods and small vertebrates, including pest species. Several studies have been conducted to understand its behavior and physiology. However, there is limited knowledge about the genetic information underlying its genome evolution, digestive demands, and predatory behaviors. Here we have assembled the chromosome-level genome of T. sinensis, representing the first sequenced genome of the family Mantidae, with a genome size of 2.54 Gb and scaffold N50 of 174.78 Mb. Our analyses revealed that 98.6% of BUSCO genes are present, resulting in a well-annotated assembly compared to other insect genomes, containing 25,022 genes. The reconstructed phylogenetic analysis showed the expected topology placing the praying mantis in an appropriate position. Analysis of transposon elements suggested the Gypsy/Dirs family, which belongs to long terminal repeat (LTR) transposons, may be a key factor resulting in the larger genome size. The genome shows expansions in several digestion and detoxification associated gene families, including trypsin and glycosyl hydrolase (GH) genes, ATP-binding cassette (ABC) transporter, and carboxylesterase (CarE), reflecting the possible genomic basis of digestive demands. Furthermore, we have found 1 ultraviolet-sensitive opsin and 2 long-wavelength-sensitive (LWS) opsins, emphasizing the core role of LWS opsins in regulating predatory behaviors. The high-quality genome assembly of the praying mantis provides a valuable repository for studying the evolutionary patterns of the mantis genomes and the gene expression profiles of insect predators.

Mouldy Matriarchs and Dangerous Daughters

Mouldy Matriarchs and Dangerous Daughters

Horizontally acquired antibacterial genes associated with adaptive radiation of ladybird beetles

BackgroundHorizontal gene transfer (HGT) has been documented in many herbivorous insects, conferring the ability to digest plant material and promoting their remarkable ecological diversification. Previous reports suggest HGT of antibacterial enzymes may have contributed to the insect immune response and limit bacterial growth. Carnivorous insects also display many evolutionary successful lineages, but in contrast to the plant feeders, the potential role of HGTs has been less well-studied.ResultsUsing genomic and transcriptomic data from 38 species of ladybird beetles, we identified a set of bacterial cell wall hydrolase (cwh) genes acquired by this group of beetles. Infection with Bacillus subtilis led to upregulated expression of these ladybird cwh genes, and their recombinantly produced proteins limited bacterial proliferation. Moreover, RNAi-mediated cwh knockdown led to downregulation of other antibacterial genes, indicating a role in antibacterial immune defense. cwh genes are rare in eukaryotes, but have been maintained in all tested Coccinellinae species, suggesting that this putative immune-related HGT event played a role in the evolution of this speciose subfamily of predominant predatory ladybirds.ConclusionOur work demonstrates that, in a manner analogous to HGT-facilitated plant feeding, enhanced immunity through HGT might have played a key role in the prey adaptation and niche expansion that promoted the diversification of carnivorous beetle lineages. We believe that this represents the first example of immune-related HGT in carnivorous insects with an association with a subsequent successful species radiation.

Bidirectional plant‐mediated interactions between rhizobacteria and shoot‐feeding herbivorous insects: a community ecology perspective

Plants interact with various organisms, aboveground as well as belowground. Such interactions result in changes in plant traits with consequences for members of the plant‐associated community at different trophic levels. Research thus far focussed on interactions of plants with individual species. However, studying such interactions in a community context is needed to gain a better understanding. Members of the aboveground insect community induce defences that systemically influence plant interactions with herbivorous as well as carnivorous insects. Plant roots are associated with a community of plant‐growth promoting rhizobacteria (PGPR). This PGPR community modulates insect‐induced defences of plants. Thus, PGPR and insects interact indirectly via plant‐mediated interactions. Such plant‐mediated interactions between belowground PGPR and aboveground insects have usually been addressed unidirectionally from belowground to aboveground. Here, we take a bidirectional approach to these cross‐compartment plant‐mediated interactions. Recent studies show that upon aboveground attack by insect herbivores, plants may recruit rhizobacteria that enhance plant defence against the attackers. This rearranging of the PGPR community in the rhizosphere has consequences for members of the aboveground insect community. This review focusses on the bidirectional nature of plant‐mediated interactions between the PGPR and insect communities associated with plants, including (a) effects of beneficial rhizobacteria via modification of plant defence traits on insects and (b) effects of plant defence against insects on the PGPR community in the rhizosphere. We discuss how such knowledge can be used in the development of sustainable crop‐protection strategies.

Dynamical Analysis of a Fractional Order Rosenzweig-MacArthur Model Incorporating Herbivore Induced Plant Volatile

Plants send signals through releasing Volatile Organic Compounds (VOCs), to attract beneficial natural carnivorous insects as reinforcement against harmful herbivorous insects which are responsible for hampering the growth of plants. In this work, we explore the dynamical behavior of a volatile mediated plant-herbivore-carnivore system with fractional order differential equations. Basic results on the existence, uniqueness, non-negativity and boundedness of the solutions, local and global stability of coexistence equilibrium points and limit cycles emerging through Hopf bifurcation are investigated. Stability behavior around coexistence equilibrium point changes with varying fractional order (α). Also the existence of Hopf bifurcation is established by considering the fractional order α as a bifurcation parameter. Moreover, the attraction factor of plant volatile to carnivore and predation rate for plant-herbivore are responsible for changing the system dynamics. Numerical simulations using matlab software are performed to support the analytical findings.

An improved core-shell microcapsule diet for rearing larvae of Mallada basalis (Neuroptera: Chrysopidae).

Green lacewings (Neuroptera: Chrysopidae) are important beneficial insects that can be raised on artificial diets for culturing experimental lines. An encapsulation method for embedding a core material within a sealed shell to prevent evaporation and biological contamination is crucial for providing food to these predatory insects. This study presents a new encapsulation process to mass produce a core-shell microcapsule diet for rearing Mallada basalis (Walker) (Neuroptera: Chrysopidae). This new process provided consistent quality control and effectiveness of the microcapsule diet (742.1 ± 11.3 μm in diameter and 44.2 ± 1.9 μm in shell thickness). Furthermore, significant differences were measured in larval development (24.0 ± 0.3 vs. 20.1 ± 0.6 days) and fecundity (465 ± 65.05 vs. 678 ± 54.91 eggs) on comparing the development of M. basalis larvae fed the old and new diets. Survival rates increased in both single- and group-rearing tests for adults fed the new diet during the larval stages. Neither diet affected predation rates for M. basalis larvae preying on nymphs of Aphis gossypii Glover (Hemiptera: Aphididae) and Bemisia argentifolli Bellows and Perring (Hemiptera: Aleyrodidae). Compared with the old process, the new encapsulation process requires reduced effort during preparation, and reduces the weight, cost and space occupied by the equipment. The results of this study suggest that this new spherical microcapsule artificial diet is suitable for group-rearing of M. basalis and may be appropriate for mass-rearing of other types of carnivorous insects. © 2019 Society of Chemical Industry.

What five insects told us about how a native plant copes with real-world problems

What five insects told us about how a native plant copes with real-world problems

The nutritional ecology of maturation in a carnivorous insect

Herbivores and omnivores, faced with a nutritionally complex diet, have evolved the capacity to balance the intake of specific nutrients. Recent studies have found that carnivores also have this capacity, despite their more nutritionally homogeneous diet. However, unlike herbivores and omnivores who prioritize protein intake when restricted to imbalanced foods, carnivores instead show much stricter regulation of fat intake. These choices to over- or under-consume nutrients when the intake target cannot be achieved are known as rules of compromise. To date, studies examining these rules have all been carried out at a single life stage, and it is unclear if these rules regarding the prioritization of nutrients are fixed or labile. We address this question with a carnivorous beetle, Nicrophorus vespilloides. We use a combination of dietary restriction and choice tests to determine the intake target and rules of compromise in reproductively mature beetles and in newly emerged adults undergoing a period of maturation feeding. We show that, despite having very similar intake targets, the rules of compromise differ between the 2 life stages. Although mature adults follow the typical carnivore rule of fat prioritization, immature adults behave more like omnivores, showing strict regulation of protein intake, resulting in obesity when restricted to protein-poor diets. These alternate rules suggest different mechanisms or capacities to cope with excess protein across these life stages. Examining how intake targets and rules of compromise change across life stages could be a valuable approach for our understanding of how animals will fare under rapidly changing environmental conditions.

Multilevel feeding ecology – an introduction

All organisms need to acquire nourishment in sufficient quantity and quality to grow and reproduce. Food sources need to be located and choices need to be made with respect to their favourability. This issue addresses host location (plants by phytophagous insects, prey by predators or parasitoids) and performance (of phytophagous and carnivorous insects), and the involvement of microorganisms and plant defence responses. All are relevant for understanding the complex interactions within insect communities and the application of biological pest control.

Mechanical defenses of plant extrafloral nectaries against herbivory

ABSTRACTExtrafloral nectaries play an important role in plant defense against herbivores by providing nectar rewards that attract ants and other carnivorous insects. However, extrafloral nectaries can themselves be targets of herbivory, in addition to being exploited by nectar-robbing insects that do not provide defensive services. We recently found that the extrafloral nectaries of Vicia faba plants, as well as immediately adjacent tissues, exhibit high concentrations of chemical toxins, apparently as a defense against herbivory. Here we report that the nectary tissues of this plant also exhibit high levels of structural stiffness compared to surrounding tissues, likely due to cell wall lignification and the concentration of calcium oxalate crystals in nectary tissues, which may provide an additional deterrent to herbivore feeding on nectary tissues.

First chromosomal study of Mantophasmatodea: Karyotype of Karoophasma biedouwense (Austrophasmatidae)

We have investigated for the first time the chromosomes of Karoophasma biedouwense, a species belonging to the Mantophasmatodea, a recently discovered order of carnivorous insects. Our study has revealed that males of this species display testes with numerous seminal tubes (follicles), as in other Polyneoptera, and short tubular seminal vesicles embedded in a utricular gland. The karyotype consists of 2n = 12A + X and biarmed, meta/submetacentric chromosomes (fundamental number of arms: FN = 26) with blocks of heterochromatin around centromeres. The autosomes are classified into two size groups, one represented by a single, very large pair of autosomes, the other by five smaller pairs which constitute a continuous series gradually decreasing in size. Among monocentric orders of Polyneoptera, K. biedouwense shares its low chromosome number, 2n = 13, as also found with some Orthoptera (Acridoidea, Grylloidea, Gryllacridoidea). Male meiosis is of the classical pre-reductional type and the X(0) sex determination system is probably an ancestral state. Use of FISH along with an 18S rDNA probe revealed multiple ribosomal clusters, which most likely represent an apomorphic condition. We identified the ancestral insect telomeric sequence (TTAGG)n in the terminal areas of the chromosomes. Currently available data on the polyneopteran orders putatively related to Mantophasmatodea showed a wide variability of cytogenetic characteristics within and between them. The only character allowing some tentative inference to be made on the ancestry of K. biedouwense is its low chromosome number, the karyotypic pattern so far unreported for the Polyneoptera except in certain Orthoptera.

Optimizing Crops for Biocontrol of Pests and Disease.

Volatile compounds and extrafloral nectar are common defenses of wild plants; however, in crops they bear an as-yet underused potential for biological control of pests and diseases. Odor emission and nectar secretion are multigene traits in wild plants, and thus form difficult targets for breeding. Furthermore, domestication has changed the capacity of crops to express these traits. We propose that breeding crops for an enhanced capacity for tritrophic interactions and volatile-mediated direct resistance to herbivores and pathogens can contribute to environmentally-friendly and sustainable agriculture. Natural plant volatiles with antifungal or repellent properties can serve as direct resistance agents. In addition, volatiles mediating tritrophic interactions can be combined with nectar-based food rewards for carnivores to boost indirect plant defense.

Essential Oils as “A Cry for Help”. A Review

This work is an update of a recently published review and is consistently referred to this article and recent findings about plants' indirect defense are added on. Herbivore induced plant volatiles (HIPVs) and their effects on the third trophic level that involves predators and parasitoids are discussed. The fact that plants are not passive individuals is confirmed on the basis of several studies. Plants can perceive and respond to cues in their environments with plastic morphological, physiological and behavioral traits. Plasticity allows plants to tailor their defenses to their current and expected risks caused by herbivores. The "cry for help" of plants is also observed from the carnivores' point of view. The volatile mixture contains crucial information for decisions of carnivorous insects. Furthermore, the most important methods to examine the behavioral response of carnivorous insects to HIPVs are presented not only in laboratory set ups but also in the field. Manipulations of plants by silencing genes or over-expressing genes can help to understand mechanisms of indirect defense. Various interesting examples of indirect defense reveal the possibility to use HIPVs in biological control. Therefore, the application of synthetic pesticides, that pollute the environment, may be reduced in the future.

Parasitism overrides herbivore identity allowing hyperparasitoids to locate their parasitoid host using herbivore-induced plant volatiles.

Foraging success of predators profoundly depends on reliable and detectable cues indicating the presence of their often inconspicuous prey. Carnivorous insects rely on chemical cues to optimize foraging efficiency. Hyperparasitoids that lay their eggs in the larvae or pupae of parasitic wasps may find their parasitoid hosts developing in different herbivores. They can use herbivore-induced plant volatiles (HIPVs) to locate parasitized caterpillars. Because different herbivore species induce different HIPV emission from plants, hyperparasitoids may have to deal with large variation in volatile information that indicates host presence. In this study, we used an ecogenomics approach to first address whether parasitized caterpillars of two herbivore species (Pieris rapae and P.brassicae) induce similar transcriptional and metabolomic responses in wild Brassica oleracea plants and, second, whether hyperparasitoids Lysibia nana are able to discriminate between these induced plant responses to locate their parasitoid host in different herbivores under both laboratory and field conditions. Our study revealed that both herbivore identity and parasitism affect plant transcriptional and metabolic responses to herbivory. We also found that hyperparasitoids are able to respond to HIPVs released by wild B.oleracea under both laboratory and field conditions. In addition, we observed stronger attraction of hyperparasitoids to HIPVs when plants were infested with parasitized caterpillars. However, hyperparasitoids were equally attracted to plants infested by either herbivore species. Our results indicate that parasitism plays a major role in HIPV-mediated plant-hyperparasitoid interactions. Furthermore, these findings also indicate that plant trait-mediated indirect interaction networks play important roles in community-wide species interactions.

Food‐availability dependent premature metamorphosis in the bean blister beetle Epicauta gorhami (Coleoptera: Meloidae), a hypermetamorphic insect that feeds on grasshopper eggs in the larval stage

AbstractLarvae of the bean blister beetle, Epicauta gorhami, feed on only grasshopper eggs and undergo hypermetamorphosis with pseudopupal diapause in the fifth instar. Whether E. gorhami larvae enter pseudopupal diapause or pupate directly from the fourth instar is controlled by temperature and photoperiod. In nature, larvae are confronted with a significant variation in the availability of food, suggesting the possibility that feeding conditions may also affect the diapause incidence. Here, we addressed this issue by changing the feeding conditions in the fourth instar under conditions of 16 h light : 8 h dark (LD 16 : 8) at 25°C. Food deprivation reduced the length of instar and increased the tendency to pupate, leading to the early eclosion of a small adult. Even non‐feeding fourth‐instar larvae pupated. Regardless of the timing of food deprivation, the post‐feeding larval period was constant and equivalent to that of ad libitum‐fed larvae, suggesting that premature exhaustion of the food supply triggers the initiation of pupation. In agreement with these results, when larvae were fed on intact grasshopper egg pods of various sizes from four species, those that fed on smaller egg pods had a decreased tendency to pseudopupate (i.e., to enter diapause). Food‐deprived larvae showed a clearer photoperiodic response and had a shorter critical day‐length. Thus, in E. gorhami, feeding conditions do not affect pupation success, but do affect the tendency to pupate or pseudopupate. This is the first report of the occurrence of premature pupation in carnivorous insects. We discuss our findings in the context of the natural history and behavioral ecology of E. gorhami.

Odor Uniformity among Tomato Individuals in Response to Herbivore Depends on Insect Species

Plants produce specific volatile organic compound (VOC) blends in response to herbivory. Herbivore-induced blends may prime the plant for future attack or attract carnivorous insects; these responses have been considered adaptive for plants. If herbivores differentially modify the VOC emission among individuals within a group of plants they feed upon, then plant responses to herbivores will not only produce specific blends but also variation in odor among individuals, i.e. individuals smell the same, then having a uniform odor. We investigated the VOC emission variation or uniformity among tomato individuals (Solanum lycopersicum L. cv. Castlemart) in response to moderate wounding by (1) nymphs of the psyllid Bactericera cockerelli (Sulc.) (TP); (2) Lepidoptera chewing-feeding larvae of Fall Armyworm (Spodoptera frugiperda Smith) (FAW) and (3) of Cabbage Looper (Trichoplusia ni Hübner) (CL), and (4) mechanical damage (MD). We used a ratio-based analysis to compare the fold-change in concentration from constitutive to induced VOC emission. We also used size and shape analysis to compare the emission of damaged and non-damaged individuals. Aside of finding herbivore-specific blends in line with other studies, we found patterns not described previously. We detected constitutive and induced odor variation among individuals attacked by the same herbivore, with the induced odor uniformity depending on the herbivore identity. We also showed that the fold-change of VOCs from constitutive to induced state differed among individuals independently of the uniformity of the blends before herbivore attack. We discuss our findings in the context of the ecological roles of VOCs in plant-plant and plant-carnivore insects’ interactions.

Mass breeding larvae of the critically endangered diving beetles Dytiscus sharpi sharpi and Dytiscus sharpi validus (Coleoptera: Dytiscidae)

For conservation purposes, and to supply critically endangered insects for laboratory use, a system for artificial breeding is crucial. However, in the case of carnivorous insects such as diving beetles, the larvae must be isolated because they are cannibalistic. We developed a method for mass breeding the larvae of two diving beetles, Dytiscus sharpi sharpi (Wehncke) and Dytiscus sharpi validus (Regimbart) (Coleoptera: Dytiscidae), which are designated critically endangered species in Japan. Ten to twenty larvae were raised in a small tank (35 cm × 25 cm × 10 cm; water depth 7 cm) with Rana ornativentris (Werner) tadpoles as prey. At low prey density, ~80 % of the larvae were cannibalized. At moderate prey density, 50–60 % were cannibalized. However, at high prey density, <3 % were cannibalized. Well-fed mass-bred adults were larger than individually bred and field-collected adults. This mass breeding method can be used for the conservation and breeding of these rare diving beetles in a manageable number of aquaria.

Contrasting patterns of herbivore and predator pressure on invasive and native plants

Invasive non-native plant species often harbor fewer herbivorous insects than related native plant species. However, little is known about how herbivorous insects on non-native plants are exposed to carnivorous insects, and even less is known on plants that have recently expanded their ranges within continents due to climate warming. In this study we examine the herbivore load (herbivore biomass per plant biomass), predator load (predator biomass per plant biomass) and predator pressure (predator biomass per herbivore biomass) on an inter-continental non-native and an intra-continental range-expanding plant species and two congeneric native species. All four plant species co-occur in riparian habitat in north-western Europe. Insects were collected in early, mid and late summer from three populations of all four species. Before counting and weighing the insects were classified to trophic guild as carnivores (predators), herbivores, and transients. Herbivores were further subdivided into leaf-miners, sap-feeders, chewers and gallers. Total herbivore loads were smaller on inter-continental non-native and intra-continental range-expanding plants than on the congeneric natives. However, the differences depended on time within growing season, as well as on the feeding guild of the herbivore. Although the predator load on non-native plants was not larger than on natives, both non-native plant species had greater predator pressure on the herbivores than the natives. We conclude that both these non-native plant species have better bottom-up as well as top-down control of herbivores, but that effects depend on time within growing season and (for the herbivore load) on herbivore feeding guild. Therefore, when evaluating insects on non-native plants, variation within season and differences among feeding guilds need to be taken into account.