Are insect pollinators more generalist than insect herbivores?

Recent community-level studies have acknowledged that generalist species are more widespread than previously thought and highlighted their preponderant impact on community functioning and evolution. It is suggested that the type of interaction, trophic versus mutualistic, should affect species generalization level; however, no direct comparison has been made yet. Here, we performed such a comparison using 44 plant–insect networks describing either pollination or herbivory communities. Our analysis shows that the type of interaction does indeed have an impact on various aspects of species generalism, from the distribution of generalism in the community to the phylogenetic diversity of the plants with which a given insect species interacts. However, the amplitude of the observed differences depends on the aspect of species generalism studied. While the non-quantitative and quantitative measures of generalism suggest that pollinators interact with more plant species and more evenly than herbivores, phylogenetic measures clearly show that herbivores interact with plant species far more closely related to each other than pollinators. This comparative approach offers a promising perspective to better understand the functioning and evolution of multispecies assemblages by pointing out some fundamental singularities of communities depending on the type of interaction considered.     

Intrinsic glycosylation potentials of insect cell cultures and insect larvae

Summary The glycosylation and subsequent processing of native and recombinant glycoproteins expressed in established insect cell lines and insect larvae were compared. TheSpodoptera frugiperda (Sf21) andTrichoplusia ni (TN-368 and BTI-Tn-5B1-4) cell lines possessed several intrinsic glycoproteins that are modified with both N- and O-linked oligosaccharides. The N-linked oligosaccharides were identified as both the simple (high mannose) and complex (containing sialic acid) types. Similarly, theT. ni larvae also possessed intrinsic glycoproteins that were modified with O-linked and simple and complex N-linked oligosaccharides. Additionally, human placental, secreted alkaline phosphatase (SEAP) produced during replication of a recombinant baculovirus inT. ni larvae was modified with complex oligosaccharide having sialic acid linked α(2–6) to galactose.     

Effect of the insect pathogenic bacterium Photorhabdus on insect phagocytes

Photorhabdus are insect pathogenic bacteria that replicate within the insect haemocoel following release from their entomopathogenic nematode symbionts. To investigate how they escape the cellular immune response we examined the effects of two strains of Photorhabdus, W14 and K122, on Manduca sexta phagocytes (haemocytes), in vitro and in vivo. Following injection of Esherichia coli into Manduca larvae, these non-pathogenic bacteria are rapidly cleared from the haemolymph and the number of free haemocytes transiently increases. In contrast, following injection of either strain of pathogenic Photorhabdus, the bacteria grow rapidly while the number of haemocytes decreases dramatically. In vitro incubation of haemocytes with either Photorhabdus supernatant reduced haemocyte viability, and the W14 supernatant caused distinct changes in the actin cytoskeleton morphology of different haemocyte cell types. In phagocytosis assays both Photorhabdus strains can inhibit their own phagocytosis whether the bacterial cells are alive or dead. Further, the supernatant of W14 also contains a factor capable of inhibiting the phagocytosis of labelled E. coli. Together these results suggest that Photorhabdus evades the cellular immune response by killing haemocytes and suppressing phagocytosis by mechanisms that differ between strains.     

The insect caspases

Developmental and tissue homeostasis is a delicate balance between cell proliferation and cell death. The activation of caspases, a conserved family of cysteine proteases, is a main event in the initiation and execution of programmed cell death. While caspases have been characterized from many organisms, comparatively little is known about insect caspases. In Drosophila melanogaster, seven caspases have been characterized; three initiators and four effectors. In mosquitoes, several putative caspases have been identified in the genomes of Aedes aegypti and Anopheles gambiae. A small number of caspases have been identified in the Lepidoptera, the flour beetle, Tribolium castaneum, and the pea aphid, Acyrthosiphon pisum. The availability of new insect genome sequences will provide a unique opportunity to examine the caspase family across an evolutionarily diverse phylum and will provide valuable insights into their function and regulation.     

Odor discrimination using insect electroantennogram responses from an insect antennal array

Insects have a highly developed olfactory sensory system, mainly based in their antennae, for the detection and discrimination of volatile compounds in the environment. Electroantennogram (EAG) response profiles of five different insect species, Drosophila melanogaster, Heliothis virescens, Helicoverpa zea, Ostrinia nubilalis and Microplitis croceipes, showed different, species-specific EAG response spectra to 20 volatile compounds tested. The EAG response profiles were then reconstructed for each compound across the five insect species. Most of the compounds could be distinguished by comparing the response spectra. We then used a four-antenna array, called a Quadro-probe EAG, to see if we could discriminate among odorants based on the relative EAG amplitudes evoked when the probe was placed in plumes in a wind tunnel and in a field. Stable EAG responses could be simultaneously and independently recorded with four different insect antennae mounted on the Quadro-probe, and different volatile compounds could be distinguished in real time by comparing relative EAG responses with a combination of differently tuned insect antennae. Regardless of insect species or EAG amplitudes, antennae on the Quadro-probe maintained their responsiveness with higher than 1 peak/s of time resolution.     

Evolution of insect olfaction

Neuroethology utilizes a wide range of multidisciplinary approaches to decipher neural correlates of natural behaviors associated with an animal's ecological niche. By placing emphasis on comparative analyses of adaptive and evolutionary trends across species, a neuroethological perspective is uniquely suited to uncovering general organizational and biological principles that shape the function and anatomy of the nervous system. In this review, we focus on the application of neuroethological principles in the study of insect olfaction and discuss how ecological environment and other selective pressures influence the development of insect olfactory neurobiology, not only informing our understanding of olfactory evolution but also providing broader insights into sensory processing.     

Aminotransferase from insect cells

The presence of transaminase activity is demonstrated in the cultured insect cell line Sf21 (Spodoptera frugiperda) at a level sufficient to enable replacement of rat liver in an undergraduate student experiment designed to demonstrate enzyme activity responsible for amino acid interconversions.     

Mechanisms underlying insect chill-coma

At their critical thermal minimum (CT_min) insects enter chill-coma, a reversible state where neuromuscular transmission and movement cease. The physiological mechanisms responsible for the insect CT_min remain poorly understood despite the regular use of chill-coma onset and recovery as a means to assess evolved or acquired variation in low temperature tolerance. In this review, we summarize the use of chill-coma as a metric of thermal tolerance to date, and synthesise current knowledge on the nature and plasticity of lower thermal limits to present probable physiological mechanisms of cold-induced failure. Chill-coma is likely to be driven by an inability to maintain ionic homeostasis through the effects of temperature on ion-motive ATPases, ion channel gating mechanisms, and/or the lipid membrane, leading to a loss of nerve and muscle excitability.