Comparative neuroanatomy of the antennal lobes of 2 homopteran species

Brain Organization of Apolygus lucorum: A Hemipteran Species With Prominent Antennal Lobes

The anatomical organization of distinct regions in the insect brain often reflects their functions. In the present study, the brain structure of Apolygus lucorum was examined by using immunolabeling and three-dimensional reconstruction. The results revealed the location and volume of prominent neuropils, such as the antennal lobes (AL), optic lobes (OL), anterior optic tubercles (AOTU), central body (CB), lateral accessory lobes (LAL), mushroom lobes, and distinct tritocerebral neuropils. As expected, this brain is similar to that of other insects. One exception, however, is that the antennal lobes were found to be the most prominent neuropils. Their size relative to the entire brain is the largest among all insect species studied so far. In contrast, the calyx, a region getting direct input from the antennal lobe, has a smaller size relative to the brain than that of other species. These findings may suggest that olfaction plays an essential role for A. lucorum.

Glomerular Organization of the Antennal Lobes of the Diamondback Moth, Plutella xylostella L

The antennal lobe of the moth brain is the primary olfactory center processing information concerning pheromones and plant odors. Plutella xylostella is a major worldwide pest of cruciferous vegetables and its behavior is highly dependent on their olfactory system. However, detailed knowledge of the anatomy and function of the P. xylostella olfactory system remains limited. In the present study, we present the 3-Dimentional (3-D) map of the antennal lobe of P. xylostella, based on confocal microscopic analysis of glomerular segmentation and Neurobiotin backfills of Olfactory Receptor Neurons (ORNs). We identified 74–76 ordinary glomeruli and a macroglomerular complex (MGC) situated at the entrance of the antennal nerve in males. The MGC contained three glomeruli. The volumes of glomeruli in males ranged from 305.83 ± 129.53 to 25440.00 ± 1377.67 μm³. In females, 74–77 glomeruli were found, with the largest glomerulus ELG being situated at the entrance of the antennal nerve. The volumes of glomeruli in females ranged from 802.17 ± 95.68 to 8142.17 ± 509.46 μm³. Sexual dimorphism was observed in anomalous supernumerary, anomalous missing, shape, size, and array of several of the identified glomeruli in both sexes. All glomeruli, except one in the antennal lobe (AL), received projections of antennal ORNs. The glomeruli PV1 in both sexes received input from the labial palp nerve and was assumed as the labial pit organ glomerulus (LPOG). These results provide a foundation for better understanding of coding mechanisms of odors in this important pest insect.

The reproductive strategy and the vibrational duet of the leafhopper Empoasca vitis

The recent description of a new vibrational mating disruption method to control the leafhopper Scaphoideus titanus Ball opened questions about its possible application to other leafhopper pests. Since the prerequisite for the method's successful application is a deep knowledge of the species mating behavior and the exact role of associated signals, we conducted behavioral assays on the green leafhopper Empoasca vitis Göthe, a pest of grapevine and other crops in Europe and Asia. Laser vibrometer recordings of single and paired individuals (male and female) during a 24-h period enabled us to detect and describe 2 male and 1 female signal. The pair formation starts when the female replies to a male call and a duet is established, then it continues through 2 different behavioral stages: Location and Courtship. The proper courtship begins only when the male locates the female. The latter is characterized by a significant change in temporal parameters that regards both the signals and the duet structure. Although the male calling activity and the female replying rate were the same during the 24 h, a lower number of matings was recorded during the night. We discuss the possible role of vision and of the species ecology as factors of reproductive success and mating strategy. Our conclusion is that the mechanical mating disruption technique seems feasible for future application to this species.

Olfaction, experience and neural mechanisms underlying mosquito host preference

Mosquitoes are best known for their proclivity towards biting humans and transmitting bloodborne pathogens, but there are over 3500 species, including both blood-feeding and non-blood-feeding taxa. The diversity of host preference in mosquitoes is exemplified by the feeding habits of mosquitoes in the genus Malaya that feed on ant regurgitation or those from the genus Uranotaenia that favor amphibian hosts. Host preference is also by no means static, but is characterized by behavioral plasticity that allows mosquitoes to switch hosts when their preferred host is unavailable and by learning host cues associated with positive or negative experiences. Here we review the diverse range of host-preference behaviors across the family Culicidae, which includes all mosquitoes, and how adaptations in neural circuitry might affect changes in preference both within the life history of a mosquito and across evolutionary time-scales.

Organization of the antennal lobes in the praying mantis (Tenodera aridifolia)

Olfaction in insects plays pivotal roles in searching for food and/or for sexual partners. Although many studies have focused on the olfactory processes of nonpredatory insect species, little is known about those in predatory insects. Here, we investigated the anatomical features of the primary olfactory center (antennal lobes) in an insect predator whose visual system is well developed, the praying mantis Tenodera aridifolia. Both sexes of T. aridifolia were found to possess 54 glomeruli, and each glomerulus was identified based on its location and size. Moreover, we found a sexual dimorphism in three glomeruli (macroglomeruli) located at the entrance of the antennal nerves, which are 15 times bigger in males than their homologs in females. We additionally deduced the target glomeruli of olfactory sensory neurons housed in cognate types of sensilla by degenerating the sensory afferents. The macroglomeruli received sensory inputs from grooved peg sensilla, which are present in a large number at the proximal part of the males' antennae. Furthermore, our findings suggest that glomeruli at the posteriodorsal part of the antennal lobes receive sensory information from putative hygro- and thermosensitive sensilla. The origins of projections connected to the protocerebrum are also discussed. J. Comp. Neurol. 525:1685-1706, 2017. © 2016 Wiley Periodicals, Inc.

Variations on a Theme: Antennal Lobe Architecture across Coleoptera

Beetles comprise about 400,000 described species, nearly one third of all known animal species. The enormous success of the order Coleoptera is reflected by a rich diversity of lifestyles, behaviors, morphological, and physiological adaptions. All these evolutionary adaptions that have been driven by a variety of parameters over the last about 300 million years, make the Coleoptera an ideal field to study the evolution of the brain on the interface between the basic bauplan of the insect brain and the adaptions that occurred. In the current study we concentrated on the paired antennal lobes (AL), the part of the brain that is typically responsible for the first processing of olfactory information collected from olfactory sensilla on antenna and mouthparts. We analyzed 63 beetle species from 22 different families and thus provide an extensive comparison of principal neuroarchitecture of the AL. On the examined anatomical level, we found a broad diversity including AL containing a wide range of glomeruli numbers reaching from 50 to 150 glomeruli and several species with numerous small glomeruli, resembling the microglomerular design described in acridid grasshoppers and diving beetles, and substructures within the glomeruli that have to date only been described for the small hive beetle, Aethina tumida. A first comparison of the various anatomical features of the AL with available descriptions of lifestyle and behaviors did so far not reveal useful correlations. In summary, the current study provides a solid basis for further studies to unravel mechanisms that are basic to evolutionary adaptions of the insect olfactory system.