Uniquely positioned at the intersection of sexual selection, nutritional ecology and life-history theory, nuptial gifts are widespread and diverse. Despite extensive empirical study, we still have only a rudimentary understanding of gift evolution because we lack a unified conceptual framework for considering these traits. In this opinion piece, we tackle several issues that we believe have substantively hindered progress in this area. Here, we: (i) present a comprehensive definition and classification scheme for nuptial gifts (including those transferred by simultaneous hermaphrodites), (ii) outline evolutionary predictions for different gift types, and (iii) highlight some research directions to help facilitate progress in this field.

We present a DNA barcoding study on the insect order Orthoptera that was generated in collaboration between four barcoding projects in three countries, viz. Barcoding Fauna Bavarica (Germany), German Barcode of Life, Austrian Barcode of Life and Swiss Barcode of Life. Our data set includes 748 COI sequences from 127 of the 162 taxa (78.4%) recorded in the three countries involved. Ninety-three of these 122 species (76.2%, including all Ensifera) can be reliably identified using DNA barcodes. The remaining 26 caeliferan species (families Acrididae and Tetrigidae) form ten clusters that share barcodes among up to five species, in three cases even across different genera, and in six cases even sharing individual barcodes. We discuss incomplete lineage sorting and hybridization as most likely causes of this phenomenon, as the species concerned are phylogenetically young and hybridization has been previously observed. We also highlight the problem of nuclear mitochondrial pseudogenes (numts), a known problem in the barcoding of orthopteran species, and the possibility of Wolbachia infections. Finally, we discuss the possible taxonomic implications of our barcoding results and point out future research directions.

Genitalia are rapidly evolving morphological structures most likely under sexual selection. Due to their internal nature they are often hidden inside the body, thus morpho-functional studies of animal genitalia are broadly lacking. Males of some bushcricket taxa bear paired genital appendices called titillators, the exact function of which is unknown since they are obscured inside the female body during pairing. To investigate titillator morphology and possible function during copulation, we studied the bushcricket Metrioptera roeselii (Hagenbach, 1822) using a novel combination of independent, yet complementary, techniques. Copulating pairs were snap-frozen and scanned by X-ray micro-computed tomography (μCT) to visualize the coupling of male and female genitalia in situ. Video recordings of copulating pairs also showed rhythmical insertion of male titillators into the female's genital chamber, where they percuss a softened structure on the female's subgenital plate. Movements did not induce damage to the female's structure, which lacks any sclerotized genital counterparts. Instead, scanning electron microscopy and histological sections show the female subgenital plate to be covered with two different types of sensory receptors at the contact zone between the male's titillator and the female genital chamber. We interpret the non-harmful function of the titillator processes, the lack of a genital counter-structure and the presence of sensory cells on the female's subgenital plate as indicators of a copulatory courtship function of titillators, subject to sexual selection by female choice.

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Sexual selection is a major force driving evolution and is intertwined with ecological factors. Differential allocation of limited resources has a central role in the cost of reproduction. In this paper, I review the costs and benefits of mating in tettigoniids, focussing on nuptial gifts, their trade-off with male calling songs, protandry and how mate density influences mate choice. Tettigoniids have been widely used as model systems for studies of mating costs and benefits; they can provide useful general insights. The production and exchange of large nuptial gifts by males for mating is an important reproductive strategy in tettigoniids. As predicted by sexual selection theory spermatophylax size is condition dependent and is constrained by the need to invest in calling to attract mates also. Under some circumstances, females benefit directly from the nuptial gifts by an increase in reproductive output. However, compounds in the nuptial gift can also benefit the male by prolonging the period before the female remates. There is also a trade-off between adult male maturation and mating success. Where males mature before females (protandry) the level of protandry varies in the direction predicted by sperm competition theory; namely, early male maturation is correlated with a high level of first inseminations being reproductively successful. Lastly, mate density in bushcrickets is an important environmental factor influencing the behavioural decisions of individuals. Where mates are abundant, individuals are more choosey of mates; when they are scarce, individuals are less choosey. This review reinforces the view that tettigoniids provide excellent models to test and understand the economics of matings in both sexes.

Copulation duration varies considerably across species, but few comparative studies have examined factors that might underlie such variation. We examined the relationship between copulation duration (prior to spermatophore transfer), the complexity of titillators (sclerotized male genital contact structures), spermatophore mass and male body mass across 54 species of bushcricket. Using phylogenetic comparative analyses, we found that copulation duration was much longer in species with titillators than those without, but it was not longer in species with complex compared with simple titillators. A positive relationship was found between spermatophore size and copulation duration prior to ejaculate transfer, which supports the hypothesis that this represents a period of mate assessment. The slope of this relationship was steeper in species with simple rather than complex titillators. Although the data suggest that the presence of titillators is necessary to maintain long copulation prior to ejaculate transfer, mechanisms underlying this association remain unclear

Males of certain bushcrickets (Orthoptera: Ensifera: Tettigoniidae) possess sclerotized internal genital devices termed titillators. These titillators are paired chitinized structures for which the function remains to be completely determined. We studied the role of the titillators during copulation in the bushcricket Metrioptera roeselii (Hagenbach, 1822), in the context of four a priori hypotheses for their function during mating and insemination: (1) bushcricket titillators act as anchors to secure matings; (2) titillators facilitate sperm removal or sperm dumping in the polyandrous females; (3) titillators stimulate the females during copulation; and/or (4) titillators are organs that assure an accurate spermatophore transfer. To distinguish between those hypotheses, virgin females were mated with males of five groups: unmanipulated (Control), males with titillator tips removed (T‐tips); males with both titillator arms cut in half (T½); and males with titillator arms completely ablated on one side (T‐1); or on both sides (T‐2). These manipulations were chosen to test the response towards an increasing removal of the titillator processes (T‐tips, T½, T‐2) and to include a strongly asymmetric manipulation for comparison (T‐1 vs. T‐2). Male titillators were observed to be rhythmically inserted into the female's genital chamber during copulation. Females generally stayed motionless during titillation, with resistance behaviours observed at a low rate but increasing to 38% when females mated with T‐1 males. In some cases, female resistance behaviour resulted in severe male damage, although pairs never separated. After remating of females, we traced no sperm attached to titillators of the second mate. This fact contradicts any sperm removal function. Titillator manipulation reduced the capacity of a male to attach the spermatophore. This spermatophore detachment was a result of titillator ablation without a significant relation to rhythmical titillator movements or correlation with female resistance behaviour. We therefore conclude that titillators in M. roeselii function as tools to stimulate the females and accurately place the spermatophore.

In Germany, the decline of insect biomass was observed in nature conservation areas in agricultural landscapes. One of the main causal factors discussed is the use of synthetic pesticides in conventional agriculture. In a Germany-wide field study, we collected flying insects using Malaise traps in nature conservation areas adjacent to agricultural land. We used a multi-component chemical trace element analysis to detect 92 common agricultural pesticides in ethanol from insect traps sampled in May and August 2020. In total, residues of 47 current use pesticides were detected, and insect samples were on average contaminated with 16.7 pesticides. Residues of the herbicides metolachlor-S, prosulfocarb and terbuthylazine, and the fungicides azoxystrobin and fluopyram were recorded at all sites. The neonicotinoid thiacloprid was detected in 16 of 21 nature conservation areas, most likely due to final use before an EU-wide ban. A change in residue mixture composition was noticeable due to higher herbicide use in spring and increasing fungicide applications in summer. The number of substances of recorded residues is related to the proportion of agricultural production area in a radius of 2000 m. Therefore, a drastic pesticide reduction in large buffers around nature conservation areas is necessary to avoid contamination of their insect fauna.