Plant-insect relationships are continuously changing (Bruce 2015) and include both mutualistic interactions (Hale et al. 2020), such as pollination (Valdovinos 2019), and antagonistic interactions, primarily herbivory (Bascompte et al. 2003). These interactions shape the structure and dynamics of plant populations and influence overall ecosystem functioning (Bruce 2015). Pollinating insects play an important role in the reproduction of many plant species (Katumo et al. 2022), and antagonistic interactions, such as herbivory, can negatively affect plant fitness and adaptability (Schoonhoven et al. 2005). Pollination contributes to maintaining genetic diversity and ecosystem productivity (Willmer 2011). In addition, biotic and abiotic factors, resource availability, and habitat changes caused by human activities (Pincebourde et al. 2017) also influence plant-insect relationships. In some cases, alterations in plant-insect interactions lead to cascading effects on other ecosystem components (Ojija 2024).

Grasslands play a central role in maintaining biodiversity, as they support a high diversity of plant and animal species. Within these grasslands, steppe relict habitats play a critical role in maintaining biodiversity and supporting food webs (Dengler et al. 2014; Wesche et al. 2016). One plant species characteristic of these steppe relict grasslands is Crambe tataria Sebeók, considered vulnerable and rare in Romania (Oltean et al. 1994) and legally protected at national level, although listed as Least Concern in Europe (Kell 2011). Recognized as a postglacial steppe relict (Béres 1996), C. tataria is confined to mesoxerophilous to mesophilous grasslands. In Romania, its distribution is limited entirely to the Continental biogeographic region. Recent field data indicate that its populations are declining, primarily due to anthropogenic pressures and habitat degradation (Chirilă 2023). The grassland habitats where this species occurs are threatened by overgrazing, mechanized mowing, grassland conversion to agricultural lands, and the spread of invasive plant species. Crambe tataria occurs in areas with moderate to steep slopes, south-facing, annual mean temperature between 6 and 10°C, elevation between 21 and 500 m a.s.l., and annual precipitation between 450 and 700 mm. The species can also be found in other types of habitats, such as orchards, agricultural lands, and vineyards (Chirilă 2023).

Crambe tataria is characteristic of the following Natura 2000 habitats (Gafta and Mountford 2008; Oroian et al. 2015, 2017): 6210* Semi-natural xerophilous grasslands and scrub facies on calcareous substrates; 6250* Pannonian steppe grasslands on loess; 6240* Sub-Pannonian steppe grasslands; and 62C0* Ponto-Sarmatian steppes. In Romania, C. tataria can be identified in the following habitats (Doniţă et al. 2005): R3131 Ponto-Pannonic thickets of dwarf almond (Amygdalus nana L.); R3404 Ponto-panonic grasslands of Festuca rupicola Heuff. and Koeleria macrantha (Ledeb.) Schult.; R3418 Ponto-panonic grasslands of Agropyron cristatum (L.) Gaertn. and Kochia prostrata (L.) Schrad.; and R3409 Pontic grasslands of Stipa lessingiana Trin. & Rupr., S. pulcherrima K.Koch, and S. joannis Čelak. Several grasslands from Moldova and Transylvania in Romania have undergone partial abandonment, shrub invasion, or local disturbances. Only a few grasslands are maintained by extensive grazing and periodic mowing.

Interactions with insects are important for understanding the ecology of some species (Herrera 1988). Crambe tataria depends largely on insects for pollination, and variation in pollen transfer efficiency, together with damage caused by herbivorous insects, can influence seed production.

Crambe tataria exhibits an active glucosinolate-myrosinase system, identified in the seeds and leaves of in vivo- and in vitro-regenerated seedlings as well as in two callus cell lines (Piovan et al. 2013). Hydrolysis of glucosinolates by myrosinase results in the formation of isothiocyanates and other sulfur compounds (Ettlinger and Hodgkins 1955; Halkier and Gershenzon 2006; Piovan et al. 2013). These products play an important role in plant-insect interactions, as they can shape how herbivorous insects feed on the plant and choose their host, and can also influence the way predators and parasitoids interact with herbivores (Hopkins et al. 2009). Some species from the genus Crambe produce various glucosinolates and volatile sulfur-containing derivatives, compounds with important roles in plant-insect interactions. For C. tataria, two major hydrolysis products have been reported: 4-Hydroxybenzyl isothiocyanate and 5-Vinyl oxazolidine-2-thione (Daxenbichler et al. 1991).

There are no published studies on pollination in C. tataria. However, other Crambe species are insect-pollinated, with bees (Hymenoptera) documented as key visitors in C. abyssinica Hochst. ex R.E.Fr. (Simioni et al. 2015), and insect pollination including flies and bees reported for C. maritima L. (Sanyal and Decocq 2015). In this context, C. tataria may follow the same type of pollination, as the floral structure is similar to that of other species in the genus Crambe. The relationship between C. tataria and phytophagous insects is supported by the presence of species, such as Melanobaris carbonaria and Lixus canescens, both associated with plant species in the genus Crambe (Yunakov et al. 2018).

Local microclimatic factors (temperature, humidity, wind) are influenced by topography (Bennie et al. 2008). These factors affect both insect activity (Willmer 1982) and plant phenology (Cleland et al. 2007). Local variations in topographic factors (aspect, slope, and elevation) modify the microclimate at the grassland level (Bennie et al. 2008) and can influence the composition and abundance of insect communities (Hodkinson 2005). These effects are relevant for C. tataria because insect activity, flowering time, and the intensity of plant–insect interactions are partly related to microclimate changes, which vary with topography. The species grows on slightly alkaline soils, with organic carbon content ranging from low to high, showing high concentrations of phosphorus, potassium, and iron, low magnesium and sodium, and increased levels of aluminium, silicon, lead, and arsenic, along with moderate nitrogen content (Chirilă 2023).

This study investigates some of the interactions between C. tataria and insect communities across four locations in the Moldova region of Romania. For the first time, we identify some of the insect species associated with this plant and assess its impact on the diversity and abundance of local insect fauna. At the same time, this research contributes to biodiversity management strategies in areas affected by environmental change and anthropization. Moreover, the study is important for understanding plant-insect interactions, which, in turn, can form a basis for developing various strategies aimed at conserving rare plant and insect species.

Plant height determines floral visibility and insect accessibility within the vegetation (Herrera 2020), and inflorescence size is an indicator of floral resource availability and insect attractiveness (Murakoshi et al. 2024). We hypothesize that plants of C. tataria with greater height and larger inflorescences attract a greater number of insects and a greater diversity of species than plants in the vegetative stage or with smaller dimensions. To test this hypothesis, we studied plant height and inflorescence circumference.

Plant-insect relationships are key elements in the functioning of ecosystems, influencing both plant reproductive success and the structure of invertebrate communities (Bruce 2015; Valdovinos 2019). Differences in insect communities between locations can reflect classical community assembly processes (Kraft et al. 2015). Mutualistic interactions with insects can support long-term persistence of plant populations with restricted ranges (Hale et al. 2020). Crambe tataria, a relict species of postglacial steppe (Béres 1996), grows in Romania in mesoxerophilous and mesophilous grasslands, belonging mainly to plant associations from the Molinio-Arrhenatheretea and Festuco-Brometea classes (Chirilă 2023).

Analyses conducted in four locations in the Moldova region showed that the structure of insect communities varied depending on the type of plant association, topographic characteristics (elevation, aspect, and slope), and functional traits of C. tataria. Inflorescence circumference and plant height showed significant positive correlations with the abundance of some species, such as Cercopis sanguinolenta, Eurydema ornata, or Bibio hortulanus, suggesting that these functional traits have probably a role in attracting certain trophic groups.

In this context, it has been shown in the literature that species such as Melanobaris carbonaria feed on vegetative parts of C. tataria (Yunakov et al. 2018). The dominance of phytophagous insects suggests that C. tataria functions primarily as a trophic resource within steppe grasslands. This shows that C. tataria serves as an essential food resource. For example, Melanobaris carbonaria (Yunakov et al. 2018) and Eurydema ventralis (Stankevych et al. 2021), could be associated with the reduction of vegetative biomass and the increase of the vulnerability of the host plant to other ecological pressures. On the other hand, the vegetative parts have an essential role for the survival of some rare or vulnerable species, such as Protaetia (Philhelena) ungarica and Lixus (Eulixus) canescens. Omnivorous and predatory species, such as Orius sp. or Coccinella septempunctata were less abundant, reflecting a possible trophic imbalance caused by resource competition or habitat disturbances. An important aspect to mention is the presence of potential pollinators, such as Apis mellifera and Andrena flavipes, which suggests that C. tataria may contribute to supporting pollination-related ecosystem functions. The presence of these species highlights the need to conserve habitats that can support such mutualistic interactions. However, Apis mellifera originates from apiaries near the investigated location and is not a wild pollinator. Therefore, it cannot fulfil the role of Andrena flavipes as an indicator of mutualistic interactions, since A. flavipes is a wild pollinator, whose foraging patterns are naturally integrated with the local flora. Pollination processes operate within a structured ecological network in which the asymmetry of interactions and the degree of nesting influence the stability of plant-pollinator systems (Jordano 2016).

Statistically significant relationships between plant height and inflorescence circumference and certain insect species, such as Bibio hortulanus and Cercopis sanguinolenta, suggest that morphological traits of C. tataria influence habitat selection and resource use by these species. This may reflect a specific ecological association or a preference for larger floral displays. In contrast, the lack of significant relationships for species, such as Camponotus piceus and Tropinota (Epicometis) hirta indicates that other ecological or behavioural factors likely drive their occurrence.

Beyond trait–insect relationships, the overall insect assemblage highlights the conservation value of habitats hosting C. tataria. Although most species were relatively common, two rare or vulnerable taxa (Lixus canescens and Clanoptilus affinis) were recorded, one of which was confirmed in the Romanian fauna after more than a century (Petri 1912; Yunakov et al. 2018). These findings emphasize the importance of continued monitoring of steppe grasslands.

Most of the species are relatively common; however, a few are particularly noteworthy, especially in relation to the vegetative parts of C. tataria. Clanoptilus (Clanoptilus) affinis (Coleoptera: Malachiidae) is a small beetle species typically found in steppe habitats, classified as a Euro-Asiatic taxon. Like other members of the Malachiidae family, adults primarily feed on pollen (Franzini 2019). It is a rare species in our fauna, likely overlooked due to its small size and the challenges associated with identifying it at the species level. There are only historical records before 1911 (Petri 1912) in Hunedoara and Sibiu counties, and the species was omitted in Mayo’s catalogue (Mayo 2007). Thus, this new record confirms the presence of this species in Romanian fauna after more than 100 years.

Another noteworthy species associated with the vegetative parts of C. tataria is Protaetia (Philhelena) ungarica (Coleoptera: Cetoniidae). This beetle species is found across Central Europe and Asia, typically inhabiting steppe-like habitats (Panin 1957). In contrast to most Protaetia species, the larvae typically develop in the burrows of mammals, particularly those inhabited by Spermophilus species (Panin 1957). The adults feed on various plants, including the shoots of C. tataria, as observed in this study (Fig. 5). Although the species has a wide range, its distribution is restricted due to several factors, including the presence of Spermophilus and other similar small mammals, as well as the integrity of steppe-like habitats, that are often overgrazed or burned, thus it is considered a vulnerable species.

Lixus (Eulixus) canescens (Coleoptera: Curculionidae) inhabits xerothermic, steppe or coastal habitats and it is distributed only in Romania, Moldova, Ukraine and the European part of Russia (Yunakov et al. 2018). Being oligophagous and developing exclusively on Crambe species, it has a relatively scattered distribution, closely linked to the distribution of its host plants. In our study, only a single pair of this species was found at one site (Horlești, Iași County), and additional fieldwork is required to confirm its presence at other locations. Lixus (Eulixus) canescens is mentioned in the Red List of Ukraine, as nearly threatened (Yunakov et al. 2018). As it is not listed in the Red Book of Invertebrates of Romania (Murariu and Maican 2021), we propose this species to be included in a future version of the book.

This is the first study to present an assessment of the insect community associated with C. tataria in Romania. The results showed that phytophagous species dominate insect communities, and the variation in functional traits is linked to the abundance of several insect species. Although insect diversity was moderate, two rare or vulnerable species were observed, highlighting the conservation value of the habitats where C. tataria occurs. Horlești and Miroslava differ the most from the other sites in insect species composition. The collected data show the importance of this steppe relict as a structural and trophic resource in dry grasslands. Further long-term studies are needed to clarify the pollination interactions, seasonal variation of insect communities, and the ecological mechanisms linking functional traits to insect visitation patterns.