Introduction
Herbivorous insects feed on host plants to obtain the nutrients necessary for normal growth and reproduction. Supplementary nutrition habits in adult insects are an important component of their life activities, directly related to growth, development, reproduction, and lifespan (Leonhardt et al., Reference Leonhardt, Lihoreau and Spaethe2020; Zhang et al., Reference Zhang, Wu, Jiang, Wen, Zhang and Sun2023; Fu et al., Reference Fu, Li, Ren, Liu, Wu, Deng, Gao, Zhang, Men and Zhang2024). In nature, most insects do not reach sexual maturity immediately after adult eclosion and need to feed on host plants to supplement nutrition for mating and oviposition, thereby completing the normal physiological processes (Liang et al., Reference Liang, Yang, Yang, Yang and Yang2008; Hematia et al., Reference Hematia, Naseri, Ganbalani, Dastjerdi and Golizadeh2012; Seong et al., Reference Seong, Uemura and Kang2023). There are certain differences in the nutritional composition of different host plants, which significantly affect the growth, development, and reproduction of herbivorous insects (Shobana et al., Reference Shobana, Murugan and Kumar2010; Hematia et al., Reference Hematia, Naseri, Ganbalani, Dastjerdi and Golizadeh2012; Lachlan et al., Reference Lachlan, Michelle and Gimme2022). For instance, both Canary Island date palm and Washington palm, on the one hand, and silver date palm, on the other hand, were, respectively, the most suitable and the least suitable host plants for the red palm weevil Rhynchophorus ferrugineus, on the basis of growth, survival, and reproduction on palm slices (Ju et al., Reference Ju, Wang, Wan and Li2011). Similarly, the oviposition quantity and period of female adults of the weevil Scythropus yasumatsui feeding on the Muzao jujube tree variety were significantly higher than on four other jujube varieties (Yan et al., Reference Yan, Wang, Li, He, Yang and Liu2021). Herbivorous insects often exhibit distinct feeding preferences across different host plants, which are influenced by factors such as plant chemistry, host resistance, and insect nutritional requirements (Fan et al., Reference Fan, Zhang, Bi, Wu and Zang2021; Wang et al., Reference Wang, Zhu and Lai2021; Li et al., Reference Li, Hao, Xu and Dai2022). Waldbauer (Reference Waldbauer1968) proposed different nutritional indices to assess the suitability of host plants for herbivorous insects, including food consumption, relative growth rate, approximate digestibility, efficiency of conversion of digested food, and efficiency of conversion of ingested food. Because the nutritional indices of herbivores vary with nutritional qualities, availability of essential nutrients to herbivores, and the level of antinutrient content of host plants, there are significant differences in the nutritional indices of herbivorous insects feeding on different plants (Lazarević and Peri-Mataruga, Reference Lazarević and Peri-Mataruga2003; Shobana et al., Reference Shobana, Murugan and Kumar2010; Wang et al., Reference Wang, He, Liu, Jing and Zhang2023).
The olive weevil Pimelocerus perforatus (Roelofs, 1873), with its synonym Dyscerus cribripennis Matsumura et Kôno, is a destructive wood-boring pest of various plants, including species of Oleaceae: Fraxinus pennsylvanica, F. griffithii, Ligustrum ibota, L. japonicum, L. obtusifolium, Syringa reticulata var. amurensis and Osmanthus fragrans; Rutaceae: Phellodendron amurense; and Meliaceae: Melia azedarach (Xue et al., Reference Xue, Feng, Zhang and Lu2018; Yoshida et al., Reference Yoshida, Mtsuda and Tokuda2018; Wang et al., Reference Wang, He, Liu, Jing and Zhang2023). This weevil is widely distributed in Beijing, Shandong, Fujian, Zhejiang, Sichuan, Gansu, Guangxi, Yunnan, Jiangxi, Chongqing, and Taiwan in China, as well as Japan, the Korean Peninsula, and Russia (Morimoto, Reference Morimoto1987; Hong et al., Reference Hong, Park and Han2011; Xue et al., Reference Xue, Feng, Zhang and Lu2018). At present, the olive weevil has caused devastating damage to F. pennsylvanica and O. europaea in China and Japan (Fujikawa et al., Reference Fujikawa, Ishihara, Ohta, Nehira, Ômura, Uy and Ohta2022; Yan and Wang, Reference Yan and Wang2024). Adult olive weevils feed on tender branches, shoots, and bark for supplementary nutrition, and repeatedly lay eggs and reproduce, posing a continuous threat (Song et al., Reference Song, Zhang, Liu, Zou, Yan and Ji2025). The victimised host plants commonly exhibit symptoms including sap extravasation, xylem discolouration, yellowing of branches and leaves, and a large number of holes in the xylem (Xue et al., Reference Xue, Feng, Zhang and Lu2018; Yoshida et al., Reference Yoshida, Mtsuda and Tokuda2018). Although the population density of olive weevils in the original host plants, Ligustrum japonicum and L. obtusifolium, is very low, densities are significantly higher on olive trees (Olea europaea) with more than 100 adults per tree in Japan (Fujikawa et al., Reference Fujikawa, Ishihara, Ohta, Nehira, Ômura, Uy and Ohta2022). Once the olive tree is infested, the pests feed on its leaves and bark, rapidly increasing in population and subsequently killing the tree (Ichikawa et al., Reference Ichikawa, Okamoto, Fujimoto, Kawanishi and Tsuboi1987, Reference Ichikawa, Okamoto, Utsumi, Kawanishi and Tsuboi1991; Mitsumoto and Yamazaki, Reference Mitsumoto and Yamazaki2024). In olive cultivation areas of China, such as Sichuan, Chongqing, Hunan and Gansu, the mortality rate of olive trees attacked by the weevil exceeds 50%, which has seriously affected the cultivation of olive trees (Su et al., Reference Su, Zhao, Liu, Jiang and Lu2015; Yan et al., Reference Yan, Zhao, Liu, Ji, Xia, Wang, Wang, Guo, Song and Yang2024). In addition, the weevil has caused serious damage to F. pennsylvanica, an important ecological tree species in northern China. In plain afforestation areas of Beijing, nearly all weakened or dying F. pennsylvanica trees are infested by this weevil (Xue et al., Reference Xue, Feng, Zhang and Lu2018; Yan and Wang, Reference Yan and Wang2024).
At present, in addition to the two host plants O. europaea and F. pennsylvanica that are clearly documented as hosts of the olive weevil, the Oleaceae family also comprises numerous other species widely distributed in China, including L. ibota, L. japonicum, L. × vicaryi, Syringa oblata and O. fragrans (Uzma et al., Reference Uzma, Townsend, Muhammad and Marlon2023; Yue et al., Reference Yue, Qiu and Wang2024). These tree species are extensively utilised in edible oil production, timber production, landscaping, fragrance industry, food processing, medicinal applications, and ecological restoration. Owing to their high economic value and important ecological functions, they play a critical role in China’s agroforestry and urban ecosystems (Chen et al., Reference Chen, Zhao, Zhang, Wang, Liao and Liu2021; Dupin et al., Reference Dupin, Hong-wa, Gaudeul and Besnard2024). However, it remains unclear whether these plant species are also susceptible to infestation and damage by the olive weevil. Therefore, in this study, five plants of the Oleaceae family (F. pennsylvanica, O. europaea, O. fragrans, S. oblate, and L. × vicaryi) were selected to investigate the supplementary nutrition feeding preferences of olive weevil adults on these five plants, along with nutritional indices, oviposition period, and number of eggs laid, aiming to identify the most suitable host plants for adult supplementary nutrition of the olive weevil.
Materials and methods
Insects and plants
Olive weevil adults were collected from Hanbo Garden, Tai’an City, Shandong Province, and reared indoors with twigs of F. pennsylvanica in a rearing box (16 mm × 12 mm × 5 mm). After mating and oviposition, the eggs were picked out and placed in a Petri dish with wet filter paper and reared in an artificial light incubator at 25 ± 0.3°C, 90 ± 5% relative humidity, and 16 L: 8D photoperiod. After hatching, the larvae were fed with semi-artificial diet (The main ingredients included: tender branch phloem powder, appropriate preservatives, vitamin mixture, soybean powder, sugar, and cholesterol), and the newly emerged adults were used as the test insects.
Twigs of five Oleaceae plants were collected from different locations at the same time (July 2024). Fraxinus pennsylvanica was collected from Hanbo Garden, Tai’an City, Shandong Province (117°11′E, 36°5′N). Olea europaea (variety Frantoio) was collected from Neijiang City (104°15′E, 29°11′N). Osmanthus fragrans, Syringa oblata, and Ligustrum × vicaryi were collected from the campus of Shandong Agricultural University (117°6′E, 36°11′N). The collected twigs were stored in a refrigerator at 4°C.
Feeding selection of olive weevil adults to five Oleaceae plants
A four-armed olfactometer (Model: QT-W1103; Manufacturer: Beijing Qudao Scientific Instrument Co., Ltd.) was used to test the feeding preference of olive weevil adults on five Oleaceae plants. There were five experimental groups in the study, including: (1) F. pennsylvanica, O. europaea, O. fragrans and S. oblata, (2) O. europaea, O. fragrans, S. oblata and L. × vicaryi, (3) F. pennsylvanica, O. fragrans, S. oblata and L. × vicaryi, (4) F. pennsylvanica, O. europaea, O. fragrans and L. × vicaryi, and (5) F. pennsylvanica, O. europaea, S. oblata and L. × vicaryi. Twelve newly emerged, 3-day-old female olive weevil adults were used in each experimental group at a time, and each experimental group was repeated four times. The number of olive weevil adults on different plants was recorded at 5, 7, 10 and 15 min.
Nutritional indices of olive weevil adults feeding on five Oleaceae plants
Two experimental groups were arranged to determine the nutritional indices of olive weevil adults feeding on different plants: the female-only group and the male-only group. Each experimental group was repeated five times, and one newly emerged, 3-day-old female adult or one newly emerged, 3-day-old male adult was used each time. One female or one male, as well as two twigs of the same plant, were placed in a box (54 mm in diameter and 35 mm in height) to determine the nutritional indices. The diameter and length of the twigs of five Oleaceae plants were 0.8-1 cm and 2-3 cm, respectively. After 48 h, the feeding status was recorded, including the weight of the adult before and after feeding, the weight of sawdust and faeces, and the weight of twigs before and after being fed. The nutritional indices mainly include growth indices (fresh weight of food ingested, consumption index, and relative growth rate), and digestibility and efficiency of conversion (efficiency of conversion of ingested food to body substance, the approximate digestibility, the efficiency of conversion of digested food to body substance). The following formulas were used to calculate the nutritional indices of olive weevil adults feeding on different plants (Waldbauer, Reference Waldbauer1968).
\begin{align}
& {\text{Fresh weight of food ingested}} \left(\text{F} \right) \left(\text{g} \right)\nonumber\\
& \quad = ({\text{twig weight before being fed}}\nonumber\\
& \qquad - {\text{twig weight after being fed}})\nonumber\\
& \qquad - {\text{sawdust weight}} - {\text{water loss of twig}}
\end{align}
\begin{equation}{\text{Consumption index }}\left( {{\text{C}}{\text{.I}}{\text{.}}} \right){\text{ = F/ }}\left( {{\text{T \times A}}} \right)\end{equation}
\begin{equation}{\text{Relative growth rate }}\left( {{\text{G}}{\text{.R}}{\text{.}}} \right){\text{ = G/ }}\left( {{\text{A \times T}}} \right){\text{ \times 100}}\end{equation}
\begin{equation}{\text{Efficiency of conversion of ingested food }}\left( {{\text{E}}{\text{.C}}{\text{.I}}{\text{.}}} \right){\text{ = G/F \times 100}}\end{equation}
\begin{equation}{\text{Approximate digestibility }}\left( {{\text{A}}{\text{.D}}{\text{.}}} \right){\text{ = }}\left( {{\text{F - B}}} \right){\text{/F \times 100}}\end{equation}
\begin{align}
& {\text{Efficiency of conversion of digested food }}({{\text{E}}{\text{.C}}{\text{.D}}})\nonumber\\
& \quad = G/({{\text{F - B}}}){\text{\times 100}}\end{align}Where A represents mean fresh weight of animal during feeding period, T represents duration of feeding period (days), G represents fresh weight gain of adult during feeding period, and B represents weight of faeces.
Oviposition and hatching rate of olive weevil adults feeding on five Oleaceae plants
One female and one male adult feeding on the same plant were paired and reared continuously on twigs of the same plant. A total of five experimental groups were arranged based on the five species of Oleaceae plants, and each experimental group was repeated five times. The first mating time, first oviposition time, and number of eggs laid on the 10th and 15th days after the first egg were recorded.
Data analysis
The results were analysed using IBM SPSS software (version 26.0, Armonk, New York, NY, USA). The Shapiro-Wilk and Levene tests were used to verify data normality (after logarithmic transformation when necessary) and homoscedasticity, respectively. Tukey’s HSD test was used to detect significant differences in feeding selection of olive weevil adults on different plants at the same time, as well as in nutritional indices, oviposition time and fecundity when feeding on different plants.
Results
Feeding selection of olive weevil female adults to five Oleaceae plants
There were significant differences in the feeding selection rates of olive weevil female adults on five Oleaceae plants after 15 min (P < 0.05). When present, O. fragrans exhibited the highest selection rates among the designed experimental groups, at par with F. pennsylvanica in the absence of S. oblata (fig. 1A–D). In the absence of O. fragrans, F. pennsylvanica exhibited the highest selection rate (fig. 1E). The selection rates for O. europaea and S. oblata were lower, and most notably, female olive weevil adults did not choose to feed on L. × vicaryi for supplementary nutrition (fig. 1B–E). The feeding selection rates of olive weevil female adults on the five Oleaceae plants can therefore be ranked as follows: O. fragrans > F. pennsylvanica > O. europaea > S. oblata > L. × vicaryi.
Feeding selection rate of olive weevil female adults on five Oleaceae plants. Each value represents the mean (±SE) of four replicates (n = 4, each replicate including 12 female adults). Different lowercase letters indicate significant differences in feeding selection rates between different plants at a given time (Tukey’s HSD test, P < 0.05). (A, without L. x vicaryi; B, without F. pennsylvanica; C, without O. europaea; D, without S. oblata; E, without O. fragrans).
Figure 1 Long description
The image contains five bar charts labeled A to E, each showing the feeding selection rate of olive weevil female adults on five Oleaceae plants over time. The horizontal axis for each chart is labeled Time (min) with intervals at 5, 7, 10 and 15 minutes. The vertical axis is labeled Selection rate (percent) ranging from 0 to 80. Chart A shows Fraxinus pennsylvanica with increasing selection rates, peaking at 15 minutes. Chart B highlights Osmanthus fragrans with the highest selection rate at 15 minutes. Chart C shows Olea europaea with moderate rates, peaking at 15 minutes. Chart D features Syringa oblata with lower rates, peaking at 15 minutes. Chart E shows Ligustrum times vicaryi with the lowest rates across all times. The legend identifies the plant groups: Fraxinus pennsylvanica, Olea europaea, Osmanthus fragrans, Syringa oblata and Ligustrum times vicaryi. Letters above bars (a, b, c) indicate statistical significance in feeding rates. The charts collectively compare the preference of olive weevil females for different plants over time, with Osmanthus fragrans generally preferred. Each chart shows distinct trends and statistical groupings, providing insights into feeding behavior.
Nutritional indices of olive weevil adults feeding on five Oleaceae plants
The nutritional indices of olive weevil adults feeding on five Oleaceae plants for supplementing nutrition showed significant differences in all indices except for A.D., including F, E.C.D., E.C.I., C.I., and G.R. (P < 0.05) (table 1). The nutritional index F values of olive weevil female adults feeding on F. pennsylvanica and S. oblata were the highest, 0.37 ± 0.02 g and 0.37 ± 0.01 g, respectively. The maximum F for male adults feeding on F. pennsylvanica was 0.38 ± 0.04 g. The F values for both female and male adults feeding on O. europaea were the lowest, 0.13 ± 0.01 g and 0.17 ± 0.02 g, respectively. Although olive weevil adults had the lowest F values when feeding on O. europaea, their nutritional indices E.C.D., E.C.I., and G.R. values when feeding on O. europaea were the highest compared to those when feeding on F. pennsylvanica, O. fragrans, S. oblata, and L. × vicaryi. In addition, the nutritional index C.I. value of olive weevil adults feeding on O. europaea was the lowest among the five plants, with 0.31 ± 0.01 1/d for females and 0.42 ± 0.06 1/d for males, indicating that olive weevil adults can feed on relatively small amounts of O. europaea to complete nutritional supplementation. The nutritional indices F and C.I. values of olive weevil female adults feeding on F. pennsylvanica and S. oblata were the highest, and they had better digestion and utilisation rates, second only to those of adults feeding on O. europaea. Therefore, we believe that F. pennsylvanica and S. oblata may be the plants that are most suitable for adult feeding and oviposition under laboratory conditions, among the five Oleaceae plants.
Nutritional indices of olive weevil adults feeding on five Oleaceae plants. Each value represents the mean (±SE) of five replicates (n = 5, each replicate including 1 female or male adult). Different lowercase letters indicate significant differences in nutritional indices when feeding on different plants of the same sex (Tukey’s HSD test, P < 0.05)
Table 1 Long description
The table reports mean nutritional indices with standard errors for adult olive weevils, separated by sex, after feeding on five Oleaceae host plants. Fresh food ingested was highest on Fraxinus pennsylvanica and Syringa oblata for females (both 0.37 g) and on Fraxinus for males (0.38 g), and lowest on Olea europaea (0.13 g for females; 0.17 g for males). Approximate digestibility was high across all plants and both sexes, generally around 90 to 97 percent, with small differences among hosts. In contrast, conversion efficiencies were much higher on Olea europaea than on the other plants: for females, efficiency of conversion of digested food was 25.56 percent and efficiency of conversion of ingested food was 20.36 percent; for males, the corresponding values were 19.41 percent and 15.38 percent. Consumption index was highest on Fraxinus, Osmanthus, and Syringa for females (about 0.89 to 0.98 per day) and highest on Fraxinus for males (0.92 per day), while Olea was lower for both sexes. Relative growth rate peaked on Olea for both sexes (about 6.4 per day) and was also high on Fraxinus (about 5.3 to 5.5 per day), but was much lower on Syringa and Ligustrum. Letter groupings indicate statistically significant differences among plants within each sex, so comparisons should be made within female rows and within male rows rather than between sexes.
Note: F represents fresh weight of food ingested, C.I. represents consumption index, G.R. represents relative growth rate, E.C.I. represents efficiency of conversion of ingested food, and A.D. represents approximate digestibility.
Oviposition and hatching rate of olive weevil adults feeding on five Oleaceae plants
The reproductive performance of olive weevil female adults exhibited significant host-specific variation (table 2), and the females failed to lay eggs when feeding on O. fragrans. There were significant differences in the pre-oviposition period among different Oleaceae plants (P < 0.05), with the shortest pre-oviposition period (6.40 ± 0.89 days) observed for olive weevils feeding on S. oblata and the longest (9.00 ± 2.12 days) for olive weevils feeding on O. europaea. The number of eggs laid by olive weevil female adults feeding on F. pennsylvanica was 19.20 ± 3.90, with no significant difference compared to those on S. oblata (18.80 ± 3.11). In addition, there was no significant difference in the first mating time and egg hatching rate of olive weevils when feeding on five Oleaceae plants. Therefore, considering only the factors of the pre-oviposition period and the number of eggs, F. pennsylvanica and S. oblata are the best plants for supplementary nutrition of adult olive weevils among the five Oleaceae plants.
Egg-laying period and hatching rate of olive weevil adults feeding on different host plants. Each value represents the mean (±SE) of five replicates (n = 5, each replicate including paired male and female adults). Different lowercase letters indicate significant differences in the same column (Tukey’s HSD test, P < 0.05)
Table 2 Long description
The table compares olive weevil reproduction on five host plants using first mating time in days, pre-oviposition period in days, number of eggs laid, and egg hatching rate as a percent, reported as means with standard errors from five replicates. Osmanthus fragrans shows zero for all measures, indicating no mating, no egg laying, and no egg hatch. Among the remaining plants, first mating time is similar at about three to five days, with Syringa oblata slightly earlier and Ligustrum × vicaryi slightly later. Pre-oviposition is shortest on Syringa oblata at about six and a half days and longest on Olea europaea at about nine days, with Fraxinus pennsylvanica and Ligustrum × vicaryi in between. Egg production is highest on Fraxinus pennsylvanica and Syringa oblata at about nineteen eggs, lower on Olea europaea at about ten eggs, and lowest on Ligustrum × vicaryi at about six eggs. Hatching rates are high and similar for all plants that produced eggs, roughly mid eighties to low nineties percent, while Osmanthus fragrans remains at zero. Letter groupings indicate statistically significant differences within each column, so comparisons should follow those group labels rather than small numeric gaps.
Discussion
Oviposition is an important component of insect growth and development. The decision of when, where, and how to lay eggs has a profound impact on the adaptability of species (Cury et al., Reference Cury, Benjamin and Gompel2019). The feeding and oviposition selection are often affected by multiple factors, including host plant species, plant volatiles, host physiological status, different varieties of the same species of host, and the colour and shape of the host plants (Jallow and Zalucki, Reference Jallow and Zalucki1996; Holl et al., Reference Holl, Reid, Zahawi, de Siqueira and Brancalion2024). Herbivorous insects usually select oviposition sites on host plants that are most conducive to offspring reproduction (Ashra and Nair, Reference Ashra and Nair2022; Fischbein and Corley, Reference Fischbein and Corley2022). A study on the host selection by the Asian longhorned beetle on four different species of Aceraceae trees showed that different tree species have varying levels of attraction to the beetle. This may be closely related to the specific volatile compounds trans-2-hexenol and ocimene produced by different plants (van der Gaag and Loomans, Reference van der Gaag and Loomans2014). Shrestha and Rondon (Reference Shrestha and Rondon2024) evaluated the host preference of Lygus hesperus for four host plants (potato, alfalfa, carrot, and pea). The results showed that the number of adults on alfalfa and potato plants was significantly higher than that on carrot or pea plants at 6, 24, and 48 hours after placing them in cages. Female L. hesperus strongly preferred potato and alfalfa plants as oviposition substrates 96 hours after release. In this study, there was a significant difference in the feeding selection of olive weevils on five Oleaceae host plants. Olive weevil female adults tended to prefer feeding on O. fragrans, which may be due to a specific volatile compound of O. fragrans having a strong attraction to female adults. The recognition of a host plant by insects occurs using either species-specific compounds or specific ratios of ubiquitous compounds (Justin et al., Reference Justin, Whitehill, Paal, Allison, Paine, Slippers and Wingfield2023). Previous research has reported that olive weevil adults preferred to feed on plants containing secoiridoid glycosides and lignans (Nakajima et al., Reference Nakajima, Kitamura, Baba, Iwasa and Ichikawa1995; Kadowaki et al., Reference Kadowaki, Yoshida, Nitoda, Baba and Nakajima2003; Xue et al., Reference Xue, Feng, Zhang and Lu2018). Therefore, the specific volatile components in O. fragrans could be further identified and subsequently used as lure components in traps, supporting early warning and population dynamics monitoring of this forest pest.
Many adult insects require supplementary feeding on host plants after eclosion to support reproductive system development, thereby enabling subsequent mating and oviposition (Rajagopalbabu, Reference Rajagopalbabu2019; Lachlan et al., Reference Lachlan, Michelle and Gimme2022). However, host plants produce secondary metabolites to defend against herbivory. The defensive components of plants may have both direct and indirect effects on the fecundity of herbivorous insects and may also directly affect their oviposition of herbivorous insects (Fernandez et al., Reference Fernandez, Sáez, Quintero, Gleiser and Aizen2021; Fufa and Getu, Reference Fufa and Getu2023). In addition, the feeding performance on different host plants can be reflected by nutritional indices, mainly including fresh weight of food ingested (F), consumption index (C.I.), relative growth rate (G.R.), Efficiency of conversion of ingested food (E.C.I.), and approximate digestibility (A.D.) (Waldbauer, Reference Waldbauer1968). Olive weevil female adults can feed on five Oleaceae plants, especially F. pennsylvanica and S. oblata. The number of eggs laid by olive weevil female adults was highest when feeding on F. pennsylvanica and S. oblata. This finding is consistent with the maternal effect hypothesis. Female insects can perceive chemical constituents released by plants via gustatory receptors, and neuroendocrine inhibition of oocyte maturation is relieved only after they ingest sufficient oviposition stimulants (Yanchula and Alto, Reference Yanchula and Alto2021; Shi et al., Reference Shi, Gols, de Boer and Harvey2025). However, olive weevil female adults did not exhibit oviposition after feeding on O. fragrans. One possible reason is that the nutrients or secondary metabolites derived from either O. fragrans in general or its northern Chinese cultivars may be unsuitable for supporting oviposition by female olive weevils.
Experience may affect subsequent selection among resources or animal searches in a resource unit (Hunt et al., Reference Hunt, Daw, Kaanders, MacIver, Mugan, Procyk, Redish, Russo, Scholl, Stachenfeld, Wilson and Kolling2021). For example, learning to avoid one noxious food or habitat may lead to selection favouring behavioural patterns (Bernays, Reference Bernays1998). According to research, flavonoids and other secondary metabolites have an impact on the feeding behaviour of some Heteroptera (Levin, Reference Levin1976; Riddick, Reference Riddick2024). In this study, newly emerged adult olive weevils were obtained by feeding F. pennsylvanica in the laboratory. If a species can benefit from prior experience, it may improve its foraging efficiency by responding appropriately to environmental changes and utilising information obtained through sampling resource patches (Boggs, Reference Boggs2009). Olive weevils may have adapted to feeding on F. pennsylvanica, which may also have an impact on their feeding selection, nutritional parameters, and oviposition performance. In addition, the results of oviposition performance showed that female olive weevil adults did not exhibit oviposition behaviour after feeding on O. fragrans. However, olive weevil female adults tended to feed on O. fragrans, which suggests that this Oleaceae species could be used as a trap plant to lure olive weevil female adults in an attract-and-kill strategy (Sarkar et al., Reference Sarkar, Wang, Wu and Lei2018). Therefore, planting O. fragrans or placing its branches at the edges of olive orchards or in forest gaps as a trap crop could effectively attract-and-kill adult insects, thereby reducing the pest pressure on olive trees.
The intrinsic mechanisms driving the feeding and oviposition behavioural decisions of insects, aside from the well-known factors such as plant volatiles and nutritional components, may be critically influenced by gut microbes in insects, which have received considerable attention in recent years (Li et al., Reference Li, Yu, Zhang, Wang, Zhang, Zhai and Zhang2023; Wang et al., Reference Wang, Wang, Chen, Luo, Zhou, Luo, Yan, Liu and Wang2024; Fowler et al., Reference Fowler, Friend, Churchill, Yu, Archetti, Bourke, Bretman and Chapman2025). Gut microbiota may indirectly affect the feeding preference of insects by regulating their nutritional metabolism and digestive efficiency (Wang et al., Reference Wang, Wang, Chen, Luo, Zhou, Luo, Yan, Liu and Wang2024). During the feeding process, adult olive weevils may learn through trial and error to associate the fitness benefits derived from specific host plants with their characteristic odours, forming a positive feedback response and thus exhibiting significant feeding preferences for different plants. The results of the feeding preference experiment in this study showed that adult olive weevils began to exhibit significant preference after 7-10 minutes of contact with the plants (fig. 1). In addition, gut microbes may also be involved in the perception and information integration of plant volatile compounds (Fowler et al., Reference Fowler, Friend, Churchill, Yu, Archetti, Bourke, Bretman and Chapman2025; Yasika and Shivakumar, Reference Yasika and Shivakumar2025). Host location in insects is highly dependent on olfactory cues (Renou and Anton, Reference Renou and Anton2020). Studies have shown that the gut microbes of insects can metabolise ingested plant materials, producing unique volatile metabolites (such as certain terpenes and esters), which may be perceived by the insects themselves or by other individuals after being released through faeces, serving as signals of host suitability (Schmidt and Engel, Reference Schmidt and Engel2021; Antonio and Jorge Álvarez, Reference Antonio and Jorge Álvarez2024; Yasika and Shivakumar, Reference Yasika and Shivakumar2025). However, for the olive weevil, whether gut microbiota modify or degrade host plant volatiles, thereby altering adult olfactory responses, remains unclear and warrants further study.
In summary, although this study did not directly measure the volatile compounds of Oleaceae plants and the gut microbiome of adult olive weevils, we speculate that both play a potential and important role in the feeding and oviposition behaviour of olive weevils. Future research will utilise various technological methods to analyse the volatile substances and toxic secondary metabolites that influence the host selection preferences of the olive weevil, as well as the differences in gut microbial community structures when the weevils feed on different plants. This will thereby clarify the mechanisms underlying the feeding and oviposition selection of the olive weevil, which may provide potential directions for developing new green control strategies.
Author contributions
C.S.: design, experimentation, and writing of the manuscript. X.Z., H.G., and D.S.: experimentation and data analysis. J.Y. and Y.L.: review, editing, and supervision. Y.J.: conceptualisation, design, review, editing, and supervision.
Financial support
This research was financially supported by the China Postdoctoral Science Foundation (2021M691971).
Competing interests
The authors declare that they have no conflict of interest.
