Food consumption rates of Bufonacris claraziana adults (Orthoptera: Tristiridae), a grasshopper pest in Patagonia, Argentina

Tasas de consumo de individuos adultos de Bufonacris claraziana (Orthoptera: Tristiridae), acridio plaga de la Patagonia Argentina

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The tristirid Bufonacris claraziana (Saussure) (Orthoptera: Tristiridae), an endemic species of Argentinian Patagonia (Cigliano et al., 2014), is considered a pest grasshopper (Mariottini, 2018; Mariottini et al., 2022; Carbonell et al., 2024). Recent registered outbreaks were in different areas of Santa Cruz, Chubut, and Río Negro provinces from 2016 to 2024. Commonly referred to as Toad grasshopper, B. claraziana is a large (up to 4.1 cm in length), bulky, apterous species (Cigliano & Lange, 2019). However, both nymphs and adults carry out considerable marching displacements in times of outbreaks. It is a univoltine grasshopper, with a long obligatory embryonic diapause and a polyphagous food regime, consuming almost any plant material that it encounters, from the tender grasses of the “mallines” (low, moist biotopes) where hatchings normally take place to the harder grasses (Stipa L., Festuca L.)of the arid Patagonian steppe, and even sometimes the lower branches of shrubs (Berberis L., Senecio L.) (Liebermann, 1958; Cigliano et al., 2014). These characteristics have allowed the development of recurrent outbreaks with devastating effects on the grasslands through which they move, considerably reducing the available forage (Cigliano et al., 2014). Available forage for livestock in the Patagonian rangeland is considerably reduced when outbreaks of the voracious bands of B. claraziana occur.

A number of authors have proved that forage loss caused by different species of grasshoppers increased as these insects grow, leading to the highest loss in the adult stage (Putnam, 1962; Hewitt et al., 1976; Hewitt, 1978; Sánchez & De Wysiecki, 1990; Bulacio et al., 2005; Torrusio et al., 2005; Mariottini et al., 2011; Mancini et al., 2023). Although the economic importance of B. claraziana has been recognized for decades, there are ecological and biological aspects of this species that are still unknown. One of these is the food consumption rate of adult individuals, which would allow knowing the degree of damage that they can cause during outbreaks. Consequently, the aim of this work was to determine the consumption rates of Festuca arundinaceae (Schreber) by adult males and females of B. claraziana under controlled laboratory conditions.

Individuals used in this study were collected as young nymphs in September of 2019 at Cushamen (42° 10′ 23″ S 70° 39′ 39″ W), west of Chubut province. Once in the laboratory, they were kept under controlled conditions of photoperiod, temperature, and relative humidity (14 L: 10 D, 28-30 °C during light, 7-10 °C during dark, and 30-40 % RH) as described in Mariottini et al. (2019). The grasshoppers were fed daily with fresh, well-washed lettuce and cabbage leaves and different species of grasses. An estimation of consumption per individual by sex and sexual maturation stage (pre-reproductive and reproductive) was obtained following the methodology used by Mariottini et al. (2011) and Mancini et al. (2023), using 150 individuals in the adult stage, 40 females and 40 males in the pre-reproductive stage, and 35 females and 35 males in the reproductive stage of B. claraziana (Fig. 1). Sex determination was performed by observation of the genitalia. Feeding trials in the pre-reproductive stage were performed within the first week after grasshoppers entered adulthood (Sánchez & De Wysiecki, 1990; Mancini et al., 2023), when they began to copulate were considered in the reproductive stage. After 12 h of fasting, each specimen was placed individually in a micro-perforated container (1 l) with a pre-weighed fresh ration of F. arundinaceae, a perennial forage grass used in the Patagonia region. After 24 h the remaining unconsumed food in each container was retrieved, and oven-dried at 60 °C for 48 h. Thirty control rations were prepared, weighed, and oven-dried at 60 °C. The average dry weight of control rations was used as a correction factor and applied to the initial fresh weight of each of the offered rations to calculate the dry weight of the food offered. The difference in weight between the rations offered and the remaining material after a trial represented the consumption during the test. Additionally, the average biomass (dry weight) of reproductive adults of both sexes was determined by individually weighting 32 males and 30 females.

Daily food consumption and the relative consumption rate by sex and stage of sexual maturation were compared using a non-parametric Kruskal Wallis test followed by a mean pair comparison between treatments. The body weight of females and males was compared by one-way ANOVA. Both tests were made using the statistical software InfoStat (Di Rienzo et al., 2011).

Figure 1.
Male adult of Bufonacris claraziana.

The results obtained indicate that the consumption observed per sex in the different maturation stages (pre-reproductive and reproductive) was significantly different (Kruskal-Wallis test, H= 88.40; p< 0.0001).Pre-reproductive females had the highest consumption rate (690.4±21.2 mg/day) (p< 0.05), followed by pre-reproductive males with an average consumption of 582±27.4 mg/day. In the reproductive stage the consumption rate of the females was higher than males, but the difference was not significant (Fig. 2). A decrease of approximately 50 % was observed between the consumption of pre-reproductive and reproductive stages in both sexes.

Figure 2.
Food consumption by sex and sexual maturation stage (pre-reproductive and reproductive) of Bufonacris claraziana.

Different letters indicate significant differences (Kruskal Wallis p< 0.05). References= PRE F: Pre-reproductive females, REP F: Reproductive females, PRE M: Pre-reproductive males, REP M: Reproductive males.

The mean body weight of reproductive adult females (690±30 mg) was higher than the average weight of adult males (520±20 mg) (p< 0.0001). The relative consumption rate (RCR) was different between sex and maturation stages (H= 89.83; p< 0.0001). Pre-reproductive stage of both sexes had a higher RCR (Females: 1±0.03 mg consumption/mg individual/day; Males: 1.12±0.052 mg consumption/mg individual/day) than in the reproductive stage (Females: 0.5±0.026 mg consumption/mg individual/day; Males: 0.56±0.025 mg consumption/mg individual/day).

In general, the relationship between food consumption rate and weight of grasshoppers has been a topic of debate among various authors, who have reported significant variations in the amount of food consumed by different species. Some studies indicate that grasshoppers consume an amount of food equivalent to their body weight daily, while other studies argue that their consumption amounts to half of their weight (Liebermann, 1961, 1971; Hewitt, 1977, cited in Capinera & Sechrist, 1982; Genovesio et al., 2011). This variable is directly related to the nutritional requirements of the different developmental stages and in their natural habitat largely, depends on the quantity, quality, and diversity of vegetation (Jonas, 2007; Ebeling et al., 2018). There are several factors that affect food selectivity in grasshoppers when it comes to consider those related to the plants involved such as quantity and quality of cellulose, water, carbohydrate, and protein content (Ibanez et al., 2013).

The results of the present study indicate that adult individuals of both sexes of B. claraziana exhibit higher food consumption during the pre-reproductive stage, ingesting an amount of daily food equivalent to their body weight, in agreement with the findings of Liebermann (1961, 1971). However, during the post-reproductive stage consumption decreases by approximately 50 %. In females, the higher consumption observed during the pre-reproductive stage may be explained by the need to meet increased energy demands for reproduction and egg production (Lockwood et al., 1996; Genovesio et al., 2011). In males, the higher consumption could be because in the pre-reproductive period, they must feed enough to generate reserves that allow them to maintain the requirements for the reproductive stage, where their feeding could be reduced because they remain in copulation with the female. Regarding food consumption by sex, females consume more food than males, which could be attributed to body weight (Table I) and their larger size, which, according to Cigliano et al. (2014) is 32 to 36.5 mm for females and 27 to 41 mm for males.

In Argentina, various studies have assessed the consumption rate of different grasshopper species, with a particular focus on those considered harmful. We have compiled the available knowledge about the consumption of 11 grasshopper species from eight different investigations (Table I). Studies that have evaluated consumption in adult individuals of both sexes, considering the pre-reproductive and reproductive stages, have identified a similar trend: consumption is higher in either sex at the onset of the mating period (Bardi et al., 2011; Mariottini et al., 2011). Furthermore, as observed in the present study, the studies cited in Table I also report higher consumption in females than in males (Sánchez & De Wysiecki, 1983; Capello et al., 2011; Mariottini et al., 2011; Mancini et al., 2023). Although many studies report daily consumption rates similar to the individual’s body weight, some others indicate consumption exceeding their own body weight. For instance, the body weight of female and male Dichroplus elongatus recorded by Mariottini et al. (2011) is significantly lower than the estimated consumption reported by Bulacio et al. (2005) for adult individuals of the same species (Table I). A trend of reduced consumption is observed when individuals are in groups. For example, in Dichroplus maculipennis, one of the main harmful grasshopper species in Argentina (Lange & Cigliano, 2019), the food consumption rate is lower when estimated as groups compared to individual evaluations (Mariottini et al., 2011, 2019). In this regard, Mancini et al. (2023) mentioned that individual consumption assessments might represent the maximum daily potential consumption for an individual at its specific developmental stage.

The results of this study constitute the first contribution to understanding the feeding impact of B. claraziana in a laboratory setting. We consider that this work, along with other research aimed at furthering the limited current knowledge on life cycle, behavior, feeding habits, and other ecological aspects, is essential for assessing the maximum individual damage this species could cause and for contributing to the rational management of this insect pest.

Table I.
Mean values of daily feed consumption data (mg/ind/day), body weight (mg) and Relative Consumption Rate (RCR) (mg/mg.individual/day) of 11 grasshopper species from eight different investigations.

Note: a= individual/group, b= mg/ind/day, c= mg/mg.individual/day, F= Females; M= Males; Pre F= Pre-reproductive females; Pre M= Pre-reproductive males; Rep F= Reproductive females; Rep M= Reproductive males.

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