Effects of temperature and moisture on Mormon cricket reproduction with implications for responses to climate change

Prolonged diapause in Mormon crickets: Embryonic responses to three measures of time

Mormon cricket eggs can remain diapausing in soil for multiple years without forming an embryo. I investigated whether embryonic development was dependent on the number of annual cycles since the egg was laid, duration of the summer period (forcing), or duration of the winter period (chilling). Male and female Mormon crickets collected in Arizona and Wyoming were paired in the lab. For each mating pair, sibling eggs were incubated 12 weeks, eggs with fully developed embryos removed, and the remaining eggs were split evenly among three treatments: a long cold period and a long warm period; a short cold period and a long warm period; and a short cold period and a short warm period, which respectively completed 2 annual cycles, 3 cycles, and 4 cycles in 60 calendar weeks. In each cycle over nine years, developed eggs and eggs that appeared inviable were counted and removed. For each mating pair, I used survival analyses to test for differences in 1) the number of annual cycles, 2) the warm period duration, and 3) the cold period duration required for the embryos to develop. For eight of 11 mating pairs, one of the three factors was not excluded as a determinant of the phenology of embryonic development. Duration of the warm period was not rejected in seven of 11 cases. Duration of the warm period required for 50 % of the eggs to develop ranged from 84 to 144 weeks. In one case from Arizona, the duration of the cold period was the only factor not rejected. Median chill time was 60 weeks, which is also more than one year. Despite this exception, I conclude that duration of the warm period is typically the factor that determines timing of embryonic development for Mormon crickets. For these two high elevation populations, median forcing or chilling exceeded one year.

A convolutional neural network with image and numerical data to improve farming of edible crickets as a source of food-A decision support system

Crickets (Gryllus bimaculatus) produce sounds as a natural means to communicate and convey various behaviors and activities, including mating, feeding, aggression, distress, and more. These vocalizations are intricately linked to prevailing environmental conditions such as temperature and humidity. By accurately monitoring, identifying, and appropriately addressing these behaviors and activities, the farming and production of crickets can be enhanced. This research implemented a decision support system that leverages machine learning (ML) algorithms to decode and classify cricket songs, along with their associated key weather variables (temperature and humidity). Videos capturing cricket behavior and weather variables were recorded. From these videos, sound signals were extracted and classified such as calling, aggression, and courtship. Numerical and image features were extracted from the sound signals and combined with the weather variables. The extracted numerical features, i.e., Mel-Frequency Cepstral Coefficients (MFCC), Linear Frequency Cepstral Coefficients, and chroma, were used to train shallow (support vector machine, k-nearest neighbors, and random forest (RF)) ML algorithms. While image features, i.e., spectrograms, were used to train different state-of-the-art deep ML models, i,e., convolutional neural network architectures (ResNet152V2, VGG16, and EfficientNetB4). In the deep ML category, ResNet152V2 had the best accuracy of 99.42%. The RF algorithm had the best accuracy of 95.63% in the shallow ML category when trained with a combination of MFCC+chroma and after feature selection. In descending order of importance, the top 6 ranked features in the RF algorithm were, namely humidity, temperature, C#, mfcc11, mfcc10, and D. From the selected features, it is notable that temperature and humidity are necessary for growth and metabolic activities in insects. Moreover, the songs produced by certain cricket species naturally align to musical tones such as C# and D as ranked by the algorithm. Using this knowledge, a decision support system was built to guide farmers about the optimal temperature and humidity ranges and interpret the songs (calling, aggression, and courtship) in relation to weather variables. With this information, farmers can put in place suitable measures such as temperature regulation, humidity control, addressing aggressors, and other relevant interventions to minimize or eliminate losses and enhance cricket production.

Increasing temperatures affect multiyear life cycle of the outbreak bush-cricket Barbitistes vicetinus (Orthoptera, Tettigoniidae)

Although outbreaks of rare species are unusual, several insect species have become emerging pests probably due to the ongoing environmental changes. Barbitistes vicetinus was first described in 1993 as an endemic bush-cricket of north-east Italy and was considered rare until 2008, when it became an established pest, causing severe damages to forests and crops. The possible role of temperature in changing its life cycle has still to be fully understood. Here, we explored the effect of summer temperature on egg diapause and the effect of winter temperature on egg survival. Field observations showed that the proportion of embryos that can complete development at the end of summer ranged from zero to nearly 90% depending on summer temperatures. A substantial shift in the rate of development from 20% to nearly 80% occurred in a thermal range of about 1 °C. On the contrary, overwinter egg survival was high and constant (90%) across a wide range of winter temperatures that go well beyond both the cold and warm thermal limits of the current species range. Overall, the results suggest a potential key role of summer temperature warming on the outbreak propensity of this species that is able to switch from a multiyear to an annual life cycle with just a 1-2 °C warming.

Effect of summer temperature on prolonged diapause of Tettigoniidae (Orthoptera) under realistic field conditions

To face recurrent temperature changes, tettigoniids inhabiting temperate climates overwinter as eggs in a diapause stage, being able to postpone embryogenesis for one or more years. To date, it is unclear if species living in warm regions, especially under the Mediterranean climate, could exhibit a diapause for a single year or enter a prolonged diapause due to higher summer temperatures experienced by eggs immediately after oviposition. In this two-year study, we tested the effect of summer temperatures on diapause of six Mediterranean tettigoniid species under natural field conditions. We found that five species can exhibit a facultative diapause depending on mean summer temperatures. For two species, a substantial shift in egg development from 50 to 90% occurred over an interval of c. 1 °C after the first summer period. All the species increased considerably their development (nearly 90%) after the second summer period irrespective of temperatures. Overall, this study suggests that diapause strategy and the different thermal sensibility of embryonic development varies considerably across species potentially affecting their population dynamics.

Effects of Soil Temperature and Moisture on the Development and Survival of Grasshopper Eggs in Inner Mongolian Grasslands

Grasshopper eggs overwinter in soil for almost half a year. Changes in soil temperature and moisture have a substantial effect on grasshopper eggs, especially temperature and moisture extremes. However, the combinatorial effect of temperature and moisture on the development and survival of grasshopper eggs has not been well studied. Here, we examined the effects of different soil moistures (2, 5, 8, 11, 14% water content) at 26°C and combinations of extreme soil moisture and soil temperature on the egg development and survival of three dominant species of grasshopper (Dasyhippus barbipes, Oedaleus asiaticus, and Chorthippus fallax) in Inner Mongolian grasslands. Our data indicated that the egg water content of the three grasshopper species was positively correlated with soil moisture but negatively correlated with hatching time. The relationship between hatching rate and soil moisture was unimodal. Averaged across 2 and 11% soil moisture, a soil temperature of 35oCsignificantly advanced the egg hatching time of D. barbipes, O. asiaticus, and C. fallax by 5.63, 4.75, and 2.63 days and reduced the egg hatching rate of D. barbipes by 18%. Averaged across 26 and 35°C, 2% soil moisture significantly delayed the egg hatching time of D. barbipes, O. asiaticus, and C. fallax by 0.69, 11.01, and 0.31 days, respectively, and decreased the egg hatching rate of D. barbipes by 10%. The hatching time was prolonged as drought exposure duration increased, and the egg hatching rate was negatively correlated with drought exposure duration, except for O. asiaticus. Overall, the combination of high soil temperature and low soil moisture had a significantly negative effect on egg development, survival, and egg hatching. Generally, the response of grasshopper eggs to soil temperature and moisture provides important information on the population dynamics of grasshoppers and their ability to respond to future climate change.

Elevational and Latitudinal Changes in Cold Tolerance of Nymph and Adult Mormon Crickets Anabrus simplex (Orthoptera: Tettigoniidae)

Insects that hatch in winter and early spring in desert and montane regions are likely to encounter extreme weather events, including precipitous drops in temperature. The susceptibility of insects to exposure to subzero temperatures is predicted to decrease with increasing latitude or elevation. Mormon crickets occur over a broad latitudinal range from southwestern United States to Canada and a broad elevational range from near sea-level to 3,000 m. Population declines have been attributed to late freezing events, but winter hatching suggests they may also be cold tolerant. Lower lethal temperature of high elevation populations in low latitude Arizona (AZ) and high latitude Wyoming (WY) was measured by exposing nymphs and adults to 6 h or 24 h of subzero temperature. From similar latitude, WY was compared with mid-elevation Idaho (ID) and low elevation Oregon (OR) populations. Contrary to the prediction, lethal temperature of third instar nymphs was lower in AZ than in the more northerly populations. Consistently, AZ was more tolerant of cold in early nymphal instars relative to populations from higher latitude. Early hatching at lower latitudes might increase the risk of early instars experiencing a severe cold snap relative to nymphs at high latitudes. Also, contrary to prediction, the lethal temperature of adults increased with elevation, whereas third instar nymphs from mid-elevation ID were the most susceptible to cold exposure. Cold tolerance in immature and mature stages is more likely to be uncoupled when life stages do not coincide, as with Mormon crickets.

Parental Photoperiod Affects Egg Diapause in a Montane Population of Mormon Crickets (Orthoptera: Tettigoniidae)

Insect diapause is a state of arrested development persisting when conditions are favorable for growth. Prolonged diapause, which occurs when insects remain in diapause for multiple years, is uncommon. Mormon crickets Anabrus simplex Haldane, a katydid and pest of rangeland forage and crops, were thought to be biennial in the Bighorn Mountains of Wyoming, but they are able to prolong diapause in the egg stage for multiple years. To test whether parental photoperiod serves as a cue to prolong diapause, mating pairs from the Bighorn Mountains were set in the same daily temperature and humidity profiles with 20 pairs on short daylength (12:12 [L:D] h) and 20 on long daylength (15:9 [L:D] h). Almost every parental pair had some undeveloped eggs after two warm periods. Females in short daylength were not more likely to have eggs with a biennial life cycle, but they were more likely than those in long daylength to lay eggs with multi-annual life cycles. Parents on short daylength were more likely to lay inviable eggs. Other fitness measures, such as hatchling mass, nymphal survivorship, and adult mass were not different between parental treatments. Diapause termination distributed over multiple years probably constitutes a bet-hedging strategy in an unpredictable environment.

Taxonomic identification and biological traits of Platystethynium triclavatum (Donev & Huber, 2002), comb. n. (Hymenoptera, Mymaridae), a newly recorded egg parasitoid of the Italian endemic pest Barbitistes vicetinus (Orthoptera, Tettigoniidae)

The little known fairyfly (Hymenoptera, Mymaridae), Platystethynium (Platystethynium) triclavatum (Donev & Huber, 2002), comb. n. from Pseudocleruchus Donev & Huber, 2002, is newly recorded as an egg parasitoid of Barbitistes vicetinus Galvagni & Fontana, 1993 (Orthoptera, Tettigoniidae). This bush-cricket is endemic to northeastern Italy (mainly Euganean Hills of Veneto Region), where it has recently become an economically significant agricultural and forest pest. Data on discovery, distribution, and some remarkable biological traits of this gregarious egg parasitoid are presented. Its identification and availability of many well-preserved fresh specimens have made possible to re-define Pseudocleruchus Donev & Huber, 2002 syn. n., with type and the only described species Pseudocleruchus triclavatus Donev & Huber, 2002, as a synonym of Platystethynium Ogloblin, 1946 and its nominate subgenus, P. (Platystethynium), and also to describe the brachypterous male of P. (Platystethynium) triclavatum. It is the first known male for the entire genus. Enlarged mandibles of the megacephalous males are used to chew holes in the hard chorion of the host egg, allowing fully winged females, whose mandibles are strongly reduced and do not cross over, to emerge after mating with the males inside it. Up to 136 individual parasitoids (about 77 on average) can hatch from a single egg of B. vicetinus, with their sex ratio being strongly female biased (80–97% females per egg).

A Laboratory Curse: Variation in Temperature Stimulates Embryonic Development and Shortens Diapause

An ongoing biological debate concerns the difference in trait expression in continuous versus cycling temperature regimes, but are even daily cycling temperatures sufficient to generate natural expression of traits? We compared embryonic development and the duration of diapause for Mormon cricket Anabrus simplex Haldeman (Orthoptera: Tettigoniidae) eggs incubated in a daily cycling temperature constant in both amplitude and thermoperiod with those in a cycling temperature that was patterned after natural fluctuations in ambient temperature. Although the proportion of eggs developing did not differ between treatments, 128 d of vernalization was required to hatch after incubation in the constant cycling treatment relative to 42 d in the more variable cycle. We then compared these same development and diapause traits for eggs incubated in a daily cycling temperature that was constant in amplitude but varied in thermoperiod with those in the cycling temperature patterned after natural fluctuations in ambient temperature. The proportion of eggs developing in this constant cycling treatment was nearly half that in the variable treatment, and 128 d was insufficient time to break diapause following the constant cycling treatment even though the thermoperiods were now more similar. We have found that variation in the cycling temperature to mimic natural fluctuations in amplitude and period broadens the time when eggs can be warmed up for hatching and improves hatching success. Daily cycling temperatures that are constant over the season are insufficient to generate natural trait expression.

Protein deficiency lowers resistance of Mormon crickets to the pathogenic fungus Beauveria bassiana

Little is known about the effects of dietary macronutrients on the capacity of insects to ward off a fungal pathogen. Here we tested the hypothesis that Mormon crickets fed restricted protein diets have lower enzymatic assays of generalized immunity, slower rates of encapsulation of foreign bodies, and greater mortality from infection by Beauveria bassiana, a fungal pathogen. Beginning in the last nymphal instar, Mormon crickets were fed a high, intermediate, or low protein diet with correspondingly low, intermediate, or high carbohydrate proportions. After they eclosed to adult, we drew hemolymph, topically applied B. bassiana, maintained them on diet treatments, and measured mortality for 21 days. Mormon crickets fed high protein diets had higher prophenoloxidase titers, greater encapsulation response, and higher survivorship to Beauveria fungal infection than those on low protein diets. We replicated the study adding very high and very low protein diets to the treatments. A high protein diet increased phenoloxidase titers, and those fed the very high protein diet had more circulating prophenoloxidase. Mormon crickets fed the very low protein diet were the most susceptible to B. bassiana infection, but the more concentrated phenoloxidase and prophenoloxidase associated with the highest protein diets did not confer the greatest protection from the fungal pathogen as in the first replicate. We conclude that protein-restricted diets caused Mormon crickets to have lower phenoloxidase titers, slower encapsulation of foreign bodies, and greater mortality from B. bassiana infection than those fed high protein diets. These results support the nutrition-based dichotomy of migrating Mormon crickets, protein-deficient ones are more susceptible to pathogenic fungi whereas carbohydrate-deficient ones are more vulnerable to bacterial challenge.

Forest litter crickets prefer higher substrate moisture for oviposition: Evidence from field and lab experiments

For insects, choosing a favorable oviposition site is a type of parental care, as far as it increases the fitness of its offspring. Niche theory predicts that crickets should show a bell-shaped oviposition response to substrate moisture. However, lab experiments with mole crickets showed a linear oviposition response to substrate moisture. Studies with the house cricket Acheta domesticus also showed a linear juvenile body growth response to water availability, thus adult ovipositing females should respond positively to substrate moisture. We used a field experiment to evaluate the relationship between oviposition preference and substrate moisture in forest litter-dwelling cricket species. We also evaluated oviposition responses to substrate moisture level in Ubiquepuella telytokous, the most abundant litter cricket species in our study area, using a laboratory study. We offered cotton substrate for oviposition which varied in substrate moisture level from zero (i.e., dry) to maximum water absorption capacity. We used two complementary metrics to evaluate oviposition preference: (i) presence or absence of eggs in each sampling unit as binary response variable, and (ii) number of eggs oviposited per sampling unit as count response variable. To test for non-linear responses, we adjusted generalized additive models (GAMM) with mixed effects. We found that both cricket oviposition probability and effort (i.e., number of eggs laid) increased linearly with substrate moisture in the field experiment, and for U. telytokous in the lab experiment. We discarded any non-linear responses. Our results demonstrate the importance of substrate moisture as an ecological niche dimension for litter crickets. This work bolsters knowledge of litter cricket life history association with moisture, and suggests that litter crickets may be particularly threatened by changes in climate that favor habitat drying.

Demographic comparison and population projection of Rhynchophorus ferrugineus (Coleoptera: Curculionidae) reared on sugarcane at different temperatures

Understanding how temperature affects fitness is important for conservation and pest management, especially in the era of global climate change. Rhynchophorus ferrugineus (Oliver) (Coleoptera: Curculionidae) is a worldwide pest of many economically important crops. Although much is known about this pest’s life cycle, its adaptability to different temperatures is not fully understood. Here, we used age- and stage-specific life tables to investigate the effects of temperature on fitness-related traits and demographic parameters of R. ferrugineus under eight constant temperature regimens in the laboratory. The growth potential of these populations was also evaluated. The greatest longevity for males and females was 158.0 d at 24 °C and 144.5 d at 21 °C, respectively, but mean total fecundity was the highest at 27 °C. The intrinsic rate of increase (r), finite rate of increase (λ), and net reproductive rate (R₀) increased initially at low temperatures and then decreased. All metrics reached a maximum at 27 °C and a minimum at 36 °C. Mean generation times (T ) decreased across the temperature range with a minimum at 36 °C. Our results indicate that the optimum temperature for growth of R. ferrugineus was approximately 27 °C. Our work will be of value for developing strategies for control management of this pest species.

Effects of Temperature on the Age-Stage, Two-Sex Life Table of Bradysia odoriphaga (Diptera: Sciaridae)

The demographics of Bradysia odoriphaga were examined with an age-stage, two-sex life table that was developed at 15, 20, 25, and 30°C under controlled conditions. The intrinsic rate of increase and mean generation time were 0.0574 and 48.08 d at 15°C, 0.1175 and 30.09 d at 20°C, 0.1369 and 26.31 d at 25°C, and 0.1247 and 26.55 d at 30°C, respectively. The gross reproductive rate (GRR), the net reproductive rate (R0), and the pre-adult survivorship (la) were consistent with the relationship R0<la×GRR<GRR. Development was slower at 15°C than at the other temperatures. The mean duration of the total pre-adult stages was 38.01, 27.62, 23.74, and 24.10 d at 15, 20, 25, and 30°C, respectively. The highest values for the intrinsic rate of increase, finite rate of increase, and fecundity (0.1369 d(-1), 1.147 d(-1), and 50.53 eggs, respectively) and the shortest mean generation time were at 25°C. Still, B. odoriphaga was able to develop, survive, and reproduce across the entire temperature range (15-30°C). This study provides insight into the temperature-dependent phenology of B. odoriphaga and will contribute to the modeling of its population dynamics and to its management in the field.