Cryptic Behavior Research Articles

Extraterritorial visits in a cooperatively breeding songbird are consistent with multiple functions

Cryptic interactions among individuals in animal societies can be challenging to detect due to their rarity or their covert nature, but they can have important fitness consequences for the individuals involved. Using radiofrequency identification (RFID) technology, we examined the pattern and function of visits to the nests of conspecifics in western bluebirds, Sialia mexicana. Western bluebirds live in kin neighbourhoods year-round and exhibit a low frequency of cooperative breeding. Various functions have been proposed for extraterritorial visits, but few studies explore multiple potential functions. We asked whether extraterritorial visits in western bluebirds are consistent with (1) seeking extrapair copulations (EPCs), (2) prospecting for future nest sites or mates and/or (3) maintaining relationships with kin. We found some evidence supporting all three functions of visits. Postdawn visits made by males to unrelated females were significantly more likely to occur during the period in which males seek within-pair matings than outside this period. We found that visiting a given nestbox or a given potential mate was associated with an increased probability of nesting in that box or with the potential mate the subsequent year, suggesting that some visits are linked to prospecting. Finally, males preferentially visited kin: the proportion of visits to relatives was greater than the expected mean proportion of visits if males visited boxes randomly while travelling the same distance. Our work supports multiple functions of extraterritorial visits and highlights the importance of rare and cryptic behaviours to understanding social behaviour.

Ступінь вивченості й сучасний стан гніздових поселень баранця великого Gallinago media на заході України

In the paper, we describe the state of knowledge of the Great Snipe population in Western Ukraine since 19 century. Almost to the middle of the XX century, the state of knowledge about this species and the size of the surveyed territory, especially within the borders of Western Polissia, were considered as insufficient. This was caused by the cryptic behavior of the species, its nocturnal activity, and generally by low population size and ra­rity. We analyzed a significant amount of ornithological resources devoted to observations of Great Snipe in Western Ukraine, which indicate historically low population size and scarcity of distribution of the species in the study area. According to the literature sources, studies of Great snipe were somewhat intensified in the XX century. At the same time, different authors pointed out drainage works in the Polissia area, as a negative factor that drives the decrease in Great Snipe numbers in the area. or even caused complete extinction in some regions. The main range of the species in the area was still localized in the Polissian part of Volyn and Rivne regions, especially in valleys of Prypiat, Turia, Tsyr and Lva rivers. At the end of XX and the beginning of XXI intensive studies of Great Snipe were conducted on the territory of Shatsk National Nature Park, where during 10 years of studies, seasons with an increase of local population were reported, but in general negative tendency was detected and the proposal to include the species into the national red list was published. Our recent studies focused on the species, allowed us to discover new lekking places of Great Snipe. Therefore, the actual information on current numbers and distribution of the species in the region of Western Ukraine is presented. Besides leks, places of occasional observations are also mentioned, which increases the information load of the paper regar­ding the current distribution of the species in the western part of the country. The current population size is estimated as 100 lekking males, based on the total sum from all known leks. We suppose, that the real population size in the region of Western Ukraine can reach 150–200 lekking males.

Suitability of passive integrated transponder tags and a new monitoring technique for at-risk madtoms (Noturus spp.)

Representative indices of population abundance for at-risk species are necessary to inform conservation decision-making. Many madtoms (Noturusspp.) are considered imperiled; however, the efficacy of frequent monitoring efforts has been questioned due to their cryptic and nocturnal behaviors. We systematically evaluated a madtom monitoring tool by (1) evaluating the use of small (8 × 2 mm), surgically implanted 125 kHz passive integrated transponder (PIT) tags for frecklebelly madtomN. munitusand (2) assessing the effectiveness of a radio-frequency identification (RFID)-enhanced artificial cover unit to index madtom abundance. Surgically implanted PIT tags had no apparent influence on madtom survival between 45 and 110 mm total length, and all tags were retained throughout a 21 d laboratory study. In experimental mesocosms, the enhanced cover units confirmed occupancy during nearly all replicates (77.6%), even at extremely low densities (n = 2 madtoms). The enhanced cover units provided representative estimates of madtom relative abundance (p < 0.01), whereas catch per unit effort was not significantly associated with previously validated visual observations (p = 0.12). Although madtom density and the number detected using the enhanced cover units were correlated, the gear was potentially saturated at relatively high densities (~20 fish per mesocosm) when deploying a single unit. In most cases, occupancy was confirmed within 12 h, and nearly half of the individuals were detected within ~72 h. Small PIT tags and RFID-enhanced artificial cover units offer novel opportunities to efficiently describe the ecology and population dynamics of madtoms.

Concealment of juvenile bull trout in response to temperature, light, and substrate: Implications for detection.

Bull trout (Salvelinus confluentus) are challenging to detect as a result of the species cryptic behavior and coloration, relatively low densities in complex habitats, and affinity for cold, high clarity, low conductivity waters. Bull trout are also closely associated with the stream bed, frequently conceal in substrate, and this concealment behavior is poorly understood. Consequently, population assessments are problematic and biologists and managers often lack quantitative information to accurately describe bull trout distributions, estimate abundance, and assess status and trends; particularly for stream-dwelling populations. During controlled laboratory trials, we recorded concealment, resting, and swimming behavior of juvenile wild bull trout in response to: (1) constant and fluctuating water temperature, (2) presence or absence of light, and (3) substrate size. Light level had the strongest influence on wild fish concealment and more fish concealed as light levels increased from darkness to daylight. Wild fish were 14.5 times less likely to conceal in constant darkness and 4.1 times more likely to conceal in 12 h light x 12 h darkness compared to constant light. Wild fish were 6.2 times less likely to conceal in small (26–51 mm) substrate compared to larger (52–102 mm) substrate. As water temperature increased, fewer wild fish concealed. Knowledge of wild bull trout concealment will improve field sampling protocols and increase detection efficiencies. These data also enhance knowledge of bull trout niche requirements which illuminates ecological differences among species and informs conservation and restoration efforts.

Development of a lateral flow test for bed bug detection

Lateral flow strip tests are a cost-effective method for detecting specific proteins in biological samples, which can be performed in the field without specialized expertise. While most recognizable in the pregnancy tests, there are many other applications for lateral flow strip technology. The pest control industry has increasingly emphasized the importance of pest monitoring to reduce unnecessary applications, focus interventions into locations with active pest infestations, and to develop records of pest infestation. Due to their cryptic behavior, the detection of bed bugs often necessitates labor-intensive, time-consuming and invasive visual inspections. A lateral flow strip test for the detection of bed bugs would represent a novel use for a well-established technology, which can enable pest control operators to rapidly confirm the presence or absence of bed bugs in a room. In the current report, we present an effort to develop and calibrate the lateral flow test devices for the detection of a bed bug specific protein. A variety of bed bug residue samples were prepared by varying several parameters: bed bug infestation level (1 bed bug/3 bed bugs), surface type (wood/fabric), feeding status (fed/unfed), and bed bug time-on-surface (1 d/7 d). Using a prototype sensor and test strip, we examined how these variables influenced the detection of the bed bug specific proteins in the sample and to what degree. We discuss how this lateral flow test device can be an effective tool to determine the presence or absence of bed bug proteins on a surface, providing highly credible evidence on bed bug infestations.

Towards yeast taxogenomics: lessons from novel species descriptions based on complete genome sequences.

In recent years, 'multi-omic' sciences have affected all aspects of fundamental and applied biological research. Yeast taxonomists, though somewhat timidly, have begun to incorporate complete genomic sequences into the description of novel taxa, taking advantage of these powerful data to calculate more reliable genetic distances, construct more robust phylogenies, correlate genotype with phenotype and even reveal cryptic sexual behaviors. However, the use of genomic data in formal yeast species descriptions is far from widespread. The present review examines published examples of genome-based species descriptions of yeasts, highlights relevant bioinformatic approaches, provides recommendations for new users and discusses some of the challenges facing the genome-based systematics of yeasts.

Occupancy patterns of an apex avian predator across a forest landscape

AbstractApex predators are integral parts of every ecosystem, having top‐down roles in food web maintenance. Understanding the environmental and habitat characteristics associated with predator occurrence is paramount to conservation efforts. However, detecting top order predators can be difficult due to small population sizes and cryptic behaviour. The endangered Tasmanian masked owl (Tyto novaehollandiae castanops) is a nocturnal predator with a distribution understood to be associated with high mature forest cover at broad scales. With the aim to gather monitoring data to inform future conservation effort, we trialled an occupancy survey design to model masked owl occurrence across ~800 km2in the Tasmanian Southern Forests. We conducted 662 visits to assess masked owl occupancy at 160 sites during July–September 2018. Masked owl site occupancy was 12%, and estimated detectability was 0.26 (±0.06 SE). Cumulative detection probability of masked owls over four visits was 0.7. Occupancy modelling suggested owls were more likely to be detected when mean prey count was higher. However, low detection rates hindered the development of confident occupancy predictions. To inform effective conservation of the endangered Tasmanian masked owl, there is a need to develop novel survey techniques that better account for the ecology of this rare, wide‐ranging and cryptic predator. We discuss the potential to combine novel census approaches that exploit different aspects of masked owl ecology to obtain more robust and detailed data.

Ecdysone Receptor (EcR) and Ultraspiracle Protein (USP) Genes From Conopomorpha sinensis Bradley Eggs: Identification and Expression in Response to Insecticides.

Conopomorpha sinensis Bradley (Lepidoptera: Gracilariidae) is the dominant insect pest of litchi (chinensis Sonn.) and longan (Euphoria longan Lour.) fruit trees. Management of this pest species is a challenging task due to its cryptic borer behavior. Controlling C. sinensis at the egg stage is the best alternative strategy to chemical control of C. sinensis adults. However, thorough studies regarding the indirect and sublethal effects of chemicals on the different developmental stages of C. sinensis are insufficient. In this study, the effect of some insecticides was evaluated on C. sinensis eggs. The ovicidal activity of chlorbenzuron, abamectin, chlorantraniliprole, and λ-cyhalothrin was confirmed by morphological observation of the defects in C. sinensis eggs. Moreover, we characterized four essential ecdysone receptor proteins in insects [i.e., two isoform ecdysone receptors (EcR: CsEcRA. CsEcRB) and two isoform ultraspiracle proteins (USP: CsUSP1, CsUSP2)] from C. sinensis eggs. The CsEcRA, CsEcRB, CsUSP1, and CsUSP2 genes consisted of 1521-, 1614-, 1410-, and 1236-bp open reading frames which encoded proteins of 506, 527, 469, and 413 amino acid residues, respectively. Furthermore, the embryonic differential responses of CsEcRs, CsUSPs, and vitellogenin receptor (VgR: CsVgR) to insecticides were evaluated by qRT-PCR. Among the five tested genes, CsVgR and CsUSP1 were the most sensitive to all the tested insecticides, with fold change of the expression diminished by 4.27–8.70 times compared with untreated control insects. The data suggests that these insecticidal compounds regulate the expression of these specific proteins, which might eventually lead to reduced viability of C. sinensis eggs. We present here the first data providing molecular elucidation of ecdysone receptor genes and their differential responses to insecticides in C. sinensis eggs. Together with our previous report of insecticide sublethal effects on two reproduction-related genes in C. sinensis adults, CsVgR and CsUSP1 seem to be appropriate molecular parameters for the evaluation of insecticide impact on C. sinensis. This study exemplifies the potential utility of transcriptional measurement of nuclear receptors as the molecular biomarkers for ecotoxicological evaluations of ovicidal impact of insecticides.

Investigation of juvenile angelshark (Squatina squatina) habitat in the Canary Islands with recommended measures for protection and management

Abstract The identification and effective protection of nursery areas is critical for elasmobranch conservation. Research on the angelshark (Squatina squatina) is in its infancy, and is particularly challenging during the early life stages, in part because of their rarity, but also because of their camouflage and cryptic behaviour. Focused research on the identification and protection of juvenile angelshark habitat in their stronghold of the Canary Islands has been identified as a priority action to help safeguard the future of this species. This study combines citizen‐science data, satellite imagery, and focused snorkel surveys to complete a first evaluation of juvenile angelshark habitat in the region, upon which further research can be built. One confirmed nursery area, 13 potential nursery areas, and 21 beaches needing further study were identified in this study, based on the existing nursery area criteria. The results were used to develop eight key recommendations on how local and national governments can better protect juvenile angelsharks in the Canary Islands. Further research is urgently needed to confirm whether other beaches in the archipelago meet the nursery area criteria.

Development of an attract-and-infect device for biological control of lesser mealworm, Alphitobius diaperinus (Coleoptera: Tenebrionidae) in poultry houses

The lesser mealworm, Alphitobius diaperinus Panzer (Coleoptera: Tenebrionidae), is the most important pest in poultry production systems worldwide. Adults and larvae serve as alternative low-quality food for chickens and as a vehicle for animal pathogens resulting in significant economic losses for farmers. Control of this pest is usually performed through insecticide application during the interval between chicken flocks. However, due to the cryptic behaviour of this pest, chemical control is usually not effective. With the aim of developing a sustainable approach to control A. diaperinus, we evaluated integration of the A. diaperinus aggregation pheromone with a highly virulent strain (Unioeste 04) of the fungus Beauveria bassiana (Bals.) Vuill. (Ascomycota: Cordycipitaceae) using an attract-and-infect device. Significant levels of A. diaperinus mortality and lower numbers of offspring (larvae) were observed in laboratory experiments using Unioeste 04. Horizontal transmission of the Unioeste 04 strain through contaminated living A. diaperinus and cadavers was also observed. In field experiments in commercial poultry houses, a significant level of A. diaperinus mortality was observed in Unioeste 04-treated arenas. The results show that the A. diaperinus aggregation pheromone can be used as an attractant in a device impregnated with infective fungal propagules, increasing adult infection and enhancing disease spread. In addition, the use of the microbial control agent inside the device allows the fungus to remain effective for longer periods in the adverse conditions of the poultry house environment.

Identification of carnivore kill sites is improved by verified accelerometer data

BackgroundQuantifying kill rates is central to understanding predation ecology. However, estimating kill rates and prey composition in carnivore diets is challenging due to their low densities and cryptic behaviors limiting direct observations, especially when the prey is small (i.e., < 5 kg). Global positioning system (GPS) collars and use of collar-mounted activity sensors linked with GPS data can provide insights into animal movements, behavior, and activity.MethodsWe verified activity thresholds for American black bears (Ursus americanus), a bobcat (Lynx rufus), and wolves (Canis spp.) with GPS collars containing on-board accelerometers by visual observations of captive individuals’ behavior. We applied these activity threshold values to GPS location and accelerometer data from free-ranging carnivores at locations identified by a GPS cluster algorithm which we visited and described as kill sites or non-kill sites. We then assessed use of GPS, landscape, and activity data in a predictive model for improving detection of kill sites for free-ranging black bears, bobcats, coyotes (C. latrans), and wolves using logistic regression during May–August 2013–2015.ResultsAccelerometer values differed between active and inactive states for black bears (P < 0.01), the bobcat (P < 0.01), and wolves (P < 0.01). Top-performing models of kill site identification for each carnivore species included activity data which improved correct assignment of kill sites by 5–38% above models that did not include activity. Though inclusion of activity data improved model performance, predictive power was less than 45% for all species.ConclusionsCollar-mounted accelerometers can improve identification of predation sites for some carnivores as compared to use of GPS and landscape informed covariates alone and increase our understanding of predator–prey relations.

Bad hare day: very low survival rate in brown hare leverets

Increased postnatal leveret mortality has been identified as the proximate factor explaining the decline of European brown hare Lepus europaeus populations in Europe. However, direct measurements of survival rates are non-existent as the leveret's cryptic behaviour makes them very difficult to study. Previously, leveret survival rates calculated using hunting bag statistics or capture–mark–recapture methods have been estimated to lie between 5% and 56% for the period between the start (January) and the end (October) of the breeding season. Such indirect approaches are known to yield inaccurate results compared to direct survival measurements. Hence, we applied novel detection methods and radio-tagged 63 wild-born leverets (aged between 1 and 22 days at capture) in two different populations in the Swiss lowlands. We located the tagged individuals daily to monitor individual fates and to directly calculate survival probabilities. We found that leveret survival is negatively influenced by precipitation. However, when leverets use edge habitats, survival is positively influenced. Daily survival rate and survival probability for the first month of life were found to be 0.94 and 0.18 respectively. Such low survival is alarming and to prevent further declines in populations of brown hares, it will be essential to mitigate against these excessive losses. Therefore, we suggest measures aimed at increasing the area of suitable habitat for leverets, where they can grow up safely (e.g. shelter from predators and bad weather).

An escape theory model for directionally moving prey and an experimental test in juvenile Chinook salmon.

Prey evaluate risk and make decisions based on the balance between the costs of predation and those of engaging in antipredator behaviour. Economic escape theory has been valuable in understanding the responses of stationary prey under predation risk; however, current models are not applicable for directionally moving prey.Here we present an extension of existing escape theory that predicts how much predation risk is perceived by directionally moving prey. Perceived risk is measured by the extent antipredator behaviour causes a change in travel speed (the distance to a destination divided by the total time to reach that destination). Cryptic or cautious antipredator behaviour slows travel speed, while prey may also speed up to reduce predator–prey overlap. Next, we applied the sensitization hypothesis to our model, which predicts that prey with more predator experience should engage in more antipredator behaviour, which leads to a larger change in travel speed under predation risk. We then compared the qualitative predictions of our model to the results of a behavioural assay with juvenile Chinook salmon Oncorhynchus tshawytscha that varied in their past predator experience.We timed salmon swimming downstream through a mesh enclosure in the river with and without predator cues present to measure their reaction to a predator. Hatchery salmon had the least predator experience, followed by wild salmon captured upstream (wild‐upstream) and wild‐salmon captured downstream (wild‐downstream).Both wild salmon groups slowed down in response to predator cues, whereas hatchery salmon did not change travel speed. The magnitude of reaction to predator cues by salmon group followed the gradient of previous predator experience, supporting the sensitization hypothesis.Moving animals are conspicuous and vulnerable to predators. Here we provide a novel conceptual framework for understanding how directionally moving prey perceive risk and make antipredator decisions. Our study extends the scope of economic escape theory and improves general understanding of non‐lethal effects of predators on moving prey.

Varying colour pattern, yet genetically similar: Pebble Crab Seulocia vittata (Stimpson, 1858) (Brachyura: Leucosiidae) from the southeastern coast of India

Five adult specimens of leucosiid crab Seulocia vittata (Stimpson, 1858) were recently collected off the coast of Palk Bay, southern India. Typical morphological examination revealed the presence of two colour patterns: grey and red. Interestingly, molecular analysis based on the barcoding gene cytochrome oxidase sub unit I (COI) revealed that both grey and red colour patterns in S. vittata showed 0% sequence divergence between the specimens. This indicates a situation of reverse cryptic behavior in this crab. Surprisingly, the evolutionary and ecological processes leading to the absence of genetic divergence and variation in morphology (colour pattern) in S. vittata complex remain to be addressed.

Kairomones effect on parasitic activity of Trichogramma japonicum against rice yellow stem borer, Scirpophaga incertulas

AbstractThe yellow stem borer (YSB), Scirpophaga incertulas, is a borer pest of low‐land rice in tropical regions of the world, reducing production and productivity. Chemical control of YSB is challenging and often less effective due to its cryptic larval feeding behaviour inside the rice culm. Biological suppression of YSB, using egg parasitoid, Trichogramma japonicum, has been well demonstrated. Kairomones, that are interspecific, play a vital role in deciding biocontrol efficiency of egg parasitoid against lepidopteran pests. However, the mechanisms involved in terms of emission of long‐ and short‐chain volatile chemicals from YSB and its by‐products and YSB damaged rice plants in attraction to T. japonicum to locate eggs of YSB are still poorly understood. In order to trace out the volatile compounds responsible for attraction of egg parasitoid, the hexane extract of YSB female whole body and acetone extract of YSB damaged rice culm were subject to GC‐MS analyses. Out of 20 chemicals, four chemicals belonging to carboxyl, alkane and saturated fatty acid [n‐hexadecanoic acid (palmitic acid), tetradecane, octadecane, n‐octadecanoic acid (stearic acid)] from female YSB hexane extract and three sesquiterpenoids (β pinene, α pinene and caryophyllene) from YSB damaged rice plant extracts were detected in greater concentrations. In laboratory assays with the synthetic form of seven chemicals, three, n‐hexadecanoic acid, n‐octadecanoic acid and octadecane, were promising in enhancing the parasitic activity of T. japonicum on YSB eggs from 26.4% to 92.6% at 200 ppm, 27.3% to 96.5% at 500 ppm and 23.6% to 82.8% at 500 ppm, respectively, in contrast to untreated eggs (87.3% at 7th day after exposure) and hexane washed eggs (16.7% at 7th day after exposure). Evaluation of these compounds revealed the key chemical cues of biocontrol potential (n‐hexadecanoic acid, n‐octadecanoic acid and octadecane) for enhancing egg parasitism activity of T. japonicum on YSB eggs.

Predicting defaunation: accurately mapping bushmeat hunting pressure over large areas.

Unsustainable hunting is emptying forests of large animals around the world, but current understanding of how human foraging spreads across landscapes has been stymied by data deficiencies and cryptic hunter behaviour. Unlike other global threats to biodiversity like deforestation, climate change and overfishing, maps of wild meat hunters' movements-often based on forest accessibility-typically cover small scales and are rarely validated with real-world observations. Using camera trapping data from rainforests across Malaysian Borneo, we show that while hunter movements are strongly correlated with the accessibility of different parts of the landscape, accessibility measures are most informative when they integrate fine-scale habitat features like topography and land cover. Measures of accessibility naive to fine-scale habitat complexity, like distance to the nearest road or settlement, generate poor approximations of hunters' movements. In comparison, accessibility as measured by high-resolution movement models based on circuit theory provides vastly better reflections of real-world foraging movements. Our results highlight that simple models incorporating fine-scale landscape heterogeneity can be powerful tools for understanding and predicting widespread threats to biodiversity.

Los censos visuales en transecto de banda subestiman la abundancia del pez león &lt;i&gt;Pterois&lt;/i&gt; spp. en arrecifes coralinos del Caribe

The visual census of band transect (CVB) is one of the most used monitoring protocol on reefs, however this study confirms that its application fail in the detection and estimation of abundance of invasive lionfish. CVB vs Lionfish Search Census (CBP) was compared on Mexican Caribbean reefs. Differences in abundance of lionfish were found between CVB and CBP. Bias among both methods was significantly correlated to the cryptic behavior of inactivity and depth of the site. Finally, the use of different lionfish sampling methods and the application of CBP for monitoring reefs in the region are discussed.

Assessment of survey protocol for estimates of abundance for elusive nocturnal primates

Abstract ContextEstimates of a species abundance and habitat preferences provide vital information on their status and the appropriate conservation management. For nocturnal arboreal primates, obtaining reliable estimates of these parameters is particularly challenging because of their cryptic behaviour, often resulting in a small number of detections. Although techniques are available for assessing the abundance of species with a low probability of detection, most require strict assumptions that are difficult to meet. AimsHere, we aimed to explore the possibility of improving nocturnal-primate abundance estimates when detection probability is low and to determine the minimal effort required to calculate reasonable estimates of their overall abundance and the effect of habitat type on abundance estimates. MethodsWe used count data obtained from spotlighting along line transects for estimating density of Bengal slow loris (Nycticebus bengalensis) in north-eastern Thailand with N-mixture hierarchical modelling, to run simulations of varying survey parameters and asses the effort needed to produce robust estimates based on the relative bias from each simulation. Key resultsN-mixture analysis showed that the data obtained from our study were still biased (9%), with a lambda of 1.79 lorises, detection probability of 0.11, 50 survey sites and a maximum of 12 sample occasions. The simulation results found that increasing the number of sample occasions to 14 per transect would produce an acceptable bias (&amp;lt;5%). ConclusionsWe recommend that future studies on nocturnal arboreal species should use preliminary surveys to gauge the specific lambda and probability of detection so as to establish the effort needed to produce reasonable estimates of abundance. ImplicationsOur study showed that count data obtained from spotlighting can be used to produce robust abundance estimates of nocturnal arboreal species. Unlike simple encounter rate, this method incorporates detection probability and habitat preferences, yet does not require additional trained field technicians.

Population Structure of the Freshwater CrabPotamon algeriense(Bott, 1967) Inhabiting Oued Zegzel, (Northeast of Morocco)

This is the first study to determine the population structure of the freshwater crabPotamon algeriensein Oued Zegzel, a mountain stream in the northeast of Morocco. Monthly collections were carried out by hand, from October 2017 to September 2018. A total of 669 individuals, 378 males and 291 females, were captured, measured, marked, and released. Due to their extremely cryptic behavior during egg incubation, few ovigerous females were caught during the entire sampling period. The average size of males (28.98 ± 10.78 mm CW) is significantly larger than that of the females (28.62 ± 8.48 mm CW). Significant deviation from 1 : 1 sex ratio during the study period was recorded, and the size distribution of the sampled population presented an abnormal distribution where specimens over 31 and under 25 mm CW were often males, whereas females were represented more in the 26–30 mm CW range.

Systematicity, persistence and efficacy of selected insecticides used in endotherapy to control the red palm weevil Rhynchophorus ferrugineus (Olivier, 1790) on Phoenix canariensis

The control of the invasive red palm weevil (RPW) Rhynchophorus ferrugineus (Olivier, 1790) is a challenge. This pest has a cryptic behavior, as it achieves most of its life cycle within host tissues, where larval instars are endophytic and are out of reach from insecticides applied as cover sprays. In order to increase the efficacy of chemical control, stem injection technique, known also as endotherapy, has been implemented and recommended as an alternative approach, which requires the use of highly systemic and persistent insecticides. In this paper, we report the results of endotherapy essays carried out on ornamental palm trees, Phoenix canariensis Chabaud in Carthage, Tunis (Tunisia) and Catania, Sicily (Italy), between 2015 and 2018, using thiamethoxam, emamectin benzoate and imidacloprid. The mobility, persistence and efficacy of these insecticides were evaluated. We found that emamectin benzoate is more systemic and persistent (up to 5 months) in palm tissues than thiamethoxam and imidacloprid. Maximum residues of emamectin benzoate (1.87 mg\kg) were detected in leaf base samples, 10 days after its injection. Residues of imidacloprid were detected 10 days after application (0.194 mg\kg), with a maximum (0.277 mg\kg) registered 2 months after its injection with a persistence period up to 3 months. Residues of thiamethoxam were detected (0.123 mg\kg) only once, 10 days after application. Then values were below the limit of detection (0.1 mg\kg). Field essays with selected insecticides applied as preventive and curative endotherapy treatments showed that emamectin benzoate is able to protect palm trees from RPW infestation up to 9 months.