Improving Trapping Efficiency for Control of American Mink (Neovison vison) in Patagonia

Two main challenges when controlling alien American mink (Neovison vison) in Patagonia are to maximize campaign efficacy and cost-effectiveness and to avoid trapping native species. We designed and tested new variants of collapsible wire box traps, compared the efficacy of a food-based bait and a scent lure and compared catch rates in different seasons of the year. We used the data to model the efficiency rate of the trapping and to determine the trapping effort required to remove 70–90% of the estimated discrete mink population. Between January 2018 and March 2021, we operated 59 trapping transects over 103 three-day trapping periods in southern Chile. Traps were first baited with canned fish, and afterwards with mink anal gland lure. We compared the efficacy of mink capture with that of our previous study. We trapped 196 mink (125 males, 71 females), with most captures in summer. The medium-sized GMV-18 trap caught more male mink, but the more compact GMV-13 caught fewer non-target rodents and no native mammals. The scent lure was more successful than the canned fish when the previous campaign’s data were included in the analysis. There was also a significant improvement in the proportion of female mink trapped and reduced labour compared with our previous campaign that used larger traps, fish bait and 400–500 m trap spacings. We caught relatively more females than males after the third night of trapping on a transect. Our data analysis supports the use of the GMV-13 variant of wire cage trap as the best trap size: it is effective on female mink, small, cheap and easy to transport. Combined with mink anal scent lure, it reduces the possibility of trapping native species compared with other traps tested in Chile. As the most efficient method for removing at least 70% of the estimated discrete mink population within the area covered by each trap transect in southern Chile tested to date, we recommend trapping campaigns using GMV-13 during summer, with a 200-m trap spacing, for up to 6 days before moving traps to a new site, with a combination of three days with a female scent gland lure, followed by three days with a male scent gland lure.

Histomorphological perspectives of preputial and clitoral glands of soft-furred field rat Millardia meltada

The present study was an attempt to understand the sexual dimor-phism of the integumentary scent glands of soft-furred field rat Millardia meltada from the perspectives of anatomy, morphology and histology with view to correlate with the sex-specific pheromones they produce. The scent gland of male is known as preputial gland, and female, the clitoral gland. The rats, that are agricultural pests were field caught, the glands of males and females of almost identical size were dissected out, and subjected to gravimetric, morphometric and histological analyses. Both glands are yellowish-brown, pear-shaped, and dorsoventrally compressed. The mean weight, length and width of preputial glands are significantly (p < 0.05) larger than that of the clitoral glands. The preputial gland is composed of sebaceous glandular lobules and apocrine glandular lobules whereas the clitoral gland is formed only of sebaceous glandular lobules. The sebaceous glandular lobules of both preputial and clitoral glands are filled with a wax-like material. Thus, the scent glands of the soft-furred male field rats exhibit sexual dimorphism in respect histoarchitecture of the glands and the nature of the secretory material. This sexual dimorphism of the scent glands may reflect control by male and female sex hormones impinging on specific roles as sex attractant pheromones.

The Morphological Characters of Egg and Relationship of Immature Stages of Hermolaus modestus (Heteroptera: Pentatomidae: Eysarcorini)

The paper investigates the biology and structure of egg and different developmental stages from 1st instar to 5th instar of Hermolaus modestus (Distant) (Pentatomidae: Eysarcorini). The experiment was conducted in the laboratory and the species was recognized as plant-sucking pest and mostly recorded on Ocimum basilicum (L.) from different areas of Karachi, Pakistan. The male and female individuals were breed under controlled laboratory condition. The maximum fertility range of Hermolaus modestus was observed 10 to 14 eggs per female and eggs were laid singly on the ventral side of plant leaves near the midrib. The incubation period was completed in 4 to 5 days. Newly emerged nymphs were dark red in colour but later colour changed into brown. The nymph passed through five instars progressively to complete the nymphal period. The first instar completed in 2 to 3 days with its specific characters. The second instar took 6 to 7 days with large clypeus. The third instar having scent gland plates and wing pads, completed in 5 to 6 days. The fourth and fifth instars of H. modestus completed in 5 to 6 and 8 to 9 days with prominent mesonotal and metanotal wing pads, respectively. The total nymphal period varied from 26 to 31 days. The total life cycle showed variation from 30 to 36 days. The total body length of male Hermolaus modestus was recorded as 4.8 mm to 5.0 mm.

The hard task of a short-tailed mouse opossum (Monodelphis) to prey a harvestman (Arachnida: Opiliones)

ABSTRACT Despite the great diversity of small insectivorous mammals and the use of scent gland secretions as a defense mechanism by harvestmen, there is no observation about the effectiveness of scent glands against predators such as small mammals. We report a remarkable harvestman defense mechanism against a small-mammal attack. When a harvestman and a mouse opossum confronted each other inside a cage, the harvestman knocked out the mouse opossum two sequential times before it could attack the harvestman. Although it is a unique observation and there is no information about its frequency in nature, this report stimulates the study of agonistic behavior between small, cryptic species, which are difficult to observe in the field.

Benzoquinones in the defensive secretion of a bug (Pamillia behrensii): a common chemical trait retrieved in the Heteroptera

Benzoquinones are a phylogenetically widespread compound class within arthropods, appearing in harvestman, millipedes and insects. Whereas the function of benzoquinones as defensive compounds against potential predators and microbes has been well established, the full extent of benzoquinone usage across arthropods, and especially within Insecta, has yet to be established. Adding to the growing list of unique evolutionary origins of benzoquinone employment, we describe in this paper the metathoracic scent gland secretion of the mirid bug Pamillia behrensii, which is composed of heptan-2-one, 2-heptyl acetate, 2,3-dimethyl-1-4-benzoquinone, 2,3-dimethyl-1-4-hydroquinone as well as one unknown compound. Similarly, to many other arthropods that use benzoquinones, Pamillia releases the contents of its gland as a defensive mechanism in response to harassment by other arthropod predators. Morphological investigation of the gland showed that the benzoquinone-producing gland complex of P. behrensii follows a similar blueprint to metathoracic scent glands described in other Heteropterans. Overall, our data further underpins the widespread convergent evolution and use of benzoquinones for defense across the Arthropoda, now including the order Hemiptera.

Potential female mate choice in a male dominated system: the female capybara, Hydrochoerus hydrochaeris

Capybaras, Hydrochoerus hydrochaeris (Rodentia: Caviidae: Hydrochoerinae), show a strict social hierarchy among males, wherein the top-ranking male gains preferential access to females. Despite minimal sexual size dimorphism, males have a prominent scent gland on their snouts that is greatly reduced in the females. Top-ranking males have a larger gland and mark more frequently than subordinate males. This species also shows a moderately complex courtship that seems to be modulated by female behavior. In this study, we evaluated several components of courtship, as well as the females’ interactions with males during and outside courtship, in relation to the hierarchy rank of males. We found that subordinate males engaged in longer courtships than top-ranking males. However, there was no difference in the number of mount attempts or the success rate of these mounts as a function of the social status of the male, despite the longer courtship performed by subordinate males in comparison to top-ranking males. Outside courtship, females directed the same number of social interactions to males regardless of status. However, during courtship, females avoided copulation by subordinate males both directly and indirectly by encouraging courtship disruption by higher-ranking males. Females’ avoidance of subordinates may force these males to invest a higher amount of effort in courtships, thus engaging in longer courtships, yet achieving similar mount success as top-ranking males. We show that the original assumption of male hierarchy as the main mechanism of reproductive distribution is incomplete, and female mate choice plays an important role in determining which males reproduce.