Shades of yellow: interactive effects of visual and odour cues in a pest beetle

Novel use of a servosphere to study apodous insects: Investigation of blow fly post-feeding larval dispersal

Blow flies (Diptera: Calliphoridae) are arguably the most important providers of an estimate of minimum post-mortem interval in forensic investigations. They usually undergo a post-feeding dispersal from the body. While previous studies have looked at dispersal of groups of larvae, recording the dispersal activity of individual larvae has not previously been demonstrated. A servosphere was used here to record the speed, directionality and phototaxis of individual post-feeding larvae of two species of blow fly on a smooth plastic surface over time. The servosphere rotates to compensate for the movement of an insect placed at its apex, thereby enabling its unimpeded locomotion in any direction to be studied and behavioural changes to external stimuli recorded. To our knowledge, the servosphere has not previously been used to study apodous insects. The objective of our study was to compare dispersal behaviour of Calliphora vicina Robineau-Desvoidy and Protophormia terraenovae (Robineau-Desvoidy), both common primary colonisers of human and animal cadavers, but showing different post-feeding dispersal strategies. Larvae of C. vicina generally disperse from the body while those of P. terraenovae remain on or close to the body. Our aims were to study (1) changes in dispersal speed over a 1-h period; (2) changes in dispersal speed once a day for 4 days, between the end of feeding and onset of pupariation; and (3) response of dispersing larvae to light. We demonstrated that (1) the movement of three C. vicina larvae tracked for 1 continuous hour on 1 day slowed from an average of 3 to <1.7 mms-1; (2) the average speed of 20 larvae of C. vicina (4.08 mms-1) recorded for 5 min once per day over a 4-day period between onset of dispersal and pupariation was significantly greater than that of P. terraenovae (2.36 mms-1; p < 0.0001), but that speed of both species increased slightly over the 4 days; (3) the responses of larvae of C. vicina to changes in light direction from the four cardinal directions of the compass, showed that they exhibited a strong negative phototactic response within 5 s, turning to move at approximately 180° away from the new light position. While conducted to observe larval calliphorid post-feeding behaviour, the results of this proof of concept study show that apodous insects can be studied on a servosphere to produce both qualitative and quantitative data.

Navigation and orientation in Coleoptera: a review of strategies and mechanisms

Spatial orientation is important for animals to forage, mate, migrate, and escape certain threats, and can require simple to complex cognitive abilities and behaviours. As these behaviours are more difficult to experimentally test in vertebrates, considerable research has focussed on investigating spatial orientation in insects. However, the majority of insect spatial orientation research tends to focus on a few taxa of interest, especially social insects. Beetles present an interesting insect group to study in this respect, due to their diverse taxonomy and biology, and prevalence as agricultural pests. In this article, I review research on beetle spatial orientation. Then, I use this synthesis to discuss mechanisms beetles employ in the context of different behaviours that require orientation or navigation. I conclude by discussing two future avenues for behavioural research on this topic, which could lead to more robust conclusions on how species in this diverse order are able to traverse through a wide variety of environments.

Plant-insect-microbe interaction: A love triangle between enemies in ecosystem

In natural ecosystems, plants interact with biotic components such as microbes, insects, animals and other plants as well. Generally, researchers have focused on each interaction separately, which condenses the significance of the interaction. This limited presentation of the facts masks the collective role of constantly interacting organisms in complex communities disturbing not only plant responses but also the response of organisms for each other in natural ecological settings. Beneficial microorganisms interact with insect herbivores, their predators and pollinators in a bidirectional way through the plant. Fascinatingly, insects employ diverse tactics to protect themselves from parasites or predators. Influences of microbial and insects attack on plants can bring changes in info-chemical frameworks and play a role in the food chain also. After insect herbivory and microbial pathogenesis, plants exhibit intense morpho-physiological and chemical reprogramming that leads to repellence/attraction of attacking organism or its natural enemy. The characterization of such interactions in different ecosystems is receiving due consideration, and underlying molecular and physiological mechanisms must be the point of concentration to unveil the evolution of multifaceted multitrophic interactions. Therefore, we have focused this phenomenon in a more realistic setting by integrating ecology and physiology to portray these multidimensional interfaces. We have shown, in this article, physiological trajectories in plant-microbe and insect relationship and their ecological relevance in nature. We focus and discuss microbial pathogenesis in plants, induced defense and the corresponding behavior of herbivore insects and vice-versa. It is hoped that this review will stimulate interest and zeal in microbes mediated plant-insect interactions along with their ecological consequences and encourage scientists to accept the challenges in this field.

Fluorescent Pan Traps Affect the Capture Rate of Insect Orders in Different Ways

To monitor and quantify the changes in pollinator communities over time, it is important to have robust survey techniques of insect populations. Pan traps allow for the assessment of the relative insect abundance in an environment and have been promoted by the Food and Agricultural Organization (FAO) as an efficient data collection methodology. It has been proposed that fluorescent pan traps are particularly useful, as it has been suggested that they capture high numbers of insects in an unbiased fashion. We use a simultaneous presentation of fluorescent and non-fluorescent pan trap colours to assess how flower-visiting insects of different orders respond to visual stimuli and reveal a significant interaction between trap fluorescence and captured insect type. In particular, Coleoptera (beetles) and Lepidoptera (butterflies and moths) were captured significantly more frequently by fluorescent traps, whilst Dipterans (flies) were captured significantly less frequently by this type of pan trap. Hymenopterans (bees and wasps) showed no significant difference in their preference for fluorescent or non-fluorescent traps. Our results reveal that the use of fluorescent pan traps may differently bias insect capture rates when compared to the typical experience of colour flower-visiting insects in natural environments. Correction factors may, therefore, be required for interpreting insect pan trap data collected with different methodologies.

Associative visual learning by tethered bees in a controlled visual environment

Free-flying honeybees exhibit remarkable cognitive capacities but the neural underpinnings of these capacities cannot be studied in flying insects. Conversely, immobilized bees are accessible to neurobiological investigation but display poor visual learning. To overcome this limitation, we aimed at establishing a controlled visual environment in which tethered bees walking on a spherical treadmill learn to discriminate visual stimuli video projected in front of them. Freely flying bees trained to walk into a miniature Y-maze displaying these stimuli in a dark environment learned the visual discrimination efficiently when one of them (CS+) was paired with sucrose and the other with quinine solution (CS−). Adapting this discrimination to the treadmill paradigm with a tethered, walking bee was successful as bees exhibited robust discrimination and preferred the CS+ to the CS− after training. As learning was better in the maze, movement freedom, active vision and behavioral context might be important for visual learning. The nature of the punishment associated with the CS− also affects learning as quinine and distilled water enhanced the proportion of learners. Thus, visual learning is amenable to a controlled environment in which tethered bees learn visual stimuli, a result that is important for future neurobiological studies in virtual reality.

Ginger and the beetle: Evidence of primitive pollination system in a Himalayan endemic alpine ginger (Roscoea alpina, Zingiberaceae)

The Himalayan endemic alpine genus Roscoea, like other members of ginger family, exhibits the combination of floral traits that would fit pollination by long distant foragers such as bees, birds or flies. We studied the pollination biology of Roscoea alpina, observed potential floral visitors and determined their foraging behaviour, visitation frequency and pollination efficiency, to seek evidence in support of the pollination syndrome hypothesis. We also measured the floral spectra of R. alpina flowers to evaluate if signals fit with the currently known framework for observed floral visitors. We found that R. alpina have autonomous selfing and pollinator-mediated crossing, but lack apomixis. We observed that a beetle (Mylabris sp.), and a moth (Macroglossum nycteris) visit the flowers of R. alpina for pollen and nectar feeding respectively. Our field observations, the stigmatic pollen count and fruit set data indicated that the visit by the beetle was legitimate, while that of the moth was illegitimate. Emasculated flowers visited by beetles set as many fruits and seeds/fruit as auto-selfed and naturally pollinated flowers, while emasculated flowers excluded from beetle visits did not set fruit and seed; indicating that a single visit of a beetle to the flowers of R. alpina can facilitate pollination. We found that flower spectral signal of R. alpina does not fit typical spectra previously reported for beetle or bee-visited flowers. Our results suggest that, to ensure reproductive success in alpine habitat, R. alpina has evolved autonomous selfing as a predominant mode of reproduction, while beetle pollination would promote genetic diversity of this plant species. The visitation of beetles to the flowers of R. alpina, despite floral signal mismatch with the classically associated beetle vision, suggests that a different visual processing may operate in this plant-pollinator interaction at high altitudes.