University of Padua

Polyethism in a social caterpillar: Exploring tent construction and foraging behaviour

Battisti, Andrea (2022) Polyethism in a social caterpillar: Exploring tent construction and foraging behaviour. [Data Collection]

Collection description

Raw Data (Polyethism in a social caterpillar: Exploring tent construction and foraging behaviour)

DOI: 10.25430/
Keywords: Colony, cooperation, pine processionary moth, sex differences, social organisation, Thaumetopoea pityocampa, Lepidoptera, Notodontidae
Subjects: Life Sciences > Ecology, Evolution and Environmental Biology: Population, community and ecosystem ecology, evolutionary biology, behavioural ecology, microbial ecology > Behavioural ecology and evolution
Department: Departments > Dipartimento di Agronomia Animali Alimenti Risorse Naturali e Ambiente (DAFNAE)
Depositing User: Andrea Battisti
Date Deposited: 07 Dec 2022 07:12
Last Modified: 22 Feb 2023 08:04
Type of data: Database
Research funder: European Union’s Horizon 2020 Program for Research and Innovation ‘HOMED’ [grant no. 771271]
Research project title: Fondazione Cassa di Risparmio di Padova e Rovigo PhD programme 2018
Collection period:
August 2020December 2021
Geographic coverage: Italy
Bounding Area:
North LatitudeEast LongitudeSouth LatitudeWest Longitude
Data collection method: In mid-August to end of September 2020, when T. pityocampa caterpillars are L1 to L2, frass production of 12 colonies in the field (Precastio Tregnago Verona Italy, 45° 31’N, 11° 10’E, 530 m) were measured and analysed. The larval instar was determined by the body and frass size. Once T. pityocampa caterpillars were L3 and older, they fed beyond the immediate branches surrounding the tent therefore, reliable frass counts were unable to be recorded. We randomly selected ten L1-2 colony tents that were maximum 1 m off the ground on Pinus nigra host trees (Supplementary Fig. S1). The frass counts were done by using a frass collecting apparatus made from a rotating disc placed directly underneath the tent where younger instar caterpillars feed in the immediate area (Uemura et al., 2020a). The rotating disc was built by attaching a 21 cm diameter circular corrugated sheet on a 24 h mechanical plug-in timer using Scotch clear extreme fastener strips. A transparent circular sheet of plastic with 24 equal slices was placed on top of the corrugated sheet, so that as the disc rotates from the 24 h mechanical plug-in timer, each slice represents one hour of the day. Coloured paperclips were used as a marker to determine where the tent was positioned on the disc. In the field, the wind caused the frass to move therefore, the plastic sheet was coated with liquid Vaseline to keep the frass in place. The rotating disc was attached to a metal ring of an 80 cm steel stand with heavy duty tape. The timers were powered using the Wolf PRO Power Bank (Litionite, Ancona, Italy) and the power bank was sheltered from the rain and wind by an umbrella tied to the tree branches. One rotating disc was placed under each colony and two colonies were surveyed for 24 h. No more than two discs could operate at one time because of the power bank battery capacity. The same colony was not used to measure the frass of more than one instar. The experiment started in the afternoon, generally when no larval activity is observed, and stopped after approximately 24 h. A photo of the disc was then taken from above using an iPhone, and the disc was cleaned and recoated with liquid Vaseline for the next frass collection. The images were cropped to each slice and the frass on each slice was counted digitally using ImageJ version 1.53 e with the Analyze Particles function. Daily caterpillar activity: Tent building and foraging Tent building behaviour of 45 T. pityocampa colonies of L1 to L4 larval instar were monitored in the field from July 2020 to February 2021. Final instar caterpillars were not used in the experiment because they are less involved in tent construction (Breuer et al., 1989), as was confirmed by observations carried out by one of the authors (pers. obs., A. Battisti) in the same site in previous years. Colonies were randomly selected from ten isolated P. nigra host trees. Protective gear against urticating setae was worn when handling colonies L3 and older to minimise the experimenter’s exposure. In mid-August to start of November 2020 when caterpillars were L2-L4, two wildlife cameras were set up on a tripod and focused to take images of a single colony each, every 15 min for 24 h. Every two to three days, the cameras were moved to capture different colonies and the same colony was not used again. The images were stored on a SD card and viewed on a computer. The time stamp and larval activity captured on each image, such as spinning silk/tent building (spinning) and feeding and returning to the tent (foraging), were noted for the colony. Spinning was determined when caterpillars were visible through the silk strands of the tent and when moving on the tent surface. Foraging was determined when caterpillars moved in a procession from the tent to pine needles nearby and engaged in feeding on the pine needle. Caterpillars returning to the tent was determined when caterpillars moved in a procession from the pine needles back to the tent and remained inside. Individual caterpillars could not be distinguished through the wildlife camera images therefore, we analysed the activities as a colony and not specific individuals. Larval activity times determined from the images were further confirmed by checking the colonies daily in the field at different times of the day and night. When observing T. pityocampa colonies at night, a red-light headlamp was used. HOBO Temperature/RH data logger (Onset Computer Corporation, Macquarie, USA) probes were placed next to the tent being monitored to measure the environmental temperature every 15 min. In October-November 2020, when caterpillars are L3 and spin the most amount of silk for tent construction, we analysed the wildlife camera images of eight colonies. From the images, as individuals are large, we were able to clearly distinguish the spinners and the foragers. The time, environmental temperature, average daily temperature, colony identification (ID), and weather condition at which the two types of activity occurred and wildlife camera orientation relative to the colony were recorded. 1.3. Polyethism We observed that not all caterpillars come out of the tent at sunset to spin silk to enlarge and build maintain the tent. We hypothesised that there could be polyethism within colonies and specific individuals come out to spin. During our observations from wildlife camera images and field visits at sunset and in the evening, we were able to identify two caterpillar activities in all T. pityocampa colonies. (1) At sunset, the early active caterpillars spun silk on the tent and foraged immediately after the cessation of spinning activity, (2) whereas the late active caterpillars emerged out of the tent and foraged from around midnight to early morning. Across two nights in November to December 2020 and five nights in November to December 2021 we collected 16 and 25 L4 caterpillar tents with pine branches respectively, from Precastio. The tents were transported to a nearby outdoor facility and individually hung across a 6 m clothesline to be able to monitor caterpillar activity throughout the night and early morning. Ten to 30 early and late active caterpillars were collected with forceps from 20 (2020: N = 10, 2021: N = 10) and 21 (2020: N = 6, 2021: N = 15) tents respectively, and stored in 70% ethanol. Protective clothing and eye wear were worn during the collection to eliminate contact with urticating setae from the caterpillars. From the onset of darkness, we used a red headlamp to determine and differentiate the behaviour of the caterpillars without disturbing their behaviour. Differentiating sex using external morphology (Lavenseau, 1982; Underwood, 1994) was difficult on T. pityocampa caterpillars. Therefore, collected caterpillars were dissected, and the presence or absence of testis located dorsally on the 5th abdominal segment, was used to determine if the caterpillar was male or female, respectively (Battisti, 1988). The head capsule width from dissected caterpillars were measured using a Leica S9i Digital Stereo Microscope at 20× magnification with an eyepiece graticule.
Statement on legal, ethical and access issues: The experiments involved insects only and therefore a licence from University of Padova was not required to conduct this study. Throughout the experiments, we took minimal number of caterpillars that were necessary for the study and returned the colonies back to the same host trees after termination of the study.
Resource language: English
Metadata language: English
Publisher: Research Data Unipd
Date: 6 December 2022
Copyright holders: The Author

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