1. Evaluating enclosure use in the sun beetle
Pachnoda marginata; implications for welfare
James Brereton1, Shelby Stanfield, and Kev Palmer1
1Reaseheath College, Nantwich, Cheshire, CW5 6DF
For correspondence,
Abstract:
Enclosure use and design has developed into an evidence-based science with the potential to improve animal welfare for a range of species. Enclosure use analysis methods could be used to objectively improve enclosure design for small zoo species, such as invertebrates. This study investigated enclosure use in a colony of sun beetles (Pachnoda marginata) over a nine-month observation period. Overall enclosure use values were calculated using the modified Spread of Participation Index (SPI). The effects of temperature, humidity and light provision were investigated, revealing that sun beetles selectively used elevated enclosure zones when basking lights were switched on (p<0.001). A Pearson’s correlation revealed that enclosure temperature showed a weak yet significant positive correlation (0.23) with SPI (p<0.001), indicating that smaller, rotten log zones were used preferentially during increased temperatures. Time of day, by contrast, showed no significant correlation with SPI (p=0.456). The outcomes of this study have implications for best practice enclosure design for P. marginata. The research also provides a foundation from which a wider range of invertebrate studies may be developed.
Introduction:
The sun beetle, Pachnoda marginata, is widely distributed throughout zoos, labs & private collections. Despite its wide availability, there has been little research investigating best practice husbandry and enclosure use. Instead, research has focused upon flight metabolism1,2, larval microbiology 3,4 and olfactory senses5.
Pachnoda larva live exclusively in soil and rotten wood substrates, so deep substrate is an essential component of a suitable enclosure. Furthermore, P. marginata adults are able to burrow and fly, so enclosures should also be sufficiently complex to encourage these behaviours. Given the shortage of knowledge, there is a need to evidence-base the husbandry of this species.
Methodology:
The observation period took place from the 1st September 2015 until the 7th May The sun beetle enclosure was separated into different zones based on biological qualities, in accordance with Plowman’s modified Spread of Participation Index (SPI) 6. Enclosure zones and measurements may be found in table 1.
Instantaneous scan samples took place ad libitum at the beginning of each hour when observers were available, counting the number of individuals seen in each enclosure zone. If the beetles were not seen in any zones, it was assumed they were in the subterranean zone. The P. marginata population size was factored into the SPI calculations, evaluating the proportion of individuals occupying each zone.
Environmental variables including temperature, humidity and light were recorded for later correlation tests.
Figure 3: A congregation of sun beetles (BugsUK, 2013).
Results:
Due to the proportionally large size of the three-dimensional subterranean zone, even enclosure use was associated with most sun beetles buried within the substrate. By contrast, uneven enclosure use occurred when individuals used the above ground enclosure zones.
Effect of time of day: Pearson’s correlation between time of day and SPI revealed a weak positive correlation (0.018) which was non-significant (r=0.018, N=1710, p=0.456).
Light provision: The average SPI values for ‘light on’ and ‘light off’ were / and / respectively. Sun beetles used significantly more of their enclosure when lights were switched off (t=1.645, n=1710, p<0.001).
Effect of temperature: A Pearson’s correlation revealed a highly significant, weak positive correlation (r=0.176, n=1710, p<0.001), suggesting that as temperature increases, SPI values also increase. In warmer temperatures, sun beetles show a more uneven enclosure use.
A regression analysis was also computed, factoring in temperature and presence of light. This revealed a weak but highly significant relationship (R2=0.057, F(2,1710)=51.42, p<0.001). The effects of temperature and presence of light accounted for 5.7% of variation in SPI. As temperature increased, enclosure use values became higher (b=0.004, SE=0.001, t(1710)=2.989, p=0.003), indicating less even enclosure use. When lights were switched on, enclosure values also became higher (b=-0.048, SE=0.007, t(1710)=-6.83, p=<0.001), also showing less even enclosure usage.
Effect of humidity: Humidity levels did not show significant correlation with SPI, and was omitted from further analyses.
Figure 1: Average SPI values depending on light setting.
Discussion:
Elevated zones: When lights were switched on, sun beetles made much greater use of elevated zones than expected, and basking behaviours were observed. Providing sun beetles with the opportunity to bask may be important for improved welfare of these beetles. Supplying elevated zones can help P. marginata to express a wider range of behaviours, including climbing and aggregative behaviour. Increased behavioural diversity is normally associated with improved welfare7: this could be investigated using further sun beetle studies.
Basking light: Turning on enclosure lighting had a significant effect on enclosure use, accounting for 5.7% of variation in SPI. It is apparent that sun beetles benefit from use of enclosure light, for they displayed use of elevated zones and clustering behaviours when light was present. It is likely that these benefits are applicable to a wide range of Pachnoda species: further research would be beneficial to investigate.
Invertebrate studies: While many zoo-based studies have focused on mammals, behavioural research for invertebrates is currently scarce. A review of the BIAZA research database8 revealed 3,605 studies, of which only 26 focused on terrestrial invertebrates. With comparatively little invertebrate behaviour understood, there is a need to initiate further projects in this sector. Research in this sector will help to show a wider scope of the work undertaken by zoos and could give insight into increasing visitor interest.
Enclosure use and preference projects could be commenced to evidence-base the husbandry of endangered invertebrates, such as the Frégate island beetle (Polposipus herculaneus) and partula snail (Partula affinis). 6.
Figure 2: Average Percentage of Sun Beetles Observed in each Zone, considering light setting.
Table 1: Measurements of Each Biologically Relevant Zone
Enclosure Zone:
1. Ground
2. Living Plants
3. Artificial Plants
4. Rotten Wood
5. Spindly Twigs
6. Subterranean
Total Area (cm2)
Area (cm2)
1574
100
1524
226
125
19,800
23,349
Conclusions:
Sun beetle enclosures should incorporate provision of basking spots, with natural or artificial light, to encourage sociality and improve welfare.
The inclusion of elevated zones is an important component of enclosure design, allowing sun beetles to climb and possibly increase social behaviours.
Further studies on invertebrate enclosure use should be initiated to better understand the biological needs of this understudied taxa.
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