Hoverfly locomotor activity is resilient to external influence and intrinsic factors

Abstract

Hoverflies are found across the globe, with approximately 6000 species described worldwide. Many hoverflies are being used in agriculture and some are emerging as model species for laboratory experiments. As such it is valuable to know more about their activity. Like many other dipteran flies, Eristalis hoverflies have been suggested to be strongly diurnal, but this is based on qualitative visualization by human observers. To quantify how hoverfly activity depends on internal and external factors, we here utilize a locomotor activity monitoring system. We show that Eristalis hoverflies are active during the entire light period when exposed to a 12 h light:12 h dark cycle, with a lower activity if exposed to light during the night. We show that the hoverflies’ locomotor activity is stable over their lifetime and that it does not depend on the diet provided. Surprisingly, we find no difference in activity between males and females, but the activity is significantly affected by the sex of an accompanying conspecific. Finally, we show that female hoverflies are more resilient to starvation than males. In summary, Eristalis hoverflies are resilient to a range of internal and external factors, supporting their use in long-term laboratory experiments.Electronic supplementary materialThe online version of this article (doi:10.1007/s00359-015-1051-2) contains supplementary material, which is available to authorized users.

Rearing and Long-Term Maintenance of <em>Eristalis tenax</em> Hoverflies for Research Studies

“…Several papers state that bee pollen is not sufficient, specifically for oviposition, and only the provision of dry or indeed fresh pollen is suitable 9 29 . Our findings indicate that by complementing bee pollen with honey and water, we see both longevity and oviposition, even after long periods of captivity, with an increase in weight seen in both sexes ( Figure 4 ) and oviposition still occurring in females after more than 5 months in captivity 39 . This increased longevity allows us to study the behaviors of hoverflies at all life stages.…”

“…The health of these lab reared hoverflies was determined by a comparison of the weight and locomotor activity of female hoverflies compared to field captured individuals. General locomotor activity was assessed using a Locomotor Activity Monitoring system (LAMS), as described previously 39 . No significant differences in weight ( Figure 3 A ) or activity ( Figure 3 B ) were observed between lab reared and wild caught hoverflies after 4 months in captivity under our artificial hibernation cycle.…”

“…The hoverflies' locomotor activity was measured in a Locomotor Activity System by them breaking an infrared beam during movement. As previously, we averaged the activity across 6.7 hours in the middle of the day, on the second full day in the Locomotor Activity Monitor System 39 (N field caught =9, N lab reared =12). The central mark of each boxplot shows the median, the edges of the box the 25 th to 75 th percentiles of the data, and the whiskers extend from the minimum to the maximum of the data.…”

“…Using our techniques ( Figure 1 ) hoverflies have been maintained in the laboratory for a period of over 1 year and successfully used in behavioral experiments after 7 months in captivity 39 . Indeed, even if it seems counterintuitive, keeping the hoverflies in a more natural environment, under 12 h light:12 h dark conditions, at room temperature, substantially decreases their life expectancy to 2-3 months.…”

“…The main factor influencing this increased longevity is likely the use of artificial hibernation at 8-10 °C. By cyclically breaking the hibernation, every 3-4 days (Step 2, Figure 1 ), we allow hoverflies to both feed and self-groom, thus maintaining the nutritional state and wellbeing of the hoverflies, as evidenced by an observed increase in weight ( Figure 4 ) and no change in locomotor activity even after long periods in captivity ( Figure 3 , and see 39 ). Indeed, reports in the literature of unsuccessful attempts at artificial hibernation do not break the hibernation cycle, thus leading to increased mortality and the presence of mold 9 .…”