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School of Natural Sciences Degree project work Elisabeth Carlsson Subject: Biology Level: First cycle Nr: 2011:Bi3 Attraction of Wasp and Bumblebee Lures
School of Natural Sciences Degree project work
Elisabeth Carlsson Subject: Biology Level: First cycle Nr: 2011:Bi3
Attraction of Wasp and Bumblebee Lures
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Attraction of Wasp and Bumblebee Lures
Elisabeth Carlsson
Examination Project Work, Biology, 15hp, Bachelor of Science
Supervisor: Rikard Unelius, Professor School of Natural Sciences Norrgård Smålandsgatan 24 SE-392 34 Kalmar Examiner: Geoffrey Lemdahl, Associate Professor School of Natural Sciences Kocken Landgången 4 SE-392 31 Kalmar
I. Abstract The introduced common wasp, Vespula vulgaris, is causing problems around the world, particularly on New Zealand. The wasps have big effects on the native animal life and the community structure. One research group on New Zealand has tried out a lure that attracts Vespula spp. In this study, this lure was tested to see if the wasps in Sweden are attracted to the same chemical signals as the wasps on New Zealand. In a subproject, a bumblebee (Bombus terrestris) lure was also tested. Delta traps with different lures were placed in two different habitats near Kalmar. During ten weeks, only five wasps and no bumblebees were trapped. At this stage it was decided to investigate which insects that had been caught and the results were focused on the butterflies (Lepidoptera) caught. Over all, more butterflies were caught on Öland than in Kalmar both in traps containing the wasp and bumblebee lures. When comparing wasp and bumblebee lures, the highest number of butterflies was caught in traps containing the bumblebee lure. The reasons for the low catches of wasp and bumblebee are discussed. The catches of butterflies are also discussed.
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II. Sammanfattning Den introducerade vanliga getingen, Vespula vulgaris, orsakar stora problem runt om i världen, speciellt på Nya Zeeland. De utgör stora påfrestningar på det ursprungliga djurlivet och deras samhällsstruktur. En forskargrupp från Christchurch, Nya Zeeland har testat och tagit fram ett bete som attraherar getingar. I denna studie har detta bete testats för att se om getingarna i Sverige attraheras till samma kemiska signaler som getingarna gör på Nya Zeeland. I ett sidoprojekt testades också ett bete för jordhumlor (Bombus terrestris). Fällor med olika beten placerades i två habitat nära Kalmar. Under tio veckor hade endast fem getingar och inga humlor fångats. I detta skede beslutades det att undersöka vilka insekter som hade fångats i fällorna och där fokuset låg på fjärilar (Lepidoptera). Det fångades fler fjärilar på Öland än i Kalmar, både i fällorna med bete för geting och i de med bete för humlor. En jämförelse mellan getingbetet och humlebetet visade att det fångats flest fjärilar i de fällor innehållande bete för humlor. De möjliga anledningarna till de låga fångsterna av getingar och humlor diskuterades. Fjärilsfångsterna diskuterades också.
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Contents I. Abstract ................................................................................................................................... 3
II. Sammanfattning ..................................................................................................................... 4
1. Introduction ............................................................................................................................ 6
1.1 Wasps ................................................................................................................................ 7
1.2 Bumble bees ..................................................................................................................... 8
2. Materials and methods ........................................................................................................... 9
2.1 Description of field sites ................................................................................................... 9
2.2 Lures ............................................................................................................................... 10
2.3 Dispensers ....................................................................................................................... 10
2.4 Field traps ....................................................................................................................... 10
2.5 Statistics .......................................................................................................................... 10
3. Results .................................................................................................................................. 11
4. Discussion ............................................................................................................................ 16
4.1 Wasp lure ........................................................................................................................ 17
4.2 Bumblebee lure ............................................................................................................... 17
4.3 Wasp lure versus bumblebee lure ................................................................................... 17
5. Conclusions .......................................................................................................................... 18
6. Acknowledgment ................................................................................................................. 18
7. References ............................................................................................................................ 19
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1. Introduction
Communication with chemical signals between insects is very important, particular among social insects like bees and wasps (Nilsson, 2009) and they have complicated communication systems to be able to do this (Xu et al., 2009). Using chemical signals, they can find rich food sites, mating partners, good hibernation sites and also observe predators (Field et al., 2000).
All chemical signals are called semi chemicals, which can be divided into pheromones and allelochemicals (Anderbrant et al., 2005). Pheromones give a reaction in an individual of the same species which is susceptible for the signal. It includes signals for mating, aggregation and alarm. Allelochemicals are used between different species, for example the signals flowers elicit to attract pollinators (Nilsson, 2009).
The insects’ olfaction system is very well-developed and very sensitive and specific (Krieger & Breer, 1999) and the receptor is usually located on the insect’s antenna (Field et al., 2000).
The introduction of wasps, Vespula spp., as new species has resulted in a severe problem at places where it has been introduced as new species, for example in New Zealand (Landolt et al., 2007). The two species that were introduced to New Zealand were the German wasp, Vespula germanica, in 1945 and the common wasp, Vespula vulgaris, in the 1970’s (Beggs, 2001). Today, V.vulgaris is the dominating species present and it has outcompeted V. germanica in the forest at higher altitudes, since it´s more efficient in collecting food (Beggs et al., 2011). The wasps in New Zealand have found a suitable habitat in the beech forests (Nothofagus spp.) which is infested by a native scale insect (Ultracoelostoma assimile). This insect produces honeydew, which is an important food source for many invertebrates, birds and also the invasive wasps (Grant & Beggs, 1989).
In the beech forest, the honeydew is the most common food source that´s similar to nectar and consists of carbons in forms of fructose, sucrose and oligosaccharides. The honeydew is a very abundant food source which makes it possible for the wasps to increase in quantity very rapidly. They are very efficient in harvesting the honeydew and they do it more frequent than the native insects and birds. Therefore, the natural animals are having problems competing with the wasps (Beggs, 2001).
The wasp population on New Zealand have grown very large because they don´t have any natural enemies there (Beggs, 2001) and the winters are so warm that the nest can persist to the next year, which is an advantage since they don´t need to build up a new nest from scratch every year (Harris & Oliver, 1993). An additional reason for that they have become so large in numbers could be that their carbohydrate source, the honeydew, can be produced at high levels. The honeydew production can reach about 4000 kg/ha/year (Beggs et al., 2005).
Despite from carbohydrates, wasps also need protein which they receive by consuming other insects. These insects are also a food source for many birds, therefore they have become very affected by the wasps who intrude their protein-source. Thereby, the introduction of the invasive wasp has led to big effects on the native life and composition of the animal community (Beggs, 2001).
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There have been many attempts to reduce the wasp colonies by creating lures that attracts the wasps. One research group (El-Sayed et al., 2009) has tested which chemical signals the wasps are attracted to and which are necessary in a lure that attracts wasps. They have developed a lure consisting of six synthetic chemicals which the wasps finds very attractive. Using the produced lure, about 80 wasps were caught per trap in only two hours (Unelius, unpublished data). During earlier attempts to reduce the wasp colonies, poisoned cat-food has been used and has been proved to attract and kill wasps (Beggs et al., 1998). The disadvantage with poisoned cat-food is that the odors vanish after just a few days, compared to the chemical lures odors, which can persist several days. With a synthetic attractant that can be released at an even rate during several days, or maybe weeks, it should be possible to reduce the wasp populations in the treated areas (El-Sayed et al., 2009).
The aims of this study were to examine if the Vespula spp. in Sweden are attracted to the same signals as the wasps on New Zealand. Also to investigate which of the signals that are the most efficient wasp attractant, if there are any differences in attraction between different habitats or during the wasp season and also see how species specific the lure is by examining the by-catch. The practical work consisted of producing traps and lures in the lab, catches out in the field and species identification. The traps were placed in two habitats, outside Kalmar and on Öland. Octyl butanoate acted as the positive control in this study as it is a well-known attractant for social wasps (Vespula spp.) (Landolt et al., 2000; El-Sayed et al., 2009).
The same research group (El-Sayed et al., 2009) has also produced a bumblebee lure to attract bumblebees, especially Bombus terrestris. B. terrestris is present in all of Europe and is an important pollinator (Gurel et al., 2008). This lure can be used in a greenhouse to attract pollinators from the field to the flowers. In plant breeding, it could be of interest to produce a scent of flower that contains some of the attractive chemicals from this bumblebee lure. This bumblebee lure was tested and the traps were placed at the same sites as the wasp traps.
1.1 Wasps Lifecycle The lifecycle of the wasp starts in early spring when the overwintered queen wakes up and begins to search for a good place to build a new nest on. First she builds cells of chewed wood fiber and saliva. She lays her eggs in the cells and the eggs hatch after five to eight days into larvae (Barlow et al., 2002).
After a couple of weeks workers develop and start to gather water and wood fiber to form new cells and rapidly enlarge the nest (Spradbery, 1971). After two weeks of food gathering, the workers mostly stay in the nest and protect the entrance from invaders. The workers die when they are a few weeks old (Barlow et al., 2002).
In the late summer/autumn the workers starts to form bigger cells where the queen can lay her eggs which will hatch into fertile females and males. These leave the nest and start to search for a partner to mate with. The males later die and the females find a dark and dry place to stay during the winter (Archer, 2000).
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Food preferences Wasps need both proteins and carbohydrates in their diet. They get proteins by consuming insects and dead animals (Spurr, 1995) and carbohydrates from honeydew, tree sap, fruits and berries (Spurr, 1996). The food preference changes during the wasp season which are due to changes in requirement in the nest, (Sackmann & Corley, 2007), changes in weather (Harris et al., 1991) and differences between different habitats (Spurr, 1996).
In the spring and midsummer the queen searches for carbohydrates to feed on. When the workers have developed, they first search for carbohydrates to feed on. Then they start to search for proteins to feed the larvae with and in the autumn they return to search only for carbohydrates (Spurr, 1996). When the wasps have found a good food site they often return to this site until the food source is completely depleted (D´adamo & Lozada, 2007).
1.2 Bumble bees Lifecycle When the bumblebee queen awakes from her hibernation in the spring, she begins to search for a place to build the nest. She builds a pot of wax and fills it with honey. She lays her eggs in the pot on top of pollen and surrounds it with wax. She brood them for four days, until the eggs hatches. During this time, the queen needs to visit hundreds of flowers each day to be able to get enough nectar to regulate her body temperature and to brood her eggs. When the first worker is developed, the nest starts to increase rapidly in size. The foraging workers collect nectar and pollen from flowers to feed the new larvae.
When the season and the life of the colony lead to its end in the late summer, the queen starts to produce reproductive individuals, queens and males, instead of workers. The queens and males leave the nest to mate and then the queen search for a good place for hibernation over the winter (Goulson, 2003).
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2. Materials and methods 2.1 Description of field sites Kalmar 1 – Two replicates were placed in a sheep pen near the sea and exposed to wind. The majority of the traps were placed in beech (Fagus sylvatica), oak (Quercus robur) and rowan (Sorbus aucuparia) branches (56º40’56.27’N) (16º22’57.96’E).
2 – Three replicates near two marshes in the forest, where the majority of the traps were placed in branches of beech, pine (Pinus sylvestris) and juniper (Juniperus communis) (56º40’49.79N) (16º22’44.82’E).
The four replicates of bumblebee traps were placed at site 2, the majority in beech branches, see figure 1. Öland 1 – Two replicates were placed at the field station “Station Linné” in Skogsby, Öland. One in the garden of the station, with flowers and fruit trees, and one in a bush line near a farming land. The majority of the traps were placed in branches of sallow (Salix caprea) and black thorn (Prunus spinosa) (56º37’06.54’N)(16º29’55.05’E).
2 – Three replicates were placed in an area near the field station. One replicate at the edge of a deciduous forest near a pond, one replicate at the edge of a deciduous forest near a grain field and one in a wind exposed tree line near a wheat field. The majority of the traps were placed in branches of hazel (Corylus avellana), alder (Alnus glutinosa) and oak (56º37’32.18’N) (16º29’58.66’E). The bumblebee traps were placed at both sites, two replicates at each site and the majority in sallow branches, see figure 2.
Figure 2. Map over the trap location on Öland. Derived from Google Earth, 8/8-11, and altered.
Figure 1. Map over the trap location in Kalmar. Derived from Google Earth, 8/8-11, and altered.
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2.2 Lures Table 1. Composition of the different treatments.
Due to an ongoing patent application, the chemicals are not shown. The lure is intended to attract wasps when they search for food. Treatment 9 containing octyl butanoate functions as a positive control for wasps and treatment C, blank, functions as negative control. The bumble bee lure contained 29.1 ml chemical G, 1.5 ml of chemical H and 0.31 ml of chemical I.
2.3 Dispensers 4 x 5cm polyethylene bags (80µm, O. Möllerström AB, Gothenburg Sweden) with a surface area at 2.8 x 5cm, containing 3.5 x 1.3cm pieces of felt (100% viscose, Ernst Textil in Östra Karup), were made in the lab using a Quick Seal (Quick Seal 200, O. Möllerström AB, Gothenburg Sweden). Using a pipette, 300µl of each treatment were distributed in separate bags. The bags were sealed using the Quick Seal and then stored in aluminum bags (O. Möllerström AB, Gothenburg Sweden) in the freezer.
2.4 Field traps Ten different treatments, with five replicates, were tested. The delta traps (Pherobank, Holland), see figure 3, were placed at two different sites, 50 traps in Skogsby on Öland and 50 traps on Svinö in Kalmar. The traps were placed randomly, around 1.5 meters above the ground and ten meters apart from each other. Sticky bases (Pherobank, Holland) were placed in the bottom of the delta traps and the polyethylene bags were placed in the middle of the sticky bases. The traps were checked once a week where the sticky bases with the dispenser were removed and replaced. At a later stage the caught insects were identified. The experiment started 15/6 and lasted until 26/8. The bumblebee traps were placed at the same sites as the wasp traps, eight in Skogsby and eight on Svinö. Two different treatments, one lure and one blank with eight replicates were tested. The experiment started 21/6 and lasted until 26/8. Permission to place the traps in Skogsby was given from the land owner and for the traps on Svinö, the county administrative board in Kalmar gave permission. 2.5 Statistics A repeated measures ANOVA was carried out. All statistics were made in Statistica.
Treatment Chemical Volume per chemical (ml)
Total volume (ml)
1 A-F 4 24 2 A-E 4.8 24 3 A-D and F 4.8 24 4 A-C and E-F 4.8 24 5 A-B and D-F 4.8 24 6 A and C-F 4.8 24 7 B-F 4.8 24 8 A-B and E-F 6 24 9 Octyl butanoate 24 24 C Blank 0 0
Figure 3. Picture of the delta trap. Derived from Pherobank, 10/8-11.
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By-catch in wasp lure traps
Öland Tr.1-9
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3. Results During these ten weeks, two wasps were caught in the trap containing treatment 7 on Öland and one in the trap containing treatment 1 in Kalmar. Two wasps were caught in the traps on Öland containing the bumblebee lure. During the period no bumblebees were caught. However, the traps caught other insect taxon, approximately 60 insects per plate.
The by-catch was determined to the appropriate taxon. In figure 4 the by-catch in the wasp lure treatments and the wasp control, both on Öland and in Kalmar during eight weeks is presented. Figure 5 shows the by-catch from the bumblebee lure and the bumblebee control during seven weeks.
Figure 4. Bar graph for the different taxons presences in by-catch over eight weeks, in the wasp lure traps.
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By-catch in bumblebee lure traps
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The results shows no significant difference in the number of butterflies (Lepidoptera) caught between the different wasp lures, (p=0.260), see figure 6. However, there was a significant difference between the wasp lure traps on Öland and in Kalmar (p<0.001), see figure 6, and also between the weeks (p<0.001), see figure 7.
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Butterflies catches by wasp lure
Kalmar
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Figure 6. Bar graph with standard deviation and the sum of the weekly mean number of butterflies caught in the wasp lure traps in Kalmar and on Öland. Each bar represents the sum of all weekly means for each respective treatment. C stands for control.
Figure 5. Bar graph for the different taxons presences in by-catch over seven weeks, in the bumblebee lure traps
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Bumblebee lure Control
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There was a significant difference between the bumblebee treatment and the control (p<0.001) but no significant difference could be proved between Öland and Kalmar (p=0.086), see figure 8, or between the weeks (p=0.051), see figure 9.
Figure 7. Bar graph with standard deviation and the treatment mean number of butterflies caught in the wasp lure traps on Kalmar and Öland per week. Each bar represents the mean of all treatments for each respective week.
Figure 8. Bar graph with standard deviation and the sum of weekly mean number of butterflies caught in the bumblebee lure traps on Kalmar and Öland. Each bar represents the mean of all weeks for each respective treatment. C stands for control.
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When comparing wasp lure treatment 1 and bumblebee lure, there was a significant difference between the two treatments (p<0.001), see figure 10. There was no significant difference between wasp lure treatment 1 and the wasp lure control (p=0.176). However, there was a significant difference between bumblebee lure and the bumblebee lure control (p<0.001), see figure 10. When comparing over time, no significant difference could be proved (p<0.001), see figure 11.
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Attraction of Wasp- and Bumblebee lures to butterflies
Figure 9. Bar graph with the weekly mean number of butterflies caught in the bumblebee lure traps on Kalmar and Öland.
Figure 10. Bar graph with standard deviation and the sum of the weekly mean number of butterflies caught in the traps. Each bar represents the sum of caught butterflies on Öland and in Kalmar.
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Attraction of Wasp- and Bumblebee lures to butterflies
Wasp Lure Treatment 1
Wasp Lure Control
Bumblebee Lure Treatment 1
Bumblee Lure Control
Figure 11. Bar graph with standard deviation and the sum of the weekly mean number of butterflies caught in the wasp and bumblebee traps. Each bar represents the sum of caught butterflies on Öland and in Kalmar.
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4. Discussion
During the ten weeks which the experiment lasted, only three wasps were caught in the traps intended for wasp catch and two in the traps intended for bumblebees. No bumblebees were caught during these weeks. A possible reason for the failing catches could be that the sticky bases are adjusted for moths and that the glue possibly weren´t hard enough to catch and retain wasps and bumblebees.
Another possible reason for the lack of caught wasps could be that the chemical compound doesn´t work in the same way as it does on New Zealand. The weather in the New Zealand field sites is warmer compared to the Swedish field sites, which could have an effect on the volatility of the lure and therefore have an effect on the odor releasing from the bags.
Another possible reason could be that there were other, more attractive scents around the field sites compared to the lure, so that the wasps didn´t react at the chemical signals as expected and that the wasps at the Swedish field sites didn´t find the lure as attractive.
The densities of wasps on New Zealand compared to the numbers in Sweden are very different. It has been shown that the mean number of wasps in the beech forest can reach 10 000 workers/ha (Thomas et al., 1990). Since the wasps on New Zealand are so many and the food sources limited they need to compete with native insects and birds and they need to search for new sources more frequently to be able to survive. In Sweden, the wasp population density are lower and the food sources may be sufficient to support the wasp population so they don´t need to search so frequently after new food sources. It has been reported that wasps often return to rich food sources and if they have found a good source they don´t try to find another until it is completely depleted (D´adamo & Lozada, 2007).
One reason for the lack of bumblebees caught in the traps could be that the bumblebees at the Swedish field sites are adapted to other odor cues than the bumblebees in the New Zealand sites. In the more favorable field sites on Öland, one reason for the lack of bumblebees caught may be that there were other and more attractive scents present compared to the bumblebee lure used. The field sites in Kalmar may be unfavorable for bumblebees and therefore no bumblebees were caught.
The traps did catch insects, and it was approximately 60 insects per plate. And with 116 plates per week, the numbers of caught insects reach on average 7000 insects per week. Therefore, the by-catch couldn´t be determined and statistically analyzed. Instead, the order Lepidoptera was chosen and the results were based on the catches of butterflies.
4.1 By-catch The by-catch in the wasp lure traps treatment 1-9 on Öland exhibit the greatest diversity, compared to the same treatments in Kalmar. It seems that the insects present in the by-catch finds wasp lure treatment 1-9 attractive, when comparing with the controls. When comparing wasp lure treatment 1-9 with the bumblebee lure, it seems that the wasp treatments were more attractive for a greater variety of insect taxon, than the bumblebee lure was. The habitat on Öland seems more favorable for insects than the habitat in Kalmar.
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As described, two replicates in Kalmar were very exposed to wind, which may have prevented the odor to attract the insects and also prevent them to localize the traps.
4.2 Wasp lure When comparing catches from Kalmar and Öland, it seems apparent that the numbers of butterflies on Öland is greater than in Kalmar. The statistics shows a significant difference between Kalmar and Öland (p<0.001).
The number of butterflies caught on Öland was higher than in Kalmar. One possible reason why the number of caught butterflies was lower in Kalmar could be that two of the replicates in Kalmar were very exposed to wind. This could affect the possibility for butterflies to get caught in the traps. The wind could make it harder for the butterflies to localize and land in the traps. One additional reason for the lower number of caught butterflies could be that three replicates in Kalmar were placed at dark sites near two marshes in a forest, with little flowering plants. The habitats on Öland are more favorable for the butterflies with big fields with flowering meadows and a flowering garden.
4.3 Bumblebee lure The results shows that there is a big difference between the numbers caught in the traps containing the bumblebee lure and those caught in the traps containing the control. The statistics also shows that there was a significant difference between the two treatments (p<0.001), and that the butterflies were more attracted to the bumblebee lure than the control There is no significant difference between Öland and Kalmar (p=0.086) and no significant difference over time (p=0.051).
4.4 Wasp lure versus bumblebee lure When comparing the wasp lure treatment 1 and the bumblebee lure, there was a significant difference between the two treatments (p<0.001). The bumblebee lure used seems more attractive towards butterflies than the wasp lure, since more butterflies were caught in traps containing bumblebee lure. When comparing wasp lure treatment 1 with the wasp lure control, there were no significant difference (p=0.176).
Butterflies have a well developed olfaction-system in order to recognize and localize scent of flowers and nectars (Hansson, 1995). This olfaction-system could be the reason why so many butterflies found the traps and got caught, since the bumblebee lure had a very sweet scent similar to nectar. Nectar is the most common food source for adult butterflies (Barp et al., 2011). The bumblebee lure is designed to attract bumblebees, which search for sugary nectar, as the butterflies also does. This could be the reason that bumblebee lure caught more butterflies than the wasp lure did, because bumblebees and butterflies search for the same kind of food and respond to the same kind of odors cues.
When comparing the wasp lures with the bumblebee lures, the highest number of caught butterflies were in week 2 and 3 in the traps containing the wasp lures, but 6 and 7 in the traps containing the bumblebee lures. Due to this temporal difference, it may be that different types of butterflies are attracted to the wasp lures and the bumblebee lures at different times during the season.
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5. Conclusions It can be speculated from this experiment that the lack of caught wasps is due to the fact that the wasp population density at the Swedish field sites are lower compared to the New Zealand sites. The difference in the number of wasps caught can be due to that the available food sources are more than sufficient to support the wasp population in Sweden. Therefore they don´t need to search for new food sources, and they don´t get caught in the traps. The lack of bumblebees may be due to adaptation to other odor cues than the ones in New Zealand.
In conclusion the number of butterflies caught was higher on Öland compared to Kalmar. A possible explanation could be that the habitat on Öland is more favorable for the butterflies with flowering meadows and fields. The number of butterflies caught was also higher in the bumblebee lure traps compared to the wasp lure traps containing treatment 1. This could be due to that the bumblebees and butterflies are searching for the same kind of sugar-rich food, nectar, or that the lure compounds are components in the normal butterfly diet.
In future studies, it could be of interest to perform the study in different types of habitats, for example a habitat where large number of wasps have been recorded or in urban surroundings. The bumblebee lure could also be tested in habitats that are more favorable for bumblebees, for example in greenhouses. Looking at the by-catch, it could be of interest to investigate the attractiveness of the lures for different species of insects. It seems that the bumblebee lure could be used in field screening of butterfly diversity.
6. Acknowledgment I would like to thank my supervisor Rikard Unelius for all help and support during the project work. I would also like to thank Geoffrey Lemdahl for being my examiner and Anders Forsman for being opponent.
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7. References
Anderbrant, O., Bengstsson, M., Högberg, H-E., Löfstedt, C., Norin, T., Petterson, J., Schlyter, F. & Witzgall, P.(2005) Feromoner och kairomoner för bekämpning av skadeinsekter. Alnarp: Institution of Plant Science at SLU. Archer, M. E. (2000) Seasonal foraging characteristics during mid-day of successful underground colonies of Vespula vulgaris (Hymenoptera, Vespidae) in England. Insectes Sociaux, 47, 117-122.
Barlow, N.D., Beggs, J.R. & Barron, M.C. (2002) Dynamics of common wasps in New Zealand beech forests: a model with density dependence and weather. Journal of Animal Ecology, 71, 663-671.
Barp, E. A., Soares, G. L. G., Giani, E. J. M, Rodrigues, D. & Moreira, G. R. P. (2011) Variation in nectar and pollen availability, sucrose preference, and daily response in the use of flowers by Heliconius erato phyllis. Journal of Insect Behaviour, 24, 200-219.
Beggs, J.R., Toft, R.J., Malham, J.P., Rees, J.S., Tilley, J.A.V., Moller, H. & Alspach, P. (1998) The difficulty of reducing introduced wasp (Vespula vulgaris) populations for conservation gains. New Zealand Journal of Ecology, 22 (1), 55-63.
Beggs, J. (2001) The ecological consequences of social wasps (Vespula spp.) invading an ecosystem that has an abundant carbohydrate resource. Biological Conservation, 99, 17-28.
Beggs, J.R., Karl, B. J, Wardle, D.A. & Bonner, K. I. (2005) Soluble carbon production by honeydew scale insects in a New Zealand beech forest. New Zealand Journal of Ecology, 29 (1), 105-115.
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