188.8.131.52. Investigating diet effects on SHB reproduction
SHBs feed on honey, pollen, and bee brood in honey bee colonies. However, they have been shown to reproduce on other diets as well (Ellis et al., 2002b; Buchholz et al., 2008). Below, we outline a method for investigating diet effects on SHB reproduction modified after Ellis et al. (2002b).
- Laboratory rear (see section 184.108.40.206.) and sex (3.1.3.) adult male and female beetles individually to ensure that mating occurs only in the food containers. In reproduction studies, it is essential to know the ratio of males and females. Only use >1 week old adults to ensure their reproductive maturity..
- Place a SHB couple (one female and one male) into a
plastic container (Fig. 12).
The container lids should contain small holes to allow sufficient ventilation.
- Prepare at least 10 containers of beetles (10 replicates) per diet tested.
- Add an appropriate amount of diet per adult container
to accommodate the amount of offspring that will be produced.
Unfortunately, there is no established formula for the volume of food that should be added given an established number of adult beetles. The investigator will have to experiment with this since this is an important consideration. For example, SHB adults reproduce explosively on bee brood but considerably less so on fruit. Therefore, larvae can quickly exhaust food resources in some circumstances. The diet should be frozen first, especially if field collected (e.g. fruit) to kill any other insect eggs that may be present.
- Move adult beetles from the food chambers to new ones
every 3-4 days to alleviate problems associated with explosive population
growth on limited food resources, if necessary.
Limiting the amount of time adults spend in a given container equally limits the number of eggs female beetles will be able to oviposit in the container, thus lessening the likelihood that food will be rapidly exhausted by larvae. This way, adults can be moved from container to container throughout their reproductive lifetime.
6. Monitor the containers daily to ensure that the beetles always have food available (only in case of ad libitum studies, otherwise adjust accordingly, e.g. let SHB starve).
In reproduction studies, larvae should be able to feed ad libitum if one is determining how diet impacts the number of larvae produced and amount of time it takes the larvae to reach the wandering phase.
- Once larvae in the diet container reach the wandering phase, empty the diet and larvae into a metal tray to facilitate capture (see section 220.127.116.11.).
- Place wandering larvae in soil pupation containers (see section 18.104.22.168.).
- Keep all rearing containers at 25°C and > 80% humidity for one week under light and then until adult emergence under dark conditions (see section 22.214.171.124.).
- Determine reproductive success.
Reproductive success is defined by Ellis et al. (2002b) collectively as the total number of offspring produced per female on a given diet (determined by counting the number of larvae produced in all of the food containers assigned to the adult pairs) and the percentage of those offspring that pupate successfully (= live adult SHB). One may also look at the reproductive capacity of the F1 generation for further evidence of reproductive success.
- Allowing SHB adults to reproduce on wet or sticky diets is of special concern because the adults can drown in the food if it becomes fermented and begins to pool in the container. In these instances, it is advisable to place a piece of paper towel in the bottom of the container to absorb moisture.
- Larvae maturing on wet or sticky diets cause the container environment to become inhospitable in many instances. So, these containers should be well ventilated (with holes that larvae cannot traverse) to facilitate airflow and checked 2-3 times daily for any problems or inconsistencies.
- Field-collected adult beetles are not suited for determining maximum reproductive capacity because their age and mating status at the time of collection is not known and they may have already reproduced prior to the experiment.
- Manipulations with adult beetles should be done under insect nets to minimize beetle escape (see section 3.1.).
- The rearing containers should be provisioned with water (moistened cotton balls (Fig. 12) similar to maintain adult bees in cages see respective BEEBOOK paper Williams et al., 2013), especially when the adults are attempting to reproduce on a dry food (such as pollen).
- Freezing the diet to kill eggs of other insects potentially present will alter its microbial balance. This could alter the diet’s nutrition or attractiveness to SHBs.
Fig. 12. Plastic container for maintenance of adult SHB (Photo: Elise Jeanerat) with standard food ad libitum (see section 126.96.36.199. pollen, honey, and a honey bee protein supplement in a 1:1:2 volume ratio), tap water in a small glass vial sealed with a piece of cotton wool to prevent draining, and two microscope slides as oviposition site (see section 3.2.4.). Food and equipment can be adjusted according to experimental needs (e.g. fruits instead of standard food and two or no oviposition sites).