Melolontha hippocastani
Melolontha hippocastani | |
---|---|
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Arthropoda |
Class: | Insecta |
Order: | Coleoptera |
Family: | Scarabaeidae |
Genus: | Melolontha |
Species: | M. hippocastani
|
Binomial name | |
Melolontha hippocastani Fabricius, 1801
|
Melolontha hippocastani, the northern cockchafer,
Geographic range
Melolontha hippocastani primarily resides in forest ecosystems in northern Eurasia. Its distribution range spans across most of Europe, excluding the northernmost and southernmost regions. This species extends its habitat into Mongolia, parts of Central Asia, and Siberia. Unlike its counterpart, the common cockchafer, which occupies diverse environments including forested and open areas, M. hippocastani is primarily a forest species, often in taiga forest.[1][2]
Genetics
Research has probed the
Mating behaviour
Mate searching
Mating behaviour primarily occurs during flight periods at
Volatiles and sexual dimorphism
One study demonstrates that male M. hippocastani are attracted to volatiles emitted by damaged leaves and
A variety of compounds have been analysed in research to identify which compound serves as a sex pheromone in M. hippocastani, and the mechanism by which it takes action. One research study determined that mate-finding behaviour in M. hippocastani is driven by males locating females using olfactory cues such as green leaf volatiles and 1,4-benzoquinone, along with the species' sexual dimorphism. Both males and females contain 1,4-benzoquinone; however studies showed that female extracts provoked a higher number of landings than male extracts. This finding led to further analysis on the quantities of 1,4-benzoquinone in each sex, which were found to be higher in females, suggesting its role in attracting males. This compound, known for its defense function in arthropods, is hypothesised to have evolved into a sex pheromone in M. hippocastani. Thus, research suggests a dual function of benzoquinones as both mate attractants and defense compounds. Further research is exploring other compounds' roles to develop semiochemical-based methods for controlling M. hippocastani populations.[5]
The role of (Z)-3-hexen-1-ol
Additional research investigated whether volatiles from freshly damaged leaves are more attractive to males than those from older damaged leaves. Analysis of volatiles from freshly damaged leaves revealed typical leaf aldehydes, while older damaged leaves predominantly emitted (Z)-3-hexen-1-ol and (Z)-3-hexenyl acetate.[6] Surprisingly, males were equally attracted to volatiles from both fresh and old damaged leaves, with a preference for the latter in synthetic mixture experiments. Further experiments identified (Z)-3-hexen-1-ol as highly attractive to male beetles, while other tested compounds were behaviourally inactive.[6] However, all tested compounds elicited comparable electrophysiological responses on male antennae. Thus, (Z)-3-hexen-1-ol plays a vital role in the sexual communication of M. hippocastani, attracting both sexes of an insect.[6]
Thus, a combination of plant volatiles and sex pheromones allow for males to find feeding females in the trees, facilitating mating behaviour.
Physiology
The mate finding technique performed by these beetles using sex pheromones are performed using specific physiologies. Melolonthinae sex pheromone glands are everted from the abdominal tip.[3] M. hippocastani show sexual dimorphism within the antenna. Male antennae consist of seven large lamellae, while female clubs have only six smaller lamellae, which suggests different olfactory abilities between sexes and the presence of a female derived sex pheromone.[3] Pheromone-degrading enzymes are present in the antennae of M. hippocastani and show considerable substrate specificity.[7]
Life cycle
Once adult female M. hippocastani lay their eggs in the soil, the larvae spend 36 months underground feeding on plant roots.[4] During this time, their growth phase is divided into three distinct phases. They pupate in summer, the year before swarming, and spend their last winter as adults.[4] The following year, in late April to early May, the adult insects emerge from the soil and feed on tree foliage. About 2 weeks after emergence, oviposition flights are observed. Females land on the ground at dusk and burrow into the soil to lay eggs in clusters. The females prefer sandy soils because they facilitate the females' digging, allow for larval movement, and allow volatile compounds from host to spread, facilitating the larval orientation and survival in the soil. Females lay an average of 24 eggs during their first egg-laying phase and 15 during their second egg-laying phase.[4]
Microbiome
Diet and digestion in M. hippocastani are facilitated by
Specifically, these microbes play a crucial role in breaking down woody food components such as lignocelluloses and xylans. When comparing the larvae and adult microbiotes of M. hippocastani, the larvae microbiotes had harsher conditions, yet harboured a richer and more diverse bacterial community compared to adult guts. A core group of bacterial phylotypes was shared between larvae and adults, indicating some degree of stability despite different feeding habits. Little overlap was observed between bacterial species from food or soil contamination and those in the gut, suggesting minimal alteration of bacterial diversity upon ingestion. Some isolates from larvae exhibited enzymatic properties related to digestion. This symbiotic relationship underscores the importance of microbes in the digestive processes across organisms.[8]
Further research on the reactions of M. hippocastani to high manganese (Mn) content in their diet revealed significant effects on their activity and fertility. As the Mn content in their food increased, the activity of adult cockchafers decreased, and females fed on high Mn diets showed zero fertility. Despite the cockchafers' ability for self-detoxification, the presence of Mn in their diet still influenced their activity. It was found that expelling Mn through the digestive system serves as the primary mechanism for the cockchafers' self-detoxification process, showing the relationship between diet, digestion, and physiological responses in M. hippocastani.[9]
Interactions with humans
The parasitic nature of these beetles has caused damage on a wide variety of foliage, which has demanded an abundance of research for strategies to understand M. hippocastani in order to mitigate their harmful impacts and protect the forests in which these beetles are local. For example, in parts of southern Germany, specifically in the states of Hessen,