Month: October 2024

Globalisation has spread thousands of invasive insect species into new world regions, causing severe losses in ecosystem services. Previous work proposed that plant invasions facilitate insect invasions through the creation of niches for non-native herbivores. Despite the impact of insect invasions, a comprehensive understanding is lacking on how invasion success varies among insect feeding groups. We therefore compiled the predominant larval trophic groups (herbivores, predators, parasites, detritivores, brood-carers) for 5,839 non-native insect species in nine world regions to compare (1) proportions of species in each group between non-native species and the world’s fauna, (2) how invasion success for each trophic group has changed over the last three centuries, and (3) how historical herbivore invasions are related to plant invasions over time, and parasite invasions are related to herbivores. We find that herbivores represent a significantly larger proportion (52.4%) among non-native insects compared to the world fauna (38.4%), whereas proportions of non-native detritivores (including fungivores), predators and brood-carers are significantly lower; parasite proportions do not significantly differ. Predators and detritivores dominated among invasions in the 18th century but subsequently diminished, likely due to changing invasion pathways, while proportions of herbivores, parasites and brood-carers increased over time. We found herbivore invasions to lag 80 years behind plant invasions, whereas parasitoids appear to co-invade with their herbivore hosts. The dominance of herbivores among non-native insects and their strong cross-correlation with plant invasions further strengthens the hypothesis that plant invasions drive the global rise in numbers of non-native insects. 

Link to the paper.

Invasions by non-native insect species can cause massive disruptions to biodiversity and ecological processes which often result in serious economic impacts. 

The trend of increasing numbers of insect invasions worldwide can be traced to a large extent to the the increasing volume  global trade and travel which results in the accidental transport of insects to new regions. Climate change can also create conditions that facilitate the establishment of non-native insects. 

However, there is another reason for the growing number of insect invasions that has garnered less attention. This reason is that the proliferation of non-native plants worldwide is creating many new ecological “niches” for plant-feeding insects thereby facilitating the establishment of a growing number of  these insect species outside their native ranges where their hosts are planted or are invasive. Aroound the world, non-native plants are increasingly common, either as a result of them being planted for purposes of ornamental landscaping, agriculture and forestry. Furthermore, many species of invasive plants are spreading and displacing native species, in forests and other natural areas.

We have just published a paper in collaboration with several international colleagues in the journal BioScience that synthesized (1) mechanisms by which plant invasions facilitate insect invasions; (2) the broad-scale patterns that shed light on the link between plant and insect invasions and; (3) case studies of plant invasions that have facilitated subsequent insect establishment. The body of evidence summarized in the BioScience paper shows that plant invasions are a major driver of insect invasions. This provides additional justification for ramping up efforts aimed at limiting the global spread of non-native plants – to avert the proliferation of non-native insects and their spillover onto native plant species. Worryingly, the evidence also suggests a massive “invasion debt” – many thousands of planted and naturalized non-native plants are waiting to welcome insects from their native ranges thereby launching many more potentially damaging invasions. The stage has unfortunately been set for furhter and growing problems with insect invasions in the future, and this hightens the value of national and international biosecurity programs targeting the exclusion of potentially damaging species.

Gyda has published a new study on accidentally dispersed insect predators and parasitoids. Introductions of insect predators and parasitoids for biological control are a key method for pest management. Yet in recent decades, biological control has become more strictly regulated and less frequent. Conversely, the rate of unintentional insect introductions through human activities is rising. While accidental introductions of insect natural enemies can potentially have serious ecological consequences, they are challenging to quantify as their movements go largely unobserved. We used historical border interception records collected by the US Department of Agriculture from 1913 to 2018 to describe the diversity of entomophagous insects transported unintentionally, their main introduction pathways, and trends in host specificity. There were 35,312 interceptions of insect predators and parasitoids during this period, representing 93 families from 11 orders, and 196 species from these families. Commodity associations varied, but imported plants and plant products were the main introduction pathway. 

Read the full paper here: Link