Investigating symbiont impacts on natural enemy susceptibility in ladybird beetles.

Background: Many insects carry heritable symbionts, bacteria that pass from parent to offspring, and these are particularly common in ladybird beetles. Past work on ladybird symbionts has emphasised reproductive parasite phenotypes such as male-killing, but it is likely that they are also an important component of defence against natural enemy attack (protective symbiosis). Here, symbionts would represent an important determinant of individual resistance and in the dynamics of the host-parasite interaction. Reciprocally, the symbiont dynamics would be driven partly by the parasite. The impact of nematodes on host fertility additionally make this an important consideration in use of ladybirds as greenfly control measures.

Objective 1. We will examine the host range, diversity, environmental and landscape correlates of parasitisation of ladybirds with tylnechid nematodes. This will involve a combination of field sampling, citizen science and development of molecular ecology methods for detecting their presence and diversity.

Objective 2: We will perform experiments to analyse if Spiroplasma bacteria provide defence against nematode attack in different species of ladybird.

Objective 3: We will determine if presence of symbionts and intensity of attack are correlated both within species over space, and between species.

Novelty: We will apply state of the art next generation sequencing methods to investigate nematode diversity with a citizen science collection and recording programme to establish nematode presence across UK ladybird species. The interface with symbionts represents novel research whilst ladybirds are a model system for natural enemy attack and for symbionts, the impact of symbionts on enemy attack has not been ascertained.

Timeliness: Despite being discovered over fifty years ago, the diversity and intensity of nematode attack in ladybirds is unknown, save in the invasive species Harmonia axyridis, where attack rates have recently been shown to be high. Very recent work in Drosophila has demonstrated Spiroplasma symbionts also found in ladybirds as a principle means of defence.