Remy L. Ware

Intraguild predation of the aphid pathogenic fungus Pandora neoaphidis by the invasive coccinellid Harmonia axyridis

Abstract 1. The ladybird Harmonia axyridis is an invasive alien species in many countries and is predicted to have a negative impact on native biodiversity. However, little is known on the status of this aphidophage as an intraguild predator of natural enemies of aphids such as insect‐pathogenic fungi.

Effects of competition, cannibalism and intra-guild predation on larval development of the European coccinellid Adalia bipunctata and the invasive species Harmonia axyridis

Abstract 1. Resource competition and intra‐guild predation (IGP) are important determinants of the structure of aphidophagous guilds. The likelihood and outcome of IGP is influenced by the density of extra‐guild prey and the characteristics of the species involved.

Chemical protection of Calvia quatuordecimguttata eggs against intraguild predation by the invasive ladybird Harmonia axyridis.

Intraspecific and interspecific predation of eggs is a well documented phenomenon amongst aphidophagous coccinellids. The invasive species Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) is known to be a top intraguild predator and reported to attack the eggs of many coccinellid species both in a laboratory setting and in the wild. A previous laboratory study highlighted that while many species’ eggs were highly palatable to H. axyridis, the eggs of Calvia quatuordecimguttata (Linnaeus) (Coleoptera: Coccinellidae) appeared to be extremely well protected from attack. Here we present the results of behavioural experiments testing the hypothesis that substances on the egg surface are responsible for this protection, and report preliminary results of GC-MS analysis of these compounds. When the coatings of C. quatuordecimguttata eggs were removed using hexane, they became significantly more susceptible to predation by neonate H. axyridis larvae. However, their overall palatability was not affected, in that complete consumption was never or rarely observed. This suggests that the surface compounds are a true indicator of unpalatability in this species. The effect of hexane-washing on already palatable conspecific eggs was also analysed but had no significant effect on the susceptibility of eggs to cannibalism. We conclude that the eggs of at least one European species are effectively protected by surface deterrents from intraguild predation by H. axyridis. This effect might be due to both the diversity and abundance of hydrocarbons present within the egg coating, the presence of alkenes and/or the presence of patches of a red substance on the eggs’ surface, which is thought to belong to the acid group. In conjunction with data on the susceptibility of other immature stages of C. quatuordecimguttata, this finding may indicate a decreased risk of the species falling victim to invasive H. axyridis, despite their coincident habitat ranges.

Seasonal phenotypic plasticity: wild ladybirds are darker at cold temperatures

Seasons vary in the average environmental conditions a species experiences, meaning that optimum strategies for concealment or feeding may also vary. Populations of the ladybird Harmonia axyridis contain both melanic and non-melanic forms and changes in allele frequency in some populations suggest that melanism may be advantageous in winter, but costly in summer. This could favour the evolution of phenotypic plasticity in colour pattern, as individuals which changed colour throughout the year would be able to maximise their fitness. We have previously shown in the laboratory that melanisation in the “non-melanic” morph of H. axyridis, f. succinea, is predominantly controlled by temperature during development. We now report that wild populations of H. axyridis f. succinea also conform to this principle: lower field temperatures during development produce individuals with more and larger spots. Furthermore, we have found that the critical period of development where temperature affects the level of melanisation covers the pupal and late larval stages, and melanisation increases with the length of time spent at cold temperature. We conclude it is likely that the temperature experienced during this period is used to predict the temperature encountered as an adult. This may allow individuals to produce the level of melanisation necessary to maintain activity levels at the temperatures encountered when they emerge. The long sensitive period seen in H. axyridis may be in order to avoid mismatches between melanisation and seasonal environment.