Seasonality and community composition of parasitoid wasps of four agromyzid leafminer species (Diptera: Agromyzidae) in Victoria

Abstract

The vegetable leafminer, Liriomyza sativae Blanchard (Diptera: Agromyzidae), was first detected in the Torres Straits in 2008, crossed over to the tip of Cape York in 2015 and now poses a threat to Australian crops. This species is an economically important secondary pest in many parts of the world; populations readily evolve resistance to insecticides and benefit from the use of chemical controls against other pests, which kill their natural enemies. Liriomyza sativae is expected to spread into Australia’s agricultural production areas and it is therefore valuable to investigate the local biological agents that could contribute to future integrated pest management (IPM). I assessed the abundance and diversity of the hymenopteran parasitoid wasps of four common agromyzid flies in southern Victoria (Liriomyza brassicae (Riley), Liriomyza chenopodii (Watt), Phytomyza plantaginis Goureau, and Phytomyza syngenesiae (Hardy)) to evaluate their potential as candidates for control of L. sativae. I monitored six sites in Melbourne over a period of 18 months by collecting mined leaves from a range of plant species and rearing adult flies and their parasitoids. Additional sites around Victoria were also sampled to offer a snapshot of the agromyzid presence across the state.

Eleven wasp species were identified in total, two of which were only classified to morphospecies level, including known parasitoids of L. sativae overseas and species reared from L. sativae populations from far north Queensland. Ninety percent of the parasitoids were eulophids (Hymenoptera: Eulophidae), with the rest consisting of opiines (Braconidae) and Pteromalinae (Pteromalidae). The adventive Chrysocharis pubicornis (Zetterstedt) was the most abundant parasitoid, reared almost entirely from Phytomyza hosts, followed by an Asecodes sp. and the introduced Diglyphus isaea (Walker). We recorded the first male Ph. plantaginis for Australia. Males were only found at Melbourne locations and these populations tended to have a female-biased sex ratio. Variation in sex ratio may be host plant dependent, as the female:male ratio was 4:1 from the host Plantago lanceolata L. while it was 1:1 in more limited samples from Plantago major L. The four common local agromyzids reached peak abundance at different times of the year and together supported a stable community of both adventive and native parasitoids. Of the species reared, several are known to attack L. sativae including D. isaea, Hemiptarsenus varicornis (Girault) and Neochrysocharis formosa (Westwood). The wasps reared include candidates for augmentative or conservation biological control that should be further considered in the event that L. sativae becomes a widespread pest of Australian crops.