Molecular phylogeny and identification of agromyzid leafminers in China,with a focus on the worldwide genus Liriomyza(Diptera:Agromyzidae)

Leaf-mining flies(Diptera:Agromyzidae)are a diverse family of small-bodied insects that feed on living plant tissues as larvae.Various species in this family are considered globally invasive and have caused great agricultural economic losses.In China,economically important vegetable crops have been seriously damaged by these pest insects,especially by species of the genus Liriomyza.However,these species are difficult to differentiate because of their morphological similarities,and the Chinese fauna remains poorly known.To explore the relevant pest species in China and their phylogeny,agromyzid leafminers were collected from 2016 to 2019,and identified based on morphological characteristics and DNA barcodes.In total,27 species from five genera of Agromyzidae were sampled and identified,including 16species of Liriomyza.Both mitochondrial and nuclear genes were used to reconstruct their phylogenetic relationships and estimate the divergence time.Highly congruent and well-supported phylogenetic trees were obtained using the Bayesian inference and maximum-likelihood methods.This analysis revealed two main clades in Liriomyza,and clade 2was inferred to have diverged from clade 1 approximately 27.40 million years ago(95%highest posterior density:23.03–31.52 million years ago)in the Oligocene.Differences were observed in the distribution patterns and host associations between the Liriomyza clades.Clade 2 species are distributed in cool,high-latitude environments,suggesting that they may have evolved into a cool-adapted lineage.

First report of the South American tomato leafminer, Tuta absoluta (Meyrick), in China

Tuta absoluta(Meyrick) originated in South America and is one of the most serious pests of tomatoes. It is also known to attack other solanaceous crops, including potato, eggplant, pepper, tobacco, and weedy species such as black nightshade. After accidental introduction into Spain in 2006, this pest spread rapidly throughout Afro-Eurasia and has become a major threat to tomato production worldwide. Here, we report the first record of T. absoluta as an invasive pest in China. It was found in tomato fields in Ili Kazakg Autonomous Prefecture, Xinjiang Uygur Autonomous Region(Ili, Xinjiang), China, and its occurrence was confirmed by both morphological and molecular approaches. In Ili, T. absoluta has been found to attack eggplant, potato, and black nightshade. We found the larvae generally mining and feeding on leaves and boring into tomato fruits, with multiple larvae sometimes observed in a single fruit. Its infestation levels differ among the tomato fields and host species. In all of the surveyed tomato fields, T. absoluta infested 100% of plants. In some of the fields, up to 90% of the eggplant and 100% of the potato plants were infested. Since no natural enemies were found under field conditions, suitable management practices are urgently needed to stop the further spread of this destructive pest in China.

Bioactivity of Indigenous Melia azedarach Extracts against the Tomato Leafminer,Tuta absoluta

Fruit extracts of indigenous Melia azedarach were tested for their insecticidal bioactivity against the tomato leafminer(Tuta absoluta)under laboratory conditions.Tomato plants were exposed to moths,after/before application of treatments.Treatments included:crushed fruit extracts of water(500,000 ppm and 200,000 ppm),methanol and ethyl acetate(200,000 ppm)with and without mineral oil(2%);M.azedarach powder extracts(2,000 ppm)in different solvents:water,methanol,ethanol,ethyl acetate,hexane and chloroform;biorational products:neem oil,mineral oil,micronized sulfur and thyme oil.The released moths were removed from treated/untreated plants at 72 h and effect of treatments on adults,eggs,larvae and pupae were recorded.Results indicated that sulfur caused the lowest number of live moths to be present on treated plants and was not significantly different in its effect from that of M.azedarach extracts and neem oil.Aqueous extracts without and with oil caused the highest%of dry eggs and were comparable to neem oil.Extracts in the two formulations(crushed fruits and/or powder)caused significant direct effects on immature instars:eggs,early larval instars and pupae.M.azedarach extracts and the tested products also caused indirect effect in form of significant decrease in number of developing the 3rd larval instars and new emerging moths compared to the control.Consecutive sprays of these extracts against eggs,larvae and pupae on same treated plants lead to very low number of moths for a second generation of the pest which contributes to low buildup of pest population in a tomato crop.

Density effect and intraspecific competition in a leaf-mining moth on bamboo leaves

When confined to a single leaf, the larvae of most leafminers should suffer intense intraspecific competition. The survival and performance of individuals are expected to decline with increasing larval density within a leaf, showing a negative density-dependent effect. The maximum density of an Elachista Treitschke(Lepidoptera:Elachistidae) miner on Indocalamus tessellatus(Munro)Keng f.(Poaceae: Bambusoideae) under natural conditions can be greater than 40 per leaf, making this a good system for studying intraspecific competition and density effects.We counted the number of leaves with different mine densities in the field and found a clumped distribution of leafminer larvae among host leaves. The emergence rates of pupae(and last-instar larvae), adults and parasitoids were inversely correlated with larval density. Pupal weight and adult weight also showed negative relationships with larval density. However, pairwise tests showed that there might be no differences in pupal or adult weight at larval densities of 1–10 mines per leaf, indicating that densitydependent effects are more obvious at densities greater than 10 mines per leaf. Intraspecific competition could lead to stable density and consistent body size in surviving individual insects, which would help maintain a sustainable population size. The density threshold could be an indicator of the balance between intraspecific competitive detriments and conspecific aggregation benefits; however, the validity of the threshold density hypothesis requires further testing and confirmation.