Quantification of dose-mortality responses in adult Diptera: Validation using Ceratitis capitata and Drosophila suzukii responses to spinosad

Abstract

Quantitative laboratory bioassay methods are required to evaluate the toxicity of novel insecticidal compounds for pest control and to determine the presence of resistance traits. We used a radioactive tracer based on 32P-ATP to estimate the volume of a droplet ingested by two dipteran pests: Ceratitis capitata (Tephritidae) and Drosophila suzukii (Drosophilidae). Using blue food dye it was possible to distinguish between individuals that ingested the solution from those that did not. The average volume ingested by C. capitata adults was 1.968 μl. Females ingested a ~20% greater volume of solution than males. Adults of D. suzukii ingested an average of 0.879 μl and females ingested ~30% greater volume than males. The droplet feeding method was validated using the naturally-derived insecticide spinosad as the active ingredient (a.i.). For C. capitata, the concentration-mortality response did not differ between the sexes or among three different batches of insects. Lethal dose values were calculated based on mean ingested volumes. For C. capitata LD50 values were 1.462 and 1.502 ng a.i./insect for males and females, respectively, equivalent to 0.274 and 0.271 ng a.i./mg for males and females, respectively, when sex-specific variation in body weight was considered. Using the same process for D. suzukii, the LD50 value was estimated at 2.927 ng a.i./insect, or 1.994 ng a.i./mg based on a mean body weight of 1.67 mg for both sexes together. We conclude that this technique could be readily employed for determination of the resistance status and dose-mortality responses of insecticidal compounds in many species of pestiferous Diptera.

Differential Responses of Ceratitis Capitata to Infection by the Entomopathogenic Fungus Purpureocillium Lilacinum.

“…Females and males express different pro les levels of Attacin-A, Ceratotoxin-A, Relish, and Defensin. This sex-speci c response was demonstrated previously with C. capitata and Drosophila suzukii 50,51 During maturation, C. capitata expressed a signi cant increase in immune-response related genes (Attacin-A, Ceratotoxin-A, Relish, and Defensin) compared to their counterparts immature virgin. This up-regulation may be explained by the process of immunity anticipation prior to mating which was previously demonstrated in Ceratitis capitata 45 .…”

The Gram-Positive Bacterium Leuconostoc pseudomesenteroides Shows Insecticidal Activity against Drosophilid and Aphid Pests

“…The abundance of hemocytes in the hemolymph of drosophilids may explain the weaker effect of septic vs. oral infection. Furthermore, the injection of 4.6 nL delivers far fewer bacteria than the oral route [77]. However, the higher efficacy of oral infection compared to septic infection with L. pseudomesenteroides contrasts with data reported for Serratia marcescens, where the test insects (D. melanogaster) succumbed within 24 h after septic infection but died much more slowly following oral infection [78].…”

How varying parameters impact insecticide resistance bioassay: An example on the worldwide invasive pest Drosophila suzukii

“…suzukii , the duration of exposure to the chemical is usually about 24 h [ 44 , 48 , 50 , 51 ] and can reach 48 or 72 h [ 4 , 43 , 45 , 47 ]. A study on the mortality induced by ingestion of spinosad on this species emphasized the importance of time elapsed (5 days) before assessing mortality, suggesting that exposure duration is crucial in different types of bioassays [ 53 ]. Bioassays can be extremely time consuming, making it tempting to minimize exposure duration to reduce the total testing time.…”

“…To date, studies have evaluated pesticide efficiency or resistance in D . suzukii populations using various protocols [ 4 , 20 , 37 , 42 – 53 ], without extensive investigations on the reliability of the methods used.…”