In addition to controlling pest organisms, the systemic neurotoxic pesticide fipronil can also have adverse effects on beneficial insects and other non-target organisms. Here, we report on the sublethal effects of fipronil on the farmland butterfly Pieris brassicae . Caterpillars were reared on plants that had been grown from seeds coated with fipronil or on leaf discs topically treated with a range of fipronil dosages (1–32 µg kg ⁻¹ on dry mass basis). Females that had developed on fipronil plants laid ca half the number of eggs than females that had developed on control plants. In the bioassay with leaf discs, longevity and lifetime egg production declined with increasing fipronil dosage. Remarkably, exposure to fipronil during larval development primarily affected the adult stage. Chemical analyses of leaf tissues collected from seed-treated plants revealed concentrations of fipronil and its degradation products close to the analytical limit of detection (less than or equal to 1 µg kg ⁻¹ ). The effective dosage was fivefold higher in the leaf-disc than in the whole-plant experiment. In the whole plant, degradation of fipronil to products that are more toxic than fipronil may explain this discrepancy. Neurotoxicity of insecticides at the level of detection decreases the probability of pinpointing insecticides as the causal agent of harmful effects on non-target organisms.

Data were collected in two experiments, a whole plant and a leaf disc bioassay.

In the whole-plant experiment plants were grown from untreated control seeds (Brassica oleracea  var gemmifera cv Cyrus, Brussels sprouts) and seeds coated with fipronil. On each plant (20 control plants, 19 fipronil plants) 5 neonate Pieris brassicae caterpillars were introduced and their survival to pupation was recorded. Pupae were collected and maintained together per plant until adult eclosion. From each plant, one female and one male were selected and they were placed together in a cage (40 x 40 x 60 cm), provided with 10% sugar water and a cabbage plant that served as substrate for oviposition. Plants were checked daily for eggs. Leaves with eggs were removed, or whole plants were replaced by new ones. The experiment was ended at day 24 post-eclosion when most females had died and females that were still alive produced no or very few eggs. All eggs were counted providing lifetime egg production per female.

In the leaf disc bioassay, neonate caterpillars (10 per dish) were fed leaf discs treated with approximated fipronil dosages of 0, 1, 2, 4, 8, 16.1, or 32.2 µg kg^-1 (10 dishes per dosage). Survival of the caterpillars was recorded until pupation. Leaf discs were replaced every other day until day 9. At this point the number of caterpillars was reduced to 5 caterpillars per dish and leaf discs were replaced daily. Pupae were collected and placed together per treatment dosage until adult eclosion. Per dosage, 5 times 6 butterflies, 3 females and 3 males, were randomly selected and placed in new cages. Each cage was provided with a cabbage plant and 10% sugar water. The plants were replaced by new ones every four days until day 12 and then every 2 days until day 35 when most females had died and only few eggs were laid by the females that were still alive. All eggs were counted. Dead butterflies were removed and recorded in both the oviposition cages and the cages with the remaining butterflies that were not released in the oviposition cages. 

There are two data files: whole_plant_exp.xlsx, dish_exp.xlsx.

The whole_plant_exp.xlsx file contains data on pupal mass, larval mortality, pupal mass, development time to pupation, daily and cumulative agg production, longevity of adult females, respectivly that are presented in separate sheets.

The dish exp_exp file contains data on on pupal mass, larval mortality, pupal mass, egg production per cage, egg production per female, respectivly, that are presented in separate sheets.