How lasting are the effects of pesticides on earwigs? A study based on energy metabolism, body weight and morphometry in two generations of Forficula auricularia from apple orchards

Non-target effects of insecticides and herbicides on earwigs

Conservation biological control in agriculture primarily relies on avoiding pesticides that may harm key natural enemies. In temperate tree fruit crops, the European earwig, Forficula auricularia (L.) has only recently become appreciated as an important predator of economic pests, particularly woolly aphids and pear psylla. Therefore, the non-target effects of orchard pesticides on earwigs are largely understudied. This is particularly true for herbicides, which earwigs are likely to be exposed to due to their foraging behavior moving between the canopy and the ground cover. We tested residues of formulated pesticides (8 insecticides and 7 herbicides) commonly used in tree fruit crops for lethal and sublethal (movement, predation rate) effects on adult female earwigs. Two herbicides, paraquat and glufosinate, and one insecticide, spinetoram, were acutely toxic to earwigs within 72 h. No tested pesticides altered earwigs' movement or resting behavior compared to the control. The insecticides spinosad and cyantraniliprole and the herbicides 2,4-D, glufosinate, halosulfuron, rimsulfuron, and oxyfluorfen reduced earwig predation on green peach aphids. Therefore, these pesticides may reduce earwig predation on pests in orchards. Our results suggest that some pesticides are of greater risk, and thus, should be carefully considered or better timed when used in tree fruit orchards where earwigs are considered for conservation or augmentative biological control.

Exposure to pyriproxyfen (juvenile hormone agonist) does not alter maternal care and reproduction in the European earwig

Sublethal exposure to pesticides can alter the survival and reproduction of a wide range of non-target organisms. However, it remains unclear whether this exposure can alter behaviours that are often essential for long-term population dynamics and maintenance, such as parental care. In this study, we tested the effect of pyriproxyfen exposure (an insect growth regulator) on maternal care in the European earwig, an insect that is both used in pest control in pip-fruit orchards and considered a pest in stone fruit orchards. We exposed 424 females at doses either 10 times lower, equivalent or 10 times higher than normal application rates in French orchards. As maternal care can change over the weeks of family life, we exposed the earwig mothers at five different days before and after egg hatching. We then measured the expression of ten forms of maternal care towards eggs and juveniles, six non-caring behaviours, eggs and juvenile development, metabolic reserves in mothers at egg hatching and females' production of a terminal clutch. First, our results revealed that the three tested doses of pyriproxyfen were non-lethal and confirmed that maternal care decreased throughout both pre- and post-hatching family life. However, we did not detect any effect of pyriproxyfen on maternal care and non-care behaviours, eggs and juvenile development, quantities of lipids, proteins and glycogen in mothers at egg hatching, and on the production of a future clutch. Overall, these findings suggest that the maximal doses of pyriproxyfen authorized in French orchards is likely to have limited effects on the short- and long-term maintenance of populations of the European earwig and raises fundamental questions about the nature of the link between juvenile hormone and parental care in insects.

Snails as Temporal Biomonitors of the Occurrence and Distribution of Pesticides in an Apple Orchard

The intensive use of pesticides in agricultural areas and the resulting effects have created a need to develop monitoring programs for their active assessment at low cost. This research entails a biomonitoring study of the pesticides in an apple orchard, using juvenile Cornu aspersum (O. F. Müller, 1774) snails exposed in field microcosms. The snails were deployed at three different locations in the orchard area and were used to assess the temporal biomonitoring of 100 different semi-volatile and non-volatile pesticides. The study was performed over an 18-week period and targeted the center, the border, and the outside of the orchard. Results showed that greater levels of pesticides were detected at the center of the orchard as compared to the other sites. The type and level of the applied pesticide influenced its environmental dissipation, as significantly greater levels of semi-volatile pesticides were accumulated by the caged snails in comparison to non-volatile pesticides. The presence of semi-volatile pesticides in the snails outside the orchard revealed the usefulness of these species in the biomonitoring of off-site pesticide emissions. The findings of this study showed that C. aspersum can serve as a reliable and effective model organism for the active biomonitoring of pesticide emissions in agricultural sites.