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Effects of the insecticide dimethoate on the behaviour of Folsomia fimetaria (L.) (Collembola: Isotomidae)
Applied Soil Ecology 9 (1998) 389±392
Effects of the insecticide dimethoate on the behaviour of Folsomia ®metaria (L.) (Collembola: Isotomidae) Henning Petersen*, Peter Gjelstrup Natural History Museum, Mols Laboratory, Femmùller, DK 8400 Ebeltoft, Denmark Received 26 July 1996; accepted 1 August 1997
Abstract Combined activity and choice experiments with single juvenile specimens of the collembolan Folsomia ®metaria were carried out in laboratory arena chambers divided into two halves. One side was treated with water and the other with a series of four dimethoate dosages from 0.1 to 5 times recommended ®eld dosage or water. Observations of location in the arena and behaviour of the test specimens were made by microscopic observation and video-recording. A good correlation was found between the occurrence of seven well-de®ned behavioural patterns and dimethoate dosage in combination with time of exposure. A tendency of preference for the untreated part of the arena was observed, but gradually deteriorating locomotory behaviour interfered with the organism's ability to choose between the treated and untreated parts. # 1998 Elsevier Science B.V. Keywords: Pesticides; Insecticides; Dimethoate; Collembola; Behaviour
1. Introduction The dramatic increases in pesticide use during recent decades and the recent detection of pesticides in precipitation (Helweg, 1995) highlight the importance of the study of pesticide effects on non-target organisms. Signi®cant effects of the insecticide dimethoate on the naturally occurring soil-inhabiting collembolan species Folsomia ®metaria (L.) and Isotoma notabilis SchaÈff were demonstrated in semi-®eld microcosm experiments (Petersen and Gjelstrup, 1995) which called for a deeper insight into the effect of the pesticides on behaviour and population dynamics of the animals. *Corresponding author. Tel.: +45 86362535; fax: +45 86361750. 0929-1393/98/$19.00 # 1998 Elsevier Science B.V. All rights reserved. PII S0929-1393(98)00094-8
Here we report results from a detailed laboratory study combining choice- and behaviour-experiments for F. ®metaria in arena chambers treated with a series of dimethoate dosages. The study relates to earlier observations by FaÂbiaÂn and Petersen (1994). 2. Methods Results for 12 day old F. ®metaria were chosen for this report because the juveniles proved more sensitive to dimethoate than adults (Petersen and Gjelstrup, unpubl.). The specimens were obtained from stock cultures derived from a local experimental ®eld (Stegelykke, Kalù). Arena chambers for the experiment were small plastic canisters (diameter: 33 mm, height: 33 mm)
390
H. Petersen, P. Gjelstrup / Applied Soil Ecology 9 (1998) 389±392
with a 1 cm deep, compact bottom layer of defaunated moist soil (Petersen and Gjelstrup, 1995) partitioned into two equal sections by a thin (0.8 mm) plastic sheet. Solutions of dimethoate-28, Esbjerg Kemi A/S, (recommended dosage in Denmark (DLG, 1991): 280 g active ingredients per ha) were used at 0 times (control), 0.5 times, 1 times, 3 times and 5 times recommended dosage per unit area. One-hundred ml solution was applied to the soil surface of one-half of each chamber. The other half was treated with an equal amount of distilled water. Half an hour later a single specimen of F. ®metaria was added to each chamber. Subsequently, the location and behaviour of each specimen was observed through a microscope and video-taped for 30 s after every half an hour for 6.5 h. One similar reading was carried out on each of the following 6 workdays. The behaviour of F. ®metaria was classi®ed according to seven behavioural patterns (Table 1) based on initial observations of dimethoate-treated specimens. Each experiment was carried out as a blind test so that the dosage of dimethoate was not known to the observer until the end of the experiment. A weighted mean time index (MT) was calculated for each behavioural state for the ®rst 6.5 h of the
Table 1 Behavioural states of Folsomia fimetaria in response to dimethoate treatment Symbol
State
Description
A
Rest
B
E
Normal locomotion Restless locomotion Unsteady locomotion Immobile
F
Rigid
G
Dead
Relaxed. Some movement of head and antennae Coordinated locomotion interrupted by short stops Restless locomotion with variable speed and direction Uncoordinated wavering/dragging locomotion Stationary. Often convulsive/shaking movements and raised abdomen. Antennae often bent backwards and quivering Stationary. No movements. Often formation of drops. Furca outstretched. Disturbance can provoke movements Permanently immobile. Movements cannot be provoked
C D
experiment (day 1) MT
X t0 ÿtn
ti Ni =
X t0 ÿtn
Ni
(1)
where t0 tn ti Ni
Time of first reading Time of last reading Duration since addition of animals Number of observations of a given state at time ti
3. Results Animals in control chambers (Fig. 1, broken line) were generally active and changed side more or less regularly throughout the experimental period. At the lowest dosage (0.1 times recommended) the same pattern of activity was observed, but with increasing dimethoate dosages the shifts between sides became more and more rare as the specimens gradually became immobile. The period when the animals were actively moving decreased with increasing dosage. The place within the chamber where the animals became immobilised seemed accidental and independent of the dimethoate treatment. However, except for the 5 times dosage, most observations of animals were made on the untreated side. The relationship between dimethoate dosage and the sum of records of each behavioural state de®ned in Table 1 through the ®rst 6.5 h of the experiment is illustrated in the lower part of Fig. 2. The upper part of the ®gure illustrates the relationship between dosage and MT for the same behavioural states. The occurrence of the ®rst three states, A±C declined with increasing dosage of dimethoate while the occurrence of states D±G increased with increasing dosage. With the exception of state D (unsteady locomotion) the MT decreased with increasing dosage for all behavioural states. Thus, the period until culmination of these behavioural states seems to shorten with increasing dimethoate dosage. While the MT curves for states A±C follow each other with the same inclination and at the same level, the curves for states D±F illustrate a largely parallel sequence with similar inclination as the curves for states A±C but at progressively higher levels so that
H. Petersen, P. Gjelstrup / Applied Soil Ecology 9 (1998) 389±392
391
Fig. 2. Folsomia fimetaria juvenile ± mean time index and number of records as related to dimethoate dosage during the first 6.5 h of arena experiment. A±G: behavioural states (see Table 1).
Fig. 1. Folsomia fimetaria juvenile ± percentage of specimens on dimethoate-treated side of arena (solid dots, unbroken line) at 5 dosages (times recommended field dosage) through the first 6.5 h and the following 6 workdays compared with control (open dots, broken line). Area of dots is proportional to percentage of specimens in the three immobile states E±G (cf. Table 1). Largest dots100%. N (at start)10.
A±C
correlated with increasing dimethoate dosage and showed nearly identical time-response patterns. States E (immobile), F (rigid) and G (dead) were interpreted as abnormal activity as their occurrence increased with increasing dimethoate dosage. Activity state D (unsteady locomotion) is intermediary and may be caused by the pesticide as well as other disturbances resulting from the experimental design. FaÂbiaÂn and Petersen (1994) concluded that F. ®metaria was able to choose a non-treated surface in preference to a dimethoate-treated surface. The present experiment could not con®rm a similar strong ability to avoid exposure to dimethoate although a tendency for preference for the untreated side was found at all except the highest dosage. Continuous observations of single specimens also showed distinct withdrawal reactions, for example, turning or backing, when passing the borderline to the treated substrate (Petersen and Gjelstrup, unpubl.). The difference between the results of FaÂbiaÂn and Petersen (1994) and those of the present study may partly be due to the
392
H. Petersen, P. Gjelstrup / Applied Soil Ecology 9 (1998) 389±392
comparatively small experimental chamber used in the present experiment. All specimens were recorded on the dimethoate-treated side of the arena sometime during the experiment. Further, Gjelstrup and Petersen (unpubl.) suggested that dimethoate in gasphase may have some effect on the behaviour of F. ®metaria. It is concluded that a relatively inef®cient preference ability interacts with a gradually deteriorating locomotory behaviour caused by dimethoate but no obvious relationship was found between the treated part of the arena and the place where the animals were immobilised. Consequently, F. ®metaria in the ®eld situation may have limited ability to avoid dimethoate by escaping from contaminated to less contaminated parts of the soil. Acknowledgements The present work was ®nanced by the Danish Environmental Protection Agency (project no.
7041-0248) and the Natural History Museum, Aarhus. Anni Kjeldsen is thanked for technical assistance. References DLG, 1991. PlantevñrnshaÊndbogen. Dansk Landbrugs Grovvareselskab, Kùbenhavn, 264 pp. FaÂbiaÂn, M., Petersen, H., 1994. Short-term effects of the insecticide dimethoate on activity and spatial distribution of a soil inhabiting collembolan Folsomia fimetaria Linne (Collembola: Isotomidae). Pedobiologia 38, 289±302. Helweg, A. (Ed.), 1995. Pesticides in Precipitation and Surface Water. Tema Nord, (Nordic Council of Ministers), 558, pp. 1±195. Petersen, H., Gjelstrup, P, 1995. Development of a semi-field method for evaluation of laboratory tests as compared to field conditions. In: Lùkke, H. (Ed.), Effects of Pesticides on Meso- and Micro-fauna in Soil. Pesticide Research from the Danish Environmental Protection Agency, 8, pp. 67±142.
Effects of the insecticide dimethoate on the behaviour of Folsomia ®metaria (L.) (Collembola: Isotomidae) Henning Petersen*, Peter Gjelstrup Natural History Museum, Mols Laboratory, Femmùller, DK 8400 Ebeltoft, Denmark Received 26 July 1996; accepted 1 August 1997
Abstract Combined activity and choice experiments with single juvenile specimens of the collembolan Folsomia ®metaria were carried out in laboratory arena chambers divided into two halves. One side was treated with water and the other with a series of four dimethoate dosages from 0.1 to 5 times recommended ®eld dosage or water. Observations of location in the arena and behaviour of the test specimens were made by microscopic observation and video-recording. A good correlation was found between the occurrence of seven well-de®ned behavioural patterns and dimethoate dosage in combination with time of exposure. A tendency of preference for the untreated part of the arena was observed, but gradually deteriorating locomotory behaviour interfered with the organism's ability to choose between the treated and untreated parts. # 1998 Elsevier Science B.V. Keywords: Pesticides; Insecticides; Dimethoate; Collembola; Behaviour
1. Introduction The dramatic increases in pesticide use during recent decades and the recent detection of pesticides in precipitation (Helweg, 1995) highlight the importance of the study of pesticide effects on non-target organisms. Signi®cant effects of the insecticide dimethoate on the naturally occurring soil-inhabiting collembolan species Folsomia ®metaria (L.) and Isotoma notabilis SchaÈff were demonstrated in semi-®eld microcosm experiments (Petersen and Gjelstrup, 1995) which called for a deeper insight into the effect of the pesticides on behaviour and population dynamics of the animals. *Corresponding author. Tel.: +45 86362535; fax: +45 86361750. 0929-1393/98/$19.00 # 1998 Elsevier Science B.V. All rights reserved. PII S0929-1393(98)00094-8
Here we report results from a detailed laboratory study combining choice- and behaviour-experiments for F. ®metaria in arena chambers treated with a series of dimethoate dosages. The study relates to earlier observations by FaÂbiaÂn and Petersen (1994). 2. Methods Results for 12 day old F. ®metaria were chosen for this report because the juveniles proved more sensitive to dimethoate than adults (Petersen and Gjelstrup, unpubl.). The specimens were obtained from stock cultures derived from a local experimental ®eld (Stegelykke, Kalù). Arena chambers for the experiment were small plastic canisters (diameter: 33 mm, height: 33 mm)
390
H. Petersen, P. Gjelstrup / Applied Soil Ecology 9 (1998) 389±392
with a 1 cm deep, compact bottom layer of defaunated moist soil (Petersen and Gjelstrup, 1995) partitioned into two equal sections by a thin (0.8 mm) plastic sheet. Solutions of dimethoate-28, Esbjerg Kemi A/S, (recommended dosage in Denmark (DLG, 1991): 280 g active ingredients per ha) were used at 0 times (control), 0.5 times, 1 times, 3 times and 5 times recommended dosage per unit area. One-hundred ml solution was applied to the soil surface of one-half of each chamber. The other half was treated with an equal amount of distilled water. Half an hour later a single specimen of F. ®metaria was added to each chamber. Subsequently, the location and behaviour of each specimen was observed through a microscope and video-taped for 30 s after every half an hour for 6.5 h. One similar reading was carried out on each of the following 6 workdays. The behaviour of F. ®metaria was classi®ed according to seven behavioural patterns (Table 1) based on initial observations of dimethoate-treated specimens. Each experiment was carried out as a blind test so that the dosage of dimethoate was not known to the observer until the end of the experiment. A weighted mean time index (MT) was calculated for each behavioural state for the ®rst 6.5 h of the
Table 1 Behavioural states of Folsomia fimetaria in response to dimethoate treatment Symbol
State
Description
A
Rest
B
E
Normal locomotion Restless locomotion Unsteady locomotion Immobile
F
Rigid
G
Dead
Relaxed. Some movement of head and antennae Coordinated locomotion interrupted by short stops Restless locomotion with variable speed and direction Uncoordinated wavering/dragging locomotion Stationary. Often convulsive/shaking movements and raised abdomen. Antennae often bent backwards and quivering Stationary. No movements. Often formation of drops. Furca outstretched. Disturbance can provoke movements Permanently immobile. Movements cannot be provoked
C D
experiment (day 1) MT
X t0 ÿtn
ti Ni =
X t0 ÿtn
Ni
(1)
where t0 tn ti Ni
Time of first reading Time of last reading Duration since addition of animals Number of observations of a given state at time ti
3. Results Animals in control chambers (Fig. 1, broken line) were generally active and changed side more or less regularly throughout the experimental period. At the lowest dosage (0.1 times recommended) the same pattern of activity was observed, but with increasing dimethoate dosages the shifts between sides became more and more rare as the specimens gradually became immobile. The period when the animals were actively moving decreased with increasing dosage. The place within the chamber where the animals became immobilised seemed accidental and independent of the dimethoate treatment. However, except for the 5 times dosage, most observations of animals were made on the untreated side. The relationship between dimethoate dosage and the sum of records of each behavioural state de®ned in Table 1 through the ®rst 6.5 h of the experiment is illustrated in the lower part of Fig. 2. The upper part of the ®gure illustrates the relationship between dosage and MT for the same behavioural states. The occurrence of the ®rst three states, A±C declined with increasing dosage of dimethoate while the occurrence of states D±G increased with increasing dosage. With the exception of state D (unsteady locomotion) the MT decreased with increasing dosage for all behavioural states. Thus, the period until culmination of these behavioural states seems to shorten with increasing dimethoate dosage. While the MT curves for states A±C follow each other with the same inclination and at the same level, the curves for states D±F illustrate a largely parallel sequence with similar inclination as the curves for states A±C but at progressively higher levels so that
H. Petersen, P. Gjelstrup / Applied Soil Ecology 9 (1998) 389±392
391
Fig. 2. Folsomia fimetaria juvenile ± mean time index and number of records as related to dimethoate dosage during the first 6.5 h of arena experiment. A±G: behavioural states (see Table 1).
Fig. 1. Folsomia fimetaria juvenile ± percentage of specimens on dimethoate-treated side of arena (solid dots, unbroken line) at 5 dosages (times recommended field dosage) through the first 6.5 h and the following 6 workdays compared with control (open dots, broken line). Area of dots is proportional to percentage of specimens in the three immobile states E±G (cf. Table 1). Largest dots100%. N (at start)10.
A±C
correlated with increasing dimethoate dosage and showed nearly identical time-response patterns. States E (immobile), F (rigid) and G (dead) were interpreted as abnormal activity as their occurrence increased with increasing dimethoate dosage. Activity state D (unsteady locomotion) is intermediary and may be caused by the pesticide as well as other disturbances resulting from the experimental design. FaÂbiaÂn and Petersen (1994) concluded that F. ®metaria was able to choose a non-treated surface in preference to a dimethoate-treated surface. The present experiment could not con®rm a similar strong ability to avoid exposure to dimethoate although a tendency for preference for the untreated side was found at all except the highest dosage. Continuous observations of single specimens also showed distinct withdrawal reactions, for example, turning or backing, when passing the borderline to the treated substrate (Petersen and Gjelstrup, unpubl.). The difference between the results of FaÂbiaÂn and Petersen (1994) and those of the present study may partly be due to the
392
H. Petersen, P. Gjelstrup / Applied Soil Ecology 9 (1998) 389±392
comparatively small experimental chamber used in the present experiment. All specimens were recorded on the dimethoate-treated side of the arena sometime during the experiment. Further, Gjelstrup and Petersen (unpubl.) suggested that dimethoate in gasphase may have some effect on the behaviour of F. ®metaria. It is concluded that a relatively inef®cient preference ability interacts with a gradually deteriorating locomotory behaviour caused by dimethoate but no obvious relationship was found between the treated part of the arena and the place where the animals were immobilised. Consequently, F. ®metaria in the ®eld situation may have limited ability to avoid dimethoate by escaping from contaminated to less contaminated parts of the soil. Acknowledgements The present work was ®nanced by the Danish Environmental Protection Agency (project no.
7041-0248) and the Natural History Museum, Aarhus. Anni Kjeldsen is thanked for technical assistance. References DLG, 1991. PlantevñrnshaÊndbogen. Dansk Landbrugs Grovvareselskab, Kùbenhavn, 264 pp. FaÂbiaÂn, M., Petersen, H., 1994. Short-term effects of the insecticide dimethoate on activity and spatial distribution of a soil inhabiting collembolan Folsomia fimetaria Linne (Collembola: Isotomidae). Pedobiologia 38, 289±302. Helweg, A. (Ed.), 1995. Pesticides in Precipitation and Surface Water. Tema Nord, (Nordic Council of Ministers), 558, pp. 1±195. Petersen, H., Gjelstrup, P, 1995. Development of a semi-field method for evaluation of laboratory tests as compared to field conditions. In: Lùkke, H. (Ed.), Effects of Pesticides on Meso- and Micro-fauna in Soil. Pesticide Research from the Danish Environmental Protection Agency, 8, pp. 67±142.