Mar 12, 1997 - Sand Hutton, York, Y04 ILZ, U.K., 2University of Glamorgan, Pontypridd,. Mid Glamorgan, CF37 IDL, U.K. and 'Model Research, 7 Kings Road,.
J. stored Prod. Res. Vol. 33, No. 4, pp. 335-346, 1991 Crown Copyright 0 1997 Published by Elsevier Science Ltd
Pergamon
Printed in Great Britain 0022-474X/97 $17.00 + 0.00
PII: SOO22-474X(97)00013-1
Evaluation of the Behavioural Responses of Anthrenus verbasci Adults and Larvae to Permethrin (ec) Using a Computerized Tracking System E. WATSON,’
G. BARSON,‘* D. B. PINNIGER,’ A. R. LUDLOW3
G. ROBERTS,2
and
‘Central Science Laboratory, Ministry of Agriculture, Fisheries and Food, Sand Hutton, York, Y04 ILZ, U.K., 2University of Glamorgan, Pontypridd, Mid Glamorgan, CF37 IDL, U.K. and ‘Model Research, 7 Kings Road, Alton, Hampshire, GU34 IPZ, U.K. (Accepted 12 March 1997)
Abstract-The behavioural responses of Ant/n-enus uerbasci adults and larvae to permethrin 25% emulsion concentrate (ec) and the insect repellent NJVdiethyl-m-toluamide (DEET) were assessed using a computerized insect tracking system. A. verbasci were exposed to filter papers half treated with 50, 100, 150 or 200 mg/m* permethrin ec or 250 mg/m* DEET. A. uerbusci larvae did not respond to DEET, however, on papers half treated with 50, 100 or 150 mg/m’ permethrin ec, significantly less time was spent on the treated side than on the untreated side. In addition, there were significantly more attempted crossings away from the treated side than away from the untreated side. Adult A. uerbusci spent significantly less time on the treated side than the untreated side of papers half treated with 250 mg/m’ DEET. Adults on permethrin made more attempted crossings away from the untreated side than away from the treated side dosed at 100 or 150 mg/m*. Crown Copyright 0 1997 Published by Elsevier Science Ltd fGq> words--Anthrenus
verbasci,
behaviour,
insecticides,
repellents,
stored
products
INTRODUCTION
The varied carpet beetle, Anthrenus verbasci (L.), can cause serious damage to household items and museum exhibits consisting of wool, fur, skins and feathers. It is a major pest in the British Isles, commonly found throughout the U.K. (Peacock, 1993), and is numerous in the suburban areas of south-east England (Woodroffe and Southgate, 1954). The larvae, which develop over a l-2-y period depending on environmental conditions (Blake, 1958), are normally found in the nests of birds, such as the house sparrow, house martin and swift, which explains the prevalence of this species in buildings (Parkin and Woodroffe, 1961). The adults emerge between the end of May and early August when they will actively fly to and feed on the pollen and nectar of hogweed (Heracleum sphondylium) and other flowering plants (Woodroffe and Southgate, 1954). A. verbasci adults are relatively easy to control using residual insecticide treatments (Tyler and Binns, 1977), although the treatment must coincide with adult activity and egg laying. The larvae, however, are more difficult to control as they often remain hidden within the food source and take *Corresponding
author:
2 Sycamore
Drive,
Frimley,
Camberley, 335
Surrey,
GU16
5PQ, U.K.
336
E. Watson et al.
a relatively long time to succumb to insecticide treatment, even after picking up a lethal dose (Parkin and Woodroffe, 1961). Permethrin has been used as a proofing agent to control A. uerbasci larvae on woollen fabrics since the late 197Os, and is known to be effective in reducing damage caused by carpet beetles and clothes moths (Friedman et al., 1979; Bry and Simonaitis, 1989). However, it has recently been demonstrated that residual insecticide treatments using permethrin and bendiocarb are relatively ineffective in controlling wandering A. verbasci larvae (Hillyer and Blyth, 1992; Morgan et al., 1993). In the light of the ability of A. verbasci to withstand residual treatments of permethrin, it was decided to investigate, using a computerized insect tracking system, the behaviour of A. uerbasci in the presence of permethrin and an insect repellent to determine whether the adults and larvae can detect and modify their behaviour in the presence of an insecticide, and hence aid their survival. The insect repellent was used as a control compound to test the insects’ sensory apparatus and the experimental design of the tracking system. MATERIALS
AND METHODS
Insects
A laboratory strain of A. verbasci was used in all the experiments, and was cultured at the Central Science Laboratory (CSL) on a diet of fishmeal, yeast and cholesterol (75 : 18 : 1) and wool felt under dark conditions (2O”C, 70% r.h.). Chemicals tested
The insect repellent, N,N-diethyl-m-toluamide 98% technical (DEET), obtained from Sigma Chemicals, Poole, Dorset, BH17 7NH, U.K., was tested at an application rate of 250 mg/m2. Permethrin 25% emulsion concentrate (ec) (Permasect 25EC), obtained from Mitchell Cotts Chemicals Ltd., Mirfield, W. Yorks, WF14 8QB, U.K., was used at application rates of 50, 100, 150 and 200 mg/m’. Tracking system
The system allowed the tracking of one insect on a filter paper arena which was defined by a 10 cm diameter ring (Fig. 1). The insects were viewed with a video camera and illuminated by low intensity, red light-emitting diodes. Further details of the system are described in Roberts and Chambers (1993). However, the delivery unit, a computer-controlled chemical presentation apparatus, was not present in this system. The optical system and hardware provided a video image of the arena on which the insect was represented by a bright spot on a completely dark background. This system was effective if one of the following applied: 1. the intensity of light from a dark insect was appreciably lower than that from any part of the arena; 2. the intensity of light from a pale coloured insect was appreciably higher than that from any part of the arena. Both adults and larvae of A. verbasci had a dark colouration and were easily tracked with the system. The tracking system recorded several variables on the treated and untreated sides of the filter paper of which the following were considered to be the most important in relation to the insect avoidance behaviour: l l l l l l l
total occupation time, Tt; total time moving, Tm; average speed of locomotion, As; crossings away from the edge, Cafe; crossings close to the edge, Ccte; attempted crossings away from the edge, Aafe; attempted crossings close to the edge, Acte.
Behavioural
responses
of Anrhrenus verbasci
337
These variables were recorded separately for both designated halves of the arena. The total occupation time was recorded as the time spent on each side of the arena. The time spent moving was the duration of time over which the insect travelled faster than 0.1 mm/s. The average speed was the mean value of individual speeds between successive sampling points, when the individual speeds were greater than 0.1 mm/s. The threshold speed of 0.1 mm/s ensured that electronic/optical noise did not inflate the time the insect was moving. Custom analysis software divided the arena into three main sections: A, untreated area; B, treated area; C, central region in the vicinity of the boundary between the untreated and treated areas (Fig. 1). It was anticipated that crossing frequencies might be dependent on the proximity of the insect to the arena perimeter. A difference obtained between attempted crossings close to the edge and away from the edge would be important as it could demonstrate the strength of reaction. An insect is generally edge bound and will go around the edge of a ring regardless of the presence of an insecticide. However, at some point, the insect stops at the boundary between the treated and untreated areas and then turns back to the untreated area, thus overcoming the edge effect. Once an insect has broken away from the edge effect, it can then wander over the complete surface. The insect appears to be more sensitive to a chemical’s presence once the edge effect has been overcome. Hence each of the main areas was divided into subareas, A, and A, etc., where p denotes the region between the perimeter and the inner circle (Fig. 1) and c denotes the central region (inside the inner circle). A successful crossing may be defined as a path from A through C into B, while an attempted crossing may be defined as a path from A through C returning to A. An insect following a path along the boundary B and C might be alternately detected in B and C, leading to inflated numbers of attempted crossings, e.g. path (a) (Fig. 1). This problem was overcome by the use of additional areas AC and BC, located just inside areas A and B respectively. Area AC can be regarded as an extension of area A or area C, depending on the route taken by the insect to enter AC; thus path
Perimeter
A
/ Inner 1
circle
/
Untreated area A
-I Boundary area C
t Treated area B
\\hun
t
r ea t ed
boundary
I Fig. 1. Divisions in the text.
of arena (diameter,
10 cm) as determined
by software
analysis.
These are described
fully
338
E. Watson
et al.
(b) (Fig. 1) is recorded as one attempted crossing. The positions used for the various lines were as follows: arena diameter, 100 mm; distance between inner circle and perimeter, 5 mm; full width of area C, 8 mm; width of areas AC and BC, 10 mm. The numbers of successful and attempted crossings from A,, A, B, and B, were calculated. Examples of insect tracks are given in Fig. 2. Experimental procedures
Permethrin ec was diluted in distilled water to give the required concentrations in 0.5 ml aliquots. Each solution was evenly applied using a 1 ml pipette to one half of an 11 cm diameter Whatman No. 1 filter paper, the filter papers having previously been divided into two equal halves by a lightly marked pencil line drawn across the diameter. DEET was applied in the same way to other papers. The treated papers were air dried under the test conditions (25°C 70% r.h.); each paper was transferred onto a glass plate, where it was weighted with a 10 cm diameter metal ring to prevent the paper from wrinkling. The papers were then left to dry overnight. Controls consisted of untreated filter papers. In previous tests, it was found that distilled water had no effect on insect behaviour. Twenty-five adults or final stage larvae were removed from culture and kept in an 8 cm diameter crystallizing dish containing a filter paper and tissue paper as a foothold; these were stored in the dark overnight without food at 25°C and 70% r.h. The following day a half treated filter paper was placed on the base of the tracking system with a 10 cm diameter ring placed centrally on top of the paper. A single insect was introduced onto the untreated side of the arena and allowed to settle down for 1 min. It was decided that the insect should be placed on the untreated side of the filter paper, giving it an opportunity to detect a chemical presence before contact and preventing initial contamination of the insect which could have biased the results. The tracking system then recorded the movements of the insect for 900 s. This process was repeated for each of 20 adults and larvae using a different filter paper for each assessment. Untreated filter papers were used as controls, where one side was arbitrarily designated as “treated”, and these were similarly assessed. Statistical analysis
The arena and recording system were designed to produce a thorough comparison of the behaviour on treated and untreated surfaces. The first stage in the statistical analysis compared the behaviour on the two sides using t-tests. The number of crossings and attempted crossings were counts which had a Poisson rather than a normal distribution, and their variance increased with their mean. To compensate for this, the counts were transformed to square roots before undertaking t-tests. A treatment may increase or lower the total number of crossings, but it cannot produce a significant difference between the two sides for this variable because if an insect crosses to one side, the next crossing must bring it back to the other and the total number of crossings in one direction can never differ from those in the other by more than one. However, the recording system separated the number of crossings close to the edge from those away from the edge, and it was possible for an insect to cross close to the edge in one direction, but away from the edge in the other. This produced a significant difference between treated and untreated halves in the number of crossings close to the edge or away from the edge (Table 1); however, because the insect is merely crossing from one side to the other, it seems appropriate to ignore such a difference. Crossings from one side to the other are dependent on where the insect last was, whereas attempted crossings are not. Thus an attempted crossing is an independent variable and, as such, breaking down the position of an insect is useful for the measurement and comparison of its behaviour. Different statistical analyses were needed when comparing behaviour on the two sides and behaviour at different doses. The first was a matched-pairs analysis where each insect was its own
Behavioural
Fig. 2. Anrhrenus verbasci larval half) with the insect repellent
responses
of Anthrenus
339
verbasci
response traces to: (A) untreated control; NJ-diethyl-m-toluamide (DEET).
(B) filter paper
treated
(top
340
E. Watson et al.
control. The second required a comparison of different groups of insects. The differences between groups could be due to the following: 1. a variation between individuals in the group; 2. a certain factor in rearing or treatment which affected the whole group; 3. the effect of treatment. The within-group variation was estimated from the data. Variation between groups was expected to be small because the insects were drawn from a culture which had been maintained in the laboratory for 30 y and which had stabilized so that day to day variation was small. Analysis of variance was therefore used to examine the dose-response relationships, using residual mean squares based on the variation between insects. RESULTS The behavioural responses of A. verbusci larvae and adults to controls, permethrin 25% ec and DEET are shown in Table 1. No knock-down of adults or larvae was observed during the time of assessment. Separate dose-responses were obtained for the insect behaviour on treated and untreated surfaces. The behaviour on the treated surface is a direct response to the chemical, whereas the behaviour on the untreated surface will be influenced by the chemical if it is volatile or if it has a persistent effect on the insect’s behaviour. A. verbasci larvae There was no significant difference in the behavioural responses of the control larvae between the “treated” and untreated sides for any of the variables measured. Similarly, there was no difference in the larval response between the sides treated with 250 mg/m2 DEET and the untreated sides of the same papers. There were, however, significant behavioural responses to the permethrin treatments. For filter paper arenas half treated with 50 mg/m2 permethrin, significantly more time was spent occupying and moving on the untreated side than on the treated side (P < 0.01); also, there were significantly more attempted crossings away from the edge on the untreated side than on the treated side (P c 0.01). For 100 mg/m* permethrin, significantly more time was spent on the untreated side of the arenas, and there were significantly more attempted crossings away from the edge on the untreated side than on the treated side (P < 0.05). At the two highest doses of 150 and 200 mg/m* permethrin, significantly more time was spent occupying (P < 0.05) and moving (P < 0.05) on the untreated side; also, there were significantly more attempted crossings close to the edge on the untreated side than on the treated side (P < 0.001). In addition, at 150 mg/m2, there were more attempted crossings away from the edge of the arenas on the untreated side (P < 0.01) than on the treated side. The total time spent on each side at each application rate of permethrin is shown in Fig. 3. The curves are necessarily mirror images because the observation period was fixed at 15 min, and an insect spending 5 min on the treated side must spend 10 min on the untreated side. Analysis of variance showed no significant change in response with dose. The total time spent moving was greater on the untreated side at all application rates of permethrin (Fig. 4). There was a significant difference in the total time spent moving on each side between the untreated controls (zero dose) and all permethrin treatments (P < 0.05), but there was no significant change from 50 to 200 mg/m2 permethrin. The total time spent moving is the product of the total time and the proportion of time spent moving. The proportion of time spent moving was therefore calculated for each side and is shown in Fig. 5. There was a significant increase between the untreated controls and all permethrin treatments (P < O.OS),but no difference between treatments from 50 to 200 mg/m2. There was no significant change in the speed of movement with dose (Fig. 6). A. verbasci adults There was no significant difference in the behavioural response of the controls between the “treated” and untreated sides for any of the variables measured. For the insect repellent DEET, the adults, in contrast with the larvae, appeared to detect 250 mg/m2, as there was significantly more
A L A L A L A L A L A L
50 Perm
A L A L A L A L A L A L
50 Penn
4.3 1.4 0.6* 0.9 1.4 1.4 1.6 1.1 2.1 1.4
1.9 1.3
Mean
CafeA
439.7 552.3** 456.1 512.5* 373.9 611.3*** 465.5 519.F 529.8* 409.5 466.9 502.8
Mean
TtA
0.48 0.79 0.50 0.23 0.49 0.49 0.49 0.70 0.67 0.70
0.70 0.80
SE.
26.97 29.35 40.29 29.74 67.74 37.75 40.60 31.79 37.23 35.49 21.88 35.49
S.E.
of the behavioural
TtB
Numbers
4.3 1.5 1.0* 0.9 1.7 1.5 1.6 1.1 2.7 1.3
1.4
2.0
Mean
CafeB
indicate
1.3 1.1 0.8 I.1 1.1 0.9 I.0 0.9 6.6 0.9
1.5* 1.4
Mean
0.9* 1.8: 0.9 1.19** 0.9 0.8 1.4 0.5 0.3 0.9
0.7 1.12**
Mean
AafeA
4.6
6.5* 4.2 7.1
4.7
6.4 5.5 5.3 5.1 4.3 4.9 5.0
0.69 0.53 0.88 0.95 0.43 0.58 0.86 0.51 0.16 0.51
0.37 0.98
SE.
0.25
0.40 0.25 0.38
0.18
0.32 0.27 0.26 0.22 0.64 0.28 0.27
SE.
half treated AsA
Mean
arenas
at P < 0.05 between
0.34 0.35 0.27 0.42 0.27 0.25 0.26 0.38 0.87 0.38
0.55 0.33
SE.
28.63
34.33 28.63 20.11
24.03
26.15 25.27 23.16 24.51 37.65 31.76 28.79
S.E.
difference*
1.5 1.0 0.5 I.0 0.9 1.0 1.0 0.9 6.1 0.8
1.2” 1.3
Mean
CcteB
279. I
27J.7* 316.8 356.4
312.1*
360.7 295.6** 347.9 335.1 287.7 234.2*** 340.0
TmB
to filter paper
Mean
a significant
0.30 0.29 0.46 0.32 0.28 0.28 0.30 0.28 0.8 0.28
0.55 0.33
SE.
33.23
348.8 CcteA
34.45 33.23 19.81
25.83
419.5* 412.1* 293.5 368.6
27.99 31.75 39.01 26.40 52.84 34.27 31.21
375.4 450** 379.8 429.1 296.5 &X6*** 372. I
Mean
and larvae
S.E.
adults
TmA
wrbasci
in bold italics
0.49 0.77 0.53 0.37 0.48 0.48 0.63 0.68 0.85 0.68
0.75 0.75
SE.
27.00 29.39 40.26 29.78 67.70 37.75 40.10 31.80 37.22 35.44 21.86 35.44
S.E.
of Anthrenus
459.7 347.4** 443.3 387.0* 435.9 288.2*** 434. I 380.3* 369.8* 490.1 432.6 396.8
Mean
response
All times given in seconds and speeds given in mm/s. P < 0.01; “‘significant at P < 0.001.
Control
250 DEET
200 Per-m
150 Perm
100 Perm
Stage
Treatment
Control
250 DEET
200 Perm
150 Perm
100 Perm
Stage
I. Measurement
Treatment
Table
the untreated
0.3* 0.8* 0.5 0.19** 0.5 0.5 0.6 0.7 0.3 0.6
0.8 0.29**
Mean
AafeB
5.3
6.0* 4.0 7.5
4.7
6.6 5.5 5.3 5.2 4.5 4.9 4.9
Mean
AsB
0.35** 0.3 0.3 0.69*** 0.2 0.5” 0.4 0.2 0.1 0.2
0.1 0.1
Mean
ActeA
0** 0.1 0.1 0.05*** 0.1 0.1* 0.1 0.3 0.3 0.1
0.1 0
Mean
ActeB
sides B; “significant
0.11 0.10 0.20 0.22 0.12 0.24 0.23 0.13 0.05 0.13
0.07 0.11
S.E.
ec or NJ-diethyl-m-toluamide
sides A and treated
0.40 0.22 0.32 0.14 0.22 0.27 1.14 0.68 0.16 0.68
0.56 0.17
S.E.
0.87
0.37 0.87 0.33
0.17
0.38 0.29 0.41 0.25 0.42 0.26 0.23
SE,
with permethrin
at
O.OO 0.05 0.06 0.05 0.07 0.11 0.07 0.16 0.11 0.16
0.05 0.00
S.E.
; $ 2.
s i z % $
,m g s. x 5 2 B : $
342
E. Watson
et al.
. untreated q
01
0
treated
I
I
I
I
50
100
150
200
Application
rate (mg/m*)
Fig. 3. Total occupation time spent on each side of the filter papers ec for Anthrenus uerbasci larvae.
half treated
with permethrin
25%
occupation time and time spent moving on the untreated side and a greater speed of movement on the untreated side than on the treated side (P < 0.05). Adults moving towards the treated side turned back at the boundary and this effect was highly significant (P < 0.001). There was a smaller effect on adults moving in the opposite direction (P < 0.05). There was no significant dose-response
. untreated
0
50
100
Application
150
200
rate (mglm’)
Fig. 4. Total time spent moving on each side of the filter papers for Anthrenus verbasci larvae.
half treated
with permethrin
25% ec
343
Behavioural responses of Anthrenus verbasci
M .e $ E z 4 : ._
0.6 0.5 -
%
0.4 -
5 ._ r : e
0.3 -
a
0.2 -
A untreated q
treated
0.1 t 0
0
I
I
50
100
Application
I 150
I 200
rate (mg/m’)
Fig. 5. Proportion of time spent moving on each side of the filter papers half treated with permethrin 25% ec for Anthrenus verbasci larvae.
for the other variables, suggesting that the matched-pairs comparison (using each insect as its own control) was more sensitive than comparing batches of insects (where individual differences were great). The behavioural response of the adults to permethrin differed from that of the larvae with respect to the occupation time and time spent moving. For the adults, there was no significant difference for these two variables between the treated and untreated sides for all doses of permethrin. However, there were differences in the crossings and attempted crossings for the permethrin treatments. At 50 mg/m2, enigmatically, there were significantly more crossings close to the edge on the untreated side than on the treated side (P < 0.05). At 100 mg/m2 permethrin, there were significantly more attempted crossings away from the edge and close to the edge on the treated side than on the untreated side (P < 0.05 and P < 0.01 respectively). There were significantly more crossings away from the edge on the untreated side than on the treated side (P < 0.05) for the 150 mg/m2 treatment, but, at 200 mg/m2, there was no significant difference between the two sides for any of the variables measured. The dose-response curves for adults were almost level or irregular for all variables. This is consistent with the matched-pairs comparison of sides, where only the number of crossings or attempted crossings differed significantly. DISCUSSION The recording and analysis system developed for these experiments provided a complex description of A. verbasci behaviour and its components, and gave some insight into the mechanisms of the insects’ response to a chemical. For example, a chemical may affect the behaviour in a variety of ways. An attractant may increase the number of directed turns, the speed of walking or the duration of walking towards a chemical. A repellent may increase one or more of these components in the direction away from the treated area. An arrestant will cause the insect to remain longer in areas where the chemical is present, as the insect may move more slowly in the treated area or its turning rate may increase so that it will be less likely to leave the treated surface as it will move in circles. The opposite effect will be found if the chemical increases the speed of movement so that the insect leaves the treated area more rapidly. This would usually be classified as a repellent effect.
E. Watson ef al.
344
Sufficient detail was recorded to identify these patterns of effect with A. verbasci adults and larvae. DEET appeared to have no effect on the larvae of A. uerbasci at the dose applied, but it had a repellent effect on the adults, increasing the time, time spent moving and speed of movement on the untreated side. There was no evidence of directed turns in response to DEET, but there appeared to be an “off-response”, so that the behaviour components of occupation time, time spent moving and speed of movement were altered as the insect left the treated area. Zaitseva and Elizarov (1980) implied that larvae of Anthrenus spp. possess an olfactory sensory system, based on a sensory pore and a coeloconic sensillum directly beneath an antenna1 cone on the second segment, and a large basiconic sensillum at the termination of the third segment. However, the lack of response to DEET in the larvae suggests that this external sensory system is less sophisticated in terms of detecting olfactory stimulants than that in the adults. There appeared to be a repellent effect to A. verbasci larvae by permethrin, with more directed turns (attempted crossings) away from the treated area. The time spent on the untreated side was therefore increased, and there was also an increase in the time spent moving on the untreated area. The proportion of time spent walking is an independent variable, i.e. it does not depend on the time spent moving on the other side; however, parallel curves were produced (Fig. 5). This implies a persistent effect of permethrin which promotes walking after the insect has left the treated area. Permethrin was slightly repellent to A. verbasci adults, as directed turns were increased, but only in the 100 and 150 mg/m2 treatments. This pattern of behavioural response for all doses of permethrin is consistent with the idea that larvae turn back when they approach or contact permethrin-treated filter paper and therefore spend more time on the untreated area. The results of Morgan et al. (1993) showed that, after 24 h of exposure to permethrin ec, many larvae had entered a state of inactivity or torpor. Results from the tracking system show that both larvae and adults reduce their speed of movement with increased concentration of permethrin ec (Fig. 6 and Fig. 7). Further work by Watson and Barson (unpublished results) has shown that, during the initial 15-min exposure period to 150 mg/m2 permethrin ec, larvae travelled at an average speed of 7.4 mm/s, whereas after 24 h of exposure the average speed was 1.8 mm/s. This demonstrates that, after an initial period of activity, larval movement diminishes considerably. Control insects did not exhibit such a marked drop in activity.
2
. untreated q
treated
t l-
0
0
I 50
Application
I
I
I
100
150
200
rate (mglm’)
Fig. 6. Speed of movement on each side of the filter papers half treated with permethrin 25% ec for Anrhrenus verbasci larvae.
Behavioural responses of Anthrenus verbasci
345
6-
5-
4-
3 . untreated q
2
treated
1 1
01 0
I
I
I
I
50
100
150
200
Application
rate (mglm’)
Fig. 7. Speed of movement on each side of the filter papers half treated with permethrin 25% ec for Anthrenus verbasci adults.
detail recorded by the tracking system gives some insight into how the chemicals are detected, i.e. whether by olfaction, contact or both, and whether the chemical has a persistent or brief effect on the subsequent behaviour. With this apparatus, a volatile chemical, such as DEET, may be present on both sides of the arena so that olfactory responses could be similar on both sides, but will be affected by the treatment dose. However, the experimental design included zero dose (controls) in which filter papers were untreated, and the effect of highly volatile chemicals was detected by comparing the behaviour at zero dose with that on papers on which one side was treated with a chemical such as DEET. Contact responses should be different on the two sides, and be dose dependent. For example, the larvae may detect permethrin more readily by contact than via the olfactory system, since more time was spent occupying the untreated side. Differences in attempted crossings by larvae were also observed at the three higher doses of permethrin. On the other hand, the proportion of time spent moving on the untreated side increased significantly with dose, suggesting a persistent effect of permethrin on this component of behaviour (Fig. 5). There was a significant increase in the time spent moving up to 150 mg/m*, followed by a decline at 200 mg/m*. This may be due to the neuronal receptors in the olfactory system becoming overloaded or saturated and hence the insects may have been unable to differentiate one side from the other. The adults, however, may detect permethrin by olfactory stimulation rather than by tarsal contact, as there were no differences between the occupation times on the treated and untreated surfaces at any dose applied. At 100 and 150 mg/m*, adults were stimulated to avoid the treated area, as there were considerably more attempted crossings from the untreated to the treated side of the arena and more crossings from the treated to the untreated side. The results of these tests confirm that A. verbasci larvae may detect and avoid contact with surfaces treated with permethrin. This behaviour, coupled with the tolerance of the larvae to residual insecticides (Morgan et al., 1993), will serve to decrease the effectiveness of control treatments. REFERENCES Blake G. M. (1958) Diapause and the regulation of development in Anthrenus verbasci (L.) (Co]., Dermestidae). Bulletin of Entomological Research 49, 751-175.
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of chemoreceptor organs of dermestids (Dermestidae,
