Buddenbrock claim s (Buddenbrock end Moller-Hacke 1952b; 1954) th at the w eevil Calandra pranaria (L, ) only responds to rnovoments over the eye from roar to fro n t and not frcxn fron t to rear. As he co rrectly p oin ts o u t, th is woul so lv e the problem for tliis p a rticu la r in s e c t. I t does not require to d iffe r e n tia te between su b ject movement (wiiich i s always fro n t to r«ar except when the animal walks backwards or turns) and o b ject movement sin ce i t ju s t does not r spond, (See a lso Aeschna nyii^>hs.
Tonner 1938). However, i t has already been shown (p .9 P ) th a t lo c u st nymphs do respond to str ip e s moving from fron t to rear of the eye, so th at in th is case the in s e c t i s faced with the problem. The follow in g experiment was an atteiip t to show th a t lo cu st nymphs could d iffe r e n tia te between t l» two situ a tio n s.
P r in c ip le .
The general p rin cip le o f experim ents r e la tin g to the above problem i s to provide two situ a tio n s in one of which the surroundings are moving and the animal sta tio n a r y , w hile in the other t i» animal i s m.^ving and the surroundings are stationar^r. I t i s a prime r e q u isite o f tn is type o f experim ent th a t the two situ a tio n s be exact op p o sites o f one another. I t i s then noted whether or not the animal behaves in the same way in both
situ a tio n s .
I t i s f e l t th a t, in the (r e se n t experim ent, the above con d ition s have Seen f u l f i ll e d to perhaps a greater ex ten t than in previous experi ments o f th a t type. Use was made of the fa c t th at nynqphs of S ciiisto cerca
lO . Bo« G loss a F ig . 24. of locust nymphs a - Side elevation of apparatus used to t e s t the a b ility X to d iffe re n tia te "subject" and "object" movement,
b - End elevation showing two p o sitio n s from which in se cts could be observed.
109.
show the fr ig h t response (p . 9 ^ ) when an ob ject or a shadow passes over them.
Apparatus. This i s shown in . I t simply C onsisted o f a square boix of sid e 14 in s . and h eigh t 18 in s . s it t in g on a wooden sled g e.
The box was illu m in ated by a 25 w att bulb 21 inches d ir e c tly overhead surrounded by a black shar o so th a t the w alls of t^ie box were s lig h t ly le s s illum inated than the flo o r . This arran^ ement stopped the animals from making repeated atten ^ ts to jump onto the w all and climb up to the lig h t . The sle d g e , box and lamp, formed one complete unit which could be moved very smoothly as shown in the diagram, the sledge slid in g over a g la ss su rface. There was a sta tio n a ry , narrow, wooden runway surrounded by a transparent c e llu lo s e tube (2 1 /2 in s . d ia. ) which was fasten ed to i t . This tube had an open end a t (A) and an opaque closed end at (B ),
The b je c t was a p iece of black cardboard 3 in s . broad and running from one sid e of the box to the other at r ig h t angles over the runway on which i t c a st a shadow. This ob ject was fastened to the box so as to move witli i t . A sm all s l i t , cu t in the sid e of the box under the o b ject
allowed the in s e c t to be observed even vhen under th e o b ject. F ig,24b nhows the 2 portions from which observation c^Aild be made.
Experimental c o n d itio n s.
(1 ) Apparatus station ary; animal walking.
In th is case the animal was pieced on the runway near (A) and allow ed to walk in to the box and r ig h t along the runway to the other end, passing under and through th e shadow. I t was found th a t an animal u su a lly stop s
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At le a s t once during th is Journey. The apparatus was com pletely sta tio n a ry .
(2) Apparatus moving; animal sta tio n a ry .
The animal was again introduced a t (A) and allowed to walk in to the box. Whenever th e in s e c t stopped tem porarily (a s in the previous s i t uation ) the complete u n it o f the sled ge e t c . , was p u lled in the d ir ec tio n shown by the large arrow in the fig u r e . In th is way the whole o f the
envircmment was made to pass a sta tio n a ry animal and the o b ject (0 ) to pass over i t . The runway e t c , , r-mained sta tion ary.
Speed. The speed at which the in se c t made th e journey in the f i r s t situ a tio n waa measured with the aid o f a stop-watch and in the second s i t uation the apparatus was moved a t i^>praximately t h is speed. The speed was u su a lly in the region o f 1 inch per second.
Animals. The animals used were 5th in sta r nymphs which were w e ll fed beforehand. Each was te s te d sev era l tim es in both s itu a tio n s . To ob viate tiie in flu en ce o f increased excitem ent as the t e s t progressed the order o f presenting the situ a tio n s was varied.
Behaviour.
(1 ) Apparatus sta tio n a ry . In alm ost a l l cases (46 out o f 52) the in s e c ts walked str a ig h t along the runway to the end, passing under the
shadow and out again without turning back. In one case the in s e c t
stopped co n y letely fo r a long period when under the shadow and in the other fiv e cases the in s e c ts turned a sid e and climbed on the w all o f the tube.
H i .
e ith e r wtien a t the f i r s t edge of the shadow (B ^), when under the shadow, or when a t the second edge (B g). The in s e c ts usually paused whenever thiey entered the lig h ted box bu t, apart from t h i s , sev era l (15 out of 52) paused when they reached the f i r s t edge of the shadow. Pausing was a lso seen in some cases (19 out o f 52) when the second ed^_e was reacued. Few animals a ctu a lly paused underneath the shadow.
Antennae waving or dipping was occa sio n a lly seen in response to the f i r s t shadow edge (15 out o f 52) but was ra rely seen under the shadow or a t th^ second edge. Some In se c ts waved th e ir antennae for the whole len gth o f the runway.
No jerkin g or backing was evexr seen in response to tlie o b ject or shadow or indeed a t a y time during these runs.
(2 ) Apparatus moving. In sharp con trast to the behaviour described above in more than h a lf the cases (37 out o f 62) where the surroundings
and the o b ject were moved p a st a station ary animal a fr ig h t response was observed. This was e ith e r a s lig h t jerk , a v io le n t jerk back, or, in a very few c a ses, a walking backwards. In four ca ses tlie In se c ts, a fte r jerkin g and backing, turned round as the o b ject moved over thwa. The fr ig h t response u su a lly occurred wh«n the f i r s t shadow edge reached the in s e c t but in a few cases there were a lso jerk s v iiile y e t tlie o b ject was at seme distan ce from the in s e c t, e .g . a t one or two in ch es. In eleven cases the in s e c ts sa t m otionless w hile the o b ject passed over. In y et another case the in s e c t, wliich was s it t in g s t i l l , merely tw itched i t s antennae s lig h t ly as the edge approached. In two cases the in s e c ts
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tr ie d to clim b on the w all o f the tube. F in a lly in eleven caeee the in s e c ts were walking when the o b ject passed over them, in some cases having ju s t sta rted to walk forward when the o b ject was clo se to them. Only one walking in s e c t, moving very slow ly showed a fr ig h t response.
R esu lts. The r e s u lts o f the experiment are presented num erically in Table. 38.
Control.
The cxily fa c to r s wtiich could perhaps have given r is e to the fr ig h t response, apart from the obvious v is u a l fa c to r , was ground v ib r a tio n . Aqy in flu en ce o f a ir v ib ra tio n had been prevented by the c e llu lo s e tube surrounding the runway. I t was p o ssib le , however, th a t although the apparatus apparently moved very smoothly there might be some v ib ra tio n o f the bench on which i t was r e s tin g . The co n tro l experiment was to evaluate th is p o s s ib ilit y .
Apparatus. In t h is case a sh ort runway with a c e llu lo s e tube was fastened to the flo o r o f the box so that the c o n siste appaz*atus moved as one u n it. Box, In sect and shadow are a l l moved togeth er.
Technique. The in s e c t was placed on the runway and allowed to en ter the box. T^henever i t had paused the apparatus was moved smoothly as in the previous e^ erim en t a t a speed of approximately 1 inch per second.
Behaviour. No fr ig h t responses were observed (ou t of a p o ssib le 2 0 ). In e ig h t cases the in s e c ts sa t p e r fe c tly s t i l l the whole tim e and in two of th ese (both d iffe r e n t animals) they sta rted to walk wh«i
U 3 .
len gth o f the runway, pause# and antennae movements being o cca sio n a lly seen . (C f. th e t e s t with the sta tio n a ry apparatus). In a fu rther two ca ses the in s e c ts f i r s t walked and then paused underneath the shadow and were s t i l l there when the apparatus stopped.
C onclusion. I t i s clea r tiierefo re th at, whatever other e ff e c t s
ground v ib ra tio n may have had on the behaviour of the nynqph , i t s presence