EFFECTS OF SELECTED PESTICIDES ON WEB-BUILDING BEHAVIOR OF LARINIOIDES-SCLOPETARIUS (CLERCK) (ARANEAE, ARANEIDAE)

Sublethal effects of four pesticides (Pirimor(R), active ingredient [a .i.] pirimicarb; Decis(R), a.i. deltamethrin; Alaxon(R) D, a.i. diazin on; Kelthane(R) EC, a. i. dicofol) on the web building behaviour of th e common gray cross spider Larinioides sclopetarius (Clerck) were inve stigated with the spider test of WITT and PETERS. Pirimicarb applied i n a dose of 0.64 mug/mg (corresponding to the application of 1.28 mug/ mg Pirimor(R)) caused neither mortality nor aberrations in web geometr y. Alaxon(R) D led in a dose of 5.10(-4) mul/mg to a mortality rate of 17.6%. Web building activity was,only slightly affected. The webs the mselves showed some changes. The area of the webs was reduced to 62% o f the original size. The regularity of the catching spiral and the med ian angles of the radii were also affected but in a lesser degree. Dec is(R) applied in a low dose of 5.10(-5) mul/mg caused 10% mortality. W eb building activity was affected (average delay in web building was 2 .32 days). The area of the webs was reduced to 72%, the number of radi i was reduced by 17%, the median angle of the radii was enlarged by 21 % and the regularity of the angles was reduced by 36%. Kelthane(R) EC, in a high dose of 9.6.10(-3) mul/mg, resulted in 10% mortality. No ne gative influence on web building activity was recorded. The webs thems elves were hardly affected: only the number of radii was reduced by 5% . The efficiency of the various pesticides can be ranked as follows: D ecis(R) (deltamethrin) >> Alaxon(R) D (diazinon) > Kelthane(R) EC (dic ofol) greater-than-or-equal-to Pirimor(R) (pirimicarb). Substance spec ific differences of the effects are discussed.