Insecticide tolerance of pregnant females of Glossina palpalis palpalis (Robineau-Desvoidy) (Diptera: Glossinidae)

Abstract

AbstractFemales of Glossina palpalis palpalis (Robineau-Desvoidy) caught in Nigeria were treated topically with acetone or different doses of insecticides. None was fed after treatment. Flies later larvipositing were considered to have been pregnant and those neither aborting nor larvipositing as nonpregnant. Pregnant flies were 1·3 times as heavy as non-pregnant ones. Relative tolerances were assessed by comparing LD50s. For organochlorines (DDT, dieldrin and endosulfan), pregnant females were 2·5—4 times as tolerant as non-pregnant ones, doubtless due to diversion of insecticideinto lipid-rich larval food during late pregnancy. Data for pregnant flies did not indicate any increased tolerance of organophosphates (malathion, fenitrothion, tetrachlorvinphos and pirimiphos-methyl), possibly due to the low lipid solubility of these insecticides.Pregnant and non-pregnant females were equally tolerant of the pyrethroid Sumithrin ((lR)-cis-trans-isomer of phenothrin); accelerated larviposition prevented diversion of insecticide into in utero larvae. Pregnant females were 2·6 times as tolerant of tetramethrin (pyrethroid) as non-pregnant ones. Twenty-five per cent, of flies treated with acetone or low insecticide-doses larviposited, but the results indicated that larviposition was inhibited by high doses of most insecticides, which killed before larviposition, and, noticeably, by intermediate doses of some pyrethroids (fenvalerate, permethrin and deltamethrin), probably causing prolonged paralysis of uterine and larval muscles. The results did not indicate there was raised tolerance of fenvalerate, permethrin or deltamethrin among pregnant females, but calculations including assumed pregnant ones (unrecognized due to inhibited larvipositions) suggested that pregnant females were 2·5–5·5 times as tolerantas non-pregnant ones. Other investigations showed that flies surviving for several days after treatment with pyrethroids can feed and thrive; if this allows time for the reversalof delayed larviposition, then pregnant females could be significantly more tolerant of some pyrethroids than non-pregnant ones.