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Experiments on timing the oral treatment of calves for cattle grub control with Trolene at 100 mg./kg. were carried out on ranches near Lethbridge, Alberta, and Kamloops, British Columbia. Groups of 30 and 25 calves, respectively, were treated in November, January, March, and April at Lethbridge and in December, January, February, and March at Kamloops.Control of the pre-hypodermal grubs was equally effective on the first three treatment dates, varying from 94 to 98 per cent mortality. However, variations in the numbers of grubs precluded stating the mortality more precisely than within a range of 95 to 100 per cent at Lethbridge and 89 to 100 at Kamloops.There was no significant difference in mortality between the two species of cattle grubs. However, the third hypodermal instar larvae of both species were less affected by the treatment (P <.01) than those of the preceding instars. Early autumn treatments are recommended to avoid the presence of third-instar larvae and to forestall early damage caused by the hypodermal grubs.Slight symptoms of toxicity, in the form of lethargy and reduced food consumption at Kamloops and ataxia of the hindquarters at Lethbridge, were observed in the calves treated in December and January, respectively. The symptoms disappeared within 48 hours of treatment without the use of antidotes at either locality. The level of treatment used in this study was lower than that reported in the literature to produce first symptoms of toxicity.

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The efiect on infestation by cattle gtubs Hypodenng spegiq of .six annual ."il"-i" i*".ticid"-ueatme-tits -m rridi"d in i-range he-ril isolated by at.least tb miles from locations where adiacent herds could have dro,ppe-d pupae. llrter t*o-tri.i-""tt tn" i"f".t"iion *li redrrced from 30.2 to-1.6 giubs per untreated calf. remaining at approximately this low level until after the fitth ffeeunent ;hilild;;r;rr"a i'.iO.i grubs'per untreated calf. After the sixth treatment ;i.;l"f;t.;;i"" p.ttitt"a;;i-z-!iout per untreated -c{f, arld', in the absence of insecticide .r""*"ni-ii trc iln-V"*, increased to 1O.2 grubs per untreated calf in-the sth v""t. S"-tn"i'fly'disiurbance-had -beeri-a long-standing herd manasement problem, but did not recur after the first systemrc lnsecncloe itJr,"i"'tii.-'uliJ-"tirg"tit"Jreiiiictea sampljng to-calves..Failure to eliminare Erubs *". "ttri6oftd to either high surviva-l of grubs in the unsampled maftr; animals, or to migration of female Hypoderm.a into the sp'ng rangei.These results piovide little basis for optimism concerning pJorects rn orgailze{ areas for control of grubs with single annual applicaflons ot cufrenuy availaDle systemic insecticides.