here. - Ministry of Forests, Lands and Natural Resource Operations

Abbott’s corrected mortality compares the mortality caused by the B.t.k. (percent mortality) to the natural mortality
observed in untreated control areas (Table 7).
Percent mortality and Abbott’s corrected mortality are calculated as follows:
% Mortality = (pre-spray density of live insects) - (post-spray density of live insects) x 100
(pre-spray density of live insects)
Abbott’s corrected mortality (%) = (treated % mortality) - (untreated % mortality) x 100
100 - (untreated % mortality)
This calculation ranged from 37% at the 1 st post-spray assessment in the Sheep Creek area to over 88% in the
Duffy Lake area. Both the Sackum and Pimainus areas had very high budworm numbers at the time of spray but
by the 2 nd post-spray assessment, Sackum had 84% larval mortality and Pimainus had over 98% larval mortality
(Table 7). Populations in the Tolman spray block decreased so drastically after spray compared to the control that
no 2 nd post-spray sample was taken (Figure 3). The majority of larvae were 3 rd instar with a good complement of
4 th instar on the Tolman spray block when treated. The lower elevation control site had an equal distribution of 3 rd ,
4 th and 5 th instars (Figure 5). The graph in Figure 5 clearly shows the development shift in the Tolman control site
to predominantly 4 th instar and 5 th instar larvae by the 1 st post-spray assessment coupled with the drastic population
decline in the spray block. Due to the extended cool, wet weather in May through June 2012 larval development
was slow but the very high larval numbers caused significant feeding damage to buds and new foliage before the
majority of the population reached 4 th instar. At the pre-spray sampling time 81% of insects sprayed were 3 rd or
4 th instars with over 50% still 3 rd instar (Figure 6). By mid-July when the 2 nd post-spray sample was conducted
in most locations approximately 64% of budworm were 5 th or 6 th instars (Figure 6). If spraying had been delayed
to allow for the insects to develop further (typically peak 4 th instar larvae are targeted) then the defoliation in
blocks would have been unacceptable.
Clockwise from above:
Snakeflies (Raphidiidae), coneworms (Dioryctria
pseudotsugella), and sawflies (Neodiprion) are commonly
encountered when conducting larval sampling.
Ministry of Forests, Lands and Natural Resource Operations, Kamloops, B.C.
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