and Integrated Pest Management - part - usaid

162 I .ST.'IICIDE MANAGLMEN1FX AND IPM INSOU'IIIF.AST ASIA
Table 3. Mortality flactors affecting immature stagcs of flower weevil.,'
Mortality l'actors % mortality Killing power
(K-value) I b
l11pai loss file to low
soil moisture 44.5 0.568
l'redlation by
S. ge'minala 30.8 0.392
Variation in natality 21.8 0.278
Other fa'ctors 2.9 0.037
!'Dry season 1985, Pangasinan, Philippines, bK-value analysis (Varley et al.
1973).
TRAP CROPS Alternate host plants play an important role in the survival of
A. II ta dUring the cotton-frce scason. All known host plant species belong to
the tribes GossvpIieueand llibisceaeof the family Malvaceae. There are essential
dillfcrenccs between the alternate host plants and the cultivated cotton. The
comparati vcly thlin petals of cotton remain attached, allowing the weevil larvae
to subseqLUCntly bore into the young boll. In contrast, the fleshy petals of other
host plaits mostly shed within the same day or at least abscise, thereby
prevcntuing entry into the fruit.
Hibiscus esculentus L. (okra; "lady fingers") is occasionally cultivated near
cotton fields. Weevil adulls were observed to strongly prefer okra flowers over
cotton flowers. I lowever, the fruits of infested okra plants were never damaged
by weevil larvae, which remained in the shed petals. Most larvae in okra petals
will s1bsCtucntly (lie through dessicalion. Table 4 demonstrates the effect of /.
esculentus as a trap crop for A. laum along the borders of cotton clusters.
It is important to adjust planting dates for okra and cotton such that
flowering occurs at about the same time. Thus most of the first invading
Table 4. Floevr weevil infestation in II. esculenta (okra) vs cotton flowersa
Date %Y,flower infestalion Mean no. of weevils/l'ower b
Okra Cotton Okra (SE)c Cotton (SE)c
Fcb.
Mar.
Mar.
Mar.
Malr.
22
1
8
12
15
19
24
93
90
85
0
5
27
86
87
0.57
0.14
1.40
1.30
5.00
(0.31)
(0.08)
(0.34)
(0.33)
(0.63)
0.00
0.03
0.33
0.86
2.87
(0.03)
(0.16)
(0.26)
(0.52)
;okra planled as border row along cotton field, tbicans highly significant (alpha
=.000 I), t-test, Cstandard error.