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ABSTRACT
The present work aimed to study the bee species which visit flowers of cotton (Gossypium
hirsutum), cultivar 187 8H, their respective pollination efficiencies in relation to crop
pollination requirements, as well as their implications in cotton ball production, quality of
fiber and seeds produced. Data were collected from May to August 2006 in commercial
cropping areas in the counties of Quixeramobim and Quixeré, state of Ceará, Brazil. The
area in Quixeramobim was small (10,000 m
2
), fertilized, close to native vegetation and
used controlled insecticide applications, while the area in Quixeré was large (240,000 m
2
),
non-fertilized, surrounded by other crop areas and submitted to systemic use of insecticide
at every eight days. The research was split into four investigations: 1 – diversity and
abundance of floral visitors to cotton flowers; 2 – foraging behavior of floral vistors to
cotton flowers; 3 - floral biology, pollination requirements of cotton flowers, and
pollination efficiency of Apis mellifera, and 4 – effect of Apis mellifera pollination in the
physiological quality of cotton fiber and seeds. Floral visitors were observed, counted and
captured by means of zig-zag walkings between the cropping lines. Experiments included
bagging floral buds and hand pollination to evaluate cotton flowers’ pollination
requirements and Apis mellifera pollination efficiency. Seed germination tests were carried
out in the Seed Laboratory of the Universidade Federal do Ceará and fiber quality was
evaluated in EMBRAPA Algodão, Campina Grande-PB. The experimental design was
entirely randomized and the crossed factorial Place x Treatment (2x5). Data were analised
using Anova F test submitted to variance analysis and compared a posteriori by the Tukey
test or by means of General Linear Models, depending on the nature of data. The following
insect species were collected visiting flowers in the experimental sites: Apis mellifera,
Brachygastra lecheguana, Polybia ignobilis, Ancyloscelis sp. 1, Ancyloscelis sp. 2,
Melissoptila uncicornis, Psaenythia sp. and Anthrenoides sp., the last three species being
new occurrences in the state of Ceará. Floral visitors, resources gathered and foraging
behavior were similar in both areas. Regarding floral biology, anthesis initiated early in the
morning, from 6:00 h onwards, and all flowers were open by 7:00h. Stigmas were
receptive from 6:00h to 13:00h, and pollen showed the greatest germinability (75%) after
10 hours of incubation. There were no significant differences (P>0.05) in fruit production
among treatments in Quixeramobim and Quixeré. However, significant differences
(P<0.05) were found among treatments within and/or between localities in variables such
as cotton ball weight, seed weight, fiber weight, and number of seeds per fruit. In general,
Quixeré showed lower means than Quixeramobim to all variables investigated. It was
concluded that floral visitors’ frequency to cotton flowers was low in Quixeré and
Quixeramobim, A. mellifera showed the greatest potential to act as biotic pollinator of
cotton flowers due to its large numbers in the areas, but Melissoptila uncicornis
Ancyloscelis sp. 1 and Ancyloscelis sp. 2 could become important native pollinators in
conditions more favorable to their presence, such as reduced use of insecticides, smaller
crop fields, less soil revolving, and more proximity to native vegetation. The cotton plant is
a species with an intermediate pollination system, being able of autopollination, however it
needs biotic agents and good nutritional conditions to maximize pollination. It was also
possible to conclude that natural pollination levels occurring in the areas studied were not
sufficient to maximize production and that plants in Quixeré were not in the best
nutritional conditions, in opposition to what was observed in Quixeramobim. It was also
concluded that A. mellifera bees could be relevant to cotton pollination since they
increased the percentage of emergence and the index of plantule emergence velocity in
cotton seeds. The intrinsic fiber characteristics were not affected by pollination.
Key-words: pollination efficiency, cotton production, crop pollination requirements.