Effects of habitat complexity and fertilization on arthropod community structure in cotton field

The effects of habitat complexity and fertilization mode on arthropod community structure in cotton fields were investigated to guide ecological control of insect pests. The study included treatments of different combinations of habitat and fertilization. In the experiment, no straw mulch (A₁) and straw mulch (A₂) were designed as simple- and complex-structure habitats, respectively. Compound fertilizer 90 kg(N)·hm^-2 (B₁), compound fertilizer 90 kg(N)·hm^-2 with biogas fertilizer 90 kg(N)·hm^-2 (B₂) and compound fertilizer 90 kg(N)·hm^-2 with urea 90 kg(N)·hm^-2 (B₃) were designed as fertilization modes. Ten cotton plants were sampled in each plot in the parallel jumping method. The species and individual number of arthropods in each plant and the 0.25 m² land surface beneath the plant were counted and recorded on a weekly basis. The results showed that the individual number of spiders (counted as individuals for every 10 plants) was higher in A₂ (391.1±70.1) than in A₁ (226.8±29.3). Also the dominant enemy species Pardosa astrigera (also counted as individuals for every 10 plants) was higher in A₂ (171.7±13.3) than in A₁ (59.3±9.8). Then the dominant index for spiders was higher in A₂ (0.527±0.089) than in A₁ (0.258±0.049). The diversity index of insect pests was higher in A₂ (1.459±0.067) than in A₁ (1.245±0.249). The evenness index of insect pests was also higher in A₂ (0.635±0.040) than in A₁ (0.588±0.100). The individual number of insect pests was significantly higher in A₂ (772.4±206.9) than in A₁ (1 156.4±243.7). Based on the number of individuals per 10 plants, the target insect pest Syleptahn derogata number in A₂ and A₁ were respectively 320.8±80.6 and 659.5±254.8. The dominant insect pest index in A₂ was 0.311±0.029 while that in A₁ was 0.400±0.107. Also the diversity index of spiders in A₂ was 0.997±0.169 while it was 1.584±0.138 in A₁. The evenness indexes of spiders in A₂ and A₁ were 0.536±0.073 and 0.803±0.052, respectively. Also based on individual number per 10 plants, the insect pests numbers in B₁, B₂ and B₃ were respectively 1 015.3±344.1, 714.0±152.2 and 1 164.0±168.9. Those of the target insect pest S. derogata in B₁, B₂ and B₃ were respectively 552.0±253.8, 280.6±63.7 and 638.0±256.0. The indexes of the dominant insect pests were 0.370±0.055 in B₁, 0.282±0.022 in B₂ and 0.414±0.111 in B₃. Then the diversity indexes of the insect pests in B₁, B₂ and B₃ were respectively 1.324±0.228, 1.511±0.066 and 1.222±0.200. Also the diversity indexes of spiders in B₁, B₂ and B₃ were respectively 1.167±0.374, 1.418±0.373 and 1.286±0.262. Then the evenness indexes of the insect pests were 0.600±0.039 in B₁, 0.683±0.043 in B₂ and 0.550±0.081 in B₃. The indexes of the dominant spiders in B₁, B₂ and B₃ were 0.457±0.175, 0.353±0.167 and 0.368±0.123, respectively. The corresponding evenness indexes of the spiders were 0.613±0.160, 0.701±0.130 and 0.695±0.168, respectively. Then the diversity indexes of predatory insects in B₁, B₂ and B₃ were 1.190±0.153, 1.496±0.179 and 1.474±0.125, respectively. The individual numbers of insect pests, the target insect pest S. derogate, the indexes of the dominant insect pests, the diversity indexes of insect pests, and the evenness indexes of the insect pests were significantly influenced by the interaction between habitat complexity and fertilization mode. The species number of spiders was also significantly influenced by the interaction between habitat complexity and fertilization mode. Habitats of the dominant species enemy P. astrigera improved under straw mulching in cotton fields. This significantly enhanced the ability of P. astrigera to control S. derogate. Population growth of S. derogate did not enhanced by compound and biogas fertilizers.