Cotton pollen and honey sustain the adult Hippodamia variegata (Goeze) population during periods of prey scarcity

Abstract

In the cotton fields of Xinjiang province, China, the cotton aphid, Aphis gossypii Golver, is a significant pest, while Hippodamia variegata (Goeze) is its primary natural enemy. Both species are present during the cotton seedling and budding stages, but as the flowering and boll-formation stage progresses, the aphid population rapidly declines, whereas the adult population of H. variegata often remains high for an extended period. To understand this phenomenon, we investigated the effects of feeding newly emerged H. variegata adults with cotton pollen and honey on their survival rate, lifespan, and reproductive capacity. The study found that pollen consumption in H. variegata adults varied significantly with age and sex, with females generally consuming more pollen than males, particularly at 10, 15, and 20 days of age. The aphid-fed group exhibited the longest lifespan (female 56.0 ± 1.8 d, male 60.1 ± 2.7 d), significantly surpassing those fed with cotton honey, collected from bees, (female 36.1 ± 2.2 d, male 31.7 ± 0.9 d) and pollen (female 12.2 ± 0.4 d, male 9.7 ± 0.8 d). While predation on aphids allowed H. variegata to produce 646.1 ± 14.6 eggs over a 30-d period (starting from the first oviposition), none of the adults fed with cotton pollen or honey laid eggs. Therefore, cotton pollen and honey play a positive role in maintaining the adult population of H. variegata in the field when aphids are absent but cannot support reproduction. Nevertheless, this maintenance effect benefits conservation biological control in cotton fields and effectively controls thrips and other pests at subsequent cotton growing stages.