The Biocontrol Agent Pyemotes zhonghuajia Has the Highest Lethal Weight Ratio Compared with Its Prey and the Most Dramatic Body Weight Change during Pregnancy

SIMPLE SUMMARY: To explore the biocontrol potential of Pyemotes zhonghuajia, we studied the paralytic process, time to lethality, efficiency, reproductive development, and the ability to search for Spodoptera litura larvae. We found that one newly emerging P. zhonghuajia female could kill a third instar larva greater than 680,000 times her own body weight. An individual P. zhonghuajia adult female was able to kill S. litura eggs and first to third instar larvae. Pyemotes zhonghuajia could develop on eggs, first to sixth instar larvae, and pupae, but only produced offspring on the eggs and pupae. The presence of 50 or 100 P. zhonghuajia resulted in significantly higher mortality rates of first, second, and third instar S. litura larvae in a 2 cm searching range compared with other searching ranges (4.5 and 7.5 cm). Therefore, P. zhonghuajia could potentially be used to control S. litura. ABSTRACT: Pyemotes spp. are small, toxic, ectoparasitic mites that suppress Coleoptera, Hemiptera, and Lepidoptera plant pests. To explore their potential use as a biocontrol agent, we studied the reproductive development, paralytic process, time to lethality and mortality, and searching ability of Pyemotes zhonghuajia on different developmental stages of the oriental leafworm moth, Spodoptera litura. Pyemotes zhonghuajia gained 14,826 times its body weight during pregnancy. One single P. zhonghuajia female could rapidly kill one S. litura egg and first to third instar larvae, but not fourth to sixth instar larvae, prepupae, or pupae within 720 min. Pyemotes zhonghuajia could develop on eggs, first to sixth larvae, and pupae, but only produced offspring on the eggs and pupae. A single P. zhonghuajia female (an average weight of 23.81 ng) could paralyze and kill one S. litura third instar larvae (an average weight of 16.29 mg)—680,000 times its own weight. Mites significantly affected the hatch rate of S. litura eggs, which reduced with increasing mite densities on S. litura eggs. Releasing 50 or 100 P. zhonghuajia in a 2 cm searching range resulted in significantly higher mortality rates of S. litura first instar larvae within 48 h compared to second and third instar larvae in searching ranges of 4.5 and 7.5 cm within 24 h. To the best of our knowledge, this is the first study to reveal that P. zhonghuajia undergoes the greatest changes in weight during pregnancy of any adult female animal and has the highest lethal weight ratio of any biocontrol agent.