By Jawwad A. Qureshi
All citrus pests in Florida have natural enemies, although some are more effective at biological control than others.
University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) researchers have been studying the activity and impact of natural enemies on pest infestations in traditional open production systems and protected systems such as citrus under protective screen (CUPS) and individual protective covers (IPCs). In comparative studies between CUPS and open orchard control, they found low infestations of scales and mealybugs in CUPS and no infestations in the open orchard control. This suggests that biological control is still functional in open orchards. Despite higher temperature and humidity in CUPS than in a traditional open orchard, several parasitoids of scales, mealybugs and citrus leafminer, as well as small predators such as predatory mites, were able to colonize citrus in the CUPS. This is further evidence of biological control’s existence and contribution in integrated pest management (IPM).
For example, captures of parasitoid Aphytis melinus averaged as high as 102 per sticky card in CUPS, where Florida red scale (FRS) was observed, compared to a few observed in the cards installed in an open orchard, where FRS infestation was not observed. A. melinus parasitism on FRS averaged 19% to 23% in the CUPS.
Leptomastix dactylopii and Coccophagus lycimnia parasitoids of mealybugs and scales were also found in the CUPS, as well as several species of parasitoids of citrus leafminer, particularly Pnigalio minio and Ageniaspis citricola. The occurrence and functioning of parasitoids of several pests indicate that biological control continues to provide suppression of citrus pests in different environments.
The Asian citrus psyllid (ACP) continues to be the most significant threat to citrus crops. UF/IFAS researchers have previously reported huge reductions in ACP populations from a complex of predators that target ACP immatures. Recent studies following cohorts of ACP nymphs developing in commercial groves showed a reduction of 66% to 95% through adulthood in colonies that remained exposed to natural enemies.
Tamarixia radiata is a parasitoid of ACP nymphs that was introduced into Florida soon after its discovery from the native range of ACP. T. radiata populations in the field are consistently being augmented through release from a mass rearing program by the Florida Department of Agriculture and Consumer Services Division of Plant Industry. T. radiata is being released in commercial and urban environments. At some of the locations where the parasitoid was released, researchers observed 30% to 50% of the nymphal colonies of ACP with evidence of parasitism and parasitized nymphs averaging between 9% and 58%. Findings of the occurrence and impact of the natural enemies on various citrus pests attest to the role of biological control as a significant component of IPM.
Jawwad A. Qureshi is an associate professor at the UF/IFAS Southwest Florida Research and Education Center in Immokalee.
Share this Post