Laboratory evaluations of the foraging success of Tamarixia radiata (Hymenoptera: Eulophidae) on flowers & extra-floral nectaries: Potential use of nectary plants for conservation biological control of Asian citrus psyllid

Authors: Patt, Joseph - Joe; ROHRIG, ERIC - Florida Department Of Agriculture And Consumer Services

Submitted to: Florida Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/21/2016
Publication Date: 3/15/2017
Citation: Patt, J.M., Rohrig, E. 2017. Laboratory evaluations of the foraging success of Tamarixia radiata (Hymenoptera: Eulophidae) on flowers & extra-floral nectaries: Potential use of nectary plants for conservation biological control of Asian citrus psyllid. Florida Entomologist. 100(1):149-156.

Interpretive Summary: The eulophid Tamarixia radiata (Waterson) (Hymenoptera: Eulophidae) is a specialist parasitoid of late instar nymphs of Asian citrus psyllid (Diaphorina citri (Kuwayama)) (Hemiptera: Liviidae), a vector of the causal agent of huanglongbing disease of citrus (Sapindales: Rutaceae). Tamarixia radiata is mass reared; however, parasitism levels following inundative releases have remained relatively low. One explanation for the low parasitism levels may be the lack of sugar resources available for adult wasps in targeted release landscapes, such as abandoned commercial citrus groves and residential areas. Establishing nectar plants can be an effective means of increasing nutritional resources in targeted sites for biocontrol agents. Certain eulophids forage effectively only on fully-exposed nectaries; i.e., those unobstructed by other floral parts. Therefore, care must be taken to select plants whose nectary architectures are compatible with chalcid morphology and foraging ability. A series of laboratory studies were undertaken as a first step to determine the potential for Tamarixia radiata (T. radiata) to obtain sugar from natural sources in target landscapes. Following contact with a sugar spot on filter paper, T. radiata engaged in stereotypical zigzagging movements, indicating arrestment and induction of localized searching behavior. Tamarixia radiata fed on sugars found in nectar (sucrose, glucose, fructose) and honeydew (melizitose, raffinose), indicating that it will feed well on both honeydew and nectar resources. At the highest concentration tested (1 M), it preferred sucrose and melizitose, but at lower concentrations it did not select among the sugars tested. Choice tests with wasps previously exposed to scented sucrose solution showed that they were stimulated and attracted by nectar odor and could learn to associate a particular odor with the presence of nectar. Observations conducted with starved wasps on freshly cut sprigs of nectar plants showed that T. radiata foraging success was highest on extrafloral nectaries and flowers with exposed nectaries. The wasps readily located the extra-floral nectaries on snap bean and cowpea and fed on them for the majority of the observation periods. Likewise, they quickly located the fully exposed nectaries in the inflorescences of euphorbiaceous plants, such as Poinsettia heterophylla ((L.) Klotzsch & Garcke) (Malphighiales: Euphorbiaceae). Tamarixia radiata foraging success declined in flowers with nectaries that were only partially exposed; its movements were deterred by floral parts or trichomes that obstructed the nectary. The wasp was unable to obtain nectar from composites and other plants with hidden nectaries. Following these straightforward laboratory evaluations, field studies can be concentrated on determining whether the addition of candidate nectary plants enhances T. radiata establishment, survival and parasitism levels within target landscapes.

Technical Abstract: Tamarixia radiata is natural enemy of the Asian citrus psyllid, the insect that transmits citrus greening disease. It is currently being mass reared for releases in Florida, Texas, and California for psyllid control. However, biological control of the psyllid following mass releases of Tamarixia radiata (T. radiata) have generally remained relatively low. One explanation for the low parasitism levels may be a lack of nutritional resources available for T. radiata at release sites. Studies have shown that establishing nectar plants can be an effective means of increasing nutritional resources for biocontrol agents. We present research results that suggest certain types of flowers might be grown at release sites to enhance the effectiveness of T. radiata.