Héctor González-Hernández

Selection of a fungal isolate for the control of the pink hibiscus mealybug Maconellicoccus hirsutus

BACKGROUNDnMaconellicoccus hirsutus Green is a widely distributed pest of numerous crops. Although synthetic pesticides are used to control this pest, entomopathogenic fungi may provide an alternative control mechanism. Three experiments were carried out to select a fungal isolate with the potential to be used as a microbial control agent. The in vitro growth of five isolates of Beauveria bassiana sensu lato (Bals.) Vuill and Metarhizium anisopliae sensu lato (Metschn.) Sorokín, along with three isolates of Lecanicillium lecanii (Zimm.) Zare & W. Gams and Isaria fumosoroseus (Wize), was assessed at four temperatures. The in vivo sporulation of eight selected isolates was then evaluated, followed by the susceptibility of third-instar M. hirsutus to a single dose (1 × 10(8) conidia mL(-1) ) of each of these isolates.nnnRESULTSnGrowth was greatest by isolates of I. fumosoroseus and L. lecanii at 15 and 20 °C and by isolates of M. anisopliae at 25 and 30 °C. In vivo conidium production was greatest when infected with B. bassiana isolate GHA and M. anisopliae isolate Ma65. Mortality was greatest when inoculated with M. anisopliae isolates Ma65 and Ma129.nnnCONCLUSIONnIsolate Ma65 shows the best potential to be developed as a microbial control agent for M. hirsutus.

Susceptibility of Diaphorina citri (Hemiptera: Liviidae) and Its Parasitoid Tamarixia radiata (Hymenoptera: Eulophidae) to Entomopathogenic Fungi under Laboratory Conditions

Diaphorina citri (Kuwayama) is a global pest of citrus that transmits the bacteria associated with the disease, Huanglongbing. Entomopathogenic fungi and the parasitoid Tamarixia radiata (Waterston) are important biological control agents of this pest and likely to interact in D. citri populations. As a basis for interaction studies, we determined the susceptibility of nymphs and adults of D. citri and adults of the parasitoid T. radiata to six fungal isolates from the species Beauveria bassiana s.l. (Bals.-Criv.) Vuill. (isolates B1 and B3), Metarhizium anisopliae s.s. (Metsch.) (Ma129 and Ma65) and Isaria fumosorosea Wize (I2 and Pae). We conducted experiments evaluating infection levels in all three insect groups following inoculation with a series of conidial concentrations (1xa0×xa0104–1xa0×xa0108 conidia mL−1). Results showed that D. citri nymphs and T. radiata were more susceptible to fungal isolates than D. citri adults. Overall, B. bassiana and M. anisopliae isolates caused the greatest infection compared with I. fumosorosea isolates in all three groups of insects. Isolates B1 (B. bassiana) and Ma129 (M. anisopliae) infected a greater proportion of adults and nymphs of D. citri, respectively. Both isolates of B. bassiana caused greater infection in T. radiata compared with isolates of the other fungal species. We propose that isolates B1 and Ma129 are the strongest candidates for control of D. citri. Our results represent the first report of entomopathogenic fungi infecting T. radiata, and the basis for future studies to design a biological control programme that uses both agents more efficiently against D. citri populations.

Susceptibility of nymphs and adults of Diaphorina citri to the entomophathogenic fungus Hirsutella citriformis

ABSTRACT The susceptibility of nymphs and adults of Diaphorina citri to infection by Hirsutella citriformis was evaluated. We also studied the ability of adult D. citri that had been contaminated with fungal conidia to transmit infection to nymphs. Diaphorina citri nymphs were more susceptible than adults. Adults were not able to transmit conidia to nymphs and cause infection.

Interactions between entomopathogenic fungi and Tamarixia radiata (Hymenoptera: Eulophidae) in Diaphorina citri (Hemiptera: Liviidae) populations under laboratory conditions

Biological control of Diaphorina citri (Kuwayama) using the parasitoid Tamarixia radiataxa0(Waterston) or entomopathogenic fungi has been attempted, but there have been few published studies on their potential interactions when used together. We studied the effect of prior residency time on the outcomes of interactions betweenxa0T. radiataxa0and the fungal pathogensxa0Beauveria bassianaxa0and Metarhizium anisopliae in D. citri nymphs. In the first experiment, nymphs infected with fungi were exposed to the parasitoid after 0, 24 and 72xa0h. Next, nymphs with parasitoids at different developmental stages (eggs, larvae or pupae) were exposed to fungal inoculation. The greatest proportion of fungus-infected nymphs occurred when they were inoculated 72xa0h prior to parasitoid exposure. The lowest parasitism rate occurred inxa0nymphs that had been infected by fungi 72xa0h prior to parasitoid exposure. The number ofxa0nymphs used for host-feeding by the parasitoid was similar, regardless of how advanced the fungal infection was. When fungal inoculations were made toxa0parasitized nymphs with different developmental stages of the parasitoid, the greatest proportion becoming infected occurred in nymphs with parasitoid eggs. The overall longevity of adult parasitoids emerging from control and fungal-infected treatments was similar; however, the longevity of adult parasitoids emerging from nymphs which had been inoculated with parasitoid larvae were lowest, with the greatest effect observed for the M. anisopliae isolate. The ecological importance and practical recommendations derived from our results are discussed.