ABSTRACT
Entomopathogenic fungi have been considered potential biological control agents against the fall armyworm Spodoptera frugiperda (J. E. Smith), the world's most important pest of maize. In this study, we evaluated the natural infection, molecular characteristics, and biological activity of Metarhizium rileyi (Farlow) isolated from S. frugiperda larvae of this insect, collected from maize crops in five Mexican locations. Natural infection ranged from 23% to 90% across all locations analyzed. Twenty-four isolates were evaluated on S. frugiperda second instars at a concentration of 1.0 × 108 conidia/mL, causing 70% to 98.7% mortality and 60.5% to 98.7% sporulation. Isolates T9-21, Z30-21, PP48-21, and L8-22 were selected to determine their phylogenetic relationships by ß-tubulin gene analysis and to compare median lethal concentration (CL50), median lethal time (LT50), and larval survival. These isolates were grouped into three clades. The T9-21, PP48-21, and J10-22 isolates were closely related (clade A), but phylogenetically distant from Z30-21 (clade B) and L8-22 (clade C) isolates. These genetic differences were not always reflected in their pathogenicity characteristics since no differences were observed among the LC50 values. Furthermore, isolates T9-21, J10-22, and L8-22 were the fastest to kill S. frugiperda larvae, causing lower survival rates. We conclude that native M. rileyi isolates represent an important alternative for the biocontrol of S. frugiperda.
ABSTRACT
Larvae of an unidentified Lepidopteran hepialid were found boring stems and crown roots of blackberry (Rubus sp.) in Michoacán, Mexico. In this study, the morphological and molecular identification of larvae and adults of this insect was performed. Preliminary aspects of biology, including information on parasitoids associated to larval stage, are also recorded. A total of 109 larvae of various instars were collected and three were reared to adult. The two females and one male were identified as Phassus huebneri (Geyer) (Lepidoptera: Hepialidae) following morphological characters. This identification was corroborated by comparing the cytochrome oxidase I (COI) barcode of two field-collected larvae (IIAFL1 and IIAFL2) with sequences of Phassus spp. obtained from GenBank. A Neighbor-Joining similarity analysis yielded a phenogram with two subclades. The first subclade grouped the IIAFL1 and IIAFL2 sequences with two other Mexican sequences categorized as P. huebneri, whereas in the second subclade other species belonging to the genus Phassus from Guatemala and Costa Rica were grouped together. Larval development of nine instars took about 14 months. Larvae reached a maximum length of 10 cm. The pupal stage lasted 39-41 days. Each of the two females laid over 1,000 unfertilized eggs within a period of 48 h. Larvae were parasitized by Dinera grisescens Fallen (Diptera: Tachinidae) and another unidentified Dinera sp. This study provides additional evidences on the distribution pattern of P. huebneri in western Mexico and presents the first record of this species feeding on one of the most economically important crops in Mexico.
