Lethal, transmission, behavioral, and physiological effects of Metarhizium anisopliae against gregarious larvae of Heortia vitessoides and synergistic effects between Metarhizium anisopliae and insecticides.

BACKGROUND: Heortia vitessoides Moore is a severe pest of Aquilaria sinensis (Lour.) Gilg, an important source of agarwood. In recent years, large amounts of chemical insecticides have been applied in A. sinensis plantations to deal with the outbreak of H. vitessoides, causing residue problems that reduce the quality and price of agarwood. Herein, we hypothesize that the widely applied biocontrol agent, Metarhizium anisopliae (Metschn.) Sorokin, can effectively kill the gregarious larvae of H. vitessoides through direct contact and horizontal transmission. RESULTS: At the concentration of 1 × 109 conidia/mL, the three M. anisopliae strains caused 100% mortality of H. vitessoides larvae. In addition, mixing donor larvae (previously treated with M. anisopliae conidia) with receptor larvae (which did not directly contact M. anisopliae conidia) caused significantly higher mortality of receptor larvae than the control receptors. This is due to the horizontal transmission of M. anisopliae conidia among live larvae, which was proven by pictures taken by scanning electron microscopy and induced activities of immunity-related enzymes of donor and receptor larvae. Behavioral bioassays showed that M. anisopliae conidia had little effect on the aggregation tendency of H. vitessoides larvae but may trigger feeding-avoidance behavior depending on M. anisopliae strains and concentrations. Interestingly, joint use of sublethal concentrations of M. anisopliae and chemical insecticides significantly increased larval mortality than each agent alone, indicating synergistic effects between M. anisopliae and insecticide against H. vitessoides. CONCLUSION: This study may provide a new strategy to suppress H. vitessoides population and reduce the use of chemical insecticides. © 2023 Society of Chemical Industry.

Fine Structure of the Visual System of Arge similis (Hymenoptera, Argidae).

External morphology and ultrastructure of the visual system of Arge similis (Vollenhoven, 1860) adults were investigated by light microscopy, scanning electron microscopy, and transmission electron microscopy. Each compound eye contains 2022 ± 89 (mean ± SE) facets in males and 2223 ± 52 facets in females. Arge similis has an apposition kind of compound eye composed of a cornea, a crystalline cone of four cone cells, and a centrally fused rhabdom made up of the rhabdomeres of eight large retinular cells. Each crystalline cone is surrounded by primary and secondary pigment cells with black spherical screening pigment granules measuring 0.60 ± 0.02 and 0.41 ± 0.01 µm in diameter, respectively. Based on our findings, the compound eye of A. similis can be expected to exhibit high adaptability to light intensity changes.

Morphological and optical features of the apposition compound eye of Monochamus alternatus Hope (Coleoptera: Cerambycidae).

The Japanese pine sawyer beetle, Monochamus alternatus Hope (Coleoptera: Cerambycidae) is currently the most destructive forest pest as it transmits the pine wilt nematode Bursaphelenchus xylophilus. Morphological, optical features and dark/light adaptational changes of the compound eyes of M. alternatus adults were examined by light, scanning and transmission electron microscopy. The eye of M. alternatus is apposition type and contains 489-712 ommatidia, depending on the beetle's body size. Each ommatidium features a large corneal lens, composed of a thick inner lens (ILU) and a thin outer lens unit (OLU); an acone-type of cone of four cone cells, a semi-fused type of rhabdom formed by eight retinular cells (two central cells: R7-R8 surrounded by six peripheral cells: R1-R6). Dark/light adaptational changes affect size and shape of the cones as well as the rhabdom's cross-sectional area and outline, to optimize the amount of light that reaches the photopigment. The compound eyes of M. alternatus have an F-number of 0.94, an interommatidial angle of 5.34°, an eye parameter P of 4.98 µm rad and a ratio of acceptance to interommatidial angle of 0.45. The eye is characterized by relatively poor spatial resolution, but can be expected to exhibit high absolute sensitivity and contrast in dim light.

Pupation Behaviors and Emergence Successes of Ectropis grisescens (Lepidoptera: Geometridae) in Response to Different Substrate Types and Moisture Contents.

Ectropis grisescens Warren (Lepidoptera: Geometridae) is one of the most severe pests of tea plants in China. This species commonly pupates in soil; however, little is known about its pupation ecology. In the present study, choice and no-choice tests were conducted to investigate the pupation behaviors and emergence success of E. grisescens in response to different substrates (sand, sandy loam 1, sandy loam 2, and silt loam) and moisture contents (5, 20, 35, 50, 65, and 80%). Moisture-choice bioassays showed that significantly more E. grisescens individuals pupated in or on soil (sandy loam 1 and 2 and silt loam) that was at the intermediate moisture levels, whereas 5%- and 35%-moisture sand was significantly more preferred over 80%-moisture sand for pupating. Substrate-choice bioassays showed that sand was most preferred by E. grisescens individuals at 20%- and 80%-moisture levels, but no preference was detected among the four substrates at 50%-moisture content. No-choice tests showed that the percentage of burrowed E. grisescens individuals and pupation depth were significantly lower when soil was dry (20% moisture) or wet (80% moisture). In addition, 20%-moisture sandy loam 2 and silt loam significantly decreased the body water content of pupae and emergence success of adults compared to 50%-moisture content. However, each measurement (percentage of burrowed individuals, pupation depth, body water content, or emergence success) was similar when compared among different moisture levels of sand. Interestingly, pupae buried with 80%-moisture soil exhibited significantly lower emergence success than that were unburied.