a-precise-autonomous-system-for-detection-insect-emergence

A Precise and Autonomous System for the Detection of Insect Emergence Patterns

Existing systems to measure insect emergence patterns have limitations; they are only partially automated and are limited in the maximum number of ...

Red River Valley Agricultural Research Center, USDA-ARS

Alfalfa seed production in the northwestern United States and western Canada is heavily dependent upon the pollinating services of Megachile rotundata (F.) (Hymenoptera: Megachilidae). M. rotundata females nest in cavities either naturally occurring or in artificial nesting blocks. Because of the physical nature of the nest, M. rotundata brood may have limited to no exposure to photoperiodic cues in order to regulate important circadian functions. Therefore, various thermoperiod regimes were used to characterize the possible role of thermoperiodism in synchronizing M. rotundata adult emergence. Adult emergence was monitored using a microprocessor-controlled event logger. Incubating bees under constant 29°C and darkness resulted in an arhythmic adult emergence pattern. Exposing developing M. rotundata to a thermoperiod synchronized emergence to the beginning of the thermophase and decreased the total number of days required for all adults to emerge. The amplitude of the thermoperiod regulated the timing of peak emergence in relationship to the increase in temperature. A thermoperiod amplitude of only 2°C was sufficient to synchronize peak adult emergence to take place during the rise in temperature. Increasing the amplitude of the thermoperiod to 4 or 8°C caused a positively correlated shift in peak emergence to later in the thermophase. Brood stored under constant 29°C and darkness for different durations (May or June early in the growing season or July or August late in the growing season) or under a fluctuating thermal regime (base temperature of 6°C and daily 1-h pulse of 20°C until September or November) maintained their capacity for entraining emergence timing by thermoperiodism. 

Thermoperiodism Synchronizes Emergence in the Alfalfa Leafcutting Bee (Hymenoptera: Megachilidae).

The alfalfa leafcutting bee, Megachile rotundata (F.), is the primary pollinator for alfalfa seed production in North America. Under current management practice, developing pupae are incubated at 29-30°C until the adults emerge for pollination. If unfavorable spring weather delays peak alfalfa bloom, managers will cool pupae to slow development, which can increase mortality and causes sublethal effects. Previously, we demonstrated that exposure to a fluctuating thermal regime (FTR) increases survival and extends the viable storage period. To determine the optimal conditions for FTR during storage of developing M. rotundata, we examined four variables: temperature of the daily warm pulse, duration of the warm pulse, number of weeks exposed to the FTR treatment, and developmental stage of the bee. Survival was measured by successful eclosion to the adult stage. Under all conditions, exposure to FTR increased survival compared with exposure to a constant 6°C. When the temperature of the daily warm pulse was 20-25°C from a base temperature of 6°C, and the pulse duration was extended to 3 h, survival rates were as high as those observed under standard storage conditions (29°C). Under this FTR storage protocol, bee managers can delay emergence for ∼8 wk without significant decreases in survival. Our findings have substantial economic implications for bee management and alfalfa seed production by increasing the flexibility and efficiency of M. rotundata adult emergence.

Optimizing Fluctuating Thermal Regime Storage of Developing Megachile rotundata (Hymenoptera: Megachilidae).

Our understanding of the mechanisms controlling insect diapause has increased dramatically with the introduction of global gene expression techniques, such as RNA sequencing (RNA-seq). However, little attention has been given to how ecologically relevant field conditions may affect gene expression during diapause development because previous studies have focused on laboratory-reared and -maintained insects. To determine whether gene expression differs between laboratory and field conditions, prepupae of the alfalfa leafcutting bee, , entering diapause early or late in the growing season were collected. These two groups were further subdivided in early autumn into laboratory- and field-maintained groups, resulting in four experimental treatments of diapausing prepupae: early and late field, and early and late laboratory. RNA-seq and differential expression analyses were performed on bees from the four treatment groups in November, January, March and May. The number of treatment-specific differentially expressed genes (97 to 1249) outnumbered the number of differentially regulated genes common to all four treatments (14 to 229), indicating that exposure to laboratory or field conditions had a major impact on gene expression during diapause development. Principle component analysis and hierarchical cluster analysis yielded similar grouping of treatments, confirming that the treatments form distinct clusters. Our results support the conclusion that gene expression during the course of diapause development is not a simple ordered sequence, but rather a highly plastic response determined primarily by the environmental history of the individual insect.

George D. Yocum

Red River Valley Agricultural Research Center, USDA-ARS

A Precise and Autonomous System for the Detection of Insect Emergence Patterns