Differences in orientation behavior and female attraction by Rhyzopertha dominica (Coleoptera: Bostrichidae) in a homogeneous resource patch

Authors: CORDEIRO, ERICK M. - UNIVERSIDAD DE SAO PAULO; Campbell, James - Jim; PHILLIPS, THOMAS - KANSAS STATE UNIVERSITY

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/23/2019
Publication Date: 8/15/2019
Citation: Cordeiro, E.G., Campbell, J.F., Phillips, T. 2019. Differences in orientation behavior and female attraction by Rhyzopertha dominica (Coleoptera: Bostrichidae) in a homogeneous resource patch. Environmental Entomology. 48(4):784-791. https://doi.org/10.1093/ee/nvz058.
DOI: https://doi.org/10.1093/ee/nvz058

Interpretive Summary: The lesser grain borer is a major beetle pest of grains such as wheat as they are stored after harvest. Wheat is typically stored in large containers such as metal or concrete bins before processing and when grain is first added to these containers it is a relatively homogeneous food resource patch that can extend well beyond an insect's short-term walking dispersal abilities. Lesser grain borers do most of their development to adulthood inside individual seeds and only chew out as adults. Little is known about the behavioral strategies for newly emerged adults or how they go about finding mates inside this large mass of grain. We tracked individual male and female movement during the first two days after the adult beetles have emerged from a wheat kernel in which they developed. We first asked if sexes show any innate orientation pattern, and found that males showed an upward orientation bias during the first day of evaluation, but not in the second, whereas females had a random pattern of orientation on both days. Since males release an aggregation pheromone which attracts both males and females, we next asked how the presence of another male influences the movement pattern of newly emerged males and females. The presence of a male, whether it was above or below a newly emerged female, changed female movement direction on the first day after emergence from random to a bias towards the male. In contrast, males exhibited the same upward movement bias on the first day regardless of the position of the male. Only on the second day did male movement change and male movement shifted to move in the opposite direction of the other male. These results reveal fundamental differences in the behavior of males and females inside the grain, and that males at least initially do not move randomly in a homogenous environment. The reason for this pattern is not clear, but our results indicate that initial upward movement doesn’t improve ability of females to locate males. Previous studies evaluating response to pheromone have shown that males and females both respond similarly to the male produced aggregation pheromone, but these studies were conducted outside of the grain mass. Our results show pheromone response can differ depending on the environment and suggest that use of the pheromone may differ depending on whether beetles are inside or outside of a grain bin.

Technical Abstract: The aim of this paper is to study how naïve beetles disperse after emerging as an adult in a homogeneous resource patch. We tracked male and female Rhyzopertha dominica movement testing two different strains during the first two days after the adult beetles have emerged from the wheat kernel in which they developed. We first asked if naïve male and female beetles show any innate orientation pattern. Males showed an upward orientation bias during the first day of evaluation, but not in the second, whereas females had a random pattern of orientation in both days of evaluation. Since males release an aggregation pheromone, we next asked if the presence of a male that is capable of producing aggregation pheromone influences movement patterns of males and females on the first two days. Because males tended to move upward on the first day we evaluated response to males when they were in the average location determined in the first experiment or in the opposite location below emergence location. The presence of male whether above or below a newly emerged female changed movement direction from random to a bias towards the male. In contrast, males exhibited the same upward movement bias on the first day regardless of the position of the male, but on the second day male movement changed with a shift to move in the opposite direction of the other male. These results reveal fundamental differences in the behavior of males and females inside the grain, and that males at least initially do not move randomly in a homogenous environment. The reason for this pattern is not clear, but our results indicate that initial upward movement doesn’t improve ability of females to locate males. Previous studies evaluating response to pheromone have shown that males and females both respond similarly to the male produced aggregation pheromone, but these studies were conducted outside of the grain mass. Our results show pheromone response can differ depending on the sex, and for males the time after emergence from kernel, and, in comparison to earlier literature, that response to pheromone may differ depending on whether beetles are inside or outside of a grain resource patch.