Stink bug rostrum length vs. stylet penetration potential

Authors: Esquivel, Jesus

Submitted to: Entomologia Experimentalis et Applicata
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/7/2019
Publication Date: 5/1/2019
Citation: Esquivel, J.F. 2019. Stink bug rostrum length vs. stylet penetration potential. Entomologia Experimentalis et Applicata. 167(4):323-329. https://doi.org/10.1111/eea.12782.
DOI: https://doi.org/10.1111/eea.12782

Interpretive Summary: Cotton is a high value commodity that continues to be plagued by insect pest species, such as stink bugs. Stink bugs use slender needle-like mouthparts (known as stylets) to penetrate into the developing cotton fruit (or boll) and potentially introduce plant pathogens. The stylets are housed within a four-segmented beak. Recent observations indicated some stink bug species with a shorter beak unexpectedly yielded deeper stylet penetration estimates than stink bugs with a longer beak. The objective of this study was to examine the relationship between beak length and known stylet penetration estimates for adults of two pairs of stink bug species: green stink bug versus brown stink bug, and rice stink bug versus redbanded stink bug. For each species, each segment of the four-segmented beak was measured to yield total lengths, and measurements were compared against known stylet penetration estimates. Green stink bugs and redbanded stink bugs possessed longer beaks than brown stink bugs and rice stink bugs, respectively, yet brown stink bugs and rice stink bugs yielded deeper stylet penetration estimates. Deeper stylet penetration by species with a shorter beak can be attributed to differences between species in the lengths of the first and second beak segments. Brown stink bug and rice stink bug had longer lengths at segments 1 and 2 than green stink bugs and redbanded stink bugs, respectively. Also, the cumulative lengths of beak segments 1 and 2 for brown stink bugs and rice stink bugs comprised a higher overall proportion of the entire beak length when compared with green stink bugs and redbanded stink bugs, respectively. Beak segments 1 and 2 are known to be instrumental in the feeding behavior of these species, and it is clear that longer lengths for these segments and their role in stylet penetration equations override the presumption that total rostrum length equates to stylet penetration potential. This newly discovered phenomenon contributes to the general knowledge base of feeding mechanics and factors influencing stylet penetration potential among differing stink bug species.

Technical Abstract: Stink bugs (Hemiptera: Pentatomidae) and related species continue to plague cotton (Gossypium hirsutum L. [Malvales: Malvaceae]) worldwide. Stink bugs utilize their stylets (housed within the rostrum) to feed upon cotton bolls and transmit pathogens that cause seed and boll rot of cotton. Stylet penetration potential of stink bugs is influenced by species and recent observations indicated a phenomenon where stink bugs with shorter rostra yielded deeper stylet penetration estimates. The objective of this study was to elucidate the relationship between rostrum length and known stylet penetration estimates for two pairs of pentatomid species: Chinavia hilaris (Say) versus Euschistus servus (Say), and Oebalus pugnax (F.) versus Piezodorus guildinii Westwood. For each species, individual rostral segments were measured to yield total lengths, and measurements were compared against known stylet penetration estimates. Chinavia hilaris and P. guildinii possessed longer rostra than E. servus and O. pugnax, respectively, yet E. servus and O. pugnax yielded deeper stylet penetration estimates. Deeper stylet penetration by species with shorter rostra can be attributed to differences in the lengths of rostral segments 1 and 2. Euschistus servus and O. pugnax each had significantly longer rostral segments 1 and 2 than C. hilaris and P. guildinii, respectively. Also, the cumulative lengths of rostral segments 1 and 2 in E. servus and O. pugnax comprised a higher overall proportion of the entire rostrum length versus C. hilaris and P. guildinii, respectively. Rostral segments 1 and 2 are instrumental in the feeding mechanics of these phytophagous species, and it is clear that longer lengths for said segments and their role in stylet penetration model calculations negate the presumption that total rostrum length equates to stylet penetration potential. This newly discovered phenomenon contributes to the general knowledge base of feeding mechanics and factors influencing stylet penetration potential among differing stink bug species.