The influence of fluctuating temperature on Megamelus scutellaris Berg (Hemiptera: Delphacidae)

Abstract

Information from unpublished reports, field, and greenhouse observations suggests that temperatures exceeding 29° C can cause reduced development and increased mortality of Megamelus scutellaris Berg (waterhyacinth planthopper), a biological control agent released for the management of Eichhornia crassipes (Mart. Solms). This document reports the results of an experiment conducted under greenhouse conditions designed to gauge temperature impacts to M. scutellaris survival and reproduction under fluctuating temperatures regimes. BACKGROUND: Waterhyacinth (E. crassipes) was first introduced into the U.S. in Louisiana during the International Cotton Exposition in 1884 (Center 2004). Since its initial introduction, the range of waterhyacinth has spread to include the southern and western regions of the United States and is expanding northward (U.S. Department of Agriculture/Natural Resources Conservation Service [USDA/NRCS] 2016). Waterhyacinth is capable of rapid growth and can quickly cover the water's surface thereby reducing light penetration to algae and submersed plants, lowering dissolved oxygen levels and pH, and ultimately leading to altered native species diversity (Getsinger et al. 2014; Center 2004; Villamagna and Murphy 2009). Mats of waterhyacinth have also been shown to obstruct waterways, impact irrigation and drinking water delivery, navigation, and recreation. Additionally, waterhyacinth has been documented as a human health hazard by increasing mosquito breeding habitats (Center 2004). NOTE: The contents of this technical note are not to be used for advertising, publication or promotional purposes. Citation of trade names does not constitute an official endorsement or approval of the use of such products.

Evaluating the establishment of a new water hyacinth biological control agent in South Africa

“…In the U.S.A., M. scutellaris has been released in several States, including Louisiana, California, and Florida et Despite extensive releases, establishment has been reported as variable in the U.S.A., and this has been attributed to summer temperatures exceeding the upper thermal limit of 39.1 °C (Coetzee, unpub. data) for M. scutellaris (Grodowitz et al 2014;Tipping et al 2014b;Pratt et al 2021). Another biotype of M. scutellaris collected from Paraguay has been released in the south-eastern U.S.A. (Foley et al 2016).…”

“…Additionally, temperatures within the canopy of water hyacinth are more stable than atmospheric conditions and, thus, provide a more suitable microclimate for the insects (Grodowitz et al 2017). For example, the three-dimensional structure of water hyacinth mats provides a temperature buffer to M. scutellaris living on the plants.…”

“…For example, the three-dimensional structure of water hyacinth mats provides a temperature buffer to M. scutellaris living on the plants. Within a closed canopy of water hyacinth, the temperatures are usually lower than the surrounding air due to cooling effects from water moving through the xylem and shading from the leaves (Grodowitz et al 2014). Therefore, M. scutellaris might behaviourally thermoregulate by moving up and down petioles to maintain a stable temperature, usually remaining near the water's surface when temperatures are warm and ascending petioles in cooler weather (Grodowitz et al 2014).…”

“…Within a closed canopy of water hyacinth, the temperatures are usually lower than the surrounding air due to cooling effects from water moving through the xylem and shading from the leaves (Grodowitz et al 2014). Therefore, M. scutellaris might behaviourally thermoregulate by moving up and down petioles to maintain a stable temperature, usually remaining near the water's surface when temperatures are warm and ascending petioles in cooler weather (Grodowitz et al 2014). However, research suggests that acclimating insects to local temperatures can be achieved prerelease to increase the propensity for population establishment at release sites that might have climates different from the rearing temperatures (Griffith et al 2019).…”

“…Such mismatches between the climates of the native and host ranges are responsible for the failures of a significant proportion of classical biological control programmes, as the natural enemies usually inhabit a narrower fundamental niche than their host plants (Harms et al 2021). May and Coetzee (2013) reported that M. scutellaris would be less likely to establish and persist in the cooler interior of South Africa, particularly when temperatures were below its developmental threshold of 11.5 °C, while others determined that the survival and fecundity of M. scutellaris in rearing cultures is significantly reduced below 18 °C and above 33 °C (Grodowitz et al 2017). Thus, the upper and lower temperature thresholds of M. scutellaris might be exceeded in parts of South Africa where these temperatures are commonplace.…”