Plant Water Stress Effects on the Net Dispersal Rate of the Insect Vector <I>Homalodisca vitripennis</I> (Hemiptera: Cicadellidae) and Movement of Its Egg Parasitoid, <I>Gonatocerus ashmeadi</I> (Hymenoptera: Mymaridae)

Abstract

Homalodisca vitripennis (Germar), a vector of Xylella fastidiosa, is associated with citrus plantings in California. Infested citrus orchards act as a source of vectors to adjacent vineyards where X. fastidiosa causes Pierce's disease. An analysis of the pattern and rate of movement of H. vitripennis and its egg parasitoid, Gonatocerus ashmeadi Girault, was conducted in a citrus orchard by using a protein mark-capture technique to quantify movement and net dispersal rates in the experimental areas. Treatments included irrigation at 100% of the crop evapotranspiration rate (ET(c)), 80, and 60% ET(c). Sex-specific net dispersal rates showed that H. vitripennis males and females moved consistently and contributed equally to the level of population change within treated areas. Trees irrigated at 60% ET(c) were the least preferred by H. vitripennis. Among all protein-marked individuals captured in the 60% ET(c) treatment, ≈ 75 and 88% in 2005 and 2006, respectively, were inflow individuals. Movement toward less preferable plants indicates that in agricultural landscapes dominated by perennial monocultures, there is a random component to H. vitripennis movement, which may result from the inability of H. vitripennis to use plant visual cues, olfactory cues, or both to make well-informed long-range decisions. The 80% ET(c) areas were a significant source of adult H. vitripennis and G. ashmeadi compared with the other treatments. Colonization rates by parasitoids were synchronized with the spatiotemporal distribution of H. vitripennis eggs. Results suggest that H. vitripennis movement from citrus into adjacent vineyards could be a result of random dispersal rather than oriented movement in response to host-plant characteristics.

How Do Plant Diseases Caused byXylella fastidiosaEmerge?

“…This behavior may be advantageous for these insects: water stressed and X. fastidiosa-infected plants have some shared physiological characteristics, of which xylem sap under high tension is of paramount relevance. Increased tension in a water column leads to a food source that is energetically expensive for insects, resulting in the ingestion of less xylem sap (Andersen et al 1992;Miranda et al 2013) and promoting the movement of vectors to another host (Krugner et al 2012). Since symptomatic plants are heavily colonized by X. fastidiosa (Newman et al 2003), avoidance of infected plants by vectors may act to reduce transmission rates when disease incidence is low (Sisterson 2008;Zeilinger and Daugherty 2014) and select for decreased bacterial virulence.…”

Mating disruption of Homalodisca vitripennis (Germar) (Hemiptera: Cicadellidae) by playback of vibrational signals in vineyard trellis

“…Suppression of GWSS populations in vineyards is an important step toward the overall goal of reducing the incidence of Pierce's disease. Although the method reported here has the potential to suppress GWSS population growth in vineyards, GWSS is a polyphagous and highly mobile insect that can feed and reproduce in habitats neighboring vineyards. In California, GWSS populations are strongly associated with citrus plantings and insect movement between vineyards and citrus orchards has been reported .…”

A potential contamination error associated with insect protein mark‐capture data

“…Second, no mark-capture research protocol used to date has applied pure proteins to the arthropods. Protein mark-capture studies published to date have applied <20% solutions of the various protein marks (Jones et al, 2006;Boina et al, 2009;Horton et al, 2009;Krugner et al, 2012;Sivakoff et al, 2012;Swezey et al, 2013Swezey et al, , 2014Peck et al, 2014). Finally, the number of protein-marked specimens (n = 30 per sample unit) placed into each sweep net sample was much higher than one would expect to encounter in mark-capture type studies.…”

“…Spot or broadcast applications of various protein marks for mark-release-recapture (MRR)-and mark-capturetype dispersal research have become an increasingly popular means for marking arthropods (Jones et al, 2006;Boina et al, 2009;Hagler et al, 2011;Krugner et al, 2012;Sivakoff et al, 2012;Swezey et al, 2013Swezey et al, , 2014. The proteins are inexpensive, easy to apply, and detectable by protein-specific enzyme-linked immunosorbent assays (ELISA).…”