Gene amplification
In the midgut of adults collected from June 9 to August 5, 2021, rbcL was amplified from plant DNA from an average percentage of 37% of the adult insects. The lowest percentage of adults with rbcL was 18% on June 16 and the highest percentage (58%) was on June 23 (Fig. 2).
Number of plant species fed on by P. brevitarsis adults
We identified the plant species found in the midgut of adults collected from June 9 to August 5, 2021, and found that the adults habitually fed on multiple plant species. Wherein, 67% of the adults contained only one plant species (F3, 24 = 56.07, P<0.0001), 31% contained two plant species, 4% contained three species, and only one adult insect contained four plant species.
Plant species eaten by P. brevitarsis adults in 2019 and 2021
In 2019, 17 species in 14 families were identified from the midguts of adults, among them, 16 species were identified at the species level, and one species was identified at only the genus level (Fig. 3a). Grape (Vitis vinifera) was the most preferred species, being found in 60% of the insects, followed by peach (23%, Amygdalus persica) and narrow-leaved oleaster (9%, Elaeagnus angustifolia).
In 2021, 21 species in 18 families were identified in adults; among them, 10 species were identified to the species level and 11 species were identified to the genus level only. Mulberry (Morus alba) was found in the most adults (25%), followed by peach (24%) and grape (23%) (Fig. 3b).
For both 2019 and 2021, 32 plant species belonging to 23 families were identified in adults (Fig. 3c). Grape was found in the most adults (40%), followed by peach (23%), mulberry (14%), narrow-leaved oleaster (7%) and purslane (5%, Portulaca).
Plant species eaten by P. brevitarsis adults from June-August
In 2019, on June 1, 74% of all adults had grape (Vitis vinifera) in the midgut, significantly more than the percentage that had other plant species (F6, 14 = 7.993, P = 0.001) (Fig. 4). On June 13, peach was found in the most adults (73%) (F4, 10 = 7.745, P = 0.004). On June 20, peach was still the most preferred species (52%) (F6, 14 = 8.111, P = 0.001). On June 27, peach (44%) and grape (42%) were equally identified in adults (F4, 10 = 10.255, P = 0.001). On July 3, 63% of the total sample were adults with grape in the midgut (F4, 10 = 9.714, P = 0.002). On July 18, grape was found in the most adults (61%) (F2, 6 = 26.607, P = 0.001), followed by narrow-leaved oleaster (35%) and peach (4%). On July 25, grape was still the significantly preferred species (63%) (F3, 8 = 34.472, P < 0.001), followed by peach (18.07%), narrow-leaved oleaster (17%) and jujube (2%). In August, a total of 45 adults were collected, and rbcL was detected only from grape. The results for 2019 indicated that most adults fed on grape in early June, most favored peach in mid-June, some included narrow-leaved oleaster in late June and early July, and most again fed on grape in August. Thus, adults went from grape to peach to grape and narrow-leaved oleaster during June-August as their preferred host plants.
In 2021, on June 9, 65% of the adults had mulberry (Morus alba) in their midgut (F3, 8 = 8.727, P = 0.007) (Fig. 5). On June 16, grape was found in the most adults (59%) (F3, 8 = 2.291, P = 0.155). On June 23, mulberry was the most identified species again (59%), which was significantly greater than the percentage of other plant species (F7, 16 = 13.574, P < 0.001). On July 11, peach was found in the most adults (64%), significantly more than the percentage that had other plant species (F11, 24 = 4.371, P = 0.001). On July 21, mulberry was found in the most adults (53%), significantly more than other plant species (F11, 24 = 6.509, P < 0.001). On July 28, among the 11 plant species we detected, there was no significant difference in their proportion (F9, 20 = 0.511, P = 0.849). On August 5, grape was found in the most adults (75%), significantly more than other plant species (F5, 12 = 4.761, P = 0.013). These results indicated that the adults shifted their hosts from mulberry and grape to mulberry and peach to grape (in June-August) as their preferred hosts.