Stage development and survival rates
Egg duration of G. molesta was not affected by fruit species (F = 0.54, df = 2, 261, P = 0.581), by collection date (F = 0.06, df = 2, 261, P = 0.941), or by fruit species by collection date interaction (F = 0.24, df = 4, 261, P = 0.914) (Table 1). Durations of other life stages were all significantly affected by fruit species (larva F = 28.16, df = 2, 144, P < 0.001; prepupa F = 4.38, df = 2, 133, P = 0.014; pupa F = 8.76, df = 2, 113, P < 0.001; larva-pupa F = 22.92, df = 2, 113, P < 0.001), by collection date (larva F = 17.43, df = 2, 144, P < 0.001; prepupa F = 7.73, df = 2, 133, P < 0.001; larva-pupa F = 11.59, df = 2, 113, P < 0.001) except pupa (F = 1.99, df = 2, 113, P = 0.142), or by fruit species by collection date interaction (larva F = 30.59, df = 4, 144, P < 0.001; prepupa F = 5.15, df = 4, 133, P < 0.001; pupa F = 8.41, df = 4, 113, P < 0.001; larva-pupa F = 16.12, df = 4, 113, P < 0.001).
Duration of the larval stage became longer in plum and apple as fruit collection date, but it showed opposite trend in peach. Among later-collected fruits (June 25), duration of the larval stage was shortest in peach.
Prepupal duration showed similar pattern as in larval duration. Pupal duration became longer as collection date in plum fruits, but no such trend was found in either peach or apple. In comparison on each collection date, no significance was found among fruits except June 25 when peach showed shortest pupal duration.
The total period from of larva plus pupa was also shortest when insects were reared on peach fruits collected on June 25 (20.33 d) compared to those reared on either plum or apple fruits collected on same date.
Hatching rate of eggs were not affected by fruit species (F = 3.44, df = 2, 4, P = 0.101), by collection date (F = 1.03, df = 2, 4, P = 0.413), or by fruit species by collection date interaction (F = 3.50, df = 4, 4, P = 0.126) (Table 2). The fruit penetration rate of first instars was not statistically different within each fruit developmental stages (F = 0.25, df = 2, 4, P = 0.789) or by fruit species by collection date interaction (F = 4.50, df = 4, 4, P = 0.087), but was significantly different between fruit species (F = 6.39, df = 2, 4, P = 0.033). For example, the fruit penetration rate was lowest in peach (0.40), compared to plum (0.87) or apple (0.83) collected on May 31 (χ2 = 19.37, df = 2, P = 0.009). The fruit exiting rate was also affected by fruit species (F = 5.35, df = 2, 4, P = 0.046) but not by collection date (F = 0.35, df = 2, 4, P = 0.720), or by fruit species by collection date interaction (F = 3.50, df = 4, 4, P = 0.126). The fruit exiting rate of mature larva was similar within each fruit species for all fruit collection dates. Among fruit species, the fruit exiting rate was highest in apple than peach on May 31 (χ2 = 10.63, df = 2, P = 0.005). Pupation rate and emergence rate were not affected by fruit species (pupation rate F = 1.37, df = 2, 4, P = 0.324; emergence rate F = 0.17, df = 2, 4, P = 0.848), by collection date (pupation rate F = 1.07, df = 2, 4, P = 0.401; emergence rate F = 1.04, df = 2, 4, P = 0.401), or by fruit species by collection date interaction (pupation rate F = 0.13, df = 4, 4, P = 0.966; emergence rate F = 0.15, df = 4, 4, P = 0.951). Total immature survival rate was affected by fruit species (F = 9.60, df = 2, 4, P = 0.014) or by fruit species by collection date interaction (F = 15.50, df = 4, 4, P = 0.011), but not by collection date (F = 0.15, df = 2, 4, P = 0.864). In general, the total immature survival rate was highest in apple collected on May 31 compared to peach (χ2 = 26.12, df = 2, P < 0.001).
Within individual fruit species, larval survival rate was similar across collection dates (F = 0.25, df = 2, 4, P = 0.789), but there were significant differences among fruit species (F = 9.03, df = 2, 4, P = 0.015), or by fruit species by collection date interaction (F = 15.50, df = 4, 4, P = 0.011). For example, larval survival rate in apple was significantly higher than other fruits, and this was true for all developmental periods (0.83, 0.73, and 0.73) compared to peach (0.27, 0.37, and 0.40) (Table 2). No significant differences in larval survival rate were observed between apple and plum in all developmental stages.
Age- and stage-specific survival rates of G. molesta larvae were highest on 11th day in both peach and apple collected on May 31 (Fig. 1). The peaks of larval survival rate became extended as fruit collection dates in plum and apple. But, the peaks of larval survival rate appeared between 10 and 15th day in peach.
Age-stage survival rate (Sxj) of Grapholita molesta in plum collected on (A) May 11, (B) May 31, (C) June 11, and (D) June 25; peach collected on (E) May 31, (F) June 11, and (G) June 25; and apple collected on (H) May 31, (I) June 11 and (J) June 25.
Longevity and fecundity of adult females
Preoviposition period and fecundity of G. molesta were significantly affected by fruit species (preoviposition period F = 6.84, df = 2, 27, P = 0.004; fecundity F = 30.21, df = 2, 27, P < 0.001), by collection date (preoviposition period F = 3.21, df = 2, 27, P = 0.065; fecundity F = 4.25, df = 2, 27, P = 0.024), or by fruit species by collection date interaction (preoviposition period F = 7.44, df = 4, 27, P < 0.001; fecundity F = 7.45, df = 4, 27, P < 0.001) (Table 3).
The preoviposition period within plum fruits was longer on June 25 (4.67 d) compared to those collected earlier. But, preoviposition period was longer on May 31 than later dates in peach while it was similar among all collection dates in apple.
Among fruit species, the highest fecundity was found for moths reared as larvae in peach (258.25) and apple (281.80) collected on June 25. Within each fruit species, fecundity was highest (205.75) in moths reared as larvae in plums collected on May 31, compared to those from fruit collected earlier. Interestingly, in peach fruit, fecundity gradually increased with fruit age and was greatest in fruits collected on June 25. Apple on all dates showed higher fecundity.
However, oviposition period and adult longevity were not affected by fruit species (oviposition period F = 1.93, df = 2, 27, P = 0.164; longevity F = 0.67, df = 2, 27, P = 0.522), by collection date (oviposition period F = 0.04, df = 2, 27, P = 0.964; longevity F = 0.18, df = 2, 27, P = 0.840), or by fruit species by collection date interaction (oviposition period F = 1.75, df = 4, 27, P = 0.167; longevity F = 0.61, df = 4, 27, P = 0.662). Peach fruits collected on June 25 or apple fruits (irrespective of collection date) were the best food sources for G. molesta larvae.
Fruit firmness
Firmness of the fruit surface was influenced by fruit species (F = 214.60, df = 2, 73, P < 0.001), by collection date (F = 44.01, df = 2, 73, P < 0.001), or by fruit species by collection date interaction (F = 4.61, df = 4, 73, P = 0.002) (Fig. 2). For all fruits, fruit firmness gradually decreased over time. Plum fruits collected on May 11 showed highest firmness (13.30 N), then firmness decreased quickly as collection date. Among all fruit species, the fruit firmness was greater in peach when collected on May 31 (11.37 N) or June 11 (11.34 N) compared to that for plum or apple.
Fruit hardness and sugar content of fruits, compared to pupal weights of Grapholita molesta on rearing fruit. Means followed by different lower case (§) letter are significantly different among collection dates within a fruit species and different upper case letter (§§) are significantly different among host fruits in each collect date.
Fruit sucrose content
Sugar content was also greatly affected by fruit species (F = 211.45, df = 2, 78, P < 0.001), by collection date (F = 60.77, df = 2, 78, P < 0.001), or by fruit species by collection date interaction (F = 6.62, df = 4, 78, P < 0.001) (Fig. 2). Sugar content in plum and apple increased with collection date. The sugar content in all fruits was highest on June 25 than those collected on May 31. Among all fruit species and stages, sugar content was highest in peach and apple collected on June 25.
Pupal weights of larvae reared on different fruits
Pupal weights of G. molesta were affected by fruit species (F = 15.64, df = 2, 125, P < 0.001), by collection date (F = 5.51, df = 2, 125, P = 0.005), or by fruit by collection date interaction (F = 10.57, df = 4, 125, P < 0.001) (Fig. 2). The highest pupal weight (13.50 mg) was found in peach collected on June 25 and apple for all collection dates. In peach, pupal weight increased with fruit age (= collection date), but did not increase in plum or apple with increased fruit age.
Effect of firmness and sugar content on larval duration, pupal weight, and fecundity
A significant regression was found between firmness and pupal weight in peach (y = − 1.32x + 26.34; R2 = 0.214; F = 6.80, df = 1, 25, P = 0.015), firmness and fecundity in peach (y = − 58.59x + 830.05; R2 = 0.576; F = 12.25, df = 1, 9, P = 0.007), firmness and larval duration in plum (y = − 0.37x + 15.73; R2 = 0.112; F = 8.74, df = 1, 69, P = 0.004), and firmness and larval duration in apple (y = − 4.42x + 43.18; R2 = 0.554; F = 83.23, df = 1, 67, P < 0.001). No relationship was found between firmness and pupal weight or fecundity in both plum and apple or between firmness and larval duration in peach.
Significant regression was found between sugar content and pupal weight in plum (y = − 1.82x + 25.31; R2 = 0.078; F = 4.91, df = 1, 58, P = 0.031), sugar content and pupal weight in peach (y = 3.37x − 21.80; R2 = 0.335; F = 12.61, df = 1, 25, P = 0.002), sugar content and fecundity in peach (y = 148.52x − 1301.14; R2 = 0.844; F = 48.72, df = 1, 9, P < 0.001), sugar content and larval duration in plum (y = 4.66x − 23.08; R2 = 0.263; F = 24.60, df = 1, 69, P < 0.001), and sugar content and larval duration in apple (y = 1.99x − 9.21; R2 = 0.554; F = 83.11, df = 1, 67, P < 0.001).
Fruit effect on life history parameters
Significant differences were observed among fruit species and stages in doubling time (DT), finite rate of increase (λ), intrinsic rate of increase (rm), net reproductive rate (RO), and mean generation time (T) (Table 4). Doubling time in plums collected on June 25 was higher than that obtained on May 11 or May 31. In contrast, doubling times of larvae reared on peach fruits were lower on June 25 than May 31. Among fruit species, doubling time was higher in plum than in peach or apple collected on June 25.
The finite rate of increase (λ) and the intrinsic rate of increase (rm) for larvae reared on plum was lower on fruits collected June 25 than May 11 or May 31. On the other hand, the finite rate of increase (λ) and intrinsic rate of increase (rm) were higher in peach collected on June 25 compared to those fruits collected on May 31. The net reproductive rate (RO) was highest on May 31 than later collection date within apple. Among fruit species, net reproductive rate (RO) was also found highest on May 31 in apple compared to peaches or plums on all collection dates. The mean generation time (T) was shortest in peach collected on June 25 compared to plum or apple collected on the same date. So, from the life table parameters perspective, peaches and apples collected on June 25 and May 31, respectively, were the best food sources for G. molesta.
Source: Ecology - nature.com
