Size variation in wild Bactrocera tryoni (Diptera: Tephritidae): only a small amount is related to the host fruit

Abstract

Body size is an indicator of fitness in fruit flies (Diptera: Tephritidae), with larger males and females having increased mating success and egg production, respectively. Based on laboratory studies, the larval diet and its nutritional composition are considered the most important factors influencing juvenile growth and subsequent adult body size. However, a very limited literature is less clear on the importance of larval diet as an adult size modifier of wild fruit flies. Bactrocera tryoni (Froggatt) is a polyphagous species with larvae feeding within the fruit of over 200 plant species. To test the impact of larval host on adult size in wild individuals of this species, we collected naturally infested fruit from the field and then reared out adults in the laboratory. The wing length and dry body weight of emergent flies were measured. Linear mixed models were used to analyse the difference in size depending on fruit type, larval density, sex and their interactions. Separate measurements of body size, wing length and dry body weight were significantly influenced by the larval host fruit collected from the field. However, only 7% and 24% of the variation of the wing discal–medial cell length and dry body weight, respectively, could be explained by larval host fruit type with high individual body size variation both within and between host fruit types. Fruit protein content was positively correlated, and water content negatively correlated, to wing discal–medial cell length. Unexpectedly, the parameters of wing length and dry body weight were only weakly correlated with each other. The results support the large body of laboratory‐based fruit fly diet work, which identifies protein as a key component of the larval diet, but do not support a general assumption that larval host is the key driver of adult body size variation in wild frugivorous tephritids. Rather, and in agreement with a small number of laboratory‐based trials, the importance of larval diet to adult fitness appears to become less important as the larval feeding environment becomes more complex.

Female–female aggression in Bactrocera tryoni (Diptera: Tephritidae) and the influence of fruit quality on combat intensity

“…The lack of size effect in our study may be due to a low variance in female size of our laboratory reared flies in comparison with wild flies. Wild B. tryoni collected from various fruit types had an dm cell range of approximately 1.5 to 2.30 mm (Newman et al 2021), that is, larger flies could be more 50% bigger than the smaller flies. The size of females in our study fell within this range, but the size variation between females was much smaller, at only around 10%–15% size difference between the smallest and the largest.…”

“…Following recording, the length of the wing dm cell for each fly was measured using ImageJ software of wing micrographs (see Newman et al 2021, for a discussion on the use of the length of the dm cell as a surrogate size measure in B. tryoni ); dm cell length measurements allowed female size to be considered as a factor in explaining competitive interactions.…”

Diet quality and conspecific larval density predict functional trait variation and performance in a polyphagous frugivorous fly

“…Larger males are more successful in defending a territory than smaller males and are more prone to gain matings Burk & Webb, 1983;Ekanayake et al, 2017). Lower body weight is associated with increased predation risk in males, and comes with reduced levels of energetic reserves, fertility and fecundity (Morimoto, Nguyen, et al, 2019;Newman et al, 2021). As is the case with length of larval development, pupal weight is strongly influenced by host quality.…”

Morphometrics of Adult Chinese Citrus Fly Bactrocera minax (Enderlein) (Diptera: Tephritidae) in Nepal

“…The larval diet and nutritional content are thought to be the most critical variables determining juvenile growth and eventual adult body size. In fruit flies, body size is an indication of fitness, with larger males and females having higher mating success and egg production, respectively (Newman et al, 2021).…”