Effect of photoperiod on adult size and weight in Harmonia axyridis (Coleoptera: Coccinellidae)

Abstract

Short photoperiods often accelerate preimaginal development in insects that overwinter as adults and thus ensure the timely development of the diapausing stage. However, fast development usually results in small adults with few reserves whereas successful overwintering is dependent on sufficient reserves of nutrients. Thus, an insect faces two opposite challenges: increase adult weight or speed up pre-adult development. One solution to this "time-size trade-off" is fast development resulting in relatively lightweight but not too small adults, which are able to survive if there is an early onset to winter and have the possibility of further increasing their weight if conditions in autumn remain favourable for longer than usual. To test this hypothesis, we determined the effect of different photoperiods (day lengths of 12 and 18 h at 20°C) on the duration of preimaginal development, size of emerging adults and dynamics of adult weight in Harmonia axyridis. The larvae reared under short-day conditions tended to develop faster and invest resources in structural growth rather than in increasing weight: the daily rate of increase in size under a 12 h long photoperiod was greater than that under a 18 h long photoperiod, whereas the rate of gain in weight showed the opposite tendency. This resulted in a significant decrease in the weight /size ratio of emerging adults. However, their low initial nutritional status was partly compensated for by adult feeding: the relative gain in adult weight of "short-day individuals" was greater than that of the beetles that developed under long day conditions.

Inheritance of diapause regulation in the multicoloured Asian ladybird Harmonia axyridis (Coleoptera: Coccinellidae)

“…Some individuals, however, at the time of dissection had both a well developed fat body and well visible follicles in their ovaries indicating, most probably, they had just matured after a short-term delay. Similar results are recorded in earlier studies (Reznik & Vaghina, 2006;Reznik et al, 2015b).…”

On the Reproductive Diapause in the Predatory Ladybird Cheilomenes sexmaculata (Fabricius, 1781) (Coleoptera, Coccinellidae)

“…Ch. sexmaculata, as can be seen from the results of our study, are limited to the termination of oviposition: the (Reznik and Vaghina, 2006;Hodek, 2012;Reznik et al, 2015b;Ovchinnikova et al, 2016), but, on the contrary, signifi cantly decreases. Obviously, in this case, induction of diapause is accompanied not by accumulation but only by the redistribution of resources, and the growth of the fat body occurs only due to the cessation of the ovary growth and development.…”

The failed invasion ofHarmonia axyridisin the Azores, Portugal: Climatic restriction or wrong population origin?

“…From a physiological approach, the maintenance of low temperatures during the coldest months is important to the successful overwintering of H. axyridis . Overwintering is induced by a decrease in temperature, and especially by a shortening day‐length (Berkvens et al ., 2008; Reznik & Vaghina, 2011, 2013; Reznik et al ., 2015a). This species has a diapause syndrome, which is (i) ovaries of hibernating females are undeveloped, corpora allata are atrophied, and the fat body is developed (Iperti & Bèrtand, 2001) and (ii) migration and overwintering‐site selection behavior occur (Nalepa et al ., 2005; Raak‐van den Berg et al ., 2013; Grez et al ., 2017).…”