Observations on the feeding behaviour of late-instar larvae ofChoristoneura fumiferana

Abstract

Laboratory observations revealed that late-instar larvae of the eastern spruce budworm (Choristoneura fumiferana (Clemens)) (Lepidoptera: Tortricidae) spend most of their time spinning, wandering, and resting; less than 10% is spent feeding. Larvae feed in a discontinuous pattern of short feeding bouts separated by much longer intervals of nonfeeding activity. Over a 2 h observation period, feeding bouts averaged 2.2 min and were separated by 17.4 min intervals for 4th-instar larvae as compared to 3.3 min bouts separated by 33.4 min intervals for 5th-instar larvae. The duration of a feeding bout was positively correlated with the duration of the subsequent interval, not with the duration of preceding intervals, suggesting that feeding-bout frequency is governed primarily by post-ingestion processes. It is postulated that short feeding bouts followed by long intervals limit the window for ingesting an efficacious dose of aerially applied insecticides such as Bacillus thuringiensis.

Prevalence, transmission and mortality associated with Nosema fumiferanae infections in field populations of spruce budworm Choristoneura fumiferana

“…Horizontal and vertical lines represent the SE associated with each mean value. Late-L4 to L6 larvae may spend less than 10% of their time actively feeding (van Frankenhuyzen & Espinasse, 2010;Holmes et al, 2012). In spring of the next year, L2 will disperse, mine into 1-and 2-year-old needles and molt to L3 (McGugan, 1954).…”

“…The likelihood of contracting infection during larval stadia will depend upon the numbers of uninfected, susceptible hosts (Dwyer, 1991;Reeson et al, 2000;Campbell et al, 2007), Nosema spore densities and on the time spent feeding during which spores can be ingested (Campbell et al, 2007). Late-L4 to L6 larvae may spend less than 10% of their time actively feeding (van Frankenhuyzen & Espinasse, 2010;Holmes et al, 2012). Some horizontal transfer of Nosema infections would have occurred in all plots but was likely greatest in Plot 1, where there were the highest densities of budworm larvae especially uninfected early instars.…”

Factors affecting oral regurgitation by larval spruce budworm

“…Regurgitation by starving larvae may thus serve to discharge potentially toxic fluids from the foregut and prevent autolysis of digestive tissue. Budworm larvae feed in short bouts of <10 min at a time (Van Frankenhuyzen & Espinasse, 2010), and the interval between feeding bouts may be in part controlled by the risk of oxidative damage to gut tissue.…”

“…The larvae usually confine their feeding to the current‐year foliage unless the level of defoliation is high (Morris, 1963). They construct a shelter by webbing shoots together, an activity that represents >40% of the time schedule of sixth instars, and feed in short bouts of 30 s to 10 min, with an interval between feeding bouts of 3 min to >1 h; feeding represents only 10% of the time schedule of larvae (Van Frankenhuyzen & Espinasse, 2010).…”

Temporal variations in abiotic conditions exert little influence on diurnal activity of late-instar spruce budworm larvae on balsam fir

“…Advantages of such partitioning may reflect the direct influence of abiotic conditions, in particular temperature and humidity, as these parameters often mediate rates of physiological processes and thus impact insect survival and developmental rate (Berridge et al 1983; Bardoloi and Hazarika 1994). Insects may also accrue indirect benefits from linking activity patterns to abiotic variation because abiotic cues can help balance rates of food intake and digestion (van Frankenhuzen and Espinasse 2010), limit exposure to natural enemies (Fitzgerald et al 1988), and help to synchronise social behaviours (Thornhill and Alcock 1983; Quiring 1994). Aside from weather, intrinsic, hormonally mediated influences such as molting, circadian rhythm, and hunger may affect the timing, frequency, and duration of activities (Wellington and Cameron 1947; Nigam 1995).…”