Dispersal of the navel orangeworm (Amyelois transitella) (Lepidoptera: Pyralidae) (NOW) Chuck Burks 1 , Tom Sappington 2 , Brad Higbee 3 . USDA, Agricultural Research Service; 1 Parlier, CA, and 2 Ames, IA. 3 Paramount Farming Company, Bakersfield, CA Part 1. Laboratory assessment of effects of age, sex, and mating status on flight capacity Part 2. Emigration—environmental effects assessed in a field population Background: • Emigration—the decision to leave the natal patch—is the first of three steps in dispersal (followed by inter-patch movement and immigration). • Factors influencing dispersal in lepiodopteran pests include population density, development conditions, photoperiod, and temperature at time of flight. • NOW overwinters in various larval stages. It has an extended spring emergence. There are then ≥2 subsequent generations during the growing season. • NOW develops best in pistachios after husk split, which occurs in September shortly before harvest. Pistachios nonetheless typically have a variably high abundance of NOW through the growing season. • Here we use an 8-year data set with two transects of pheromone traps associated with the edge of a large, isolated patch of pistachios to examine factors associated with emigration. Objective: Characterize endogenous and exogenous factors affecting emigration of NOW Effect of mating status on flight capacity (longest single flight) Box plots are used to present results from 36-77 moths flown for mated and unmated males and females of each age tested (total 855). The solid and dashed center lines respectively represent the median and the mean; the ends of the boxes represent the 25th and 75th percentile, the whisker represent the 10th and 90th percentile, and the individual points represent 5th and 95th percentile. Methods: • Mated and unmated adults tested on flight mills 2, 3, 5 and 7 days post eclosion • Adults of the same class (age, sex, mating status) flown overnight in groups of ≤15 • Conditions: 26°C, 14:10 L:D, 75% R.H. • Analysis: mixed model ANOVA, with test nested in age × sex × mating status as a random factor (df based on number of tests rather than number of individual insects tested) Duration Distance Longest flight Total of flights Longest flight Total of flights Predictor F P F P F P F P Mated a,b 3.63 0.0599 5.49 0.0212 3.24 0.0752 2.54 0.1144 Age c 6.06 0.0008 6.27 0.0006 7.41 0.0002 8.73 <0.0001 Sex b 14.16 0.0437 14.16 0.0003 8.62 0.0042 18.48 <0.0001 Mated×Sex b 3.04 0.0844 1.31 0.2566 2.63 0.1084 3.45 0.0663 ANOVA: Effects of age and sex strong and consistent; much weaker effect from mating status a Mating status; i.e., mated or unmated. b Degrees of freedom = 1,93 (numerator, denominator). c Degrees of freedom = 3,93. Day Number of adults flown Duration, longest single flight Duration, total of all flights Distance, longest single flight Distance, total of all flights 2 199 238 ± 14a 331 ± 14a 6.4 ± 0.48a 8.0 ± 0.49a 3 246 203 ± 12ab 314 ± 12a 5.1 ± 0.36ab 6.8 ± 0.39ab 5 209 199 ± 13ab 294 ± 14ab 4.6 ± 0.40ab 6.0 ± 0.42bc 7 201 150 ± 12b 244 ± 13b 3.7 ± 0.40b 5.0 ± 0.42c Loss of flight performance was generally significant by 7 days post eclosion, but often not before then Category Number of adults flown Duration, longest single flight Duration, total of all flights Distance, longest single flight Distance, total of all flights FM 207 224 ± 14 330 ± 14 5.9 ± 0.45 8.0 ± 0.49 FU 221 215 ± 14 331 ± 13 5.8 ± 0.50 7.5 ± 0.39 MM 218 150 ± 11 235 ± 11 3.3 ± 0.40 4.5 ± 0.42 MU 209 205 ± 13 291 ± 13 4.8 ± 0.40 5.9 ± 0.42 Loss of flight performance after mating was nominally more pronounced in males than in females Mated females (FM), unmated females (FU), mated males (MM), and unmated males (MU) Conclusions: • There were statistically significant differences in flight capacity between the sexes and by mating status • A substantial flight capacity was nonetheless observed in all adults up to 7 days post eclosion • Peak capacity occurs early in life for both flight and oviposition (oviposition data from other studies) Conclusions: • The potential for emigration was greatest was in the fall. • No association of percent emigration with abundance. • No effect of exogenous factors (temperature, photoperiod) on emigration by overwintered moths. • Emigration in current-season adults was associated with interactive effects of photoperiod and temperature at time of flight. Methods: • Pheromone traps in two transects were monitored weekly from 2005 to 2012 • These transects extended out of the orchards into pasture and arid grassland devoid of suitable NOW hosts • The proportion of males captured in the traps outside the orchard were used as an index for emigration • Observations with a sum of ≤20 males captured in all traps were discarded as insufficiently informative. Of the remaining 349 observations, 90% were between Julian dates 85 (March 2) and 298 (October 25). • Trapping records were matched to concurrent environmental data (temperature, day length, and degree days from the California Irrigation Management Information System (CIMIS), the U.S. Naval Observatory (UNSO), and the UC IPM online degree-day calculator. Environmental predictors examined included: • Developmental temperature: Average DD°C/day over the 425 degree-days prior to the trapping date (=0 if <425°C accumulated since January 1)(425°C = 765 DD °F). • Night length: hours from sunset to sunrise (as defined by the USNO) for the study site. Night length for the trapping date used. • Flight temperature: An index obtained from the mean of the average daily temperature for the 7 days up to and including the trap date (i.e., an average over the trap monitoring period) Results 1) No consistent relationship between season and abundance, and no association between dispersal and abundance r 2 = 0.008, P = 0.08 ρ = 0.057, P = 0.29 2) There was, though, a significant temporal trend in emigration Overwintered Current Season • Percent emigration is not constant over the season, as demonstrated by a significant fit (r 2 = 0.32, P < 0.0001) to a quadratic model (solid line, above). • The relationship of emigration with time (Julian date) differed between overwintered and current- season adults. 3) There was a significant association between interactive effects of night length and flight temperature on current season adults… …not so, however, for overwintered adults. Overwintered a Current-season b Coefficient F P F P Night length 0 0.39 0.42 0.52 Flight temperature 0.12 0.78 8.88 0.0032 Night length × flight temperature 0.22 0.40 11.64 0.0008 Year 3.17 0.0001 3.82 0.0006 Transect 16.62 <0.0001 16.16 <0.0001 Coefficients for regression models incorporating night length and flight temperature for overwintered and current-season NOW males a Model: F 11,93 = 4.67, P < 0.0001; r 2 = 0.36. b Model: F 11,230 = 17.43, P < 0.0001; r 2 = 0.45. View publication stats View publication stats