Submitted to: Environmental Entomology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/1/2011
Publication Date: 6/9/2011
Citation: Burks, C.S., Higbee, B.S., Siegel, J.P., Brandl, D.G. 2011. Comparison of trapping for eggs, females, and males of the navel orangeworm Amyelois transitella (Walker) in almonds. Environmental Entomology. 40(3):706-713. Interpretive Summary: A previous study indicates that the 2-4 egg traps per block currently used to monitor the navel orangeworm in almonds in California is not sufficient to detect changes in female egg-laying for that block. In this study, we compare the proportion of egg traps with eggs and mean eggs per trap with trapping for females and males, and use laboratory data to examine the effect of female age and fertility on the number and proportion of eggs laid on preferred and non-preferred hosts. Field data show that the egg trap proportions and the means are highly correlated, but that the proportion of traps with eggs better correlates with captures of females and males. Laboratory show that female age and fertility and host preference affect the number of eggs laid on the preferred host more than the proportion of hosts with eggs. While these data suggest binomial sampling using eggs would improve detection of egg-laying, they also suggest that similar benefits could be obtained with the more practical approach of trapping females. The navel orangeworm, is the principal insect pest threatening California’s >$2 billion/yr almond crop. Improving monitoring and damage prediction will improve reduce unnecessary insecticide application on this crop, which occupies 5% of California’s agricultural landscape.
Technical Abstract: The navel orangeworm is the primary insect pest of almonds in California, and egg traps are the primary means of monitoring this pest. A previous study found that the current use of 2-4 traps per block usually is not sufficient to provide management information specifically for that block. In this study we compare data from large grids of egg traps in varied commercial almond orchards with trapping data for females and males with the objective of finding a more cost-effective monitoring program using currently available attractants. The proportion of egg traps with eggs was highly correlated mean eggs per egg trap and with females and males trapped simultaneously at the same location. Almond variety and the type of bait used had little impact on the relationship between the proportion of egg traps with eggs and the number of eggs per traps. Traps in orchards with more mummy almonds had more eggs, suggesting that navel orangeworm abundance affected traps more than competition from mummies. Laboratory experiments comparing age-specific oviposition in two-choice and no-choice situations found that younger, more fecund females laid a greater proportion of eggs on the preferred substrate in a two-choice situation, but that age-specific fecundity was not different between substrates in no-choice tests. These findings indicate that the proportion of egg traps with eggs provides a more stable indication of navel orangeworm phenology than mean eggs per trap. We suggest that similar information could be obtained in a more cost-effective manner with female trapping.