Seasonal dynamics, dispersion, sequential sampling plans and treatment thresholds for the citrus leafminer, Phyllocnistis citrella Stainton (Lepidoptera: Gracillariidae), in a mature lemon block in coastal New South Wales, Australia

Abstract

Studies of citrus leafminer in a coastal orchard in NSW, Australia indicated that an increase in abundance to about one mine per flush was followed during the midseason flush by a rapid increase in population that was related to an increase in the percentage of leaves infested within flushes and the number of mines per leaf. The fits of frequency distributions and Iwao's patchiness regression indicated that populations were highly contagious initially, and as the exponent k of the negative binomial distribution increased with increasing population density, the distribution approached random. Concurrently, the coefficient of variation of mines per flush (which was strongly related to the proportion of un-infested flushes) decreased to about unity as the proportion of un-infested flushes reached zero and fell further as the number of mines per flush increased. Both numerative and binomial sequential sampling plans were developed using a decision threshold based on 1.2 mines per flush. The binomial sampling plan was based on a closely fitting model of the functional relationship between mean density and proportion of infested flushes. Functional relationships using the parameters determined from Iwao's patchiness regression and Taylor's power law were equally satisfactory, and one based on the negative binomial model also fitted well, but the Poisson model did not. The three best fitting models indicated that a decision threshold of 1.2 mines per flush was equivalent to 50% of flushes infested. From a practical point of view, the transition from 25% infestation of flushes through 50% is so rapid that it may be prudent to take action when the 25% level is reached; otherwise, the 50% may be passed before the crop is checked again. For valuable nursery stock should infestation be detected in spring, it may be advisable to apply prophylactic treatment as the midseason flush starts.

Dispersion, contagion, and population stability of red scale, Aonidiella aurantii, in citrus orchards with low or zero insecticide use

“…The question as to why there is such variation in the degree of clumping at any of the sites requires further investigation. Analogous data for the citrus leaf miner, Phyllocnistis citrella Stainton, obtained from nearby citrus blocks exhibited far less variation from functional models similar to those used here although the reason could be that the adult females of that species are motile and can avoid causing local overcrowding of their offspring (Liu et al, 2008).…”

“…Analogous data for the citrus leaf miner, Phyllocnistis citrella Stainton, obtained from nearby citrus blocks exhibited far less variation from functional models similar to those used here although the reason could be that the adult females of that species are motile and can avoid causing local overcrowding of their offspring (Liu et al, 2008). Analogous data for the citrus leaf miner, Phyllocnistis citrella Stainton, obtained from nearby citrus blocks exhibited far less variation from functional models similar to those used here although the reason could be that the adult females of that species are motile and can avoid causing local overcrowding of their offspring (Liu et al, 2008).…”

“…This is often known as the functional response model (Liu et al, 2008) but is not to be confused with the Holling functional response for predators and parasitoids (e.g., see Meats & Castillo Pando, 2002). This is often known as the functional response model (Liu et al, 2008) but is not to be confused with the Holling functional response for predators and parasitoids (e.g., see Meats & Castillo Pando, 2002).…”

“…Both the TPL and the IPR can be used to relate scale density to proportion of infested fruit or trees. This is often known as the functional response model (Liu et al, 2008) but is not to be confused with the Holling functional response for predators and parasitoids (e.g., see Meats & Castillo Pando, 2002).…”

“…The practical importance of the type of model in Figure 4 is in determining action thresholds for pest control (Liu et al, 2008). Smith et al (1997) recommend action at >3 scales per fruit for Australian growers.…”