Biomedical subjects

N M Endersby

Publications and source records attributed to N M Endersby.

3 recordsLinked to original sources

PubMed2006

Microsatellites reveal a lack of structure in Australian populations of the diamondback moth, Plutella xylostella (L.).

The diamondback moth, Plutella xylostella, is renowned for developing resistance to insecticides and causing significant economic damage to Brassica vegetable crops throughout the world. Yet despite its economic importance, little is known about the population structure and movement patterns of this pest both at local and regional scales. In Australia, the movement patterns and insecticide resistance status of P. xylostella infesting canola, vegetables, forage brassicas and weeds have fundamental implications for the management of this pest. Here we use six polymorphic microsatellite loci to investigate population structure and gene flow in Australian populations of P. xylostella. Samples of P. xylostella from New Zealand, Malaysia, Indonesia and Kenya were also scored at these loci. We found no evidence of population structure within Australia, with most populations having low inbreeding coefficients and in Hardy-Weinberg equilibrium. In addition, a sample from the North Island of New Zealand was indistinguishable from the Australian samples. However, large genetic differences were found between the Australia/New Zealand samples and samples from Kenya, Malaysia and Indonesia. There was no relationship between genetic distance and geographic distance among Australian and New Zealand samples. Two of the loci were found to have null alleles, the frequency of which was increased in the populations outside the Australia/New Zealand region. We discuss these results with reference to insecticide resistance management strategies for P. xylostella in Australia.

Analysis of Variance↗

PubMed2006

Evaluation of fixed sample-size plans for Plutella xylostella (Lepidoptera: Plutellidae) on broccoli crops in Australia.

Fixed sample-size plans for monitoring Plutella xylostella (L.) (Lepidoptera: Plutellidae) on broccoli and other Brassica vegetable crops are popular in Australia for their simplicity and ease of application. But the sample sizes used are often small, approximately 10-25 plants per crop, and it may be that they fail to provide sufficient information upon which to base pest control decisions. We tested the performance of seven fixed sample-size plans (10, 15, 20, 30, 35, 40, and 45 plants) by resampling a large data set on P. xylostella in commercial broccoli crops. For each sample size, enumerative and presence-absence plans were assessed. The precision of the plans was assessed in terms of the ratio of the standard error to the mean; and at least 45 and 35 samples were necessary for the enumerative and presence-absence plans, respectively, to attain the generally accepted benchmark of < or = 0.3. Sample sizes of 10-20 were highly imprecise. We also assessed the consequences of classifications based on action thresholds (ATs) of 0.2 and 0.8 larvae per plant for the enumerative case, and 0.15 and 0.45 proportion of plants of infested for the presence-absence case. Operating characteristic curves and investigations of the frequency of correct decisions suggest improvements in the performance of plans with increased sample size. In both the enumerative and presence-absence cases, the proportion of incorrect decisions was much higher for the lower of the two ATs assessed, and type II errors (i.e., failure to suggest pest control upon the AT is exceeded) generally accounted for the majority of this error. Type II errors are the most significant from a producer's standpoint. Further consideration is necessary to determine what is an acceptable type II error rate.

Animals↗

PubMed2004

A dynamic binomial sequential sampling plan for Plutella xylostella (Lepidoptera: Plutellidae) on broccoli and cauliflower in Australia.

Binomial sequential sampling plans have been used widely for monitoring invertebrate pest populations. Such plans are typically based upon a single action threshold (AT), which represents the level of infestation that the grower is prepared to accept before using a control measure. For many cropping systems this acceptable infestation level is likely to vary, being dependent on factors such as the growth stage of the crop and the value or demands of the destination market (e.g., local or high-quality export). We developed and validated a computer-assisted plan that uses a dynamic AT. The plan has been developed for monitoring diamondback moth, Plutella xylostella (L.) on broccoli (Brassica oleracea variety botrytis L.) and cauliflower (Brassica oleracea variety botrytis L.), but the concepts and methodologies could be readily applied to other systems.

Animals↗